Spotlight on the banana congress Breeding better bananas Cell death and disease resistance The roots’ health support system Soil fertility in East Africa Marketing partnerships How to contain bacterial wilt Vol. 13 No.2 December 2004 The International Journal on Banana and Plantain InfoMusa - Vol. 13 - No.2 1 INFOMUSA Vol. 13, No. 2 Publisher: International Network for the Improvement of Banana and Plantain Publishing director: Claudine Picq Editor: Anne Vézina Editorial Committee: Jean-Vincent Escalant, Richard Markham, Nicolas Roux, Charles Staver Layout: Crayon & Cie Printed in France ISSN 1023-0076 Editorial Office: INFOMUSA, INIBAP, Parc Scientifique Agropolis II, 34397 Montpellier Cedex 5, France. Telephone + 33-(0)4 67 61 13 02; Telefax: + 33-(0)4 67 61 03 34; E-mail: inibap@cgiar.org Subscriptions are free for developing countries readers. Article contributions and letters to the editor are welcomed. Articles accepted for publication may be edited for length and clarity. INFOMUSA is not responsible for unsolicited material, however, every effort will be made to respond to queries. Please allow three months for replies. Unless accompanied by a copyright notice, articles appearing in INFOMUSA may be quoted or reproduced without charge, provided acknowledgement is given of the source. French-language and Spanish-language editions of INFOMUSA are also published. An electronic version is available at the following address: http://www.inibap.org/publications/infomusa/ infomusa_eng.htm To avoid missing issues of INFOMUSA, notify the editorial office at least six weeks in advance of a change of address. Views expressed in articles are those of the authors and do not necessarily reflect those of INIBAP. InfoMusa Vol. 13 No.2 Cover photo: Banana worker in northern Peru. (Anne Vézina, INIBAP) Contents A review of conventional improvement strategies for Musa Kodjo Tomekpe, Christophe Jenny and Jean-Vincent Escalant 2 Can model plants help banana improvement through biotechnology? Martin B. Dickman 6 Diseases and pests: A review of their importance and management Randy Ploetz 11 Population genetic structure and dispersal of Mycosphaerella fijiensis Jean Carlier 17 Soil quality problems in East African banana systems and their relation with other yield loss factors P.J.A. van Asten, C.S. Gold, S.H. Okech, S.V. Gaidashova, W.K. Tushemereirwe and D. De Waele 20 New technologies to increase root health and crop production Richard A. Sikora and Luis E. Pocasangre 25 Partnership and networking in the tropical fruit industry: the experience of the International Tropical Fruits Network Khairuddin Tahir 30 Focus on the Musa congress 32 Focus on bacterial wilt 38 Thesis 41 MusaNews 42 Forum 46 In memory of Dr Maribona 48 The mission of the International Network for the Improvement of Banana and Plantain is to sustainably increase the productivity of banana and plantain grown on smallholdings for domestic consumption and for local and export markets. INIBAP is a programme of the International Plant Genetic Resources Institute (IPGRI), a Future Harvest centre. InfoMusa - Vol. 13 - No.2 1 We are pleased to offer you a special issue of INFOMUSA focusing on the First International Congress on Musa held in Malaysia from 6 to 9 July 2004. Organized by INIBAP and the Malaysian Agricultural Research and Development Institute (MARDI), the congress brought together some 250 delegates from all over the world, and from disciplines as far apart as genomics and fruit marketing, to share discussions and experiences under the theme Harnessing research to improve livelihoods. In addition to seven of the eight keynote addresses presented at the Congress (the one by Charles Staver on Farmer learning and plantain management in Nicaragua will be published in the June 2005 issue), this issue also contains a summary of the four sessions in the Focus on section. By publishing the keynote addresses so soon after the Congress, rather than filing them away while we prepare a formal proceedings that would be partly out of date by the time it is published, one of our aims is to reach a larger audience in a timely manner. We realize it is not a complete rendering of the Congress (the abstracts of the oral presentations and posters are available on our website, www.inibap.org). However, using INFOMUSA not only makes it possible to draw attention to the topical questions raised during those four days, it also provides an outlet to continue the discussion in our Forum section. We are also interested in your reaction to the format of the articles. Although this issue may seem to depart from INFOMUSA’s usual offering of scientific articles, in many ways it is not so different from past instalments. In the first years of its existence, the articles published in INFOMUSA were written in a more informal style than the scientific articles we currently publish, in keeping with its mission to inform readers “of INIBAP’s activities and present findings of the network”. But as stated in the first issue, INFOMUSA was also meant to “report on Musa research and activities worldwide”. Inevitably, at first, many of the articles were commissioned to our partners, but as the magazine became better known, submissions from researchers came to dominate its contents. As we are discovering with our survey, some readers would like a return to the less formal, some would say less scientific, and more newsy INFOMUSA. Others, however, would like to see it become a peer-reviewed journal. There is still time to let us know what you think by filling in the questionnaire on our website. We will be bringing you the results in the next issue. We will end with a few apologies. After urging our would-be authors to avoid jargon in their manuscripts, we were taken to task by people who answered the survey and were stumped by the expressions “upstream” and “downstream” research and “open-access” journal. By upstream research we mean the research done to develop innovative concepts and technologies, as opposed to downstream research, which integrates technology and knowledge in projects that have practical implications for farmers. Open-access journals are those that use a funding model that does not charge readers or their institutions for access. We also wish to apologise for suggesting, in the previous issue of INFOMUSA, that black leaf streak disease, caused by Mycosphaerella fijiensis, is now present in India. In the article “Evaluation of new banana hybrids against black leaf streak disease”, the disease against which the hybrids were evaluated was Sigatoka disease, caused by Mycosphaerella musicola. We regret the error. As far as we know, there has been no official record of black leaf streak disease in India. We are grateful to the vigilant readers who brought this to our attention. The editors The banana congress up close Editorial InfoMusa - Vol. 13 - No.22 InfoMusa - Vol. 13 - No.2 3 A review of conventional improvement strategies for Musa Kodjo Tomekpe, Christophe Jenny and Jean-Vincent Escalant M ost cultivated bananas are triploids. Although triploidy confers a certain vigour to the plant, it also contributes to the sterility that greatly limits the use of hybridization in banana improvement and constitutes a challenge to conventional breeding methods. In spite of these difficulties inherent in the banana crop, notable progress has been made over the last twenty years and it is not unusual nowadays to find artificial hybrids in various research stations, contributing to rural development, and even being grown on family farms. This progress stems from several conventional breeding programmes (Menendez and Shepherd 1975, Rowe and Rosales 1992, Shepherd 1968, Soares Filho et al. 1992, Swennen and Vuylsteke 1990, Bakry and Horry 1992, Jenny et al. 1994, Tomekpé et al. 1998). In Honduras, the Fundación Hondurena de Investigación Agricola (FHIA) is the oldest existing programme and works on several dessert and cooking bananas. It is the only programme to improve the ‘Gros Michel’ dessert banana. The FHIA has developed various types of hybrids, some of which are currently being distributed in several countries. In France and in Guadeloupe, the Centre de coopération internationale en recherche agronomique pour le développement (Cirad) has concentrated for some twenty years on the creation of new triploid dessert bananas for export, using a simple and original scheme based on a knowledge and exploitation of the existing diversity in diploid dessert varieties (Bakry et al. 1997). In Nigeria, Cameroon and Uganda, the International Institute of Tropical Agriculture (IITA) has been breeding plantains for about twenty years, and more recently has been engaged in improving East African highland bananas. In Cameroon, the Centre africain de recherches sur bananiers et plantains (CARBAP, ex-CRBP) has specialized for about the last twelve years on improving plantains, of which it possesses the largest collection in the world. In Brazil, the Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA) works on bananas of the Pome and Silk sub-groups, which are highly prized in that country. The 3x/2x strategy Two factors were decisive in the development of the 3x/2x strategy: the discovery of residual female fertility in certain triploid cultivars on the one hand, and the observation of a substantial proportion of tetraploids among their descendants on the other, due to the formation of unreduced triploid gametes that enable the conservation of the entire triploid genome. This strategy has been widely used to try to create tetraploid hybrids resistant to diseases and of good agronomic value by pollinating susceptible triploids with male fertile diploids that are resistant. The best-known examples of dessert hybrid tetraploids from FHIA arose from crosses between dwarf mutants of ‘Gros Michel’ and ‘Prata’ and improved diploids resistant to black leaf streak and Sigatoka diseases, and to the nematode Radopholus similis. As to cooking bananas, one can distinguish CRBP-39 from CARBAP and FHIA-21 (plantain hybrids) and BITA 3 from IITA (a cooking banana hybrid) all of which are resistant to black leaf streak and are currently being adopted by, or are already grown in, certain countries (Figure 1). It should however be noted that nearly all the AAAB hybrids (resulting from crosses between an AAB and an AA) can show symptoms of banana streak disease caused by the activation of viral sequences integrated in the B genome of these cultivars. Furthermore, the low fertility of the rare fertile cultivars means that only small populations can be generated, and a considerable number of crosses have to made to have a chance of useful results. Another problem is the high water content in tetraploid fruit, which ripen and soften rapidly. Moreover, hybrid tetraploids, AAAB as well as AAAA and AABB, often inherit male and female fertility from the fertile diploid parent. Consequently they are liable to produce bananas containing seeds if they are pollinated, which obviously reduces Genetic improvement InfoMusa - Vol. 13 - No.22 InfoMusa - Vol. 13 - No.2 3 Figure 1. Tetraploids resistant to black leaf streak. Left to right, FHIA-21 produced by FHIA, CRBP 39 produced by CARBAP and Bita 3 produced by IITA. Figure 2. Natural and improved diploids bred by FHIA. Left to right, 3362, 3142, PJB, 3437, 2989, C-IV, 2095 and Lidi. their quality. Removing the flowers avoids unwanted pollination. One must also bear in mind that the 3x/2x strategy also enables numerous types of AA diploid hybrids to be created. More than 50% of the hybrids generated by certain plantains are AA diploids. Improvement of diploids Unlike triploids, diploids are very fertile and contain considerable genetic diversity; they may be wild, semi-wild or parthenocarpic, often with one or more sources of resistance (or tolerance) to diseases and pests, together with various organoleptic qualities. They have various levels of heterozygosity and some of them are the ancestors of the triploid cultivars that need to be improved. They are therefore good parents and ideal material for the genetic and cytogenetic studies needed for optimizing the genetic improvement of bananas. After intensely using wild diploids, breeders came to the conclusion that the choice of the ‘resistant donor’ should also take into account its agronomic characteristics and, if possible, certain features of fruit quality. Hence the introduction of strategies for developing improved diploids. The great genetic diversity of the diploids collected in southeast Asia and India has led to the selection of wild, semi- parthenocarpic and parthenocarpic diploids such as ‘Calcutta 4’ (Musa acuminata ssp. burmanicoïdes) and ‘Pisang lilin’ ( a fertile parthenocarpic diploid with seedless fruit). These have been used to improve triploid cultivars and have also provided the basis for developing improved diploid parents. Notable among these is M53 (resistant to the leaf spot diseases caused by Mycosphaerella and to Fusarium wilt), bred in the fifties by the improvement programme of the former Jamaican Banana Board, and the elite diploids developed by FHIA, some of which have multiple resistance (to leaf spot diseases, nematodes and Fusarium wilt) and markedly longer fruit than the small fruit of wild diploids (Figure 2). Moreover, numerous monospecific AA and interspecific AB diploid hybrids have been created by the National Research Centre on Banana (NRCB) and the Tamil Nadu Agricultural University, in India. More recent is the use of fertile diploid AA hybrids as parents or as starting material for developing elite diploids. In particular, these are plantain hybrids resistant to leaf spot diseases and with a fruit quality similar to that of plantains. This approach is used especially by CARBAP and IITA to develop diploids specific to certain sub-groups such as plantains and the East African highland bananas. Fr om le ft t o r igh t: F HI A, C AR BA P an d I ITA InfoMusa - Vol. 13 - No.24 InfoMusa - Vol. 13 - No.2 5 AAw AAcv AAcv AAcv AAw BBw AAcv AAw AAcv AAcv BBw AAcv ABcv AAAAcv AABBcv (1) (2) AAAAcv AAAAcv AAAAcv AABBcv AABBcv AAAcv AAAcv AABcv (3, 4) (3, 5) AABcv AABcv colchicine Tetraploid development Triploid development colchicine x x x x x x x x Figure 3. 4x/2x breeding scheme used by CIRAD and CARBAP. 1. Nealy 20 clones developed at CARBAP and CIRAD. 2. Actually stopped because of BSV concern. 3. Annual hybrid population size of nearly 400 plants in the field. 4. 98% of the progeny is triploid. 5. Actually stopped because of BSV concern. The 4x/2x strategy As part of the 4x/2x strategy, triploid hybrids are created by hybridization of a diploid parent with a tetraploid parent, previously obtained by chromosome doubling of an ancestral diploid or an improved diploid hybrid using colchicine (Figure 3). This strategy imitates the natural process of banana evolution, the natural triploid cultivars apparently having resulted from ancestral diploids by the accidental production of unreduced gametes in one of the diploid parents during hybridization (Simmonds 1962). The meiotic error that resulted in these unreduced gametes is replaced in the 4x/2x strategy by a chromosome doubling of one of the parents by colchicine treatment (Bakry et al. 1997, Stover and Buddenhagen 1986, Vakili 1967). The hybridization cannot continue since the product obtained is almost completely sterile and can therefore no longer be improved using conventional methods. Unlike the 3x/2x strategy, the 4x/2x strategy does not try to improve existing varieties but rather to create new improved varieties, which closely approximate the objectives, by using ancestral varieties. These hybrids should therefore bring together all the characteristics that are usually improved, plus the improved characters for which the strategy was established. This strategy, used in particular by Cirad, has been made possible thanks to a better knowledge of the evolution of bananas based on their morphological and molecular characters (Fauré et al. 1994, Jenny et al. 1999). The genetic variability in the acuminata genome has been related to variability in fruit quality in the main cultivated groups. The most striking example is probably the relationship between the subspecies Musa acuminata spp. banksii and cooking bananas. As a result, cooking triploid hybrids of purely acuminata origin have been produced. The variability in the acuminata genome also makes it possible to vary the type of fruit and plant, dessert or cooking, but also the sugar content and acidity, fruit length, degree of suckering and yield etc. Among the first results obtained, CARBAP has identified, among the several hundred individuals obtained from crossing BB x AAAA, (AAAA being susceptible and BB partially resistant to black leaf streak), about 20% of hybrids showing useful resistance to black leaf streak. Moreover, by combining diploid plantain hybrids with cooking acuminata triploids obtained at Cirad, CARBAP was able to obtain populations of several hundred individuals, among which several triploid AAA acuminata hybrids resistant to black leaf streak are undergoing the selection process. To sum up, this strategy offers unques- tionable advantages: a large number of available parents, better prediction of heritability of valuable characters and better fertility of diploid parents, resulting in larger populations, enabling the initiation of a real selection programme that can even include several improvement criteria. Broadening the choice of diploid parents by developing an improvement strategy for diploids or by carrying out new exploration for material in the regions of interest could increase the potential of this strategy. In this respect, CARBAP is currently developing improved second- and third-generation diploids (secondary and tertiary diploids) from plantain diploid hybrids resistant to black leaf streak by crossing diploid plantain hybrids with sources of resistance that are undergoing chromosome doubling. We note, however, that the AAB hybrids resulting from AAAA x BB crosses are also liable to suffer from BSV. In view of the problems associated with the 3x/2x strategy and the fertility of the tetraploids thus obtained, the latter were soon InfoMusa - Vol. 13 - No.24 InfoMusa - Vol. 13 - No.2 5 regarded as intermediate products. Hence they have been quite naturally crossed with diploids to obtain triploids ‘genomically’ closer to the initial triploid cultivars, known as primary triploids, while the triploids arising from 4x/2x crosses are called secondary triploids. The 3x/2x strategy is in fact used in this case as the only possible way to extract useful characteristics from the popular triploid cultivars. This material is then better exploited on a larger scale using more fertile tetraploid and diploid hybrid parents (F1 hybrids) capable of generating larger populations of F2 hybrids that are in fact the grand-children of popular triploid cultivars. However one should not lose sight of the fact that the genetic gain obtained by nuclear restitution of the preceding stage will be reduced by the recombination that will occur during meiosis of the tetraploid. The choice of diploid parents for the F1 cross, and also for the F2 cross, is thus very important and on it will depend the quality or the reconstitution of the secondary triploid hybrids. The latter should retain the desired characteristics of their grand-parents (the original triploid cultivars) to which should be added characters of resistance to diseases and pests. This strategy has allowed IITA, EMBRAPA and FHIA to obtain hybrid populations of sufficient size to make worthwhile selections of good quality secondary triploid hybrids. CARBAP also uses this approach to generate large populations of secondary triploid hybrids from primary tetraploids derived from several rare dwarf plantain bananas. The main advantage of this two- stage strategy is to obtain, via primary hybrids, several hundred second generation descendants from very sterile triploid cultivars. The example of dwarf-type triploid hybrids obtained from primary tetraploid hybrids that themselves arose from triploid cultivars of dwarf plantain bananas is worthy of note. Conclusion In spite of the difficulties inherent in the plant and the meagre resources devoted to banana improvement, substantial progress has been made over the last twenty years, notably with bananas for local consumption, i.e. those that are not sold by the big companies. Things are somewhat different for dessert bananas for export: the big companies want resistant varieties that must also comply with very precise pre- and post- harvest management standards. This is one of the reasons why the tetraploid dessert banana hybrids created by FHIA have not been adopted by the banana industry. Greater progress could be made if adequate resources were devoted to conventional breeding and if cooperation was encouraged. Progress should also be made in molecular studies to improve marker- assisted breeding. These studies should include the identification of resistance genes and also of those linked to abiotic stress tolerance, parthenocarpy and fruit quality. Many useful improvements can be made by conventional methods but the latter should be combined with unconventional techniques under development such as mutagenesis, genetic transformation and even protoplast fusion. Only a comprehensive approach can sustainably resolve all the problems that the cultivars must confront. Moreover, one must not lose sight of the need to include the improvement strategies into a global approach to sustainable management of the banana crop, as improved varieties alone cannot solve all the problems. References Bakry F. & J.P.Horry. 1992. Tetraploid hybrids from interploid 3x/2x crosses in cooking bananas. Fruits 47:641-655. Bakry F., F. Carreel, M.-L. Caruana, F.X. Côte, C. Jenny & H. Tézenas du Montcel. 1997. Les bananiers. Pp. 109-140 in L’amélioration des plantes tropicales (A. Charrier, M. Jacquot, S. Hamon et D. Nicolas, eds). CIRAD and ORSTOM. Fauré S., J.-L. Noyer, F. Carreel, J.P. Horry, F. Bakry & C. Lanaud. 1994. Maternal inheritance of chloroplast genome ant paternal inheritance of mitochondrial genome in bananas (Musa acuminata). Current Genetics 25:265-269. Jenny C., F. Carreel, K. Tomekpé, X. Perrier, C. Dubois, J.P. Horry & H. Tézenas du Montcel. 1999. Les bananiers. Pp. 113-139 in Diversité génétique des plantes tropicales cultivées (P. Hamon, M. Seguin, X. Perrier et J.C. Glaszmann, eds). CIRAD, Montpellier. Menendez T. & K. Shepherd. 1975. Breeding new bananas. World crops May/June 104-112. Rowe P. & F. Rosales. 1992. Genetic improvement of bananas, plantains and cooking bananas in FHIA, Honduras. Pp. 243-266 in Breeding bananas and plantains : proceedings of an International Symposium on Genetic Improvement of Bananas for their Resistance to Diseases and Pests (J. Ganry, ed.). CIRAD-FLHOR, Montpellier, France. Shepherd K. 1968. Banana breeding in the West Indies. Pest articles and news summaries 14:370-379. Simmonds N.W. 1962. The evolution of the bananas. Longmans, Green & Co, London. Kodjo Tomekpe works at the Centre Africain de Recherches sur Bananiers et Plantains (CARBAP) in Cameroon, Christophe Jenny at the Centre de coopération internationale en recherche agronomique pour le développement (Cirad), Guadeloupe and Jean-Vincent Escalant at INIBAP, France InfoMusa - Vol. 13 - No.26 InfoMusa - Vol. 13 - No.2 7 Can model plants help banana improvement through biotechnology? Martin B. Dickman Bananas must cope with numerous environmental challenges, particu-larly with fungal and bacterial pathogens as well as pests and abiotic stresses. This situation is exacerbated by the limited diversity of cultivars. Moreover, traditional breeding strategies are problematic due to a low female fertility, sterility, ploidy and poor seed set. As a result, classical genetics is difficult and limited, as well as being extremely time consuming. Taken together, the difficulty in conventional beeeding, limited genetic diversity and poorly controlled diseases all point to the necessity of developing alternative strategies for banana improvement. Biotechnological approaches are particularly appropriate for this crop. This review will focus on two distinct, but overlapping issues: (i) the role of model plants in providing avenues leading to approaches for banana improvement through biotechnology and (ii) conceptual approaches for generating bananas with enhanced resistance to disease and other environmental stresses. The attraction of genetic engineering While the “track record” regarding successful applications of recombinant DNA approaches in generating transgenic plants with enhanced agronomic traits (especially involving disease resistance) is limited at best, it is also fair to say that this technology has considerable experimental power. It is now evident that many important techniques (e.g. genetic transformation, gene silencing) are now possible in bananas (James Dale, personal communication) and are mainly limited by the choice of gene(s). In other words, what do we insert? Moreover, while the technology for gene manipulation has been available for a number of years for many plants, success under field conditions has been hampered by our overall lack of understanding of the essential determinants and pathways mediating stress/disease. However, thus more effective genes and strategies are likely to ensue given the availability of genome sequences. Model plants This section will discuss two model plants; Arabidopsis and rice. Arabidopsis has served as an invaluable model plant in numerous aspects of plant biology, including pathology and stress physiology, with many insights viewed to be directly applicable to crop plants. In addition, Arabidopsis has a number of key experimental features: the genome is sequenced, microarray chips are commercially available and a considerable number of mutants have been characterized. In addition, reverse genetics will continue as a powerful tool to examine gene function in Arabidopsis. However, Arabidopsis is a dicot and is not a crop plant. On the other hand, rice is both a monocot (and thus may be more closely related to banana) and a crop plant, but is not so well genetically characterized, although the complete sequence of the rice genome will soon be available. Moreover, Soares Filho W., S. Dos, Z.J.M. Cordeiro, K. Shepherd, J.L.L. Dantas, S. de Oliveira e Silva & M.A.P. da Cunha. 1992. The banana genetic improvement programme at CNPMF/EMBRAPA, Brazil. Pp. 339-346 in Breeding bananas and plantains : proceedings of an International Symposium on Genetic Improvement of Bananas for their Resistance to Diseases and Pests (J. Ganry, ed.). CIRAD-FLHOR, Montpellier, France. Stover R.H. & I.W. Buddenhagen. 1986. Banana breeding: polyploidy, disease resistance and productivity. Fruits 41:175-191. Swennen R. & D. Vuylsteke. 