CCJ/)mlJ¡fA.~ 000 6~ Coping with Drought: Strategies to Improve Genetic Adaptation of Cornrnon Bean to Drought-Prone Regions-ef.Af.¡:i:Gfl¡; -- --- - -.- --------"1 ¡ :-~; --"(::-:"'(::-', :;: I V::<' CSO[]V ; --'-.- - .;} { ~" ~. í ¡ ' COlECClON HISTORIC~ • " " ' Jo_ ~ . _ _ _ __ ....... -._ .., . ---. . .... -. ... _._-- Soil water content (%) Scenario 111 Scenario IV Phenological stages CIAT Occasional Publication Series, No_ 38 Centro Internacional de Agicultura Tropica Intemational Center lar Tropical Agriculture Copi ng with Drought: Strategies to Improve Genetic Adaptation of Common Bean to Drought-Prone Regions of Africa Soil water content (%) fI!f (S0CifU ." -" Scenario IV Phenological stages '-------_. Jnfemalional Cen!E!( lar Tropical AgricuJlure CIAT Occasional Publication Series, No.38 Coping with Drought: Strategies to Genetic Adaptation of Common bean in Prone Regions of Africa Improve Drought Tilahun Amede l , Paul Kimaní2, Wilson Ronn./. Luhanga Lunze4 and Nkoko Mbika/ ISystems Agronomisl, Inlernationa! Centre for Tropical Agriculture (CIAT) ! Afrie.n Highlands Iniliative (AHI), Addis Ababa, Ethiopia. 2professor, University of Nairobi! Regional Bean Breeder-CIA T, Nairobi, Kenya. J Bean Programme Leader, Katumani Research Centre, Kenya Agricultura! Research Institute, K.tumani, Kenya. 4Bean Programme Researehers, PNLlINERA- Mulungu. Dlt. C~ .. _ 1 \.Y' 7~_L .~~:-. ~~'~;; 1) :. .i\ . , ••. January, 2004 ; ,. - " .. ' .. Network on Bean Research in Afrie., lnternationa! Centre for Tropical Agriculture (el A T) < . , Hi Table of Contento Page Acknowledgement IV Acronyms V Preface VI l. Introductíon I 2. Objectives 2 3. B ack ground 3 3.1 Definition of drought from regional perspective 3 3.2 Responses of heans to drought 3 4. Developing drought protocol. 7 4.1 Characterísation of drought-prone environmenls 7 4.2 Experimental melhods in drought research 12 5. Indioator. of drought resistance 14 S I Processes in identífíeation of índicatíve trait. 17 6. Determination of drought resistance indieators 19 6.1 Indicators of plant water status 19 6.2 Indicator of drought escape 21 6.3 lndíeators of growth and productívity 22 6.4 lndieator. of developmental plasticity 23 7. Indieators of drought beyond the plant 25 8 Breedíng for drought resístance 26 8.1 Prerequisites in breeding for drougbt resístance 26 8.2 Soreening teehniques 26 8.3 Rating seales 27 8.4 Souroes of resistance 27 8.5 Genetics of drought resistance 28 8.6 Breeding methods 29 8.7 Strategíes in breedíng fo. drought tolerance 29 9. References 35 10. Appendix 38 iv Ackllowledgemellt The authors wou!d like lO Ihank DL Mukishi Pyndji, Coordinalor of Easl and Centra! Afríean Bean Research Nelwork (ECABREN), for facilitating Ihe BIW ADA working group meeting and DL Roger Kirkby for his conslructive eommen!s, Mr Hassan Khalid Ali from the Sudan and Mr. D, Irongo from Selian Agricultural Research Centre, Tanzania, have contributed in !he discussion and Dr, LM, Rao of CIAT-Cali improved Ihe manuscrípt. We are grateful for their contribulions, v ACRONYMS BIWADA = Bean Improvement for Water Deficit in Africa CIAT = International Centre for Tropical Agriculture R WC = Relative Water Content DAE = Day after Emergency OTF = Oays to flowering DTM = Days to Maturity ECABREÑ = Eastern and Central Afdea Bean Research Network LWP = Leaf Water Potential RGR = Relatíve Growth Rate SI = Sensitivity lndex VI PREFACE Screening bean (Phaseo/us vulgaris) genotypes for drougltt resistance dates 10 1980s in lhe regional bean networks from sub-Saharan Afriea (SSA) However, no much progress has been made by scientists in identifying drougltt resistant be.n geootypes In May 1999, regional scientist. from Eastem and Central Africa Bean Researeh Network (ECABREN) initiated a working group 00 drougltt ca11ed 'Bean Improvement for Water De/leit in Afríea' (BIW ADA) which has becn operating across bean networks working groups, The BIW ADA group had difficully in starting its activities. During several tield visits lO some member eountries in the region, it was observed tha! there was lacle of standardized protoco! for screemng bean genolypes lo drougltl resistanee Certain parameter. tha! were used for assessing germpla.m lo drought resistanc. had no direct correlation with drought, This book demonstrates an important tool to develop drought resistant genolypes and covers different aspec!S including metbodo!ogies in breeding fer drought resistance, how to develop protocols for drough! resistance; indieators of drought resistance; and methodo!ogies for deterrnining indieaters of drougltt resistance. 