1990. Aspects of plantain breeding at IITA. Pp. 252-266 in Sigatoka leaf spot disease: Proceedings of an international workshop (R.A. Fullerton & R.H. Stover, eds). San José, Costa Rica. Tomekpé K., P. Rowe, H. Tezenas du Montcel & D. Vuylsteke. 1995. Plantain and Popoulou/Maia Maoli Breeding: current approaches and future opportunities. Workshop INIBAP/MARDI, Serdang, Malaysia. Vakili N.G. 1967. The experimental formation of polyploidy and its effect in the genus Musa. Amer. J. Bot. 54: 24-36. Genetic improvement InfoMusa - Vol. 13 - No.26 InfoMusa - Vol. 13 - No.2 7 many of the experimental features available in Arabidopsis are being developed for rice; some of which are already in use (e.g. rice T-DNA knockout lines). The rice genome is relatively small; about 3-4 times larger than Arabidopsis (Resink and Buell 2004). Moreover, a number of predicted genes found in rice have homologs in Arabidopsis (Rice Chromosome 10 Sequencing Consortium 2003). Another important consideration is the fact that rice, along with other closely related plants, exhibit a relatively high degree of synteny (Gale and Devos 1998). Since banana genomics is in its infancy with limited sequence information, it is premature to draw conclusions as to a singular comparative strategy and to what degree synteny will be conserved. However, initial studies have been done (Aert et al. 2004). Interestingly, comparison of the banana genome structure and organization, derived from preliminary studies of BAC end sequencing, with the ones of rice and Arabidopsis suggested that banana may actually be closer to Arabidopsis than to rice (Chris Town, personal communication). If this preliminary observation holds up, then banana is positioned in a rather unique place, a monocot with more affinity to dicots than other monocots. Gene transfer across species The Arabidopsis NPRI gene is a well- characterized central player in regulating systemic acquired resistance (SAR). When overexpressed in Arabidopsis, enhanced disease resistance occurs. To evaluate the role of NPRI in monocot plants, the Arabidopsis gene was overexpressed in rice and transgenic plants were challenged with the rice bacterial blight pathogen Xanthromonas oryzae pv. oryzae. Transgenic plants exhibited enhanced levels of resistance, although not as pronounced as the resistant cultivar (Chern et al. 2001). These studies indicated that a dicot gene can be expressed and confer a useful phenotype in a monocot and suggests that monocot and dicot plants share a conserved pathway that mediates resistance. The identification and characterization of major resistance genes (R genes) is an important, active field of investigation, and banana is no exception ( McDowell and Woffenden 2003, James Dale personal communication). Monocot R genes appear to be in the CC (coiled coil), NBS (nucleotide binding site) and LRR (leucine rich-repeat) structure class as opposed to the TIR (toll-like inverted repeat) NBS LRR that predominates in dicots, including Arabidopsis (for a review of R genes, see Martin et al. 2003). Hulbert and colleagues recently described an interesting approach for identifying novel sources of resistance (Zhao et al. 2004 ). This group inoculated a number of maize lines with the bacterium that causes leaf streak of rice. Lines that induced a hypersensitive response (HR) when challenged were identified. This phenotype suggests that these maize plants were able to recognize the rice pathogen. Following crosses, genetic control of the HR segregated as a single dominant locus, suggesting the possibility of a single R gene. The responsible maize gene was map-based cloned and, when inserted into rice, conferred resistance to the bacterial streak disease pathogen (S. Hulbert, personal communication). This is more than just a demonstration, as this disease is very severe in areas (e.g. China) where hybrid cultivars are extensively utilized and are very susceptible to leaf streak. Moreover, these studies suggest that the same genes may be involved in non-host resistance and specific resistance. Programmed cell death Multicellular organisms eliminate unwanted, damaged or used cells by a gene-directed programmed cell death (PCD) process. PCD is genetically controlled cellular suicide and plays a critical role in a wide variety of normal physiological processes. In humans and other animals, dysregulation of this natural cell death pathway contributes greatly to diseases characterized by either excessive cell accumulation (cancer, autoimmune diseases) or inappropriate cell death (stroke, myocardial infarction, inflammation, AIDS, Alzheimer’s and other neurodegenerative diseases). In addition, most viruses and intracellular bacteria control the cell death pathway in the host cells they infect, thus linking apoptosis to infectious diseases. InfoMusa - Vol. 13 - No.28 InfoMusa - Vol. 13 - No.2 9 By far, the most common of the cell suicide responses in animal species is “apoptosis”. Apoptosis refers to a constellation of characteristic morphological changes that animal cells typically undergo when dying by activation of the endogenous cell suicide program. The execution of this program is often associated with cell shrinkage, membrane bleeding, nuclear and cytoplasmic condensation, and DNA fragmentation. These DNA fragments coalesce to form membrane- bound apoptotic bodies that, in animals are rapidly phagocytosed and digested by macrophages. In this way, the dead cells are rapidly and cleanly removed and cellular leakage of noxious and possible dangerous contents in avoided. In contrast, necrosis results from cellular injury, cells swell and lyse, releasing cytoplasmic material, which in animals often triggers an inflammatory response. While the distinction between these two forms of death is not always clear, in necroses, the cell is not an active participant in its demise. Apoptosis is usually also associated with the activation of nucleases that degrade chromosomal DNA into small oligonucleosomal fragments, which when electrophoresed, result in a characteristic “DNA ladder”. The genes that control programmed cell death are conserved across wide evolutionary distances, defining a core set of biochemical reactions that are regulated in diverse ways by inputs from myriad upstream pathways. These genes encode either anti-apoptotic (e.g. Bcl-2, Bcl-xl, CED-9, IAP) or pro-apoptotic proteins (e.g. Bax, Bid, caspases), which do battle with each other in making life-death decisions for the cell. Ectopic overexpression of certain types of anti-apoptotic genes can render animal cells markedly resistant to a wide range of cell death stimuli, including nutrient deprivation, irradiation, cytotoxic chemicals, hypoxia and disease (Navarre and Wolpert 1999). Programmed cell death in plants In plants, programmed cell death plays a normal physiological role in a variety of processes, including (a) deletion of cells with temporary functions, such as the aleurone cells in seeds and the suspensor cells in embryos; (b) removal of unwanted cells, such as the root cap cells found in the tips of elongating plant roots and the stamen primoridia cells in unisexual flowers; (c) deletion of cells during sculpting of the plant body and formation of leaf lobes and perforations; (d) death of cells during plant specialization, such as the death of tracheary element (TE) cells; and (e) leaf senescence (Dickman and Reed 2003). Regulation of cell death pathways also occurs in response to abiotic stimuli (Jones and Dangl 1996). In some cases, cell suicide programmes are also activated during pathogen attack in both resistant and susceptible plant-pathogen interactions (Beers 1997, Mitsuhara et al. 1999). Though the biochemical mechanisms responsible for cell suicide in plants are largely unknown, a variety of reports suggest similarities to the programmed cell death that occurs in animal species. For example PCD in plants typically requires new gene expression, and thus can be suppressed by cycloheximide and similar inhibitors of protein or RNA synthesis (Dickman and Reed 2003). The morphological characteristics of plant cells undergoing PCD also bear some striking similarities to apoptosis in animals, though the presence of a cell wall around plant cells imposes certain differences. Akin to animal cells, PCD in plants is associated with internucleosomal DNA fragmentation (DNA ladders) and the activation of proteases (Ryerson and Heath, 1996, Solomon et al. 1999). In addition to its role in developmental processes in plants, cell suicide plays an important role in interactions of plants with a variety of pathogens, including bacteria, fungi and viruses (Mittler and Lam 1996). One of the best studied of these plant responses to pathogens is the hypersensitive response (HR). Upon exposure to certain pathogens, plant cells in the immediately affected area undergo a rapid cell suicide response that is theoretically intended to kill the cells near the site of infection, thereby limiting spread of pathogens. The HR is associated with the expression of a variety of plant defense genes and the induction of programmed cell death. The HR is usually preceded by rapid and transient responses, including ion fluxes, alterations InfoMusa - Vol. 13 - No.28 InfoMusa - Vol. 13 - No.2 9 The model plant Arabidopsis whose genome has been sequenced in protein phosphorylation patterns, pH changes, changes in membrane potential, release of reactive oxygen species (ROS), and oxidative cross-linking of plant cell wall proteins (Richberg et al. 1998). Although plant cell suicide (HR) may be effective in limiting the spread of certain viruses, bacteria, and fungi (in particular, those with a biotrophic lifestyle), it is counterproductive for limiting necrotizing pathogens that utilize the decaying cell corpse as a food base in the case of certain bacteria and fungi. For example, hallmark features of apoptosis have been observed in plants (during compatible interactions) that are sensitive to toxin-producing necrotrophic fungi, including Fusarium moniliforme (fumonisin), Alternaria alternata (AAL toxin), and Cochliobolus victoriae (victorin) (Navarre and Wolpert 1999, Piedras et al. 1998). Thus, plant programmed cell death can accompany both susceptible and resistant reactions, suggesting common biochemical pathways during both interactions. Engineering resistance to pathogens Proof-of-concept experiments indicate that it is possible to genetically engineer plants for pathogen resistance without interfering with normal programmed cell death responses needed for plant development. For example, Mitsuhara et al. demonstrated that the expression in tobacco of cytoprotective Bcl-2 family of proteins from humans (Bcl-XL) and nematodes (CED-9) resulted in increased cellular resistance to UV irradiation and paraquat. Work in my lab has provided further evidence indicating that Bcl-2 proteins function in plants. Transgenic tobaccos were generated harboring various anti-apoptotic proteins including human Bcl- 2, chicken Bcl-XL, nematode CED-9 and baculovirus Op-IAP (Dickman et al. 2001). When the necrotrophic fungal pathogen Sclerotinia sclerotiorum, which has an extremely broad host range (more than 400 species), was inoculated onto tobacco plants harboring these transgenes, the usually susceptible plants became highly tolerant and in most cases, completely resistant. Eventually, the fungus stops growing, presumably after having depleted its nutritional source, and, importantly, the fungus fails to colonize and infect transgenic plant tissue even with extended incubation. Similar results occurred with other necrotrophic fungi including Botrytis cinerea and Cercospora nicotianae. A unifying aspect of these results with the fungi tested is that all three fungal pathogens are necrotrophs; thus, these fungi require host plant cell death to grow, colonize and reproduce in the host milieu. In the case of the broad host-range pathogen S. sclerotiorum, it has been assumed that this aggressive, indiscriminate pathogen with an impressive arsenal of destructive enzymes and toxins simply overwhelms plants. Our data suggest that this interaction is more sophisticated; the pathogen specifically interacts with the plant by triggering host cell death pathways. Inhibition of this pathway, presumably by anti-apoptotic gene products, prevents fungal infection even though the fungus has its full complement of virulence factors. Thus, necrotrophic pathogens may co-opt plant host cell death pathways for successful colonization and disease development. Redirection of plant cell death pathways by necrotrophic pathogens may be essential for disease development to occur. Still, these results do not prove that plants and animals share common features of apoptosis. However, when S. sclerotiorum Ma rtin D ick ma n InfoMusa - Vol. 13 - No.210 InfoMusa - Vol. 13 - No.2 11 was inoculated onto wild type tobacco, DNA fragmentation was observed in the form of characteristic “ladder”, a common feature of apoptotic responses. Further, fungal induced DNA fragmentation was detected by terminal deoxynucleotide transferase-mediated dUTP end labeling (TUNEL) of DNA 3'-OH groups which also indicated the presence of apoptotic bodies. Importantly, when transgenic plants were inoculated with S. sclerotiorum, not only were the plants resistant, but there was no laddering nor were there any TUNEL positive cells. In addition, experiments with tobacco mosaic virus shows that in N gene mediated resistance, the resulting HR exhibits TUNEL reacting tobacco cells and that in transgenic tobacco containing anti-apoptotic genes, cell death (HR) is suppressed. Thus, we have evidence for apoptotic pathways being involved in both susceptible and resistant plant responses. Induction of these pathways is dependent on the genetics of the host/pathogen and the life style of the pathogen. Moreover, we have recently demonstrated that these same transgenic plants are tolerant to heat, cold, salt and drought (Li and Dickman 2004). Importantly, these data clearly suggest that homologous pathways are operative in plants and animals. We are currently in the process of generating transgenic bananas harboring these anti-apoptotic genes. The two major fungal diseases of bananas (black leaf streak and Fusarium wilt) both fit the conceptual framework for disease control; in other words, there are necrotrophic fungi. Thus we are cautiously optimistic that the transgenic bananas will exhibit tolerance/ resistance. We will also evaluate such lines for tolerance to abiotic stresses (heat, cold, salt, drought). Conceivably, enormous opportunities exist for using animal models of programmed cell death to dissect cell death pathways in plants. Such information can lead to a mechanistic understanding of the regulation of plant cell death, an area that is not well understood and is of fundamental importance for plant biology. Thus understanding and eventual exploitation of cell life/death pathways in plants can be used for protection of banana against pathogens and environmental stresses. References Aert R., L. Sagi. & G. Volckaert. 2004. Gene content and density in banana (Musa acuminata) as revealed by genomic sequencing of BAC clones. Theor. Appl. Genet. 109:129-139. Beers G.P. 1997. Programmed cell death during plant growth and development. Cell Death and Differentiation 4:649-661. Chern M.-S., H.A. Fitzgerald, R.C. Yadov, P.E. Canalas, X. Dong & P.C. Ronald. 2001. Evidence for a disease- resistance pathway in rice similar to the NPR1 - mediated signaling pathway in Arabidopsis. Plant J. 27:101-113. Dickman M.B. & J.C. Reed. 2003. Paradigms for Programmed Cell Death in Animals and Plants. Pp. 26-43 in Programmed Cell Death in Plants (J. Gray, ed). Blackwell Publishing, UK. Dickman M.B., Y.K. Park, T. Oltersdorf, W. Li, T. Clemente & R. French. 2001. Abrogation of disease development in plants expressing animal anti-apoptotic genes. Proc. Nat’l. Acad. Sci. 98:6957-6962. Gale M.D., & K.M. Devos. 1998. Comparative genetics in the grasses. Proc. Nat’l. Acad. Sci. 95:1971-1974. Jones A.M. & J.L. Dangl. 1996. Logjam at the Styx: programmed cell death in plants. Trends in Plant Science 1:114-1109. Li W. & M.B. Dickman. 2004. Abiotic stress induces apoptotic-like features in tobacco that is inhibited by expression of human Bcl-2. Biotech. Letters 26:87-95. Martin G.B., A.J. Bogdanove & G. Sessa. 2003. Understanding the functions of plant disease resistance proteins. Annu. Rev. Plant Biol. 54:23-61. McDowell J.M. & B.J. Woffenden. 2003. Plant disease resistance genes: recent insights and potential applications. Trends in Biotechnology 21:178-183. Mitsuhara I., K.A. Malik, M. Miura & Y.Ohashi. 1997. Animal cell-death suppressors Bcl-x(L) and Ced-9 inhibit cell death in tobacco plants. Curr. Biol. 9: 775-778. Mittler R. & E. Lam. 1996. Sacrifice in the face of foes: pathogen-induced programmed cell death in plants. Trends in Microbiol 4:10-15. Navarre D.A. & T.J. Wolpert. 1999. Victorin induction of an apoptotic/senescence-like response in oats. Plant Cell 11:237-249. Pennell R.I. & C. Lamb. 1997. Programmed cell death in plants. Plant Cell 9:1157-1168. Piedras P., K.E. Hammond-Kosack, K. Harrison & J.D.G. Jones. 1998. Rapid Cf9 and Avr-dependent production of active oxygen species in tobacco suspension cultures. Mol. Plant Micro. Interact 11:1155-1166. Rensink W.A. & C.R. Buell. 2004. Arabidopsis to rice. Applying knowledge from a weed to enhance our understanding of a crop species. Plant Physiol. 135: 622-629. InfoMusa - Vol. 13 - No.210 InfoMusa - Vol. 13 - No.2 11 Diseases and pests: A review of their importance and management Randy Ploetz Rice Chromosome 10 Sequencing Consortium. 2003. In depth view of structure. Activity and evolution of rice chromosome 10. Science 300:1566-1569. Richberg M.H., D.H. Aviv & J.L. Dangl. 1998. Dead cells do tell tales. Curr. Opin. Plant Biol. 1:480-488. Ryerson D.E. & M.C. Heath. 1996. Cleavage of nuclear DNA into oligonucleosomal fragments during cell death induced by fungal infection or by abiotic treatments. Plant Cell 8:393-402. Solomon M., B. Belenshi, M. Delledonne, E. Menachem & A. Levine. 1999. The involvement of cysteine proteases and protease inhibitor genes in the regulation of programmed cell death in plants. The Plant Cell 11:431-444. Zhao B.Y., E. Ardales, E. Bresset, L.E. Claflin, J.E. Leach & S.H. Hulbert. 2004. The Rxo1/Rba1 locus of maize controls resistance reactions to pathogenic and non- host bacteria. Theor. Appl. Genet. 109:71-79. Martin B. Dickman works at the University of Nebraska, Department of Plant Pathology, Lincoln, Nebraska 68583 USA D iseases and pests are increasingly limiting factors in smallholder and export production, and can cause catastrophic losses (Jones 2000a). Diseases are the reason breeding programs were established in Trinidad, Jamaica, Honduras and Nigeria, and have been cited as a primary reason for the creation of INIBAP (Buddenhagen 1993). It is most appropriate that a session of this meeting is devoted to these production constraints. Musa diseases and pests are significant problems worldwide. Diseases affect all portions of the plants, are caused by fungi, bacteria and viruses, and have been the subjects of entire books (Jones 2000a, Stover 1972, Wardlaw 1961). Pests, although of an overall lower importance, are nonetheless serious production factors in their own right (Gold et al. 2001, Gold et al. 2002, Gowen and Quénéhervé 1990). This short review lists the most important of these problems and concludes with a discussion of some current issues. The major diseases Fungal diseases Diseases that are caused by fungi are most common and destructive (Jones 2000). Leaf spot diseases caused by species of Mycosphaerella result in moderate to severe damage wherever significant rainfall occurs (Jacome et al. 2003). Black leaf streak disease, better known as black Sigatoka and caused by Mycosphaerella fijiensis, is most important. It occurs throughout the humid, lowland tropics and has a wide host range that includes the Cavendish subgroup (AAA) and plantains (AAB). In some areas, eumusae leaf spot, caused by Mycosphaerella eumusae, Sigatoka, caused by Mycosphaerella musicola, and speckle, caused by Mycosphaerella musae, are equally or more important. Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), is a lethal and widespread problem on this crop (Ploetz and Pegg 2000). It devastated the export trade that depended on ‘Gros Michel’ AAA until ca. 1960. A recently recognized variant, tropical race 4 (TR4), affects Cavendish cultivars and threatens export and smallholder production of it and many other cultivars outside its endemic, Southeast Asian range. Of serious but lesser concern are: the leaf spot diseases cladosporium speckle, caused by Cladosporium musae, and freckle, caused by Guignardia musae; the post-harvest problems anthracnose and crown rot, caused primarily by Glomerella musae; and root rots caused by Cylindrocladium/Calonectria spp. (Jones 2000b, Jones 2000c, Muirhead and Jones 2000, Ploetz et al. 2003a). Bacterial diseases Bacteria cause several types of diseases, the most significant of which are vascular wilts (Thwaites et al. 2000). With the exception of the Philippines, Moko, caused by race 2 of Ralstonia solanacearum, is restricted to the Western Hemisphere. It has eliminated the highly susceptible ‘Bluggoe’ (ABB) in many production areas in the west. In contrast, blood disease, caused by a Ralstonia sp. Pests and diseases InfoMusa - Vol. 13 - No.212 InfoMusa - Vol. 13 - No.2 13 Figure 1. Damage caused by nematodes (possibly solanacearum), is found in the Eastern Hemisphere in only some islands in the Indonesian archipelago. Moko and blood disease produce similar symptoms on banana and have modes of transmission that include transmission by flying insects. Recently, the pathogen that causes bacterial wilt of enset, Xanthomonas campestris pv. musarum, has been implicated in a devastating epidemic on banana in Uganda (Thwaites et al. 2000, Tushemerierwe et al. 2003, S. Eden-Green personal communication 2004). A fruit rot, Bugtok, which is caused by R. solanacearum, is restricted to the Philippines. Less important, but more widely spread, are rots of the rhizome and pseudostem that are caused by Erwinia spp. (Thwaites et al. 2000). Viral diseases There are four significant diseases of banana that are caused by viruses (Jones 2000, Ploetz et al. 2003a). Bunchy top is the most damaging and total losses can occur if early diagnosis and strict sanitation is not practiced. It is most likely caused by Banana bunchy top virus (BBTV) (cause and effect have not been demonstrated in artificially inoculated plants), and with the exception of three islands in the Hawaiian chain is only found in the Eastern Hemisphere. Bract mosaic, caused by Banana bract mosaic virus (BBMV), has a more restricted distribution in the east, and is less destructive than bunchy top. In contrast, banana streak, caused by Banana streak virus (BSV), and banana mosaic, caused by Cucumber mosaic virus (CMV), are present in most areas where banana is grown. They usually cause minor damage, but severe strains of each exist. Before BSV and streak were described (Lockhart 1986), streak symptoms were often confused with those of mosaic (Stover 1972, Wardla 1961). At least four strains of BSV that are linked to the B genome can be activated (become episomal) in A X B germplasm via meiosis and tissue culture-induced stress (Geering et al. 2001, Geering personal communication 2004). They threaten progress in banana breeding programmes and the safe movement of hybrid germplasm. The major pests Nematodes are the most important pests of banana and, depending on environment and geographic location, four species can cause significant damage (Gowen and Quénéhervé 1990) (Figure 1). The burrowing nematode, Radopholus similis, is the most widespread (Sarah et al. 1996). Pratylenchus coffeae and Pratylenchus goodeyi cause equally serious damage but are, respectively, less prevalent and relatively uncommon on banana worldwide (Bridges et al. 1997). All of the above impact production in the tropics, whereas the spiral nematode, Helicotylenchus multicinctus, causes greater damage in the subtropics (McSorley and Parrado 1986). The weevil borer, Cosmopolites sordidus, is the most prevalent and important insect on banana (Gold et al. 2001). Management Options for the sustainable management of these problems are usually limited. Cultural measures can be very successful against some diseases, and the sanitation and roguing procedures that are used against bunchy top and Moko disease are prominent examples (Thomas and Iska-Caruana 2000, Thwaites et al. 2000). However, they are marginally effective in other situations, most notably deleafing for the management of black leaf streak in high rainfall areas (although deleafing played a major role in the recent eradication of the disease in the Tully area in Australia, it coincided with unusually dry weather). Chemical control is effective against leaf spots, but due to its high cost it is not an Gi se lla O Rj ed a, IN IB AP InfoMusa - Vol. 13 - No.212 InfoMusa - Vol. 13 - No.2 13 Figure 2. Plot infested with Xanthomonas campestris in the Democratic Republic of Congo (left) and infected fruit (right). option for smallholders. In contrast, export production of the Cavendish cultivars would not be possible without the liberal use of fungicides. To a lesser extent, banana pests can also be managed chemically. The environmental impacts and human health issues that are associated with pesticide usage in banana production have received considerable attention (Ploetz 2000, Ploetz et al. 2003b). Genetic resistance is environmentally benign and very effective against some diseases and pests. Resistance to the Mycosphaerella leaf spots, Fusarium wilt and R. similis exists among the land races. They have been used to replace susceptible clones and, whenever possible, as parents in conventional breeding programs. To a lesser extent, resistance also exists in land races against Moko, other nematodes and C. sordidus; in general, it has not been used in breeding programs. With few exceptions, poor natural resistance exists for the bacterial and viral problems and nematodes other than R. similis. Thus, nonconventional approaches, in particular genetic transformation, have received considerable attention when these problems have been considered in improvement programmes. The extent to which transformed or genetically modified bananas will solve these problems and whether consumers will accept them are presently unknown. I conclude with a closer look at a few important problems. New threats Bacterial wilt epidemic in Uganda Until recently bacterial wilt (BXW), caused by X. campestris pv. musacearum, was viewed as a problem on enset, Ensete ventricossum, but not banana (Thwaites et al. 2000). Banana was known to be susceptible, but because it is an unimportant crop in Ethiopia, BXW was not viewed as an important banana disease. The rapidity with which BXW has moved is alarming. First recognized on a single farm in the Mukono District in October 2000, the disease was reported in 15 sub- counties in four more districts by June 2003 (Tushemereirwe et al. 2003). By October 2003, the disease was confirmed in 10 total districts and suspected in eight more (see map at: http://www.cabi-bioscience.org/Html/ GlobalPlantClinic.htm). Currently, the disease has been confirmed in 18 districts in Uganda as well as the Democratic Republic of Congo (G. Blomme personal communication 2004, S. Eden-Green personal communication 2004). Up to 70% of the plants have been lost in some fields (Figure 2). Both exotic and East African highland bananas (EAHB) are susceptible. Since the pathogen is apparently moved via flying insects and the disease occurs in a resource- poor area, where eradication and/or control measures would be difficult to implement, continued spread is probable. BXW clearly threatens vast areas of banana throughout East Africa. TR4 of Fusarium wilt The recognition of TR4 as distinct pathotype of Foc is recent. Isolates of VCG01213/ Gu y B lom me , IN IB AP Gu y B lom me , IN IB AP InfoMusa - Vol. 13 - No.214 InfoMusa - Vol. 13 - No.2 15 Figure 3: Leaf symptoms of black leaf streak disease (left) and eumusae leaf spot disease (right) 01216 have been recovered from samples sent to the author from Sumatra by R.H. Stover in early 1992, and by 1994 the VCG had been recovered from Cavendish plantations in peninsular Malaysia and Indonesia. The pathogenicity of several of the isolates was demonstrated on ‘Silk’ (AAB), ‘Bluggoe’ (ABB) and ‘Grande naine’ (AAA) (Ploetz unpublished). TR4 is now found in Australia (Northern Territory), Indonesia (Halmahera, Irian Jaya, Java, Sulawesi and Sumatra), Malaysia (Peninsular), Papua New Guinea, and Taiwan (Ploetz et al. 2003a). It is pathologically distinct from subtropical race 4 in that damage occurs in the absence of predisposing conditions (e.g. cold weather). It is also genetically distinct and comprised of only isolates in VCG 01213/01216. That TR4 devastates Cavendish in the tropics has dire implications for export production in Southeast Asia and the extensive Cavendish trades in the Western Hemisphere (Ploetz et al. 2003b). Since TR4 affects other important groups, such as the AAB plantains, it also threatens smallholder production in Western Africa and Latin America Minimising the spread of TR4 depends on the strict observance of quarantine measures against the movement of suckers and rhizomes. This would protect production in the west, but additional information would be needed to combat the problem in Southeast Asia, where the epidemiology of the disease is not well understood. Since the pathogens appeared where banana had not been grown recently and in plots that had been established with tissue culture plantlets, their source is a mystery. Relevant questions include: 1) How long can the pathogens survive in the absence of a banana host? 2) What alternative, non-banana hosts are present in these production areas, and what is their distribution and impact? 3) If the tissue culture plantlets were pathogen-free, was the pathogen moved to the above sites by some other means? Research is needed to answer these questions and combat the situation in Southeast Asia, and a watchful eye and set of contingency plans, if TR4 arrives, is needed in the west (Ploetz 2003, Ploetz et al. 2003b). Unclear or developing threats Eumusae leaf spot Since eumusae leaf spot has been recognised less than a decade ago, important attributes of the pathogen and disease are not known. The geographic distribution of the disease is poorly understood and probably underestimated due to its resemblance to black leaf streak (Figure 3). Work to determine the disease’s occurrence and prevalence outside the known affected areas should continue. In addition, basic studies on the disease’s epidemiology, management, host range and impact are needed. Banana streak Work is needed on the epidemiology of banana streak and its variable impact on production. Only partially understood is what distinguishes areas where serious problems occur from those where ‘Mysore’ AAB is essentially the only cultivar that is affected or where infection reduces yields only slightly (Daniells et al. 2001). Severe strains of BSV undoubtedly play a role, but recent results from neighboring Uganda suggest that heavily impacted areas might also be those in which diverse vectors are present (Harper et al. 2004). All of the factors that influence symptom expression are also not known (Lockhart and Jones 2000, Ploetz et al. D. Jo ne s Ci rad InfoMusa - Vol. 13 - No.214 InfoMusa - Vol. 13 - No.2 15 2003a). Although temperature and different developmental stages of the host have been associated with this variation, other factors may be involved. Research should continue on the varied genetic makeup of the pathogen and the activation of some integrated strains. Declining productivity in Uganda Banana has been cultivated in Uganda for over 1000 years and is the basis for subsistence agriculture in much of the East African highlands (Purseglove 1972). In recent decades, yields have declined in central Uganda (Abera et al. 1999). Although these reductions have been well documented, their cause(s) remain(s) obscure. Declining fertility in these long-lived production systems (some plantings have existed for several generations) has been suggested, as has reduced management (Abera et al. 1999). A recent study indicates that nitrogen and potassium fertility probably play secondary roles in this phenomenon and that the primary roles are more likely played by diseases and pests (Smithson et al. 2001). If Smithson et al. (2001) are correct, which diseases and pests are responsible and why they only recently impacted these old agroecosystems need to be determined. The list of factors that may be involved is long and includes nematodes, the banana weevil, several leaf spots and BSV. Given this long list it is clear that a thorough investigation of the variables would be an enormous task. That said, a focused, multidisciplinary approach to understanding this problem, wherein the major candidates were tested in factorial experiments against one or two important EAHB, could yield valuable insight into this problem. It is hoped that BXW will not make such insight moot. A final problem Biocontrol studies on Fusarium wilt Fusarium wilt is among the most difficult diseases to manage on banana. Effective fungicides are not available, resistance is not always an important breeding target, and infested soils remain so for decades (Buddenhagen 1990, Stover 1962). Were they available, effective biological control measures for this disease would be most useful. Fusarium wilt of banana is an especially difficult target for biocontrol. The soil environment in which the pathogen resides complicates protection of the infection site, and the vascular location of the pathogen, once infection has occurred, protects it from many potential biocontrol agents. Most importantly, disease control must be highly effective and long lasting since banana is usually grown as a perennial. In a recent review, the only successful example of the biological control of a Fusarium wilt on a perennial crop was of soils that suppressed the development of Fusarium wilt of banana (Fravel et al. 2003). To date, this trait has not been transferred to a disease conducive soil (i.e. it appears to be restricted to certain soil types). Although papers on the biological control of this disease have been published in referred journals, none offer real hope that this approach will be successful. Most of these studies do not address disease reduction in the field. Rather, they focus on in vitro inhibition of the pathogen by microbial agents (Sivamani and Gnanamanickam 1988, Thangavelu et al. 2004), biochemical traits of the host, pathogen, or their interactions (Thangavelu et al. 2003), or disease reduction in pot studies in glasshouses (Saravanan et al. 2003, Thangavelu et al., 2004). When field studies have been reported the results have been disappointing. To date, the best result from a field study reported an 18% loss after 11 months (Saravanan et al. 2003). After 5 years, this rate would result in total losses of over 70%! Clearly, future work in this area needs to focus on disease reduction in field situations. Without such a focus, biocontrol research on this disease will continue to be open to substantial and justified criticism. References Abera A.M.K., F. Bagamba, C.S. Gold, E.B. Karamura & A. Kiggundu. 1999. Geographic shifts in the highland cooking banana (Musa spp., group AAA-EA). International Journal for Sustainable Development & World Ecology 6:45-59. Bridge J., R. Fogain & P. Speijer. 1997. The root lesion nematodes of banana:Pratylenchus coffeae (Zimmermann, 1898) Filip. & Schu. Stek., 1941, Pratylenchus goodeyi Sher & Allen, 1953. Musa Pest Fact Sheet No. 2. INIBAP, Montpellier, France. Buddenhagen I.W. 1990. Banana breeding and Fusarium wilt. Pp. 107-113 in Fusarium Wilt of Banana (R.C. Ploetz, ed.). APS Press, St. Paul. InfoMusa - Vol. 13 - No.216 InfoMusa - Vol. 13 - No.2 17 Buddenhagen I.W. 1993. Whence and whither banana research and development? Pp. 12–26 in Biotechnology Applications for Banana and Plantain Improvement. INIBAP. Montpellier, France. Daniells J.W., A.D.W. Geering, N.J. Byrde & J.E. Thomas. 2001. The effect of Banana streak virus on the growth and yield of dessert bananas in tropical Australia. Annals of Applied Biology 139: 51-60. Fravel D., C. Olivain & C. Alabouvette. 2003. Fusarium oxysporum and its biocontrol. New Phytologist 157: 493-502. Geering A.D.W., N.E. Olszewski, G.Dahal, J.E. Thomas & B.E.L. Lockhart. 2001. Analysis of the distribution and structure of integrated Banana streak virus DNA in a range of Musa cultivars. Molecular Plant Pathology 2: 207-213. Gold C.S., J.E. Peña & E.B. Karamura. 2001. Biology and intergrated pest management for the banana weevil Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae). Integrated Pest Management Reviews 6:79-155. Gold C.S., B. Pinese & J.E. Peña. 2002. Pests of banana. Pp. 13-56 in Tropical Fruit Pests and Pollinators: Biology, Economic Importance, Natural Enemies and Control (J.E. Peña, J.L. Sharp & M. Wysocki, eds). CABI Publishing. Wallingford, Oxon, UK. Gowen S.R. & P. Quénéhervé. 1990. Nematode parasites of banana, plantains and abacá in Plant Parasitic Nematodes in Subtropical and Tropical Agriculture (M. Luc, R.A. Sikora & J. Bridge, eds). CABI Publishing. Wallingford, Oxon, UK. Harper G., D. Hart, S. Moult & R. Hull. 2004. Banana streak virus is very diverse in Uganda. Virus Research 100: 51-56. Jacome L., P. Lepoivre, D. Marin, R. Ortiz, R. Romero & J.V. Escalant (eds.). 2003. Mycosphaerella leaf spot diseases of bananas: present status and outlook. Proceedings of the 2nd international workshop on Mycosphaerella leaf spot diseases held in San José, Costa Rica, 20-23 May 2002. INIBAP, Montpellier, France. 318pp. Jones D.R. (ed.) 2000a. Diseases of Banana, Abacá and Enset. CABI Publishing. Wallingford, Oxon, UK. 544pp. Jones D.R. 2000b. Cladosporium speckle. Pp. 108-111 in Diseases of Banana, Abacá and Enset. (D.R.Jones, ed.). CABI Publishing. Wallingford, Oxon, UK. Jones D.R. 2000c. Freckle. Pp. 120-125 in Diseases of Banana, Abacá and Enset (D.R Jones, ed.). CABI Publishing. Wallingford, Oxon, UK. Lockhart B.E.L. 1986. Purification and serology of a bacilliform virus associated with banana streak disease. Phytopathology 76:995-999. Lockhart B.E.L. & D.R. Jones. 2000. Banana streak. Pp. 262-274 in Diseases of Banana, Abacá and Enset. (D.R. Jones, ed.). CABI Publishing. Wallingford, Oxon, UK. McSorley R. & J.L. Parrado. 1986. Helicotylenchus multicinctus on bananas: an international problem. Nematropica 16:73-91. Muirhead I.F. & D.R. Jones. 2000. Anthracnose. Pp. 199- 203 in Diseases of Banana, Abacá and Enset (D.R. Jones, ed.). CABI Publishing. Wallingford, UK. Ploetz R.C. 2003. “Yes. We won’t have bananas.” What realistic threats do diseases pose to banana production? Pesticide Outlook 14:62-64. Ploetz R.C. 2000. Management of the most important disease of banana, black Sigatoka. Pesticide Outlook 11:19-23. Ploetz R.C. & K.G. Pegg. 2000. Fusarium wilt. Pp. 143-159 in Diseases of Banana, Abacá and Enset (D.R. Jones, ed.). CABI Publishing. Wallingford, UK. Ploetz R.C., J.E. Thomas & W. Slaubaugh. 2003a. Diseases of banana and plantain. Pp. 73-134 in Diseases of Tropical Fruit Crops (R.C. Ploetz, ed.). CABI Publishing . Wallingford, Oxon, UK. Ploetz R.C., L.W. Timmer & S.M. Garnsey. 2003b. Management of tropical fruit diseases: Current overview and future outlook. Pp. 465-481 in Diseases of Tropical Fruit Crops (R.C. Ploetz, ed.). CABI Publishing. Wallingford, Oxon, UK. Purseglove J.W. 1972. Tropical Crops. Monocotyledons 2. Longman Press, London. 349 pp. Sarah J.L., J. Pinochet & J. Stanton. 1996. The burrowing nematode of bananas, Radopholus similis Cobb, 1913. Musa Pest Fact Sheet No. 1. INIBAP, Montpellier, France. Saravanan T., M. Muthusamy & T Marimuthu. 2003. Development of integrated approach to manage the fusarial wilt of banana. Crop Protection 22:1117-1123. Smithson P.C., B.D. McIntyre, C.S.Gold, H. Ssali & I.N Kashaija. 2001. Nitrogen and potassium fertilizer vs. nematode and weevil effects on yield and foliar nutrient status of banana in Uganda. Nutrient Cycling in Agroecosystems 59:39-250. Sivamani E. & S.S. Gnanamanickam. 1988. Biological control of Fusarium oxysporum f.sp. cubense in banana by inoculation with Pseudomonas fluorescens. Plant and Soil 107:3-9. Stover R.H. 1962. Fusarial wilt (Panama disease) of bananas and other Musa species. CMI, Kew, Surrey, UK. 117pp. Stover R.H. 1972. Banana, Plantain and Abaca diseases. Commonwealth Mycological Institute, Kew, Surrey, UK. 316pp. Thangavelu R., A. Palaniswami & R. Velazhahan. 2004. Mass production of Trichoderma harzianum for managing fusarium wilt of banana. Agricultural Ecosystems and Environment 103:259-263. Thangavelu R., A. Palaniswami, S. Doraiswamy & R. Velazhahan. 2003. The effect of Pseudomonas fluorescens and Fusarium oxysporum f.sp. cubense on induction of defense enzymes and phenolics in banana. Biologia Plantarum 46:107-112. Thomas J.E. & M.L. Iskra-Caruana. 2000. Bunchy top. Pp. 241-253. in Diseases of Banana, Abacá and Enset (D.R. Jones, ed.). CABI Publishing. Wallingford, Oxon, UK. Thwaites R., S.J. Eden-Green & R. Black. 2000. Diseases caused by bacteria. Pp. 213-239 in Diseases of Banana, Abacá and Enset (D.R. Jones, ed.). CABI Publishing. Wallingford, Oxon, UK. Tushemereirwe W., A. Kangire, J. Smith, F. Ssekiwoko, M. Nakyanzi, D. Katuma, C. Musitwa & R. Karyaija. 2003. An outbreak of bacterial wilt in Uganda. InfoMusa 12(2): 6-8. Wardlaw C.W. 1961. Banana Diseases including Plantains and Abaca. Longmans, Green and Co Ltd., London, UK. 648pp. Randy Ploetz works at the University of Florida, Tropical Research and Education Center, 18905 SW 280th Street, Homestead, FL 33031-3314 USA InfoMusa - Vol. 13 - No.216 InfoMusa - Vol. 13 - No.2 17 Population genetic structure and dispersal of Mycosphaerella fijiensis Jean Carlier T o ensure the sustainability of production systems, the strategies elaborated to manage diseases should take into account the evolutionary and epidemiological factors that affect the pathogens. But since such strategies will be applied on spatial and temporal scales not amenable to experiments, simulation models have to be developed in order to evaluate their efficiency and sustainability. To be realistic, these models need to be fed parameters measured in the field, hence the importance of conducting studies on the epidemiology and populations of pathogens. Among the epidemiological and evolutio- nary factors that need to be evaluated, dispersal processes and their impact on gene flow are fundamental to the development of epidemics and pathogen evolution. Rapid aerial dispersal of pathogens at the global and continental scales can have extreme consequences on plant diseases (Brown and Hovmøller 2002). These authors made a distinction between two forms of dispersal from an inoculum source. The first is a rare, unpredictable single–step invasion involving the transport of spores over very long distances and even between continents. This stochastic form of dispersal can also be the result of transporting infected plant material and tends to occur mainly at a global scale. The second form consists in the gradual expansion of the range of pathogen populations within a continent through normal pathogen dispersal processes. However, single-step invasions may also be involved in the dispersal of a disease at a continental scale. Mycosphaerella fijiensis, which causes black leaf streak disease in bananas, is an example of a recent fungal epidemic that has spread through the tropical world. Like Mycosphaerella musicola, which causes Sigatoka disease, this leaf spot disease originates in Southeast Asia (Mourichon and Fullerton 1990, Pasberg-Gauhl et al. 2000). It is still spreading and replacing M. musicola as the dominant leaf spot pathogen. Mycosphaerella fijiensis is an haploid and heterothallic ascomycete fungus that spreads through three modes: the movement of infected plant material (infected suckers and diseased leaves used to wrap food or other goods), the dispersal of ascospores (produced during sexual reproduction) and the dispersal of conidia (produced during asexual reproduction) (Gauhl et al. 2000). Whereas conidia are mainly dispersed over short distances on the plant and to nearby plants, viable ascospores might be carried a few hundred kilometers by wind (Parnell et al. 1998). Recent population and epidemiological studies of M. fijiensis mainly provide information on the level and distribution of variability of the fungus and on its dispersal. Population structure and dispersal processes The population structure of M. fijiensis was analysed at the global and plant scales by using molecular markers (Carlier et al. 1996, Hayden et al. 2003a, Rivas et al. 2004). The results indicate that a high level of genetic diversity has been maintained at the plantation and plant scales. The loci were at gametic equilibrium in most of the samples analysed, suggesting random-mating popu- lations of M. fijiensis, even at the scale of the plant. Founder effects were detected at the global and continental scales. The level of genetic differentiation between populations was highest at the global scale (Fst = 0.52 between some continents) and almost nil at the local scale (Fst = 0 between nearby plantations) (Figure 1). The population structures observed at the global and continental scales reflect the dispersal history of M. fijiensis. Southeast Asia had the highest level of genetic diversity, supporting the hypothesis that the pathogen originated in the region. In the Latin America and Caribbean region, the highest levels of genetic diversity were observed in populations from Honduras and Costa Rica, corroborating the hypothesis that the pathogen entered the continent in this area (Pasberg-Gauhl et al. 2000). In Africa, the Fungal diseases InfoMusa - Vol. 13 - No.218 InfoMusa - Vol. 13 - No.2 19 levels of genetic diversity in most countries were similar, making it difficult to locate the place(s) where the pathogen first entered the continent (Pasberg-Gauhl et al. 2000). It is possible that the samples from Africa did not include ones from or near the original population(s). The lowest levels of genetic diversity were detected in Côte d’Ivoire and the Comoros, countries respectively located at the western and eastern extremities of the distribution of the disease in Africa. The results reflect the relative importance of dispersal through infected plant materials and ascospores depending on the geographical scale (Figure 1). At the global scale, the introduction of the disease on the different continents is probably from infected plant material. The spread of the disease within a continent probably results from the limited dispersal of ascospores (Figure 2) over a few hundred kilometers or from the movement of infected plant material. The dispersal of M. fijiensis over long distances appears to be stochastic, which has led to founder effects, a limited gene flow between established populations and, as result, a high level of genetic differentiation between them. As the distance decreases, dispersal through ascospores becomes more important, which results in a lower level of genetic differentiation. Finally, the existence of random-mating populations of M. fijiensis at plant and plantation scales are in agreement with investigations showing the important role played by wind in the dispersal of ascospores at these scales (Rutter el al. 1998). The data could not be used to evaluate the relative importance of dispersal through ascospores and conidia at the plant and plantation scales since the cloned isolates came from ascospores only. Estimating the dispersal distance of ascospores Two complementary approaches were used to estimate gene flow and the dispersal of ascospores at the scale of a plantation and a production area (over a few hundred kilometers). An indirect population genetic approach based on the isolation by distance model (Wright 1951) was used at the scale of a production area. In this model, dispersal occurs preferentially between nearby subpopulations, leading to a correlation between geographic and genetic distances. The study was conducted in Costa Rica and Cameroon in 300-km-long production areas (Rivas 2003, Coste unpublished results). In total, more than 300 cloned monoascospore isolates from 10 to 15 banana plantations distributed along a transect were analysed by using PCR-RFLP (Zapater et a.l 2004) and microsatellites (Neu et al. 1999, Zapater unpublished results) markers. The data were analysed by using the method developed by Rousset (1997). A strong isolation by distance was detected in both countries, suggesting that the mean dispersal of ascospores is very much inferior to 300 km. A direct approach based on the analysis of the disease gradient (McCartney and Fitt 1998) was also used. The dispersal from an inoculum source was analysed in an isolated plantation during a period corresponding to one sexual cycle (around 4 weeks) (Abadie unpublished results). Significant spatial autocorrelations were detected, suggesting the existence of a disease gradient. The distribution of the disease fitted a negative exponential curve. The estimated dispersal distance of ascospores was around 30 meters, a distance very much inferior to 300 km. The results obtained using population genetic and epidemiological approaches appear coherent. Figure 2. In vitro germinated and non germinated ascospores of Mycosphaerella fijiensis. Ascospores Conidia Infected plant material Single-step invasion Rare dispersal events Gradual extension Frequent dispersal events Scale: Level Fst : 0.0 0.0 0.13 0.30 0.52 Plant Plantation Locality Country Continent Globe Figure 1 . Hypothetical relative importance of the three dispersal modes of the fungus Mycosphaerella fijiensis as a function of geographical scales and genetic differentiation between populations (estimated by Fst). Je an C arl ier , C ira d InfoMusa - Vol. 13 - No.218 InfoMusa - Vol. 13 - No.2 19 Perspectives Similar population structures have also been obtained for M. musicola (Hayden et al. 2003b, Carlier et al 2003). The newly discovered pathogen Mycosphaerella eumusae, which causes eumusae leaf spot disease (Crous and Mourichon 2002), has been observed mainly in Southeast Asia (Carlier et al. 2000), which is not only the centre of origin of all three pathogen but also of the host genus Musa (Stover and Simmonds 1987). Studying the distribution and population structure of the three Mycosphaerella pathogens in Southeast Asia would help localize zones of co-evolution. Such zones are potential sources of resistance and the host-pathogen interactions of the three pathogens could be compared. Studying the pathogen populations in their natural systems should provide better knowledge on their epidemiology and their evolution. With regards to M. fijiensis, the effect of genetic recombination, genetic drift and gene flow on the pathogen population structure according to its reproductive strategy, population size and dispersal process is only beginning to be understood. However, the relative importance of sexual and asexual reproduction over short distances has yet to be estimated. This proportion can be determined by using molecular markers and samples of conidia obtained by cloning (Chen and McDonald 1996). Although the relative importance on a continental scale of dispersal through ascospores and infected plant material is not known, improving quarantine measures might limit the risk of introducing the disease in new areas and exchanges between existing populations in different countries. Since the dispersal distance of ascospores appears to be restricted to only a fraction of the length of a production area that is a few hundred kilometers long, disease management should also try to limit the natural dispersal of the pathogen at the scale of a production area in order to limit gene flow between pathogen populations. This epidemiological characteristic should be exploited to devise efficient and sustainable disease management strategies at the scale of producing areas. The estimated dispersal parameters could also be used in regional models to test the effect of varying host distribution and host resistance in space and time. The results of such modelling exercises can be used to evaluate the need to conduct other experiments on the dispersal of M. fijiensis ascospores. Parameters related to the selection pressure exerted on pathogen populations by fungicides and host resistance should also be integrated in the models developed to test the sustainability of disease management strategies, but the experiments set up to estimate these parameters should try to limit gene flow. For example, in a study conducted at a local scale to evaluate the selection pressure exerted by host resistance, gene flow was so high that it probably counteracted the effect of selection (Abadie et al. 2003). References Abadie C., A. El Hadrami, E. Fouré & J. Carlier. 2003. Efficiency and durability of partial resistance components of bananas against black leaf streak disease. Pp. 161-168 in Mycosphaerella leaf spot diseases of bananas: Present status and outlook. (L. Jacome, P. Lepoivre, R. Marin, R. Ortiz, R. A. Romero and J. V. Escalant, eds). INIBAP, Montpellier. Brown J.K.M. & M.S. Hovmøller. 2002. Aerial dispersal of pathogens on the global and continental scales and its impact on plant disease. Science 297:537-541. Carlier J., M.H. Lebrun, M.F. Zapater, C. Dubois & X. Mourichon. 