1 am convineed that Ibis precious document will be used no! only by be.n scienti.t., but also by sclentists working on various erops; ¡hey could adapt breeding and screening methodologies to tbeír respective erops. 1 wish to thank Dr. Tilahun Amede who accepted the responsibilily of coordinating the BIW ADA meetíng, and the African Highlands Initiativo for makíng him avai!able. He also spent his efforts and time to have Ibis documenl published for use by regional seienlÍs!s, Le! me also ¡hank Ihe network plan! physiologists, breeders., and agronomists, for their fuI! eommitmen! to work harmoniously for avaíling Ihis working paper to scienlific community in Ihe African regions. Mukishi M. Pyndjí, Ph.D. Coordínator, East and Central African Bean Research Network (ECABREN) March 13, 2003 CIAT Occasional Publícalion No. 38 l. INRODUCTION Common bean is enjoying resurgence in interes! and an enhanced level of consumption as a majar souree of protein for Afriean households owing to an outrageous inerease in priee of animal products. It also serves as a break erop in Maize-hased and rice- based systems to reduce decline in soil fertility. However, frequent drougbt and diseases Iimit productivity of beans in Ihe region. It is partly because bean production in recent years has c"panded into semi-arid regions, due to an inerease in population pressure. While drought IS yet one of the most limiting faetors to bean production on a global scale, tbe situation wi II expectedly deteriorate in Afríe!! if the curren! trend of land degradation cannot be reversed. In addition, climatie variability will increase as it bas been postulated in a scenario of global warming. Drought has affected beao production in East, Central and Soutbern AfríeR eRusing losses of more than 395,000 t each yeaL Drought, which inc1udes moisture and beat stress, acts in conjunction with biotic stresses, especially diseoses and pests, and other abiotic stresses. Soil fertility related stresses, the most important being low soil P and N, soil aeidíty and the associated aluminíum and manganese toxicity, are known to aggravate drought effeets. These multiple constraints are often actiog eoncurrently with a considerable negative effeet on the quantity and quality of crop production. The mos! efficíent approach lo reduce the effee! of multiple stresses is to introduce resistance genes into beaos to enable tbem witbstand the majar stress agents. The regional breeding programs in East, Central and Southern Afriea have adopted this strategy. Tbe need for multíple stress resistance in bean improvement is partícularly relevant in tbis region because tbe farmers are resouree poor. They can hardly afford expensive inputs. For low-priced crops such as beans, use of such inputs is oflen uneconomical. Límited water availability to tbe beao crop can be caused by physical and climatic factors of the environment, lhe soil- preclpltation relationship, the soil-plant relation.hip, lhe atmosphere-plant relatíonship, excessive demand by lhe plaot, or any combioatíon of lhese (Nilson at;ld Orcutt, 1996). The major cause of water defici! ín bean growing regions of Africa ís low precipitatíon. Despite tbe alarming demand for droughl-resístant cultivars, breeders are slow in achieving lhis goal due to the difficulty io identifying traíl. tha! reflect true drought resistanee. There is, lherefore, mucb interest in trying to ímprove bean yields under soil water deficil condítions. Although screening for potential drought resistant material s has been earded out