1996. Genetic structure of the global population of banana black leaf streak fungus, Mycosphaerella fijiensis. Molecular Ecology 5:499- 510. Carlier J., M.F. Zapater, F. Lapeyre, D.R. Jones & X Mourichon. 2000. Septoria leaf spot of banana: A newly discovered disease caused by Mycosphaerella eumusae (anamorph Septoria eumusae). Phytopathology 90(8):884-890. Chen R.S. & B. A. McDonald.1996. Sexual reproduction plays a major role in the genetic structure of population of the fungus Mycosphaerella graminicola. Genetics 142:1119-1127. Carlier J., H. Hayden & G. Rivas-Platero. 2003. Genetic differentiation in the Mycosphaerella leaf spot pathogens of bananas. Pp.123-129 in Mycosphaerella leaf spot diseases of bananas: Present status and outlook. (L. Jacome, P. Lepoivre, R. Marin, R. Ortiz, R. A. Romero and J. V. Escalant, eds.). INIBAP, Montpellier. Crous P.W. & X. Mourichon. 2002. Mycosphaerella eumusae and its anamorph Pseudocercospora eumusae spp. Nov.: causal agent of eumusae leaf spot disease. Sydovia 54:35-43. Gauhl F., C. Pasberg-Gauhl, & D.R. Jones. 2000. Black leaf streak. Disease cycle and epidemiology. Pp. 56-62 in Disease of bananas, Abaca and Enset (D.R. Jones, ed.). CABI, Wallingford. Hayden H.L., J. Carlier & E.A.B. Aitken. 2003a. The genetic structure of Mycosphaerella fijiensis from Australia, Papua New Guinea and the Pacific Islands. Plant Pathology 52:703-712. Hayden H.L., J. Carlier & E.A.B. Aitken. 2003b. Population differentiation in the banana leaf spot pathogen InfoMusa - Vol. 13 - No.220 InfoMusa - Vol. 13 - No.2 21 Mycosphaerella musicola, examined at a global scale. Plant Pathology 52:713-719. Mourichon X. & R.A. Fullerton. 1990. Geographical distribution of the two species Mycosphaerella musicola Leach (Cercospora musae) and M. fijiensis Morelet (C. fijiensis), respectively agents of Sigatoka disease and black leaf streak disease in Bananas and Plantains. Fruits 45:213-218. Neu C., D. Kaemmer, G. Kahl, D. Fischer & K. Weising. 1999. Polymorphic microsatellite markers for the banana pathogen Mycosphaerella fijiensis. Molecular Ecology 8:523-525. Parnell M., P.J.A. Burt & K. Wilson. 1998. The influence of exposure to ultraviolet radiation in simulated sunlight on ascospores causing black Sigatoka disease of banana and plantain. International Journal of Biometeorology 42:22-27. Pasberg-Gauhl C., F. Gauhl & D.R. Jones. 2000. Black leaf streak. Distribution and economic importance. Pp. 37-44 in Disease of Bananas, Abaca and Enset (D.R. Jones, ed.). CABI, Wallingford. Rivas G.G. 2003. Effets de fondation et différenciation génétique aux échelles continentale et locale chez Mycosphaerella fijiensis, champignon responsable de la maladie des raies noires du bananier. Thesis, Ecole national supérieure agronomique de Montpellier. Rivas G.G., M.F. Zapater, C. Abadie & J. Carlier. 2004. Founder effect and stochastic dispersal at the continental scale of the fungal pathogen of bananas Mycosphaerella fijiensis. Molecular Ecology 13:471- 482. Rousset F. 1997. Genetic differentiation and estimation of gene flow from F-statistic under isolation by distance. Genetics 145:1219-1228. Rutter J., P.J.A. Burt & F. Ramirez. 1998. Movement of Mycosphaerella fijiensis spores and Sigatoka disease development on plantain close to an inoculum source. Aerobiologia, 14:201-208. Stover R.H. & N.W. Simmonds. 1987. Bananas. Willey & Sons, New York. Wright S. 1951. The genetical structure of populations. Annals of Eugenics 15:323-354. Zapater M.-F., A. Rakotonantoandro, F. Cohen & J. Carlier. 2004. PCR-RFLP markers for the fungal banana pathogen Mycosphaerella fijiensis. Molecular Ecology Notes 4:80-82. Soil quality problems in East African banana systems and their relation with other yield loss factors P.J.A. van Asten, C.S. Gold, S.H. Okech, S.V. Gaidashova, W.K. Tushemereirwe and D. De Waele I n the banana growing areas of the East African highlands (Uganda, Rwanda, Burundi, East Democratic Republic of Congo, Northwest Tanzania, and West Kenya), bananas occupy up to 30% of the cultivated land. The area is characterized by medium to high altitudes (900 - 2000 masl) and the presence of moderate to steep slopes that are prone to erosion. However, erosion under the permanent banana canopy is much smaller (<30%) than in annual cropped fields (Lufafa et al. 2003). In the last decades, concerns that banana yields in this region are declining have been voiced so often, that it is now considered as an established fact (Anonymous 2001, Baijukya and Steenhuijsen Piters 1998, Rishirumuhirwa 1997, Woomer et al. 1998). However, most reports on yield decline are based on farmers perceptions (Gold et al. 1999), since there is a general lack a good quality yield documentation. Unfortunately, it is very difficult to obtain reliable yield data from farmer fields because: (i) there is no single harvest period, (ii) bunch weights are season dependent, (iii) the length of the crop cycle is highly variable and depends on cultivar, plant nutrition and climate, (iv) bunch weights show high spatial variability at regional, village and farm level, and (v) bananas are often cultivated in mixed cropping systems and at mixed densities, complicating yield calculations on a per hectare basis. Yield data presented by FAO and government bodies are mostly based on rough estimates. Their data show that yields were mostly stable, while production and cultivated area increased steadily over the last 40 years (FAO 2004). Nonetheless, reports on banana yield decline go back to the 1940s and 1950s (McMaster 1962, Masefield 1949) and have persisted ever since. The lack of reliable banana production figures makes it difficult to quantify yield decline and the importance of different yield loss factors. Whether there is a yield decline or not, whether production figures are accurate or not, it is clear that actual yields of 5-30 t ha-1 yr-1 are very far from the 60-70 t ha-1 yr-1 attained in on-farm and on-station Jean Carlier works at the UMR 385 Biologie et Génétique des Interactions Plante-Parasite, CIRAD, TA 41/K, Baillarguet international campus, F-34398 Montpellier Cedex 5, France Soil fertility InfoMusa - Vol. 13 - No.220 InfoMusa - Vol. 13 - No.2 21 trials in the region (Smithson et al. 2001; Tushemereirwe et al. 2001). Actual soil quality problems The hypothesis that soil fertility decline contributed to declining banana yields in the region was first advanced by Masefield (1949) and McMaster (1962) and has been repeated ever since (Baijukya and de Steenhuijsen Piters 1998, Bekunda and Woomer 1996, Sseguya et al. 1999). However, there are very few data to test this hypothesis. In Uganda, Smithson et al. (2001) and Ssali and Vlek (unpublished) have attempted to compare quantitative soil data from the 1960s and 1990s. Both studies failed to find a change in organic matter content, but Ssali and Vlek observed a decrease in soil pH, exchangeable Ca2+ and K+. Most highland bananas are grown on ferralsols and acrisols soils, which have a low fertility. However, a substantial proportion of the bananas in the region is grown near the homestead (Rishirumuhirwa 1997, Rufino 2003). These homestead plots receive organic household residues and are more often mulched than plots further away. Bekunda and Woomer (1996) and Wortmann and Kaizzi (1998) found that most farmers transferred annual crop residues to banana fields. Farmers also tend to allocate their best land to the banana crop (Gold et al. 1999). Both land choice and soil management for bananas explain why banana fields contain more nutrients (especially P and K) than annual cropped fields and plots further away from the homestead (Bosch et al. 1996, Rufino 2003, Wortmann and Kaizzi 1998). Researchers worldwide (Bertsch 1986, Delvaux 1995, Lahav and Turner 1983, Landon 1991, Lopez and Espinoza 2000, Rubaihayo et al. 1994, Twyford 1967, Walmsley et al. 1971) have published guidelines for the interpretation of chemical soil data for banana farmers. These guidelines mostly address commercial desert bananas (AAA). Although the minimum soil requirements published vary (e.g. from 0.2 to 1.5 meq 100g dry soil for exchangeable K), most banana soils in the region (Banananuka and Rubaihayo 1994, Godefroy et al. 1991, Rufino 2003, Smithson et al. 2001, Wortmann and Kaizzi 1998, Rubaihayo et al. 1994) have optimum soil fertility according to the average of the guidelines (Van Asten et al. 2004). However, one should be cautious to draw conclusions on nutrient deficiencies from soil chemical analysis alone, since most studies find a poor correlation between soil fertility parameters and bunch yields (Bananuka and Rubaihayo 1994, Rufino 2003, Smithson et al. 2001). Most of the studies that used foliar analysis (Bosch et al. 1996, Gold et al. 1999, Okech et al. 2004, Rufino 2003, Smithson et al. 2001, Smithson et al. 2004, Ssali et al. 2003) identified K deficiency as a major constraint, often followed by N and Mg. Phosphorus deficiency does not seem to be a frequent problem for East African highland bananas. Little research has been conducted on micronutrients. Bosch et al. (1996) found very low Zn and Cu when compared to DRIS norms established for other AAA cultivars. Another method to detect nutrient deficiencies is by conducting fertilizer trials. Several studies that applied moderate fertilizer doses of N (100 kg), P (<100 kg) and K (25-200 kg) per hectare observed yield increases from 10-12 to 16-25 t ha-1 yr-1 (Okech et al. 2004, Rubaihayo et al. 1994, Zake et al. 2000). However, fertilizers seem to be less effective when nematode and weevil pressure are high (Smithson et al. 2001, Ssali et al. 2003), or when prolonged drought stress occurs (Okech et al. 2004). Soil physical properties and topsoil depth directly affect the rootability and water holding capacity of the soil. The latter influence the ability of roots to extract water and nutrients. Taulya (2004) observed that bunch weight increase from 8 to 16 kg when moving from soils with a shallow (<20 cm) to a deep (>30 cm) A-horizon. Despite the fact that soil moisture stress can lead to more than 60% yield loss (Okech, unpublished), soil physical aspects have received relatively little attention in the region. Potential soil quality problems Over the last decades, bananas have increasingly become a cash crop in the region to satisfy the growing urban markets. As a consequence, more and more nutrients are being lost from the farm and end up in urban areas from which recycling back to agriculture is barely feasible (Bekunda and Manzi 2004) (Figure 1). The banana bunches, especially the peel, are particularly rich in K and exportation of this element is of major concern. If nutrients exported from InfoMusa - Vol. 13 - No.222 InfoMusa - Vol. 13 - No.2 23 banana fields are not replenished by organic or inorganic fertilizers, then this leads to the mining of soil nutrient stocks and inevitably to yield decline in the long run. This problem can be observed in many African farming systems (Smaling 1993, Hartemink 2003). Wortmann and Kaizzi (1998) found that loss of N and P at four Ugandan banana sites was compensated by the large amounts of organic materials that were transferred from other land use types (annual crops, grassland) to the banana plots. Although N and P balances might sometimes be positive for banana plots, the transfer of nutrients from annual crop plots and grassland plots to banana plots leads to an acceleration of soil exhaustion at the majority of the farm land and cannot prevent a general decline in soil nutrient stocks at the farm level. In addition, soils under annual crops lose many nutrients through harvest and erosion (Wortmann and Kaizzi 1998), a process that is further accelerated when vegetation cover is reduced due to soil fertility decline. Some researchers suggest that an increase in livestock should be part of the solution, but Bekunda and Woomer (1996) and Sseguya et al. (1999) have shown that the use of cattle manure is closely related to farm size and that the latter is continuously shrinking under increasing land pressure. Although both farmers and researchers agree that mulch is beneficial for banana plant growth, no recommendations exist on what the minimum mulch quality and quantity should be to economically address soil fertility, soil microclimate and soil pest constraints. Profitable minimum mulch recommendations are especially important now that access to mulch has declined due to the shortage of uncultivated land. In order to compensate for nutrients lost, Smithson and Giller (2002) pleaded for the judicious use of mineral fertilizers to maintain soil fertility. According to them, the use of organic fertilizers and leguminous crops is important, but can not compensate for all nutrients lost from the system in most cases. Most commercial banana growers elsewhere in the world use mineral fertilizers to sustain high yield levels. However, less than 5% of banana farmers in the East African highland region use chemical fertilizers (Bekunda and Woomer 1996, Sseguya et al. 1999, Kelly et al. 2001). In general, the use of mineral fertilizer in this region is amongst the lowest in the world. Both Bekunda et al. (2001) and Sseguya et al. (1999) showed that non-availability of credit is one of the major constraints for the adoption of chemical fertilizers. Also, farmers often lack knowledge on which fertilizers to use and how to apply them, and smallholder farmers tend to be risk averse. Another constraint that hampers adoption of fertilizers might be the long duration of the banana crop cycle, requiring the farmer to be patient before he sees a return on his investment. Furthermore, Bekunda and Woomer (1996) concluded that there is a lack of research on optimal fertilizer recommendations and rates for banana. Bekunda and Manzi (2004) found that those farmers that did use mineral fertilizers were putting more emphasis on N fertilization than on P and K fertilization, although the authors agree with Wortmann and Kaizzi (1998) that in the long term, there is a greater need for P and especially K fertilizers, than for N fertilizers. The greatest problem is that the cost of maintaining soil fertility may not be compensated by an increase in crop production. On the other hand, the costs to restore degraded soils may be higher than those required to maintain the soil in favorable condition for crop production (Hartemink 2003). This is particularly true in the East African highlands, where high transport costs lead to high fertilizer costs. Figure 1. It is estimated that up to 100 trucks full of bananas enter Kampala daily. On an annual basis, this represents the export from rural areas of over 1.5 million kg K and 0.5 million kg N. Pie t v an As ten InfoMusa - Vol. 13 - No.222 InfoMusa - Vol. 13 - No.2 23 Interaction with other yield loss factors Soil born pests, such as nematodes (Radopholus similis and Pratylenchus goodeyi) and the banana weevil, Cosmopolites sordidus (germar), attack the plant root and vascular system. This reduces the capacity of the plant to take up water and nutrients, which may aggravate drought and nutrient stress in the plant. There is also a clear interaction between soil fertility level and the expression and severity of diseases; e.g. in Uganda, Murekezi (pers. comm.) and Tushmereirwe (unpublished) observed that crop damage due to Banana streak virus and black leaf streak disease decreased with improved soil fertility management. In many cases, a well- fertilized host plant will outgrow the attacks by pest and diseases, thereby maintaining sufficient healthy biomass to sustain optimum growth. Okech and Gold (1996) concluded from a literature review that phytophagous insects are sensitive to nutritional changes in host plants. Bosch et al. (1996) suggested that damage caused by the banana weevil might be related to plant and soil phosphorus and cation concentrations, with special emphasis on the K/Mg ratio. However, the relationship between plant nutritional status and damage by weevil infestation has never been confirmed. Talwana (2002) found higher Ca concentrations in nematode infected East African highland bananas (AAA) and hypothesized that Ca plays a role in the plant defense mechanism. Similarly, Bwamiki (2004) suggested that mechanisms of nematode suppression are linked to K, Ca, Mn, and Zn uptake. Borges Perez et al. (1983) found that imbalance in P/Zn and K/Mg ratios led to Fusarium wilt in a cultivar that was supposed to be resistant. Likewise, Hecht Buchholz et al. (1998) found that Zn-deficient bananas were more affected by Fusarium wilt than non-deficient plants. Hence, a range of studies on various pests and diseases all seem to suggest that the plant’s defense mechanisms are closely related to the cation balance and micronutrient concentrations in the plant tissue, but the underlying processes have not yet been identified. Numerous researchers (McIntyre et al. 2000, Rukazambuga et al. 2002, Smithson et al. 2001) have demonstrated that the positive effect of (in)organic soil amendments is greatly reduced if pest pressure is high. Hence, soil fertility management should best be combined with pest management in order to increase the profitability of the soil fertility interventions. If we want to improve the sustainability of banana systems, we should look beyond the banana field and address soil fertility constraints at the farm level. The role of banana-intercropping systems, the role of the permanent banana canopy for soil- and water conservation, and the effect of pests and diseases on the profitability of soil management interventions deserve special attention. Acknowledgements The authors would like to acknowledge the ‘Vlaamse Vereniging voor Ontwikkelingshulp en Technische Bijstand’ (VVOB) for supporting P.J.A. van Asten’s position at IITA-ESARC, Uganda. References Adupa R. & D.S. Ngambeki. 1994. Demand and consumption of bananas in Uganda. African Crop Science Conference Proceedings 1:379-383 Anonymous. 2001. Rwanda development indicators 2001. Ministry of Economy and Finance 4:28-33. Bananuka J.A. & P.R. Rubaihayo. 1994. Banana management practices and performance in Uganda. Pp. 177-182 in African Crop Science Conference Proceedings Vol. 1 African Crop Science Society, Uganda. Baijukya F.P. & B. de Steenhuijsen Piters. 1998. Nutrient balances and their consequences in the banana- based land use systems of Bukoba district, northwest Tanzania. Agric Ecosyst Environ 71:147–158. Bekunda M. & G. Manzi. 2004. Use of the partial nutrient budget as an indicator of nutrient depletion in the highlands of southwestern Uganda. Nutrient Cycling in Agroecosystems 67:187-195. Bekunda M.A. & P.L. Woomer. 1996. Organic resource management in banana-based cropping systems of the Lake Victoria Basin, Uganda. Agriculture, Ecosystems and Environment 59:171-180. Bekunda M.A., S.T. Nkalubo, H. Sseguya, P.L. Woomer & R. Muzira. 2001. Better banana-based agriculture in Uganda (BETBAN): identifying the limiting nutrient(s) as a basis for rehabilitating degraded banana fields. Pp.95-98 in Forum working document No. 2: summaries of forum research and development activities at Makerere University 1993-2000. Bertsch F. 1986. Manual para interpretar la Fertilidad de los Suelos. Oficina de publicaciones de la Universidad de Costa Rica. San José, Costa Rica. 81pp. Borgez Perez A., I. Trujillo Jacinto del Castillo, F. Gutierrez Jerez & D. Angulo Rodriguez. 1983. Estudio sobre el mal de Panama en las Islas Canaria. II. Influencia de los desequilibros nutritivos P-Zn y K-Mg del suelo, en la alteracion de los mecanismos de resistencia de la platanera (Cavendish enena) al mal de Panama. Fruits 38:755-758. Bosch C., A. Lorkeers, M.R. Ndile & E. Sentozi. 1996. Diagnostic survey: constraints to banana productivity in InfoMusa - Vol. 13 - No.224 InfoMusa - Vol. 13 - No.2 25 Bukoba and Muleba districts, Kagera region, Tanzania. Working paper no. 8. Tanzania/Netherlands Farming Systems Research Project, Lake Zone. Ari Muruku, Bukoba, Tanzania. 119pp. Bwamiki D.P. 2004. Role of Plant Nutrition on Growth Parameters of Banana and the Suppression of Populations and Damage of Radopholus Similis. PhD thesis. Cornell University, United States of America. Delvaux B. 1995. Soils. Pp. 230-257 in Bananas and Plantains. (S. Gowen, Ed.). Chapman and Hall, London, UK. FAO. 2004. Faostat agricultural data. Internet: http: //apps.fao.org Gold C.S., E.B. Karamura, A. Kiggundu, F. Bagamba & A.M.K. Abera. 1999. Geographic shifts in highland cooking banana (Musa spp., group AAA-EA) production in Uganda. International Journal of Sustainable Agriculture and World Ecology 6:45-59. Godefroy J., V. Rutunga & A. Sebahutu. 1991. Les terres de bananeraies dans la région de Kibungo au Rwanda : résultantes du milieu et des systèmes de culture. Fruits 46:109-124. Hartemink A.E. 2003 Soil fertility decline in the tropics with case studies on plantations. 360 pp. ISRIC-CABI, Wallingford. Hecht-Buchholz C., A. Borges-Perez, M. Fernandez Falcon & A.A. Borges. 1998. Influence of zinc nutrition on fusarium wilt of banana – an electron micropscopic investigation. Acta Horticulturae 490:277-283. Kelly V.A., E. Mpyisi, A. Murekezi & D. Neven. 2001. Fertilizer consumption in Rwanda: past trends, future potential, and determinants. Paper presented at Policy Workshop on Fertilizer Use and Marketing. 22-23 February 2001. MINAGRI & USAID. Rwanda Lahav E. & D.W. Tuner. 1983. Banana Nutrition. Bulletin 7. International Potash Institute, Woblaufen-Bern, Switzerland. 62pp. Landon J.R. (Ed.). 1991. Booker Tropical Soil Manual; a Handbook for Soil Survey and Agricultural Land Evaluation in the Tropics and Subtropics. Longman, Essex, England. 474pp. Lopez A. & J. Espinosa. 1995. Manual de Nutrición y Fertilizatión del Banano. INPOFOS. Quito-Equador. Lufafa A., M.M. Tenywa, M. Isabirye, M.J.G. Majaliwa & P.L. Woomer. 2003. Prediction of soil erosion in a Lake Victoria basin catchment using a GIS-based Universal Soil Loss Model. Agricultural Systems 76:883-894. Masefield G.B. 1949. The Uganda Farmer. Longman, London. McIntyre B.D, P.R. Speijer, S.J. Righa & F. Kizito. 2000. Effects of mulching on biomass, nutrients and soil water in bananas inoculated with nematodes. Agronomy Journal 92:1081-1085. McMaster D.N. 1962. A Subsistence Crop Geography of Uganda. The world land use survey. Occasional papers no. 2. Geographical Publications Limited. Bude, Cornwall, England. 111pp. Okech S.H.O. & C.S. Gold. 1996. Relationships of the banana weevil with its host plant and soil fertility; literature review with emphasis on studies in eastern and central Africa. The African Highlands Initiative Technical Reports Series no. 2. International Centre for Research in Agroforestry. Uganda. 22pp. Okech S.H., P.J.A. van Asten, C.S. Gold & H. Ssali. 2004. Effects of potassium deficiency, drought and weevils on banana yield and economic performance in Mbarara, Uganda. Uganda Journal of Agricultural Sciences 9:511-519. Rishirumuhirwa T. 1997. Rôle du bananier dans le fonctionnement des exploitations agricoles sur les hauts plateaux de l’Afrique centrale. Thèse EPFL No. 1636. Lausanne. 321pp. Rubaihayo P.R., O.J.B. Odongo & J.A. Bananuka. 1994. Some highland banana production constraints in Masaka district of Central Uganda. Pp. 188-192 in African Crop Science Conference Proceedings vol. 1. African Crop Science Society, Uganda. Rufino M. 2003. On-farm Analysis of Nematode Infestation and Soil Fertility as Constraints to the Productivity of Banana-based Production Systems in Uganda. MSc Thesis Plant Sciences, Wageningen University, Wageningen. 91pp. Rukazambuga N.D.T.M., C.S. Gold, S.R. Gowen & P. Ragama. 2002. The influence of crop management on banana weevil, Cosmopolites sordidus (Coleoptera: Curculionidae) populations and yield of highland cooking banana (cv. Atwalira) in Uganda. Bulletin of Entomological Research 92:413-421. Smaling E.M.A.. 1993. Soil nutrient depletion in sub- Saharan Africa. Pp 53-57 in The Role of Plant Nutrients for Sustainable Food Crop Production in Sub-Saharan Africa. (H. Van Reuler and W.H. Prins, eds). Dutch Association of Fertilizer Producers (VKP), Leidschendam, Netherlands. Smithson P.C., B.D. McIntyre, C.S. Gold, H. Ssali, & I.N. Kashayij. 2001. Nitrogen and potassium fertilizers vs. nematode and weevil effects on yield and foliar nutrient status of banana in Uganda. Nutrient Cycling in Agroecosystems 59:39-50. Smithson P.C. & K.E. Giller. 2002. Appropriate farm management practices for alleviating N and P deficiencies in low-nutrient soils of the tropics. Plant and Soil 245:169-180. Smithson P.C., B.D. McIntyre, C.S. Gold, H. Ssali, G. Night & S. Okech. 2004. Potassium and magnesium fertilizers on banana in Uganda: yields, weevil damage, foliar nutrient status and DRIS analysis. Nutrient Cycling in Agroecosystems 69:43-49. Ssali H., B.D. McIntyre, C.S. Gold, I.N. Kashaija & F. Kizito. 2003. Effects of mulch and mineral fertilizer on crop, weevil and soil quality parameters in highland banana. Nutrient Cycling in Agroecosystems 65:141- 150. Sseguya H., A.R. Semana & M.A. Bekunda. 1999. Soil fertility management in the banana-based agriculture of central Uganda: farmers constraints and opinions. African Crop Science Journal 7:559-567. Talwana H.L. 2002. Spatial Distribution and Effect of Plant-Parasitic Nematodes on Root Systems and Plant Nutritional Status of Bananas in Uganda. Doctoral Thesis No. 512. Faculty of Agricultural and Applied Biological Sciences of the Katholieke Universiteit Leuven. 133pp. Taulya G. 2004. Topsoil depth-banana yield relationshiops on a chromic luvisol in a Lake Victoria basin microcatchment. MSc thesis. Makerere University, Uganda. 72pp. Tushemereirwe W.K., D. Karamura, H. Ssali, D. Bwamiki, I. Kashaija, C. Nankinga, F. Bagamba, A. Kangire & R. Ssebuliba. 2001. Bananas (Musa spp). in Uganda. Pp. 281-321 in Volume II: Crops. (J.K. Mukiibi, Ed.). Agriculture, Fountain Publichers, Kampala, Uganda. Twyford I.T. 1967. Banana nutrition: a review of principles and practice. J. Sci. Food Agri. 18:177-183. Van Asten P.J.A., C.S. Gold, J. Wendt, D. De Waele, S.H.O Okech, H. Ssali & W.K. Tushmereirwe. 2004. The contribution of soil quality to banana yield problems and its relation with other banana yield loss factors in Uganda. African Crop Science Journal. Proceedings of the banana IPM workshop held in Kampala, December 2003. In press. P.J.A. van Asten, C.S. Gold and S.H. Okech work at the International Institute of Tropical Agriculture, P.O. Box 7878, Kampala, Uganda, S.V. Gaidashova at the Institut des Sciences Agronomiques du Rwanda, B. P. 138, Butare, Rwanda, W.K. Tushemereirwe at the Kawanda Agricultural Research Institute, P.O. Box 7065, Kampala, Uganda, and D. De Waele at the Katholieke Universiteit Leuven, Kasteelpark Arenberg 13, B- 3001 Leuven, Belgium. InfoMusa - Vol. 13 - No.224 InfoMusa - Vol. 13 - No.2 25 Wamsley D., T. Twyford & I.S. Cornforth. 1971. An evaluation of soil analysis methods for nitrogen, phosphorus and Potassium, using Banana. Tropical Agriculture (Trinidad) 48:141-155. Woomer P.L., M.A. Bekunda, N.K. Karanja, T. Moorehouse & J.R. Okalebo. 1998. Agricultural resource management by smallholder farmers in East Africa. Nature and Resources 34:22-33. Wortmann C.S. & C.K. Kaizzi. 1998. Nutrient balances and expected effects of alternative practices in farming systems of Uganda. Agriculture Ecosystems and Environment 71:115-129. Zake Y.K., D.P. Bwamiki & C. Nkwiine. 2000. Soil management requirements for banana production on the heavy soils around Lake Victoria in Uganda. Pp. 285-292 in Proceedings of the first International Symposium on Banana and Plantain for Africa (K. Craenen, R. Ortiz, E.B. Karamura & D.R. Vuylsteke, eds.). Acta Horticulturae 540. International Society for Horticultural Science, Leuven, Belgium. New technologies to increase root health and crop production Richard A. Sikora and Luis E. Pocasangre T he burrowing nematode Radopholus similis is a major root health problem in banana and plantain. The nematode causes large root lesions that are subsequently colonized by deleterious fungi and bacteria. This syndrome leads to severe necrosis and the girdling of individual roots, yield loss and often pseudostem toppling. Control of the burrowing nematode in established plantations is usually accom- plished with systemic nematicides/insecticides. These pesticides usually only inactivate the nematode within the host tissue or in the soil for a limited length of time and are in most cases not nematicidal. After microbial degradation of the compounds, the nematode recovers and damage to the root continues. Due to this short-term improvement in root health, yield increases following treatment in areas where the nematode is above the damage threshold level. Whether or not treatment is required is either open to question or determined by past yield experience or, in some cases, by monitoring root population densities. Lack of treatment in heavily infested fields results in lower yield. However, because the nematode is only inactivated by most of these pesticides, repeated treatment within a cycle is required to prevent damage over time. The repeated use of nematicides has led to rapid microbial breakdown in some areas, and the need for an increase in the number of treatments per cycle. In some plantations in Central America up to four applications are currently being used to reduce damage. This situation is unacceptable both economically to the growers and environmentally to the community at large. With the loss of and/or phasing out of nematicides for economic or environmental reasons, new approaches to nematode control in perennial crops are needed (Sikora et al. 2005). In banana production where high yields are correlated with effective nematode control and a healthy root system, alternative methodologies, whether biological, plant based or chemical nature, are urgently required. Biological enhancement One recently developed alternative to pesticides is biological enhancement of banana planting material with beneficial microorganisms to increase plant resistance to infection. The fact that most of the major pests and diseases of banana attack the plant through the roots or corm has led to research on the use of biological enhancement technologies using mutualistic fungal endophytes to manage nematodes, wilts and weevils (Amin 1994, Schuster et al. 1995, Pocasangre 2000, Pocasangre et al. 2000, Griesbach 1999, Niere et al. 1998). These unique antagonists are isolated at random from the endorhiza of healthy banana root or corm tissue following surface sterilization (Figure 1). The isolates are then: 1) placed in pure culture 2) identified 3) mass fermented 4) inoculated onto tissue culture plantlets 5) allowed to colonize 6) challenged with target organisms 7) and then antagonistic activity measured. Soil fertility InfoMusa - Vol. 13 - No.226 InfoMusa - Vol. 13 - No.2 27 Isolates effective at controlling the burrowing nematode have been recovered from Indonesia, Uganda, Kenya, Cuba, Honduras and Costa Rica and, in our opinion, will be detected in the healthy tissue of all banana plants. Under normal field conditions these endophytes are usually not effective because their densities are low and they must compete with other microorganisms for food and space. Biological enhancement gives these microorganisms a head start and competitive advantage. Biological enhancement also reduces overall treatment costs as well as environmental side effects caused by pesticides since 2500 sterile tissue culture plants can be treated in pots, as opposed to treating with pesticides large quantities of soil in the field. The approach until now has been based on a “blind” screening system in which fungi are randomly isolated from healthy plant tissue and tested on inoculated banana plantlets for biological control activity. A large percentage of the isolates obtained from the endorhiza have demonstrated significant antagonistic activity toward the burrowing nematode (Pocasangre 2000, Niere et al. 1998). Activity against Fusarium wilt was not adequate (Pocasangre 2000). However, some isolates were shown to be pathogenic on eggs of Cosmopolites sordidus and to have negative effects on the growth of weevil larvae (Griesbach 1999, Gold et al. 2003). Biological enhancement has been shown to be effective in reducing nematode attack in the first cycle under controlled conditions and is being tested in the field in Africa and Central America. Whether or not control is sustainable over multiple crop cycles also is under investigation. The system is presently targeted for use in 1) single-cycle high density banana production, 2) single- cycle high density plantain production, 3) organic bananas and 4) nursery production of resistant banana cultivars. Suppressive soils and biological enhancement The term suppressiveness is traditionally used to describe soils in which disease development is suppressed even though a pathogen or pest is present in the field (Baker and Cook 1974, Huber and Schneider 1982). It is an umbrella term encompassing biocontrol activity based on parasitism, predation, inhibition, competition, disease and other antagonist interactions with pests or disease where reduced infection occurs in the presence of a susceptible host plant. Suppressive soils have been identified for fungal pathogens (Huber and Schneider 1982, Alabouvette et al. 1979, Weller 1988) and plant parasitic nematodes (Kerry et al. 1982, Pyrowolakis et al. 2002). To our knowledge this phenomenon has not been observed for soil-borne insects. Suppressiveness is usually directly related to the level of the antagonistic potential in the soil (Sikora 1992) which is regulated by specific components of rhizosphere specific microbial communities (Vilich and Sikora 1998). Suppressive soils are - the exception and not the rule - in agricultural ecosystems. We believe however that in perennial crop production they may be more common than once thought. We believe this to be the situation in all crops where plant parasitic nematodes are a major pest problem and where constant use of nematicides is the rule and not the exception. Suppressive soils and banana In reviewing the literature on banana, there is a void with regards to the detection of soil that suppress nematodes. The presence of suppressive soils may have been over- looked in crops such as banana, coffee, citrus or pineapple, due to an extensive use of soil pesticides. A suppressive soil cannot be detected if nematode densities are continuously lowered with pesticides. Moreover, if a suppressive soil is identified can it be used for pest and disease management purposes? Figure 1. Techniques used in the isolation of fungi growing inside healthy tissue of banana (Sikora & Schuster 1999). rhizome Isolation of endophytic fungi from banana tissue inner outer general cutting of infested tissue material cutting of small tissue pieces surface sterilization NaOCI water agar transfer of mycelium pure culture root InfoMusa - Vol. 13 - No.226 InfoMusa - Vol. 13 - No.2 27 This vacuum has been recently filled by the detection of suppressive soils in banana plantations in Central America (Figure 2). The burrowing nematodes present in these fields were unable to multiply and reach damaging population densities even though a highly susceptible cultivar was being grown (zum Felde 2002, zum Felde et al. 2004). Fields that suppress R. similis have also been detected in fields in Costa Rica (Pocasangre et al. 2004, Cañizares 2003). Biodiversity in suppressive soils Suppressive activity in any soil is regulated by the antagonistic potential in that soil (Sikora 1992). One or more microorganisms – working singly or in combination and sim- ultaneously or sequentially – are responsible for suppressive activity. Suppressiveness is not driven by abiotic factors, but is a biologically based system. Biological enhancement to control R. similis in most studies has been based on inoculation of tissue culture plantlets with fungal antagonists. Griesbach (1999) attempted to inoculate East African highland banana suckers with endophytes but obtained only low levels of colonization. Recent studies by Pocasangre et al. (2004), however, have demonstrated that R. similis densities in plantain suckers inoculated with endophytic fungi were reduced by up to 86% over the controls. In Table 1, the extremely high level of fungal biodiversity in the endorhiza of healthy banana root and corm tissue in Thailand is presented (Sikora et al. 2003). These results demonstrate that we have only touched the peak of an enormous volcano of biotic potential that can be used for plant health improvement. The organisms involved in forming a suppressive soil in other crops have been identified and, in a limited number of cases, commercially produced for field use. Grower acceptance is often limited, because of the large variability in effectiveness and the costs of application. Controlling the pest requires treating 2500 tonnes of soil per hectare in the top 25 cm inhabited by the targeted pest or pathogen. The detection of suppressive soils in banana plantations in Central America and the isolation of large numbers of mutualistic fungal endophytes from plants growing in these fields should affect how future research is conducted (zum Felde 2000, zum Felde et al. 2004). The question that arises is, is this phenomenon important for banana production and can it be used effectively in pest management systems? The following applications can be envisioned 1) suppressive fields could be used for nurseries to produce suckers for surrounding fields, 2) biologically enhanced plantlets could be produced from multiple isolates from these fields, and 3) biologically enhanced suckers could be inoculated with multiple isolates from these fields. In planta suppressiveness The concept of “in planta suppressiveness” proposed here is based on the premise Figure 2. Total number of nematodes recovered from banana roots in sampled farms in October 2001 (zum Felde et al. 2004). (Columns with different letters are significantly different at P ≤ 0.05, using the one-way ANOVA test in StatsGraphics Plus 3.1). Table 1. Fungal endophyte biodiversity in banana root and rhizome tissue of ‘Pisang awak’ (ABB) from Thailand (Sikora et al. 2003). Fungal species Roots Central cylinder Rhizome cortex Overall (%)* (%) (%) (%) Acremonium spp. 15.4 6.7 7.5 9.9 A. stromaticum 11.5 6.7 5.0 7.7 Aspergillus spp. 5.4 5.3 2.5 4.4 Colletotrichum musae 2.3 9.3 11.2 7.6 Cylindrocarpon spp. 3.1 1.3 5.0 3.1 Fusarium Sect. Arthrosporiella 5.4 10.7 11.3 9.1 Fusarium Sect. Liseola 2.3 4.0 3.7 3.3 Fusarium oxysporum 7.7 6.7 15.0 9.8 Fusarium solani 0.8 6.7 6.3 4.6 Fusarium spp. 3.1 4.0 1.2 2.8 Gongronella spp. 7.7 6.7 3.8 6.1 Penicillium spp. 21.5 10.7 5.0 12.4 Zygomycetes 4.6 4.0 1.2 3.3 Other species** 9.2 17.2 21.3 15.9 * Percentage of total number of fungal isolates from a total of 285 isolates identified. The number of fungi isolated from roots, central cylinder and rhizome cortex were respectively 130, 75 and 80. ** Mainly fungi belonging to the genera: Cladosporium, Cylindrocladium, Dreschslera, Lasiopdiplodia, Plectosporium, Thielaviopsis and Trichoderma. 80000 70000 60000 50000 40000 30000 20000 10000 0 Nu m be r o f n em at od es / 10 0 g ro ot El Real Maya Creek Farms a a b c Lourdes Radopholus similis Helicotylenchus spp. Meloidogyne spp. InfoMusa - Vol. 13 - No.228 InfoMusa - Vol. 13 - No.2 29 that plants actively select health-promoting microorganisms from the rhizosphere. Plants lose up to 33% of their assimilates to the soil. The exudates move through the endorhiza onto the rhizoplane before leakage moves them into the rhizosphere. The production of these nutrients utilizes significant amounts of plant energy, which are ultimately lost by the plant. We believe plants expend this energy to maintain a health support system made up of “endorhiza and rhizosphere specific microbial communities”. These organisms live in a mutualistic and/or symbiotic association with the plant. The well-known arbuscular mycorrhizal fungi are part of this microbial community and have been shown to have both plant growth and health promoting activity (Jaime Vega and Rodriguez-Romero 2004). The detection of fields suppressive to a migratory endoparasitic nematode also suggests that the basis of suppressiveness may be plant-bonded. Biological control activity may occur mainly in the plant and not in the soil, with the plant selecting out a microbial community conducive to plant health. If this is the case, then examination of suppressive plants could yield isolates and combinations that could be used effectively to biologically enhance planting material. This could be more productive than the standard random method of “blind selection” of isolates from root tissue. Selection of isolates from plants growing in suppressive soils might also insure that biologically enhanced plants have in planta suppressiveness that gives both short and long term management. Mode of action Up until recently, little has been known about the mechanisms of action involved in the endophyte control of nematodes. This knowledge is extremely important since it determines how this management system is categorized: biological enhancement or biological pesticides. This of course has importance in registration and therefore for overall costs of development. There are many possible mechanisms of action: 1) parasitism or pathogenicity to the nematodes or eggs; 2) suppression of nematode development or fertility; 3) inhibition of mobility, 4) interference with attraction or recognition; 5) inhibition of penetration; 6) repellent activity; 7) induced resistance and 8) plant growth promotion induced tolerance. Studies in Bonn, Germany and at INIBAP-CATIE, Turrialba, Costa Rica, have shown repeatedly that many of the fungal endophytes studied significantly reduced penetration by R. similis. More recent observations also indicate that growth promotion occurs (Figure 3). This could affect plant tolerance to infection by increasing root system biomass (Pocasangre unpublished data). There are indications that some fungal isolates directly parasitize nematodes in the soil (zum Felde 2000, Meneses et al. 2003, Cañizares, 2003). Banana roots colonized by endophytes have recently been shown to have nematode repellent activity toward R. similis (Vu et al. 2005). This research has also demonstrated that some isolates are able to induce systemic resistance to the nematode. A number of fungi have been shown to produce toxic metabolites in vitro. This is not considered important under field conditions where nutrients are at a minimum and microbial competition high. The results demonstrate that each endophytic isolate may have a different mode of action and must be examined individually for this factor. In addition, the large spectrum of activity forms indicates that multiple-isolate- inoculants may be more successful in producing higher levels of control and long- term control by targeting multiple sites in the nematode’s life cycle. The use of biological enhancement in the field on a commercial basis is dependent on a number of factors: 1) efficacy; Figure 3. Effect of endophytic fungi on plant growth promotion: plants inoculated with Trichodema atroviride (right) and non inoculated control plant (left). InfoMusa - Vol. 13 - No.228 InfoMusa - Vol. 13 - No.2 29 2) mode of action; 3) durability of control; 4) environmental concerns; 5) economics of production and 6) registration requirements. Commercial companies producing tissue culture plantlets on a large scale could use this technology. For biological enhancement to become a useful management tool more research is needed in the following areas: 1) testing isolates for plant pathogenicity using Vegetative- Compatibility Standards; 2) molecular analysis to determine their relationships to all endemic fungal populations; 3) production characteristics i.e. fermentation efficacy, storage, formulation; 4) multiple inoculants to mimic in planta suppressiveness; 5) multi-cycle control efficacy; 6) control of other nematodes and diseases as well as weevils and 7) presence of isolates with significant growth promotion activity. References Alabouvette C., F. Roussel & J. Louvet. 1979. Characteristics of Fusarium wilt-suppressive soils and prospects for their utilization in biological control. Pp. 165-182 in Soil-Borne Plant Pathogens (B. Schippers and W. Gams, eds). Academic Press, London. Amin N. 1994. 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Occurrence of mutualistic fungal endophytes in bananas (Musa spp.) and their potential as biocontrol agents of the banana weevil Cosmopolites sordidus (Germar) (Coleopotera: Curculionidae) in Uganda. PhD thesis, University of Bonn, Germany. Huber D.M. & R.W. Schneider. 1982. The description and occurrence of suppressive soils. Pp. 1-8 in Suppressive soils and plant disease (R. W. Schneider, ed.). American Phytopathological Society Press. St. Paul, Minnesota. Jaime-Vega M.C. & A.S. Rodriguez Romero. 2004. Uso de micorrizas en banano: Logros y perspectivas. Pp.143-160 in Memorias, XVI Reunion Internacional de ACORBAT, Oaxaca, México. Kerry B.R., D.H. Crump & L.A. Mullen. 1982. Studies of the cereal cyst nematode, Heterodera avenae, under continuous cereals, 1974-1978. I. Plant growth and nematode multiplication. Annals of Applied Biology 100:477-87. Meneses A., L.E. Pocasangre, E. Somarriba, A. Riveros & F. Rosales. 2003. Diversidad de hongos endofiticos y abundancia nematodos en plantaciones de banano y plátano en la parte baja de los territorios indígenas de Talamanca. Agroforesteria de las América 10 (37-38): 59-62. Niere B.I., P.R. Speijer, C.S. Gold & R.A Sikora. 1998. Fungal endophytes from bananas for the biocontrol of Radopholus similis. Pp. 313-318 in Proceedings of the Banana IPM Meeting. Nelspruit, South Africa. Pocasangre L. 2000. Biological enhancement of banana tissue culture plantlets with endophytic fungi for the control of the burrowing nematode Radopholus similis and Panama disease (Fusarium oxysporum f. sp. cubense). PhD thesis, University of Bonn, Germany. Pocasangre L.E., R.A. Sikora, V. Vilich & R.-P. Schuster. 2000. Survey of banana endophytic fungi from Central America and screening for biological control of Radopholus similis. Acta Horticulturae 531:283-290. Pocasangre L.E., A. zum Felde, A. Meneses, C. Cañizares, A.S. Riveros, F.E. Rosales & R.A. Sikora. 2004. Manejo alternativo de fitonematodos en banano y plátano. Pp.106-112 in Memorias, XVI Reunion Internacional de ACORBAT, Oaxaca, México. Pyrowolakis A., A. Westphal, R.A. Sikora & J.O. Becker. 2002. Identification of root-knot nematode suppressive soils. Applied soil Ecology 19:51-56. Schuster R.-P., R. A. Sikora & N. Amin. 1995. Potential of endophytic fungi for the biological control of plant parasitic nematodes. Communications in Applied Biological Sciences 60:1047-1052. Sikora R.A. 1992. Management of the antagonistic potential in agricultural ecosystems for the biological control of plant parasitic nematodes. Annual Review of Phytopathology 30:245-270. Sikora R. A., J. Starr & J. Bridge. 2005. Management practices: an overview of integrated nematode management technologies. Pp. 793-825 in Plant parasitic nematodes in tropical and subtropical agriculture (M. Luc, R.A. Sikora & J. Bridge, eds) 2nd Edition. CAB International, Wallingford, UK. Sikora R.A., B. Niere & J. Kimenju. 2003. Endophytic microbial biodiversity and plant nematode management in African agriculture. Pp. 179-192 in Biological control in IPM systems in Africa. (P. Neuenschwander, C. Borgemeister and J. Langewald, eds). CAB International, Wallingford, UK. Vilich V. & R.A. Sikora. 1998. Diversity in Soil-Borne Microbial Communities: A Tool for Biological System Management of Root Health. Pp 1-15 in Plant-Microbe Interactions and Biological Control (G.J. Boland & L.D. Kuykendall, eds). Marcel Dekker Inc., New York, USA. Vu T.T., R.A. Sikora & R. Hauschild. 2005. Endophytic Fusarium strains induce systemic resistance against Radopholus similis penetration into banana roots. Nematologica (In review). Weller D. 1988. Biological control of soilborne plant pathogens in the rhizosphere with bacteria. Annual Review of Phytopathology 26:379-407. zum Felde A. 2002. Screening of endophytic fungi from banana (Musa spp.) for antagonistic effects towards the burrowing nematode Radopholus similis ( Cobbb) Thorne. MSc thesis, University of Bonn, Germany. zum Felde A., L.E. Pocasangre, R.A. Sikora. 2004. Use of microbial communities inside suppressive banana plants to increase biocontrol of the burrowing nematode, Radopholus similis in Proceedings of Workshop on Banana Root Systems: towards a better understanding for its productive management, 3-5 Nov. 2003, San Jose, Costa Rica (D. W. Turner and F. E. Rosales, eds). (In press) Richard A. Sikora works at the Soil Ecosystem Phytopathology and Nematology, Institute for Plant Diseases, University of Bonn, Nussallee 9, 53115 Bonn, Germany, and Luis E. Pocasangre at the INIBAP regional Office for Latin America and the Caribbean, Apartado Postal 60-7170- CATIE, Turrialba, Costa Rica InfoMusa - Vol. 13 - No.230 InfoMusa - Vol. 13 - No.2 31 Partnership and networking in the tropical fruit industry: the experience of the International Tropical Fruits Network Khairuddin Tahir Marketing G lobalization is teaching us many valuable lessons, if we care to learn from these lessons. Those who are not ready to learn or are too slow to adapt to this wave of change may find themselves at a disadvantage, or worse, in perpetual frustration, not knowing what hit them and why. Governments are working hard to position their economy to face the new rules of global competition. In turn, businesses need to make radical adjustments if they want to survive and prosper. Organizations also have to reinvent themselves in order to stay relevant. At the international level, standards for participating in the global trade regime often change and become harder to achieve. The goal posts seem to keep moving in an increasingly non-level playing field. The mantra of the market place is faster, cheaper, better and safer. To play this globalization game one has to comply with the rules or run the risk of being left behind. Dynamic business environment Becoming savvy in information and commu- nication technologies (ICT) is necessary but not sufficient for success. One must also be creative and innovative in packaging ideas, tools and approaches into viable and sustainable integrated systems. The International Tropical Fruits Network (TFNet), established four years ago, has to operate in the challenging, and sometimes ruthless, environment of the agriculture sector, in which the players are numerous and the resources limited. We often get the impression that we are in a “dog-eat-dog” situation, where the mighty and powerful take on the new and small players, drive them into submission and eventually eliminate competitors. Fortunately, the laws of nature seem balanced and kind to us. We found many people and organizations willing to collaborate, network and form strategic partnerships with TFNet, especially among our own members, now numbering 55. We are cooperating in order to better compete with others. It is still possible to create a win- win situation for everybody, as long as we are not blinded by immediate and short-term benefits. TFNet’s membership, which consists of governments, NGOs, private entrepreneurs and professional individuals with diverse interests in tropical fruit production, processing, consumption, marketing and international trade, constitutes a rich resource. The challenge for TFNet is to play an effective “linking or networking” role and at the same time provide an independent platform where stakeholders of the tropical fruit industry can interact and articulate their needs and concerns, and, more importantly, find solutions together. Obviously, fostering networking and forging partnership has become one of TFNet’s core businesses and primary activities. It is not our wish or intention to be an exclusive club and we cannot afford to be a charitable organization, given our limited resources. Although categorized as a not-for-profit international organization, we need to generate income for the operations of TFNet’s lean secretariat and to service our members. TFNet is open to collaborating with parties, especially our members, who share our objectives, goals and aspirations, as can be seen from the various projects implemented with and for our members. Clientele Let us move on to what really matters, i.e. serving our clientele, which in our case includes our members and small- scale farmers, small and medium-scale entrepreneurs, traders, exporters, pro- cessors, etc. We believe that farmers, regardless of whether they are in Belgium, Bolivia or Bangladesh, are basically the same and have the same aspirations and expectations to better their livelihood and quality of life for themselves and their children. Like people in other businesses, they have to live with fluctuating harvests, or InfoMusa - Vol. 13 - No.230 InfoMusa - Vol. 13 - No.2 31 revenues, and they sometimes suffer losses due to natural calamities or to other people’s decisions that are beyond their control or influence. The difference between these farmers, depending on which country they live, may lie in their resource endowment and to some extent in the support or incentives they get from their governments, especially during times of natural calamity and economic turbulence. When setting up partnerships and projects with its clientele or a rural community, the main concern of an organization like TFNet is to listen diligently and patiently, and then to evaluate its client’s needs (versus its wants), resource endowment, knowledge and technology gaps, infrastructual deficiency, etc. Those involved in rural development know this and have developed a comprehensive