in many national programmes and even at the regional level (for example lhe = 5. INDICATORS OF nROUGHT RESISTANCE In Ihe literature, !raíts that may endure drought resistance of erop. are advocated based on theoretical modules, laboratory experimentation, or mathematical eorrelation between the presenee of the trait and yield under drought, withoul sufficieot atternpt to demonstrate whether and how Ihe particular Iraít contri bu tes lO final yield. Proline accumulatíon is a good eumple of su eh a Irail, without any proof of ils value as an indicator of drought resistance (Ludlow & Muchow, 1990). Sorne of the mos! probable indicator. are presented in Tables 4&5. Table 4. POlenlial rneehanisms oí drought resistance in eommon bean. grown in intermíttent or terminal stress (Arnede, 2001) lntermíttenl stress . Terminal stress _._----~ .. • Synchrony of fast growth • Synchrony of flowering/early stages 10 water supply pod filling to water supply • Early vigour • Mobilization of assimilates • Stomatal regulation frorn source lO sin k • Developmental plastieity • Rooting depth • Root depth and density • (Osmotic adíustment of roots l. Leaf are a maintenance and shoots) !. Olher survival strategies Table 5. Sorne indieators and melhods of detecting Drought resistance in Beans (Ronno, 2001)~ I ludiealors or i Drought . Resistanee . ~_sí_s_ta_D.~e~e ___ .-.~ ____ -+~~~e~e~h~a~n~ís~m~ ______ -+·~D~e~t~e~c~t~io~n~~~e~l~h~o~d~ __ _ a ~ orPII 01 ogic,-o:a"J ___ -+;;c:- --;---,-;----+OO:-----:---;--....,-,--~~_ 1 Conlinued leaf Drought avoidanee Determínation of leÚ area expansion of primary and tolerance. following míld and and secondary moderate drOught stress; trifolíate at lowered determination of leaf water soil water potential potenlial (L WP) for 50% (SWP) I reduction. _.--~~ ... -c;---"--~--+= 2. Formalion of rapidly Drought avoTdance growing deep and extensi ve roots system Determinalion of root length and volume under moderate droughl stress. 1 CIAr Qccasional Publicalion No.38. ________ ~ ____ _ 1. INRODUCTION Common bean is enioyiog resurgence in interest and 3n enhanced level of consumption as a major source of protein for Afriean households owing to an Gutrageous increase in price of animal products. It al so serves as a break crop in Maize-based and rice- based systems to reduce decline in soil fertility. However, frequent drought and díseases limit productívity of beans in the region. lt is partly because bean produclion in recenl years has expanded inlo semi-arid regions, due to an increase in populalion pressure. While drought is yet one of the mosl limiting factors lo beao produetion on a global scale, Ihe situalion will expeetedly deteriorate in Afdea if Ihe current treud of land degradalion eannot be reversed. In addition, climatíe variability will increase as it has beeu postulated in a seenario of global warming. Drought has affected bean production in Easl, Central and Southern Afdea causing los ses of more than 395,000 I each yeaL Drought, whieh in eludes moisture and hoa! stress, ae!s in conjunction witb bintic stresses, especiaJly diseases and pests, and other abiotic stresses. Soil ferlility related stresses, the most important being low soil P and N, soil acidity and Ihe assoeiated aluminium and manganese toxieíty, are known to aggravate drought effeets. These multiple constraínls are often actíng eoneurrently with a considerable negative effeel on lhe quantity and quality of erop production. The most efficienl approach lO reduce Ihe effeet of multiple stresses is to introduce resistance genes into beans to enable them withstand the major stress agents. Tbe regional breeding programs in East, Central and Southern Afriea have adopted this strategy. The need for multiple stress resistance in bean improvement is partieularly relevant in this region because the farmers are resource poor. Tbey can hardly afrord e"pensive inputs. For low-priced erops such as beans, use of sueh inputs ís often uneconomical. Limited water avaílability to the bean crop can be eaused by physical and climatie factors of the