checklist. The next step is how partners can be a catalyst and provide the incentives and appropriate mechanisms that will push the clientele, or rural community, to higher levels of productivity, or from subsistence farming into a market economy. Farmers, like all of us, are rational economic beings. They are not culturally destined to remain poor and the role of partners is to empower them so that they can redeem their dignity through participatory income generating projects. Governments and international organizations Governments, international organizations, including regional ones, and specialized UN agencies, are important partners in networks as they provide valuable data, information, technical and financial resources. On the international scene, these bodies use various multilateral platforms to provide guidance, direction and coordination to ensure an orderly and sustainable development of various aspects of life. In many developing countries, governments are major players at the national level and tend to dominate rural development activities. This is often the only channel for partners to get involved in rural community projects. Both government and international organizations are continuously undergoing structural and functional changes, consolidating their activities and positioning themselves to meet new challenges and demands. However, many factors have been identified that may affect partnership with governments and international organizations, among them: • Slow decision making due to multilevel bureaucratic processes, may take 2 to 5 years for project approval and implementation; • Competing with the private sector in certain businesses and duplicating the functions of others; • Lack of flexibility in project design and implementation; • Preoccupation with their internal programmes and activities leaving little resources and time to collaborate with others; • Lack of focus and specialization. NGOs and the private sector Generally, non-governmental organizations (NGOs) are good partners in networks as they tend to be focused and specialized and not too bureaucratic. NGOs tend to be flexible, forward-looking and adaptive in their relationship with partners. However, some NGOs lack accountability or are perceived as having radical views on some mainstream issues. Some NGOs are also suspicious of other NGOs when they compete for similar resources, especially funds, clientele or target groups. Small and medium-scale entrepreneurs (SMEs) are excellent partners because they tend to get “squeezed” between public companies and multinational corporations and, as a result, are willing to work with autonomous bodies, like TFNet. SMEs are innovative and ready to try new ideas to improve their revenues and market share (Figure 1). They are also willing to share their technical and market knowledge and information with partners as leverage for expanding and improving their business. TFNet has had positive experiences working in partnership with SMEs. Larger corporations are also open to partnerships, often to enhance their image as good corporate citizens, especially when their products or services are under public scrutiny. However, they tend to favour partnerships with governments, and to a lesser extent with SMEs and NGOs. But in a highly competitive global environment, business relationships are rapidly changing as large corporations increasingly outsource jobs to efficient SMEs in order to cut costs and deliver their goods and services on time. This InfoMusa - Vol. 13 - No.232 InfoMusa - Vol. 13 - No.2 33 partnership is already prevalent in the food supply chain, especially in the logistics, trans- portation and packaging sectors. Ingredients for success How can partnership and networking be established, fostered and sustained? From TFNet’s experience, the following factors contribute to the success of a partnership and a network: • Shared vision and goals • Trust • Leadership • Transparency and accountability • Being accommodating, flexible and adaptive • Creativity and innovation • Patience and resilience • Application of ICT and knowledge management • Win-win situation. Conclusion Obviously, no single body or organization, including government, can pretend to monopolise the task of bringing about socio- economic changes to a particular sector or community. Partnership and networking become essential functions in efforts to mobilize resources for a common or noble cause. At the same time, one must not assume that partnership and networking are just a matter of common sense. On the contrary, they need to be learned, experienced, promoted and nurtured. Partnership and networking go beyond the sharing of knowledge and technical competency, and involve the fusion of cultures and work ethics among multidisciplinary stakeholders. Partnership and networking result in having to redefine one’s worldview and value system. For too long, many promises have been made to farmers to improve their livelihood and they have been patient with us despite numerous shortcomings. To avoid repeating past mistakes, fresh and creative ideas are needed to ensure successful partnerships and networking. It is imperative that we think out-of-the-box and try to do things differently. Figure 1. Small-scale entrepreneurs – like Mrs Olomi whose company, Banana Investments Ltd. in Arusha, Tanzania, now hires 70 fulltime employees – are innovative and ready to try new ideas to improve their revenues and market share. Khairuddin Tahir is the CEO of International Tropical Fruits Network (TFNet), 43400 Serdang, Selangor, Malaysia Highlights on the First International congress on MusaFocus on the Musa congress The first two days of the First International Congress on Musa featured presentations from breeders, geneticists and molecular scientists with a session on genetic resources and improvement and the 4th International symposium on the molecular and cellular biology of bananas. Kodjo Tomekpe, head breeder and director of the Centre Africain de Recherches sur Bananiers et Plantains (CARBAP) opened the Congress with a review on conventional breeding strategies (see article on p. 2), their achievements but also their limitations. Advances in breeding The first strategy was pioneered by the Fundación Hondureña de Investigación Agrícola (FHIA). It involves crossing a susceptible triploid cultivar with a diploid that is disease resistant in order to produce a resistant tetraploid. This is possible when the female parent transmits the totality of her triploid genome, by not undergoing meiosis, and the male parent contributes, in his haploid genome that has been through the normal process of meiosis, the desired resistance genes. But since the male parent provides much more than resistance genes, Jo hn Ja gw e InfoMusa - Vol. 13 - No.232 InfoMusa - Vol. 13 - No.2 33 the resulting tetraploid hybrid is not an exact replica of the triploid cultivar the breeders are trying to improve. As Tomepke remarked, the impact of the 3X x 2X strategy is limited by the low number of triploid cultivars possessing the level of female fertility that would allow their use in crossings. Moreover, the few that are fertile enough tend to be interspecific hybrids of Musa acuminata and Musa balbisiana and as such are likely to contain activable sequences of the banana streak virus (BSV) integrated in the balbisiana genome. However, as the presentations made by the other breeders present at the Congress have shown, the BSV problem has not stopped them from trying to improve the local cultivars that contain the B genome by using variants of the conventional strategy. Sebastiao de Oliveira e Silva reported that, in Brazil, the Empresa Brasileira de Pesquisa Agropecuaria (Embrapa) has developed several promising hybrids, among them ‘Tropical’ (AAAB), which resembles ‘Maça’ (AAB), a Silk cultivar, and ‘Preciosa’ (AAAB), which has characteristics similar to those of ‘Pacovan’ (AAB), a Pome cultivar. At the International Institute of Tropical Agriculture (IITA), tetraploids obtained from crossing a triploid with a resistant diploid were crossed again with improved diploids to produce secondary triploids. Six triploid hybrids have been produced this way to improve the locally important group of East African highland bananas, reported Michael Pillay, the breeder in charge of the IITA breeding programme in Uganda. Their agronomic performance will be evaluated in the field by farmers. The six hybrids being tested all have the same yellow flesh as the cultivars but other hybrids with good disease and pest resistance have a white flesh that may not be accepted by consumers and is probably associated with a lower level of Vitamin A precursors. The latter are being crossed with yellow-fleshed accessions from Papua New Guinea to improve their color. As a secondary centre of banana diversity, India has no shortage of cultivars that need a helping hand to resist diseases, which in this part of the world are mainly Sigatoka disease caused by Mycosphaerella musicola, Fusarium wilt and the burrowing nematode Radopholus similis. Dr Kumar from the Tamil Nadu Agricultural University in southern India, presented results from crossing triploids with diploid hybrids bred for parthenocarpy and higher male fertility and disease resistance. Some of the cultivars they are trying to improve are ‘Karpooravalli’ (‘Pisang awak‘, ABB), ‘Red Banana’ (AAA), ‘Rasthali’ (Silk, AAB), ‘Nendran’ (AAB) and ‘Poovan‘ (Mysore, AAB). They are also experimenting with gamma radiation and chemical mutagens to produce improved mutants and with colchicine and oryzalin to double the number of chromosomes. Tetraploids have been generated from four local diploid cultivars of the AA and AB genomic groups and are currently being tested in the field. Doubling the number of chromosomes is also the starting point of a strategy adopted by the Centre de coopération internationale en recherche agronomique pour le déve- loppement (Cirad) and CARBAP. The scheme starts off with diploids, wild or improved. The chromosome number of improved diploids is doubled by treating them with colchicine. The induced tetraploid is then crossed with another diploid parent to produce a triploid hybrid. Cirad has used this method to develop triploid dessert banana, whereas CARBAP has used it to produce AAA plantains by inducing tetraploidy in a diploid Musa acuminata spp. banksii with plantain-like characteristics. As Tomekpe noted in his keynote address, the success of this strategy relies on a clever choice of parents guided by a good knowledge of their genetic structure, which has increased with the development of molecular tools. The banana family tree Molecular techniques are also used to study the genealogy of Musa cultivars. In her review on molecular markers, Françoise Carreel of Cirad in Guadeloupe explained how scientists have taken advantage of the maternal transmission of chloroplast DNA and paternal transmission of mito- chondrial DNA to establish the lineages of monospecific and interspecific cultivars. The speaker also reminded the audience that M. acuminata and Musa balbisiana are not the only species that have hybridized to produce cultivars. Molecular studies have confirmed, and in some cases revealed, the presence of the australimusa (T) and schizocarpa (S) genomes, a finding that should eventually lead to the reclassification of certain accessions. InfoMusa - Vol. 13 - No.234 InfoMusa - Vol. 13 - No.2 35 Even when it comes to M. acuminata and M. balbisiana, however, we rarely know which variants of their genomes played a role in the evolution of cultivars. Hugo Volkaert from the Center for Agricultural Biotechnology in Thailand presented the results of a study done in collaboration with Sasivimon Swangpol from Mahidol University in Bangkok, Rachel Sotto from the Institute of Plant Breeding, in the Philippines and Tosak Seelanan from Chulalongkorn University in Bangkok, Thailand. After analysing the chloroplast DNA of Thai cultivars, they concluded that three M. acuminata subspecies (malaccensis, banksii, and zebrina) accounted for the ancestral maternal lineages in AA, AAA, AAB, AB and ABB hybrids. The results also indicate that AAA cultivars have a hybrid origin and that the cultivars in the Namwa group have a single BB maternal origin, probably introduced from the Pacific Islands. The speaker suggested designating some ABB cultivars as BBA to better reflect their maternal lineage. A first peek into the genome Martin Dickman from the University of Nebraska in the USA opened the 4th International symposium on molecular and cellular biology with a talk on the role of model plants in improving bananas through genetic transformation and on how programmed cell death can be used to engineer resistance to pathogens (see article on p. 6). As the speaker pointed out, Arabidopsis – the first plant to have its genome sequenced because of the smallness of its genome and the ease with which the plant can be manipulated in the lab – is a dicotyledon and as a result it was thought that the banana, a monocotyledon, would be closer genetically to rice, another ‘monocot’ whose genome is almost completely sequenced. If the results presented at the Congress are confirmed, the banana may not be as close to rice as expected. Researchers working on the genome can sift through the BAC libraries constructed from the genomes of M. acuminata (two libraries of ‘Calcutta 4’) and M. balbisiana (‘Pisang klutuk wulung’) that have been made publicly available by the Global Musa Genomics Consortium (a BAC library of ‘Grande naine’ developed by Cirad should be made available soon). The first glimpses into the banana genome (some 500-600 Mbp) were presented by Chris Town, from The Institute for Genomic Research (TIGR), a non-profit research institution in the USA, and Rita Aert from KULeuven. The scientists at TIGR sequenced and annotated 13 BAC clones, totaling around 1.4 Mb, from the ‘Calcutta 4’ BAC library. The gene density was high and generally comparable to that seen in Arabidopsis and rice (one gene every 4-5 kb). Of the annotated genes that had a high quality match with genes of another species, 78 were with Arabidopsis genes and 59 with rice genes. Based on the content and distribution of glutamine and cytosine along the coding sequence, 175 genes were more Arabidopsis-like whereas only 33 were more rice-like. Meanwhile at KULeuven, Rita Aert and her collaborators randomly chose two BAC clones from the M. acuminata ‘Calcutta 4’ BAC library. The analysis of the first BAC (82 723 bp) revealed 12 putative proteins, representing a gene density of one gene per 6.9 kb. Only 7 coding regions were discovered in the second BAC (73 268 bp), for an overall gene density of one gene per 10.5 kb. The gene organization of these clones resembles the sequences of Gramineae genomes, where genes are clustered in gene-rich regions separated by gene-poor DNA containing transposable elements. By contrast, the genes on chromosomes 1 and 4 of the Arabidopsis and rice genomes are fairly evenly distributed. Tracking BSV The publicly available BAC libraries are also used by researchers from Cirad, Centro de Investigación y de Estudios Avanzados (CINVESTAV), National Institute of Agrobiological Sciences (NIAS) and the Queensland Department of Primary Industries (QDPI) to study the mechanisms leading to the activation of the banana streak virus (BSV) integrated in the nuclear genome of Musa cultivars containing the so-called B genome inherited from M. balbisiana. Strong experimental evidence suggests that some of these integrated sequences, which never result in infections in M. balbisiana, can be expressed and produce episomal forms of the virus that give rise to infections under stress conditions in hybrids, including the hybridization process itself. This InfoMusa - Vol. 13 - No.234 InfoMusa - Vol. 13 - No.2 35 phenomenon represents a serious limitation to the creation of Musa hybrids containing the A and B genomes and to their diffusion. Pierre-Yves Teycheney from Cirad showed how his team used the complete genomes of four BSV strains (BSV-Ol ‘Obino l’ewai’, BSV-Gf ‘Gold finger’, BSV-Im ‘Imove’ and BSV-Mys ‘Mysore’) as probes to screen BAC libraries for the presence of integrated viral sequences in chromosomes of the A and B genomes. In the M. balbisiana ‘Pisang klutuk wulung’ BAC library, they identified 10 BAC clones positive for BSV-Ol, 9 BAC clones positive for BSV-Gf and 24 BAC clones positive for BSV-Im. Screening of the ‘Calcutta 4’ and ‘Grande naine’ BAC libraries revealed no BSV sequences. The BAC clones containing BSV sequences were further characterized by BAC-end sequencing and RFLP fingerprinting and the BAC clones containing BSV-Ol or BSV-Gf sequences were completely sequenced. As part of this research project conducted at Cirad, Gandra Saiprasad from the Indian Institute of Horticulture Research tested various stress factors, such as an antibiotic (hygromycin), a polyamine (spermidine), a demethylating agent (5-Aza cytidine) and heat shock (60°C for 1 h) in the hope of triggering the expression of some integrated sequences. The episomal form of BSV in stressed plants of cv. ‘Penkelon’ (AAB) was checked by PCR. It turned out that BSV activation was very random, with only 2-4 % of the plants treated with an antibiotic and a demethylating agent developing an infection after 72 hours. Suppressive subtractive hybridization (SSH) libraries were constructed by selecting the RNA that was not common to the BSV activated and BSV non-activated plants. Four SSH libraries, with about 1500-2000 expressed sequence tags (ESTs) each, have been constructed and will be used for the isolation of host factors involved in BSV activation. Pests and diseases BSV is only one of the many organisms associated with bananas. In his review of the major diseases and pests of bananas, Randy Ploetz from the University of Florida also covers the new threats and the ones that might spell problems in the future (see article on p. 11). The other keynote address to open the session on plant protection was given by Jean Carlier of Cirad and focused on the genetic population structure of one of the most devastating of those threats, the fungus Mycosphaerella fijiensis, in order to develop sustainable and effective management strategies to control the disease it causes (see article on p. 17). As Ploetz pointed out in his keynote, as a perennial, banana needs long-term pest management solutions but few of the existing strategies are sustainable. Of course, a lot depends on the problem at hand. In another talk on the biological control of Fusarium wilt, Ploetz concluded, somewhat discouragingly for the speakers who were presenting talks on the biocontrol of Fusarium wilt, that there is no evidence that biological control is effective against Fusarium wilt in the field. Fusarium wilt is an especially difficult target for biocontrol, said Ploetz. The soil in which the pathogen resides complicates protection of infection sites, naturally suppressive soils are rare and the vascular location of the infection protects the pathogen from many potential biocontrol agents. Diverse microbes have been tested – arbuscular mycorrhizal fungi, Bacillus spp., pseudomonads, non- pathogenic endophytes and Trichoderma spp. – but few of these studies have been conducted in the field. What has been more commonly reported in journals is an in vitro inhibition of the pathogen or a disease reduction in pot studies. When field studies have been conducted, the results have been disappointing. The best result found in a refereed journal is an 18% loss after 11 months, which would amount to a cumulative loss of over 60% after 5 years. Given the nature of Opening ceremony of the First International Congress on Musa held in Penang in July. Xu Li nb ing InfoMusa - Vol. 13 - No.236 InfoMusa - Vol. 13 - No.2 37 the pathosystem, the speaker believes that Fusarium wilt of banana will be difficult to control with biological agents and wondered whether the resources spent on looking for biocontrol solutions would not be better invested elsewhere. Biological control is one of the features of the International Banana Action Plan, which Gert Kema of Plant Research International B.V. in the Netherlands announced at the Congress. The aim of the plan initiated by the Wageningen University and Research Centre is to reduce pesticide input in banana production by at least 50% over the coming decade. The plan will focus on the control of Mycosphaerella leaf spot diseases and Radopholus similis and will address fundamental as well as applied questions. It is divided into seven themes: 1) pathogen genomics and genetics, 2) genetics and breeding for resistance, 3) epidemiology and population genetics, 4) soil science, 5) biological control, 6) precision farming and disease management strategies and 7) extension and social impact programmes. Nematodes In East Africa, nematodes seem to be contributing to a shift from cooking bananas to the more tolerant dessert and beer cultivars. Dany Coyne from IITA presented some of the results from a project on nematode management in Uganda using mutualistic endophyte fungi. The project is done in collaboration with the Uganda National Agricultural Research Organization, Makerere University, Pretoria University in South Africa and the University of Bonn in Germany. Endophytes are common asymptomatic parasites that cause no damage to the host plant but can suppress or repel potential parasites. In Uganda, the most frequently isolated endophytes are avirulent strains of Fusarium oxysporum. For this study, isolates of F. oxysporum from corms and roots were screened for in vitro activity against the burrowing nematode, R. similis. The multiplication of the nematode was suppressed in tissue culture banana plants and control of the population was still observed seven months after inoculation. The speaker concluded that fungal endophytes could provide a tool for nematode management, which should have its greatest impact when applied to tissue culture plantlets. In a similar vein, Dirk de Waele from KULeuven advocated inoculating with arbuscular mycorrhizal fungi (AMF) banana plantlets that are destined to be transplanted into nematode-infested soils. AMF are obligate symbionts that colonize the root cortex of host plants. These fungi help the plant acquire water and mineral nutrients from the soil and in return obtain carbon as an energy source. In addition, AMF increase the ability of a plant to overcome abiotic and biotic stresses and to reduce colonization by soil-borne pathogens, namely nematodes. However, the magnitude of this response, expressed as the relative mycorrhizal dependency (RMD), depends on the cultivar. The higher the RMD, the greater the effect of inoculating myccorrhiza. For small-scale farmers in places where in vitro plantlets are not an option, Kim Jacobsen from the INIBAP regional office in Cameroon, is exploring cultural practices to control nematodes in a project conducted in collaboration with IITA and KULeuven. As a result of reduced land availability, fallow periods tend to be shorter and pest populations, including R. similis, are increasing and bringing down yields. In her talk, she presented results on the efficiency of fallow and hot water treatments on ‘Essong’ (AAB, French) and ‘Ebang’ (AAB, False Horn plantain). Jacobsen tested two fallow periods, long fallow (15 years) and short fallow (4 years), the effect of adding, or not adding, fertilizers and of treating, or not treating, suckers with hot water (20 min at 52°C). Sampling was done at 15 and 21 months after planting to coincide with the flowering/harvest of the first production cycle and 6 months later. After 15 months, the number of nematodes was significantly lower on the hot water-treated plants for both fallow systems and the root system was healthier, but after 21 months, the increase in nematode number in the short fallow plots outweighed these benefits. The best banana yields in the short fallow plots were not as good as the worst results in the long fallow system. Although farmers are better off using long fallow, they may not be able to practice it for much longer. Unless short fallow cultural practices are improved, their yields are bound to suffer. InfoMusa - Vol. 13 - No.236 InfoMusa - Vol. 13 - No.2 37 Finally, Omolara Rotimi from the Federal University of Technology in Nigeria talked about the effect of mulching on the susceptibility of ‘Agbagba’ to nematodes. She compared heavily mulched and non-mulched management regimes. The nematode population consisted of Helicotylenchus dihystera, Helicotylenchus multicinctus, Hoplolaimus pararobustus, Meloidogyne spp. and R. similis. In the absence of nematodes, the yield in mulched plots was 8.1 tonnes per hectare compared to 3.6 tonnes per hectare in the non-mulched plots. In the presence of nematodes, yield reduction was 46% in heavily mulched plots compared to 54% in the non-mulched plants. However, a higher incidence of toppling (23%) was observed in mulched plots, compared to 16 % in the non-mulched ones. Evidently, there are complex interactions involved in mulching systems that need to be resolved. Propping up production systems Richard Sikora from the University of Bonn in Germany and Piet Van Asten from IITA- ESARC in Uganda, opened the third session of the Congress on sustaining the natural resource base in Musa cropping systems. Sikora revisited the topic of biological control but from the point of view of the microbial communities that live in the rhizosphere and are important for root health and growth (see page 25). Specific fungi, and probably even bacteria, have health-promoting abilities that are believed to suppress pests or diseases when the microbial communities are established and functioning properly. The speaker explored whether they can be enlisted in the fight against pests and diseases. In his talk (see p. 20), Van Asten highlighted a nutrient deficit in the smallholder banana farms of East Africa. With the urban population steadily growing, banana products and their nutrients are increasingly exported from farms to urban centers, a situation that is exacerbated by the fact that East African banana farmers seldom use mineral fertilizers to replenish soil nutrients. Instead, they rely mainly on manure and crop residues, causing further soil fertility decline in annually cropped fields. In Uganda, for example, the speaker estimates that at the current mineral fertilizer prices, it would cost over 2 million US dollars annually to replace in rural areas the potassium and nitrogen contained in the bananas shipped to Kampala. Although the management and maintenance of soil fertility is critical to ensure the sustainability of production systems, the topic is just starting to attract the attention of banana scientists, hence the relatively small number of talks presented at the Congress, many of which reported research that had been published in recent issues of INFOMUSA. Clearly, this is an area that deserves future investment and effort in the future. Nurturing enterprises and improving livelihoods In the fourth session of the Congress, on postharvest and processing for the diversification of incomes, the participants were treated to talks on enterprise deve- lopment, an often overlooked topic, despite its importance in providing farmers with the means and incentives to invest in soil fertility and improved crop protection. Charles Staver from INIBAP, opened the session with a talk on a NORAD-financed project in which he worked before joining INIBAP (see next issue of INFOMUSA). Set in Nicaragua, the project aimed to develop a participatory group learning approach for agro-ecological pest and crop management in Musa. Resource-limited Nicaraguan farmers tend to cultivate bananas with minimal inputs and labour. This low-risk strategy is often complicated by an inadequate management of pests and diseases that leads to reduced bunch size and fewer production cycles. With commercial pesticides being beyond the financial reach of most farmers, pest management strategies have been developed that are consistent with the low risk/low input strategy that makes Musa production a useful commercial and home consumption complement in rural areas. In the other keynote address (see p. 30), Khairuddin Hatir, the CEO of the International Tropical Fruits Network (TFNet), explained the network’s mandate as promoting the sustainable development of the production, consumption, processing, marketing and international trade of the tropical and sub-tropical fruit sector. According to the speaker, the key factors instrumental in fostering lasting partnerships are leadership, InfoMusa - Vol. 13 - No.238 InfoMusa - Vol. 13 - No.2 39 good governance, transparency, knowledge management, creativity and empowerment. Lois Englberger’s talk on carotenoid levels in cultivars from Micronesia (see INFOMUSA 12(2):2-5) drew a lot of interest, not only from the participants but also from the media. Her data show that some traditional varieties contain enough provitamin A carotenoids at realistic consumption levels to prevent Vitamin A deficiency (VAD), a major cause of debilitating health problems in developing countries and a significant contributor to infant and maternal mortality. Lois also pointed out that there are many yellow- and orange-fleshed bananas in other countries – such as ‘Pisang raja’, ‘Pisang berangan’, ‘Pisang mas’, ‘Champa’ in Bangladesh, ‘Nendran’ in India and ‘Lakatan’ in the Philippines – which could have an impact on eliminating VAD and improving general health. Finally, a number of speakers from Africa and Asia presented national and local initiatives to foster the development of banana enterprises. The abstracts of the oral presentations and posters are available on INIBAP’s website at www.inibap.org. How can the advance of banana xanthomonas wilt be halted? Focus on bacterial wilt Since its detection in central Uganda in 2001 (Tushemereirwe et al. 2003), banana xanthomonas wilt disease (BXW, also referred to in Uganda as banana bacterial wilt) has spread to at least 21 districts throughout the eastern, central and north- western parts of the country, probably mediated by airborne (most likely insect) vector(s). Although the distribution within these districts is still localised and patchy, the disease is rapidly filling in the gaps. It is also moving south and westwards towards some of the most important banana growing areas in the country that are not yet affected. All of the commonly grown genotypes are succumbing to this new disease, which destroys the fruit bunches and can reduce yields to zero, threatening the livelihoods of millions of people. An outbreak has also recently been confirmed in the North Kivu region of the Democratic Republic of Congo (see Musanews), and the disease is poised to enter Rwanda, Kenya and neighbouring countries. There is increasing public awareness of the plight of those who have already suffered severe hardship from the disease and concern for those at risk. BXW has many similarities to bacterial wilts of banana in other parts of the world (Moko, blood, bugtok diseases) that are caused by Ralstonia (formerly Pseudomonas) solanacearum and closely related organisms (Thwaites et al. 2000). Control depends on measures that are designed to reduce disease infection and to rehabilitate areas that are already infected (i.e. management), and to reduce or prevent the spread of disease to areas that are not yet infected (i.e. containment). Experience with these diseases shows that once they have become established in smallholder banana cropping systems, then control is very difficult and Figure 1. Affected mats do not always die, so once the disease has become established in smallholder production systems, it is very difficult to eradicate. Sim on E de n-G ree n InfoMusa - Vol. 13 - No.238 InfoMusa - Vol. 13 - No.2 39 eradication effectively impossible (Figure 1). Farmers and consumers have to get used to massively reduced yields. Interventions in these “zones of occupation” need to focus on helping farming communities to manage, or learn to live with, the disease, including introducing alternative crops and food staples and gaining their acceptance. This will be a daunting task in Uganda, emphasizing the importance of containment. Disease containment depends on two key actions: promptly removing sources of inoculum; and reducing or eliminating opportunities for spread. These are mutually reinforcing: the greatest degree of control will be obtained when infection sources are eliminated promptly and the risks of transmission are reduced. Many sources of infection are known or suspected for BXW, including standing infected plants, plant residues, contaminated soils and water, and traded products (fruits, leaves and planting materials). The contribution these sources make to the spread of the disease depends on the survival of bacteria and the mode (and probability) of transmission. Although the relative importance of many of these factors is unknown, tentative conclusions about factors likely to be most important for disease containment can be drawn from field observations on the behaviour of the disease in Uganda and from knowledge of other banana bacterial wilts. A remarkable feature of all these diseases is that infection appears to occur via the male bud, probably following transmission by flying insects that collect or feed on nectar and pollen. Although it is not known at present whether the same or similar insects are involved, this is a striking example of parallel evolution: at least three taxonomically distinct pathogens of banana appear to have evolved a similar mechanism of transmission on different continents. Fortunately, this also presents similar opportunities for controlling the spread of disease1. Observations at advancing disease fronts in Uganda suggest that transmission to the male bud is the primary means of spread. Not only are diseased buds often the first symptom to be observed but these are also most commonly seen on ABB banana types, which are known to be particularly susceptible to insect transmission in other banana bacterial wilt diseases (Buddenhagen and Elsasser 1962). This suggests that, as with these other diseases, airborne infection via male flower parts is the main mechanism driving the current epidemic. Thus timely removal of the male bud should interrupt the transmission cycle and prevent the spread of the disease, especially if this can be done in those types that are considered to be at greatest risk to infection via thus route. Herein lies the main challenge for controlling the epidemic in Uganda where the ABB type ‘Pisang awak’, known locally as kayinja, is widely grown for the production of “banana beer”. At the margins of the disease front, and throughout areas already affected, kayinjas and other ABB types such as ‘Bluggoe’ (Kivuvu) can be found with typical symptoms of inflorescence infection (Figure 2). Farmers themselves have come to recognise that these are usually the first types to become infected. Control options seem obvious enough – reduce the rapid rate of spread by destroying, or at least debudding, the ABB types and then concentrate on preventing other modes of spread (contaminated tools, infected plant materials) and clean up areas already infected. Unfortunately however, plots Figure 2. Infected male bud. Sim on E de n-G ree n 1 See discussion forum at http://www.banana.go.ug/cgi-bin/ discus/discus.cgi InfoMusa - Vol. 13 - No.240 InfoMusa - Vol. 13 - No.2 41 of kayinjas are frequently neglected or at best semi-cultivated and whilst harvesting rights may be established by local custom, ownership and responsibility for maintenance is often obscure. Under these circumstances, it is understandably difficult to persuade individual farmers to debud healthy plants or to cut down or destroy mats that have become diseased but may still produce the occasional usable bunch of fruit – let alone to remove plots of kayinjas that are not yet affected. Financial inducements or compensation are unlikely to be feasible given the magnitude and continuing nature of the problem, and the costs and logistics involved. Can some form of community awareness and action succeed, perhaps backed by coercion or enforcement? And to what extent can individual farmers take action to protect their own banana plantings for themselves? Two broad approaches can be suggested: firstly, a series of cordons sanitaires at the margins or “disease fronts” of the epidemic, involving intensive control measures including phytosanitation, eradication of all diseased plants, debudding of healthy ones, and strict controls on the movement of people and planting materials. This would require actions both within and in advance of a diseased area in order to create a “firebreak”, or zone of zero tolerance of both sources of inoculum (diseased plants) and infection courts (male buds). Given the difficulties of managing kayinjas, a high degree of community participation, mobilisation and support would be required. The resources necessary to achieve this may be justified when the stakes are particularly high, as for instance in preventing further movement of the disease to the intensive banana cultivation areas in southwest Uganda. Even so, it is difficult to conceive of the high levels of adoption (and enforcement) of control measures that are likely to be necessary on the broad front over which the disease is progressing. The second approach depends on what individual farmers can do for themselves. Farmers may be able to do little to control sources of infection (and hence inoculum) that surround their own plants, but they can take steps to prevent their bananas from becoming infected through their own actions (use of contaminated tools, footwear, planting materials) and by preventing airborne spread. The question, as yet inadequately untested, is how effective are such individual courses of action. Can individual farmers, with fields of on average no more than 1-2 ha, prevent the disease from becoming established by debudding on such a small scale? At present, the experiments remain to be done but the stakes are high. If only a small proportion of farmers were to succeed by adopting such measures, then others would surely follow and “green islands” would emerge amidst the surrounding devastation. The evidence is certainly encouraging: unconfirmed reports suggest that some farmers have greatly reduced or even prevented the spread of disease in their fields since adopting debudding, cutting out infection and other phytosanitary measures. As reported in this issue’s Musanews, it is surely no accident that Dwarf Cavendish, a variety with floral morphology resistant to insect-borne infection, survives virtually unscathed alongside diseased kayinjas in Ethiopia. Can it be coincidence that in the Congo, where inflorescence infection appears to be rare, the disease has so far spread slowly? Whilst prevention of airborne dispersal of the bacteria between inflorescences may be the most important means of controlling the primary spread of the disease, especially between farms and villages, other modes of infection undoubtedly occur and are critical to containment. The necessary measures can be summarised as follows: • Intensive surveillance and reporting to identify the current disease distribution and presence of suspected new outbreaks; • Prompt follow-up actions to investigate reports of new outbreaks and to take action to eradicate or neutralise them; • Strict control on the movement of plant materials from diseased to non-diseased areas, especially planting materials; • Availability and strict observance of phytosanitary practices, especially disin- fection of cultivation tools, footwear etc.; • Strict control of infection, and preferably total destruction, of ABB types at the disease front; • Strict enforcement of debudding of all types at, and in advance of, the disease front by breaking off (not cutting) the male buds as soon as the last fruits have set. Simon Eden-Green, Consultant to the Banana Bacterial Wilt Project at Kawanda Agricultural Research station, Uganda (funded by NARO and the Gatsby Charitable Foundation, UK). EG Consulting; 470 Lunsford Lane, Larkfield, Kent ME20 6JA, UK. Email: egc@eden-green.co.uk InfoMusa - Vol. 13 - No.240 InfoMusa - Vol. 13 - No.2 41 References Buddenhagen I.W. & T.A. Elsasser. 1962. An insect spread bacterial wilt epiphytotic of bluggoe banana. Nature 194:164-165. Thwaites R., S.J. Eden-Green & R. Black. 2000. Diseases caused by bacteria. Pp. 213-240 in Diseases of Banana, Abaca and Enset (D.R. Jones, ed.). Wallingford, UK, CABI Publishing. Tushemereirwe W., A. Kangire, J. Smith, F. Ssekiwoko, M. Nakyanzi, D. Kataama, C. Musiitwa, & R. Karyaija. 2003. An outbreak of bacterial wilt on banana in Uganda. INFOMUSA 12(2):6-8. Effect of soil compaction on the architecture of the banana root system growing in an andosol F. Lecompte Thesis PhD thesis submitted in 2002 to the Institut National Agronomique Paris- Grignon and the Avignon Institut National de Recherche Agronomique, France Despite the coexistence of several banana production systems in the West Indies, mechanized monocultures remain important. Heavy machinery, soil tillage and frequent planting lead to the degradation of soil structure and decreased soil fertility, while monoculture favors pests. Andosols are very frequent in the traditional banana growing area of Guadeloupe and naturally promote the development of the root system. However the dynamics of soil colonization by banana plants remain largely unknown and as a result cultural practices cannot be adapted to the uptake and anchoring abilities of the roots. Experiments were conducted to characterize the architecture of the banana root system three months after plantation in an andosol. Experiments in rhizotrons, containers, and in the field helped determine the parameters pertaining to four main functions: root emission, root growth, root branching and senescence. Root emission was fairly similar to what is observed in other monocotyledons, like maize and rice, and was correlated with shoot development. The diameter at the root apex increased between planting to emission and changed over the life of the root. Two original methods based on static morphological observations were used to determine the in situ root growth rates. The root growth rates ranged from 0.1 cm/day in quaternary roots to 3.5 cm/day in primary roots and were closely related to the diameter at the apex. Root branching was almost strictly acropetal (from base to apex). The density of root branching was less the further away from the base of the root and the smaller the diameter of the main root. Root senescence was not explicitly characterized, but is related to the duration of the growth phase of the root, which seems proportional to its mean diameter. The impact of soil compaction on the architecture of the root system was studied in pots (static compaction with an hydraulic press) and in the field (dynamic compaction with tractor wheels) to study the response of the roots to pressures ranging from 50 kPa to1200 kPa. A slight decrease in the growth of dry matter in shoots was observed when the soil was highly compacted. Only the growth of the large roots was affected by a lower soil macroporosity: an 8% reduction in total porosity (corresponding to a 65% reduction in air filled spaces) reduced their growth rate by 50%. A multiple linear regression between growth rate and three factors (diameter at the apex, soil porosity and total degree days) accounted for 92% of the observed variance. Soil compaction increased the death rate of primary roots by a factor of 4 but did not globally affect root trajectory, which tends to be horizontal. Roots growing in compacted soils had a more tortuous trajectory. A model of the architecture of the banana root system was built to simulate the development of the root system under various soil conditions. Once validated, this model could help understand the effect of various mechanization scenarios on root absorption and the stability of the plant. InfoMusa - Vol. 13 - No.242 InfoMusa - Vol. 13 - No.2 43 Vitamin content of unripe bananas and derived products Maria Teresa Borges Thesis PhD thesis submitted to Universidade Estadual de Campinas, Unicamp, SP, Brazil, November 2003 Brazil, one of the largest producers of bananas, is also one of the countries with the highest proportion of waste. The use of the green bananas offers a way to minimize this problem. The objective of this work was to evaluate the vitamin content of bananas with the aim of improving the uses of the fruit. The levels of the vitamin B complex (PP, B1, B2, B6 and folic acid), pro-vitamin A (β- carotene) and vitamin C (L-ascorbic acid (LAA) and dehydroascorbic acid (DHAA)) were measured in the fruits of the cultivars ‘Nanicão’ and ‘Prata’ from the orchards of the Taperão Farm in the town of Brotas, from the emergence of the fruit to senescence, and with and without induction of the ripening process. The vitamin content of banana bread and nhoque* made with unripe banana pulp was also determined and compared with the one of similar products (potato nhoque and integral bread). A sensory test was also conducted with untrained panelists to evaluate the acceptance of these foods. Unripe fruits of ‘Nanicão’ and ‘Prata’ had respectively 0.57 and 0.84mg/100g of B1, 1.4 and 1.1mg/100g of B6, 135 and 104μg/100g of folic acid, 17.6 and 20.2mg/100g of LAA, 6.1 and 5.8mg/100g of DHAA, and 1073 and 441μg/100g of β-carotene. The levels in the mature fruits were respectively 0.63 and 1.08mg/100g of B1, 0.75 and 0.63mg/100g of B6, 12.4 and 19.2mg/100g of LAA, 3.6 and 4.5mg/100g of DHAA, and 1682 and 1072μg/100g of β-carotene. No vitamin B2 was found in the samples analysed. The vitamin levels in the products made from unripe banana pulp were similar to the ones in the fruits and the other products, except for the various forms of vitamin C. The acceptance sensory tests suggested some modifications to be made in the recipes proposed to the panel.*Gnocchi Musa News Poster competition A panel headed by Dr Yasmin Othman of the University of Malaya in Kuala Lumpur, Malaysia, selected the best posters presented at the 1st international banana congress. We would like to thank Synergy Farms of Malaysia for graciously offering prizes to the winners listed below. Winners of Session 1 S. Subramaniam, M. Maziah, M.P. Abdullah and M. Sariah for Agro-bacterium-mediated transformation of ‘Rastali’ H. Khanna, D. Becker, J. Kleidon and J. Dale for Agrobacterium-mediated trans- formation of Cavendish and `Lady finger’ embryogenic cell suspensions W.C. Wong, R.Y. Othman and K.N. Khalid for Biolistic-mediated transformation of cv. `Mas’ with a transcription factor associated with early flowering E. Santos, S. Remy, B. Coemans, E. Thiry, S. Windelinckx, R. Swennen and L. Sagi for Isolation of plantain promoters using the firefly luciferase reporter gene R. Sutherland, J.-V. Escalant, K. Kunert, N. van den Berg, A. Kiggundu and A. Viljoen for Establishment of a banana transformation facility in South Africa for engineering Fusarium wilt and banana weevil resistance J. Bartos, O. Alkhimova, M. Dolezelova, E. De Langhe and J. Dolezel for Diversity in genomic distribution of ribosomal DNA and nuclear genome size in Musa InfoMusa - Vol. 13 - No.242 InfoMusa - Vol. 13 - No.2 43 Winners of Session 2 R.A. Zorilla, T.O. Dizon, D.C. Pantastico, J.I. Orajay, F.S. de la Cruz Jr., I. Van den Bergh and D. de Waele for Survey of nematodes in Quezon province, Philippines A. Belgrove, B. Nel and A. Viljoen for Characterization of fungal endophytes as possible biological control agents against Fusarium oxysporum f.sp. cubense M.A. Jimenez, J. Bermeo, M. Jama, L.Perez and R. Maribona for Sensibility of Mycosphaerella fijiensis populations to triazole and strobilurin fungicides in Ecuador Winners of Session 3 M. Onyango, F. Nguthi, J. Mutisya and F. Muniu for Characterization of banana cultivars, production practices and constraints of production for farmers in banana growing areas of Kenya Babita Jhurree-Dussoruth for Evaluation of `Petite naine’ in Mauritius Nor Aini M. Fadzillah, Intan Nasrah Omar Shukri, Siti Khalijah Daud and Zakaria Wahab for Aluminium toxicity induces lipid peroxidation and affects antioxidant enzyme activities in cultivars of Musa sp. Winners of Session 4 Che Rahani Zakaria and Rahil Mohd for Development of fruit rolls from banana Sam Zainun Che Ahamad for Quality of frozen breaded banana K.P. Baiyeri for Moisture level of plant residues used as storage media influenced post harvest behaviour of mature plantains MusaNewsAn outbreak of banana xanthomonas wilt (Xanthomonas campestris pv. musacearum) in the Democratic Republic of Congo In January 2004, following a request from FAO Goma, the first author accompanied local agricultural officers on a visit to the Masisi region, North Kivu province, in order to investigate a banana disease (Ndungo and Kijana 2004). These initial observations suggested that the disease might be bacterial wilt caused by Xanthomonas campestris pv. musacearum, which has recently been reported in Uganda (Tushemereirwe et al. 2003). Subsequent visits were made in May and August 2004 and this report confirms the earlier diagnosis. Local farmers first observed the disease in 2001 at Bashali Mokoto village, 72 km northwest of Goma in North Kivu (Figure 1). The altitude at the site ranges between 1700 and 1740 m. The varieties grown include ‘Pisang awak’ (ABB) (90% of all bananas), beer and cooking East African highland bananas (AAA), the dessert bananas ‘SukariNdizi’ (AAB) and Cavendish (AAA), and plantains (AAB) (Ndungo 2004). As in Uganda, all banana genotypes are affected but ‘Pisang awak’ seems to be the first to get infected and the Cavendish varieties last, after the matooke and beer clones. The symptoms were similar to those observed in Uganda (Tushemereirwe et al. 2003) but tended to be more severe. These include progressive yellowing, wilting and blackening of leaves, as if scorched by fire. Internally, yellow or brown vascular streaks were seen throughout the plant and pockets of pale yellow bacterial ooze were especially prominent in airspaces at the leaf base of the pseudostem. Premature ripening and internal discoloration of fruits was observed, as was blackening and shrivelling of the male bud. The latter, however, was much less common than what has been observed on the same varieties in Uganda, where in newly affected areas the first symptoms were often seen on the flowers. Using methods described by Tushemereirwe et al. (2003), the bacteria isolated at CABI Bioscience were indistinguishable from the X. campestris pv. musacearum samples from Uganda. The isolates caused rapid wilting following inoculation into young banana plants. As in Uganda, the disease was first reported in 2001 but the situation in the Democratic Republic of Congo is different. Contrary to the situation in Uganda, where the disease has spread at the average alarming rate of 75 km per year, probably by insects visiting the male buds, the disease in DRC has spread very slowly, from an initial InfoMusa - Vol. 13 - No.244 InfoMusa - Vol. 13 - No.2 45 site of a few plants in one village (Bwere hill) to a radius of approximately 10 km. Towards the centre of this area the yield is almost reduced to zero, which has an alarming impact on food security. Many bananas continue to produce suckers but these are invariably infected from the motherplant and rarely flower (Ndungo and Kijana 2004). The disease is also more intense close to five small lakes. The first and second authors have recently observed a new disease focus about 20 km from the first one, so continued vigilance and control actions are necessary. Infected flowers are much less common and it appears that the principal mode of spread may differ from the one in Uganda. In DRC, control will be more a matter of trying to eradicate the disease and cleaning up infected fields rather than removing male buds to prevent insect transmission. It is impossible to ascertain the origin of the outbreak. One hypothesis is that the disease has recently spread from wild enset plants, which are found on nearby hillsides and swampy areas. It may thus be prudent to destroy enset plants in the immediate vicinity of cultivated bananas and the presence of the disease in enset should be investigated. Apart from enset, no other alternative host has been demonstrated so far. It is possible that the bacteria can infect other closely related species (such as Zingiberaceae, Marantaceae and Cannaceae) but so far there is no evidence that this occurs in nature, and even if it does, it may not be important for the spread of the disease. References Ndungo V. 2004. La situation de la culture du bananier et du bananier plantain en République Démocratique du Congo, Communication présentée à la septième réunion du comité de pilotage de MUSACO, Limbé, Cameroun, 7-11 June 2004. Ndungo V. & R. Kijana. 2004. Diagnostic et stratégies pour la lutte durable contre la maladie des bananiers et bananiers plantain dans la collectivité des Bashali, Territoire de Masisi, Province du Nord–Kivu, DRC, Goma, 26–29 January 2004. 21pp. Tushemereirwe, W., A. Kangire, J. Smith, F. Ssekiwoko, M. Nakyanzi, D. Kataama, C. Musiitwa & R. Karyaija. 2003. An outbreak of bacterial wilt on banana in Uganda. InfoMusa 12(2):6-8. V. Ndungo works at the Faculté des sciences agronomiques de l’Université Catholique de Graben, Butembo, Nord-Kivu, DRCongo, ndungovigheri@yahoo.fr, K. Bakelana at INERA Mvuazi Research Centre, P.O.Box 2039, Kinshasa, Gombe, RDCongo, inera@raga.net S. Eden-Green at EG Consulting. 