environment, the soil- preclpltation relationship, the soH-plant relationship, the atmosphere-plant relationship, .xeessive demand by the plant, or any cambination of these (NHson .I)d Oreull, 1996). The major cause of water deficit in bean growing regions of Afriea is low precipitation. Despite the alarming demand for drought-resístant cultivars, breeders are slow in aehieving this goal due to the difficully in identifying trails thal reflec! true drought resistance. There is, therefore, mueh interest in trying to improve bean yields under soil water deficit conditions. Although screening fOf potential drought resistan! materials has been earded out in many national programmes and even at the regional level (fof .xample Ihe Coping wilh Drought A frican Drought Nurseries of ECABREN), these materials were afIen nol meeting Ihe preferences of the farmers and consumers, Tbe metbodology for screcoiog was based only on yield and early malurily, Drought resistance IS polygenic and is commonly accompanied by oegative impacIs on grain yield (Amede, 1998), Grain yield formation in beans is a more inlricate process lhan in eereals in Ihat the developmenl of generative organs in beans ís relatively gradual .nd could be prolonged ir the exl~rnal conditions, like water and nutrient., are readily available, Therefore, selection for drougbt resistance based on yield a10ne may not briog about the required genetic sbifl in specifie physiological attributes, as the component of genetic vafÍanee is low when compared lo envíronmental or genetic-environment-interaction variance under stress environments (Rosielle & Hamblin, 1981), The BIW ADA team, recognising the importance of drought and its anomaly, decided to hold a meeting lo discuss issues that may ¡.ad to rapid advance in achieving high-yieldíng varietíes with stabilised yields in soil water daficit environments, 2. OBJECTlVES The objectives of the BIW ADA meeting were lO: ;;. Characterise the incidence of drought in various bean-growing environments of East, Central snd Southern Afríe., ~ identify plant traits ss.ociated or cOff.laled with drought resistance in beans ;;. Review snd identify potential indieators of drought resistanee to be used in developing drought resistant varíeties, ? Develop protoeols for drought resistance sereening ? Review slrategies for breeding for drought resistanee in beans CIATOccasíonal Publícgtíon No.38 3 3. BACK GROUND 3.1. Definition uf Drought in Regional Context Drought denotes a prolonged períod without considerable precipitation Ihat may result in reduetion in soil waler eontent and, thus, cause planl water deficil. It can be defíned in terms of eilher Ihe external water status at Ihe boundaries of Ihe plant (soil, air) Of Ihe internal plant water status within the tissue (Tardieu, 1996). The first approach defines water stress as an imbalance between supply and demand, Iínked to the atmospherie saturation defieit following lhe water pOlenlial gradient and leaf area. The second defínition associates waler stress wíth Ihe control mechanísms of Ihe plant, where plant water status is regulated wíthin the plant aceompanied by changes in water flux with or without change in plant water potential under low soíl water potential conditions (Amede, J 998). However, a deerease in leaf water potential or turgor of a plant per se may not truly indicate absolute water stress, as sorne plants wítb closed stomata and/or ínhibited growth could remaín without altered planl water slatus (Turner, 1986; Tardieu, 1996). 