470 Lunsford Lane, Larkfield, Kent ME20 6JA, UK egc@eden-green.co.uk and G. Blomme at INIBAP Regional Office, P.O.Box 24384, Kampala, Uganda g.blomme@cgiar.org Musa News Enset (Ensete ventricosum) is a staple food for over 12 million people in the southern highland areas of Ethiopia. It grows best at altitudes ranging from 2000 to 2700 m (Brandt et al. 1997). Enset bacterial wilt was first reported in Ethiopia by Yirgou and Bradbury (1968) and is currently found in all the enset growing regions and on wild enset plants, although it has not been reported on enset in other countries. It is mainly spread through infected farm tools, infected planting material, repeated transplanting that damage the corm and roots, animals fed infected plants and possibly insects feeding on the foliage. Since cultivated enset is harvested for its starchy pseudostem and corm, it is not normally allowed to flower. As a result, the question of insects infecting flowers does not normally arise, but symptoms typical of insect transmission have been observed on banana flowers (Yirgou and Bradbury 1974). An enset and banana pest and disease survey, funded by the Flemish Association for Development, Co-operation and Technical Assistance (VVOB), has recently been conducted in the main enset and banana growing regions. The largest banana producing area is located at Arba Minch in southern Ethiopia (1200 m) (Figure 1). This area is geographically separated from the wetter highland areas where enset is grown. No banana bacterial wilt has been reported so far in this area. The second banana growing area is located in western Ethiopia and most of the bananas are found between 1050 and 1700 m (Figure 1). Distances of over 100 meters between plots are very common. Although it is not the main crop, enset is also grown in this area and enset bacterial wilt is present. Most farmers indicated that the disease (locally called cholera) has been present on enset and banana for some 20 years. The varieties grown in this region are ‘Kenya’ (‘Dwarf Cavendish’), ‘Faranji muz’ (‘Pisang awak’), ‘Abesha muz’ (a matooke Bacterial wilt (Xanthomonas campestris pv. musacearum) on enset and banana in Ethiopia InfoMusa - Vol. 13 - No.244 InfoMusa - Vol. 13 - No.2 45 clone) and ‘Red abesha’ (‘Uganda red’), all sweet bananas. Bacterial wilt seems more common on banana than on enset. The farmers indicated that banana bacterial wilt mainly attacks ‘Pisang awak’ and in some cases ‘Red abesha’. Male bud infection was observed on a large number of ‘Pisang awak’ mats in the areas below 1700 m. A few farmers reported infection in their matooke clones. ‘Dwarf Cavendish’, which is very widely grown in this region, apparently does not get infected. It is believed that the absence of male bud infection is linked to the persistent male bracts, which could constitute a barrier to insect transmission. This observation is in agreement with a report from Bakelana and Ndungo (2004), who stated that the Cavendish varieties present in eastern Democratic Republic of Congo (DRC) were the last genotypes to get infected. Scattered banana mats are also found in the south-central enset growing region, in areas over 1700 m. Male bud infection has not yet been observed in this region, possibly because the higher altitude and lower temperatures are not favourable to insect vectors. This is in agreement with observations made at over 1700 m in North Kivu, DRC, where male bud infection is very uncommon. In contrast, male bud infection has been postulated to be one of the primary causes of new infections in Uganda (<1600 m), and is widespread in south- western Ethiopia (<1700 m). Numerous extension activities have been conducted or are ongoing in Ethiopia to control enset bacterial wilt. However, no active banana bacterial wilt eradication programme is currently operational. Early removal of the male bud is not practiced. Given that the cultivation of bananas is a growing activity, focus should be put on controlling the disease and preventing its spread through timely debudding, the removal of infected plants, the use of clean farm tools and clean planting materials. References Bakelana K. & V. Ndungo. 2004. La maladie de Bwere: une bactériose dévastatrice de la culture de la banane dans la province du Nord-Kivu en République Démocratique du Congo. Rapport de mission FAO. 11pp. Brandt S.A., A. Spring, C. Hiebsch, J.T. McCabe, E. Tabogie, G. Wolde-Michael, G. Yntiso, M. Shigeta & S. Tesfaye. 1997. The «Tree Against Hunger»: Enset-based Agricultural Systems in Ethiopia. American Association for the Advancement of Science, Washington, DC, USA, 56pp. Yirgou D. & J.F. Bradbury. 1968. Bacterial wilt of Enset (Ensete ventricosum) incited by Xanthomonas musacearum sp. Phytopathology 58:111-112. Yirgou D. & J.F. Bradbury. 1974. A note on wilt of banana caused by the Enset wilt organism Xanthomonas musacearum. East African Agricultural and Forestry Journal 40(1):111-114. Temesgen Addis and Fikre Handoro work at the Southern Agricultural Research Institute (SARI), in Awassa, Ethiopia, and Guy Blomme at the INIBAP Regional Office in Kampala, Uganda. Recommended names of banana diseases and their pathogens MusaNews Three plant pathologists with experience with banana diseases, David Jones, Chris Hayward and John Thomas, have worked with the International Society for Plant Pathology’s Committee for Common Names of Plant Diseases (ISPP-CCN) to prepare a list of recommended names of diseases of bananas. This list is accompanied by a second list of pathogen names (mainly bacteria, fungi and viruses), which includes selected important literature references. These two lists have been placed on the ISPP-CCN website at http://www.isppweb.org/names/ common.asp. Choosing the “best” name for a disease can be difficult. A disease may have multiple names, depending on the country, locality or user. Internationally, as many SUDAN KENYA ETHIOPIA Addis Ababa Enset growing areas Banana growing areas Figure 1. Main enset and banana growing regions in Ethiopia (adapted from Brandt et al. 1997). InfoMusa - Vol. 13 - No.246 InfoMusa - Vol. 13 - No.2 47 as seven or eight names may be used for the same disease. Nobody is happy to find that a name they have long used is not the name recommended for international standardization. It has not been easy to reach a consensus on some names, even within the ISPP-CCN. In choosing the recommended names, the ISPP-CCN has kept in mind certain principles (guidelines) with which the best names of diseases should be consistent. In particular, a name should include a suitable descriptor, indicating a major disease symptom. A meaningless name, even if it is short and memorable, is relatively unhelpful to people not familiar with a disease. In recommending names, the ISPP-CCN has tried to be consistent with certain working rules. For instance, disease names should be in English, because of its wide use in international communications. Also, only well-studied diseases of importance are included in an effort to avoid future name changes. One important banana disease for which choosing the name has proved difficult is the leaf spot disease caused by Mycosphaerella fijiensis. This is called “Black Sigatoka (leaf spot)” in many countries, but “Black leaf streak” in some others. As a compromise, both names are accepted as valid alternatives. Another example is the wilt disease caused by Fusarium oxysporum f. sp. cubense. The recommended name is “Fusarium wilt”, consistent with the name widely used for similar wilt diseases of both banana and many other hosts. The alternative name, “Panama”, is included in the disease list as a non-preferred name. A third example is the bacterial wilt disease caused by Ralstonia solanacearum race 2. The recommended name is “Moko bacterial wilt”, combining the commonly used name “Moko” (the name of a particularly susceptible banana clone) with the descriptive name “bacterial wilt” often used for wilt disease caused by R. solanacearum in both banana and other hosts. Names for diseases in the list recommended by the ISPP-CCN can be challenged by anyone preferring a different name. You are invited to communicate your suggestions to the Chair of the ISPP-CCN, David Teakle, d.teakle@uo.edu.au It is expected that, following consideration of challenges, names approved by the ISPP- CCN will be commonly used as “standard” names in international publications, inter- national meetings, etc. In conversation, personal communications and locally some approved names will no doubt be abbreviated for convenience, or alternative “traditional” names in English or other languages will be used. Planting depth In the early 1980s, I had the privilege of spending a few days with the late George Wilson (Vol. 13 No. 1) during his visit to Gabon. We discussed planting depth, which is also the topic of an article by S.B. Bakhiet and G.A.A. Elbadri in the same INFOMUSA issue. We concluded that there was no need to plant banana deep given its inherent shallow root system, which is largely concentrated on the top soil layer, with some of the roots growing in the mulch (where there is mulching). Nevertheless, from my largely African experience, the issue of planting depth with regards to bananas (and other perennial crops) remains an unresolved subject that deserves further investigation (such as participatory on-farm research), appropriate extension and information communication, as well as experience sharing. The paper by Bakhiet and Elbadri can be an entry point for a discussion on banana planting depth after some clarifications are provided. For example, which cultivar was used in the trial? Was the crop irrigated and, if so, how was water provided? Was the trial about depth of planting or size of the hole, or both? If the focus was on depth of planting, was the size of the hole similar for the different planting depths? Which criterium was used for measuring depth of planting? Was it the bottom point of the sucker? What was the size of the sword suckers and how homogeneous was the size of the suckers used in the trial? Forum InfoMusa - Vol. 13 - No.246 InfoMusa - Vol. 13 - No.2 47 Planting depth may be a different issue in a commercial plantation or under smallholder condition, e.g. whether mechanization is involved or not. Other factors that may also have an influence include the genomic group (e.g. AAA, AAB or ABB), the presence of pests and diseases, mixed or sole cropping and land husbandry. Planting depth is an important issue because of its impact on agronomic performance and sustainability, and on labour and economic issues, and merits further discussion. Guy Evers, Senior Agricultural Officer FAO Investment Centre Division Southern and Eastern Africa Service (TCIS) E-mail: Guy.Evers@fao.org Exports from an organic banana paradise In these days far from my country, six years after the start of the organic banana project in the Chira valley, supported by the Peruvian Ministry of Agriculture and the watchful collaboration of INIBAP, export of organically produced banana from Peru is beginning to take its place as the star of export production, having been the most dynamic fruit export sector over the past years. In addition to the benefits organic bananas have generated in Peru, as published in INFOMUSA June 2004, we can expect they will continue to produce strategic benefits such as the generation of new sources of work and improved income for small-scale growers in northern Peru. The objective of the project, described as “An organic banana paradise” in the INIBAP 2003 annual report, was to improve the revenues of small-scale banana producers affected by El Niño by exporting bananas. Despite the predictions of well-known export firms saying that the banana production areas in Peru were too remote from the markets in the North, this project started exports in 2000 in the context of organic agriculture as an alternative for the thousands of producers who were receiving ever lower prices for their banana production while paying increasingly higher prices for inputs. Looking at today’s export figures, we can say that we have met the challenge to develop our comparative advantages, which we had set for ourselves in 1998. The export of banana is not only a reality, but it keeps on increasing. More private firms are involved in commercialisation, competition has increased, our organic bananas are increasingly eaten in a greater number of countries, quality is steadily improving and the perspective of growth of organic banana increasingly lends itself to the involvement of efficient private firms which produce, locally, inputs for the banana industry. In 2004, the volume of bananas exported from Peru increased by 34% and their value increased by 39% in comparison with the previous year, as a result of the higher selling prices. In 2004, 10 organic banana export companies settled in northern Peru, compared to two firms in 2000. To date, the transnational Dole captured 59% of the export value, whereas Bioorgánika and Gronsa captured 22%. The remaining value of exports was captured by Banano del Norte, Bio Costa, Inka Banana, Organia, Grupo Orgánico Nacional, AgroPiura, Biofruit, Productos Orgánicos de Piura, Tumpibanana and the recently created Agrorganic. The firms Biofruit and Tumpibanana sent 100% of their export to neighbouring Ecuador, which then re-exported organic bananas to countries such as the USA. The transnational Dole was responsible for 83% of the volume exported to the USA and 52% of exports to Belgium, at an average price of US$6.4 per box. Seventy five per cent of the volume exported to The Netherlands was by the firm Bioorgánica, at an average price of US$8.1 per box. The firms Inka Banana and Organia exported 51% and 34% respectively of the total volume to Japan. The German and British markets were recently penetrated and for the first time there was participation in the Chinese market. Last year, Japan, Belgium and The Netherlands markedly increased their imports, while the rate of export to the United States decreased over the past four years and the growth rate may be negative by the end of 2004 . This situation could be caused mainly by competition from countries that are closer such as the Dominican Republic, Mexico and Ecuador. From the start of the project to the present, organic banana from Peru has penetrated 10 countries, the USA (61%), Belgium (16%), The Netherlands (12%), Germany (5%), Japan (4%), France, UK, Ecuador, Spain and China. InfoMusa - Vol. 13 - No.248 The average rate of change in FOB* prices grew at a rate of 10% between 2001 and 2004, from US$5.6 per 18 kg box in 2001 to US$7.4 in 2004. The increased banana prices were mainly due to the opening of new markets, such as Japan, and the growth of sales to markets with better prices, such as The Netherlands and Belgium, not forgetting that the FOB prices of exports to the USA also increased progressively. The totality of production is achieved by small-scale producers who sell their production to export firms who then certify the production, processing and commercialization of the organic bananas, and at the same time provide technical assistance to producers. The growth in value of the exports increases the awareness of small-scale producers regarding the protection of the environment and the importance of producing safe and nutritious food. Moreover, the participation of more private firms, supported by regional research organizations and certification agencies, will generate, in the medium term, the development of a production chain that will result in the generation of complementary activities for improved production and provision of services. The development of applied research, the creation of private firms involved in the production of inputs for export and, of course, a marketing strategy positioning Peru as “A Paradise of Organic Bananas”, are the main themes that need to be addressed to develop the production chain of organic bananas in Peru. Salomón Soldevilla Canales E-mail: ssalomon@colpos.mx Erratum In the article “Evaluation of new banana hybrids against black leaf streak disease”, published in the previous issue of INFOMUSA, we wrote that the disease against which the hybrids had been evaluated was black leaf streak disease, caused by Mycosphaerella fijiensis. In fact, it was Sigatoka disease, caused by Mycosphaerella musicola. We regret the error. * FOB: free on board. On 31 October 2004, the banana and biotechnology community lost one of its most active collaborators, Dr Rodolfo Heriberto Maribona Hernández, the director of CIBE (Centro de investigaciones biotecnologicas del Ecuador) at ESPOL (Escuela Superior Politecnica del Litoral) in Guayaquil, Ecuador. Born in Cuba in 1939, he showed an early interest in science. He studied medicine and biology at Harvard University in the US and obtained a PhD from Lomonosov university in Moscow in 1979. After his return to Cuba, he dedicated himself to the genetic improvement of sugar cane through somaclonal variation. He arrived in Ecuador as a consultant to ESPOL in 1997 and in 1998 became the scientific director of SEBIOCA (Sociedad Ecuatoriana de Biotecnología). He initiated collaboration projects with Flemish univer- sities in Belgium, concentrating on the In memory of Dr Maribona banana-black leaf streak disease model because of the importance of the disease in Ecuador. In 1999, he headed the Musa biotechnology project for sustainable agriculture, which led to the creation of CIBE. In addition to being a research centre, CIBE provided extension to farmers via lectures and field demonstrations as part of its BANARED unit. Its collaboration with organic banana farmers has also become the foundation of ground-breaking work on the molecular and biochemical mechanisms underpinning the plant’s defenses. Those who knew and worked with Dr Maribona will remember him for his unflagging support to young people who embarked in a career in science, his vast scientific knowledge and his pleasant personality. Isabel Jimenez, CIBE, Ecuador Rony Swennen, KULeuven, Belgium InfoMusa - Vol. 13 - No.248 I NFOMUSA is an international journal published twice a year in English, French and Spanish. Our focus is to provide an outlet for research results and reports of interest to the Musa community. As INFOMUSA publishes articles on any Musa-related issue, authors should aim for simple and clear phrases that avoid unnecessary jargon in order to make their paper accessible to readers in other disciplines. Manuscripts should be prepared in English, French or Spanish and should not exceed 2500 words, including references. They should be double-spaced throughout. All pages (including tables figures, legends and references) should be numbered consecutively. Include the full name of all the authors of the paper, together with the addresses of the authors at the time of the work reported in the paper. Indicate also the author nominated to receive correspondence regarding the paper. Manuscripts can be sent as e-mail attachments or put on a 3.5-inch disk for PC-compatible machines. Please indicate the name and version of the word processing software used and the author’s e-mail address. In either case, we will need to receive by mail two printed copies of the manuscript. Title: The title should be as short as possible and should not have numbers, acronyms, abbreviations or punctuation. Abstract: An abstract, not exceeding 200-250 words, should be provided. It should concisely summarise the basic contents and should be sent in the same language as the manuscript. Translations (including the title) into the two other languages should also be sent if this is possible. Key words: Provide a maximum of six key words, in alphabetical order, below the native-language abstract. Introduction: The introduction should provide the rationale for the research and any relevant background information. Since it is not meant to be an exhaustive review of the topic, the number of references should be kept to a minimum. Introductions on the importance of bananas as a staple food or a traded commodity should be avoided, unless they are absolutely necessary for the comprehension of the article. Materials and methods: The authors should provide enough details of their experimental design to allow the reader to gauge the validity of the research. For commonly used materials and methods, a simple reference is sufficient. Results: The unit should be separated from the number by a single space and follow SI nomenclature, or the nomenclature common to a particular field. Unusual units or abbreviations should be defined. Present data in the text, or as a figure, or a table, but never in more than one of these ways. Avoid extensive use of graphs to present data that could be more concisely presented in the text or in a table. Limit photographs to those that are absolutely necessary to show the experimental findings. Discussion: The discussion should not contain extensive repetition of the results section nor should it reiterate the introduction. It can be combined with the results section. References: All references to the literature made in the text should be referred to by author(s) and year of publication (e.g.: Sarah et al. 1992, Rowe 1995). References to not widely circulated documents, such as annual reports, and citations of personal communications and of unpublished data should be avoided. A list of references, in alphabetical order, should be provided at the end of the text. Please follow the style shown below: Periodicals: Sarah J.L., C. Blavignac & M. Boisseau. 1992. Une méthode de laboratoire pour le criblage variétal des bananiers vis-à-vis de la résistance aux nématodes. Fruits 47(5):559-564. Books: Stover R.H. & N.W. Simmonds. 1987. Bananas (3rd edition). Longman, London, United Kingdom. Articles (or chapters) in books: Bakry F. & J.P. Horry. 1994. Musa breeding at CIRAD-FLHOR. Pp. 169-175 in The Improvement and Testing of Musa: a Global Partnership (D.R. Jones, ed.). INIBAP, Montpellier, France. Illustrations and tables: These should be numbered consecutively and referred to by these numbers in the text. Each illustration and table should include a clear and simple caption. Figures and tables should be inserted after the references or in separate files. Graphs: provide the corresponding raw data with the graphs, if possible in Excel format. Drawings: provide originals if this is possible. Photographs: We prefer hard-copy printouts of photographs (bright paper with good contrast for black and white photographs; good quality proofs and films or original slides for colour photographs), but please remember that we will not return them. We will publish pictures that have been scanned or taken with a digital camera as long as the resolution is high enough (1 million pixels or a minimum of 300 dpi when the photograph is in real size). Acceptable file types are JPEG, TIFF and EPS. Avoid sending photos inserted in a Word or Power Point document, unless they are accompanied by a better quality alternative. Acronyms: These should be written in full the first time they appear in the text, followed by the acronym in parenthesis. Cultivar names: The name of the cultivar should be placed between single quotation marks. If the name is a compound noun, only the first word starts with a capital letter, unless the other refers to a place or person. Use the most commonly agreed upon name, such as ‘Grande naine’ and avoid local variations or translations, such as ‘Gran Enano’. Note: When plant material used for the experiments reported originates or is registered in the INIBAP genebank, its accession number (ITC code) should be indicated within the text or in a tabular form. Instructions to authors Thank you in advance for following these instructions. This will facilitate and accelerate the editing work. INIBAP addresses INIBAP Publications w w w. in ib ap .o rg • Headquarters:Parc Scientifique Agropolis II 34397 Montpellier Cedex 5 - FRANCE e-mail: inibap@cgiar.org Fax : (33) 467 61 03 34 Director: Dr Richard Markham e-mail: r.markham@cgiar.org Coordinador, Musa Genetic Improvement: Dr Jean-Vincent Escalant e-mail: j.escalant@cgiar.org Coordinator, Musa Genomics and Genetic Resources Conservation: Dr Nicolas Roux e-mail: n.roux@cgiar.org Coordinador, Musa Agroecosystems and Channels for Added Value: Dr Charles Staver e-mail: charles.staver@cgiar.org Coordinator, Information/Communications: Ms Claudine Picq e-mail: c.picq@cgiar.org Officer in charge MGIS: Ms Elizabeth Arnaud e-mail: e.arnaud@cgiar.org Accountant: Mr Emmanuel Gonnord e-mail: e.gonnord@cgiar.org Impact assessment specialist: Ms Charlotte Lusty e-mail: c.lusty@cgiar.org • Regional Office for Latin America and the Caribbean Regional Coordinator: Dr Franklin E. Rosales Associate Scientist, Musa technology transfer: Dr Luis Pocasangre c/o CATIE Apdo 60-7170 Turrialba, Costa Rica Tel./Fax: (506) 556 2431 e-mail: inibap@catie.ac.cr • Regional Office for Asia and the Pacific Regional Coordinator: Dr Agustín Molina Associate Scientist, Musa technology transfer: Dr Inge Van Den Bergh c/o IRRI, Rm 31, GS Khush Hall Los Baños, Laguna 4031 Philippines Fax: (63-49) 536 05 32 e-mail: a.molina@cgiar.org • Regional Office for West and Central Africa Regional Coordinator: Dr Ekow Akyeampong Regional information officer for Africa: Mr Josué Tetang Tchinda Associate Scientist, Musa technology transfer: Ms Kim Jacobsen c/o CARBAP - BP 12438 Douala, Cameroon Tel./Fax: (237) 342 91 56 E-mail: inibap@camnet.cm • Regional Office for Eastern and Southern Africa Regional Coordinator: Dr Eldad Karamura Associate Scientist: Musa technology transfer: Dr Guy Blomme PO Box 24384 Kampala, Uganda Fax: (256-41) 28 69 49 e-mail: inibap@imul.com • INIBAP Transit Center (ITC) Officer in charge: Ms Ines Van Den Houwe Katholieke Universiteit Leuven Laboratory of Tropical Crop Improvement Kasteelpark Arenberg 13, B-3001 Leuven Belgium Fax: (32-16) 32 19 93 e-mail: ines.vandenhouwe@agr.kuleuven.ac.be Latest publication INIBAP 2004. INIBAP Annual Report 2003. International network for the Improvement of Banana and Plantain, Montpellier, France. Recent publications S. Mohan Jain and R. Swennen (eds). 2004. Banana improvement, cellular, molecular biology, and induced mutations. This 392-page book, co-published by FAO/IAEA and INIBAP, presents the results from the FAO/IAEA Coordinated Research Project entitled “Cellular biology and biotechnology including mutation techniques for creation of new useful banana genotypes”. The book also contains several review papers providing up-to-date information on biotechnological tools that can be used to produce new Musa varieties with desirable characters in a more rapid and efficient way. Coming soon D.W. Turner and F.E. Rosales (eds). 2005. Banana root system: towards a better understanding for its productive management. Proceedings of an International Symposium. To obtain a complete list of our publications, consult our website or contact Leila Er-rachiq at INIBAP headquarters in Montpellier. E-mail : l.er-rachiq@cgiar.org