3.2 Response of Bealls to Drougbt Grain yield in beans is lbe product of number of plants (m fruitful axes) per unit area, number of pods per plant, numbor of seeds per pod and thousand seed weígbt. Tbese yield factors are crucial for produeing economíc yíeld, and vary in time seale. The number of plants per unil area depends on Ihe numbor of plants tha! emerge andlor survive lill maturity. For Ihis yield factor, droughl at Ihe beginning of the growing season is very detrimental Number of pods per plant or seeds per pod depends on Ihe number of branches produeed and the number of well-developed pods/seeds. In this case, intermittent and terminal drought could dictate pod formation, seed settiog and seed filling by altering the source-sink relationship by way of affeeting assimilate produetion, transloealion and partílioning. Number of pods per plant is the most variable Iraíl to affee! grain yield in beans, and is responsible for the signifieant reduetion of yíeld during droughl al or after flowering. Drought al flowering is known to cause abortion of f1owers/pods, through assímílate shortage resulting in yield reductíon. Whenever bean plants experience a rapíd water defícít, bean lcaves are known to orient themselves parallel to the incídent light, and also alarm (he biochemical systems If the time of stress ís extended to hours or days, physíologíeal aClivíties would diver! from funetions of eeU expansíon and growth to mechanism of restitutíon of the physiologieal integrity (Fig I l. Bean plants may reaet to the stress through short-term strategíes, like changes in hydraulic signals or stomatal adjustment. At this stage photosynthetic rate __________ ,('-',<;Jpr?Jí'!1J1ggjfwilh DroUg!>1 could be comparable to Ihat ín non-stressed planl' bul assímilalion could be favoured lo develop long-term stress tolerance mechanísms al Ihe expense of growlh (Amede, 1998). Bean planls exposed to water stress for days to weeks may develop long term physíologieal slrategles .ueh .as ahenng Ihe leaf area, modifying rool to shoot rallo and Ibe hke. When avaílable sod water ís reduced, plants u,ually undorgo three progressíve stages of dehydration (Sinelaír aud Ludlow, 1986). Figure 1. A Phase model of stress events and responses (After Larcher, 1987) Pbaseof AIann Restitutioo Pbaseof Rfsistance Pbaseof Exhaustion Adjustrnent nmrtionof~ Al the initial stage of mild drought, .ssímilation and transpiration are comparable to those of well-watered plants as long as soil water uptake meets evapo-transpirational requírements. In the seeood stress period, Ihe photosynthetic eapacity of the plan! is reduced below the maximum potential leveL This is considered to be Ihe mosl dynamic slage to develop adjustment mechanisms and lo regulate processes for Ihe maínlenance of metabolic aclivilies (Amede, 1998). In the Ihird phase, plan!s merely survive and delay de.th. Recovery after rain or irrigatioo depends 00 the duration of stress and type of species. For instan ce, Tepary bean (Phaseolus acutífoUus) was more drought-toletant than common bean (Phaseolus vulgarís) when grown under stress condítioos (Parsoos & Howe, 1984) When crop plants are exposed to drought, they may alter cel! solute concentralion by re-allocating resources so tha! the osmoti. poteolial of the ce)) is reduced, and turgor is maintained (osmotic CJA T Occasional Publication No. 38 5 adjustment). It allows turgor-driven physiological processes, such as stomatal movement and cell growth, to continue des pite low plant water potential. It could al so in crease grain yield under stress conditions through modifying the soil-plant water gradient thereby increasing the amount of water transpired. Osmotic adjustment, through accumulation of effective osmotica is thus an important mechanism of drought resistance in legumes (Amede, 1998). However, accumulation of solutes in the plant cell per se does not guarantee osmotic adjustmen!. In addition lo osmotic adjustment, solute deposilion in plant cells under drought slress could have four principal causes (Amede, 1998). Firstly, plants may lose substanlial amounl of waler Ihal may lead to a reduction in the expansion rale of Ihe lissue (reduced cell volume), and Ihereby lO an accumulalion of solules in Ihe cell. Secondly, sorne primary metabolites (proleins, carbohydrates or lipids) may be degraded at higher stress intensities, and the by-products could accumulate as secondary metabolites in the cell. Thirdly, decrease in cell elongation (growth) may cause slowing down of assimilation biosynthesis but effective import of assimilates to the sink cells could be high enough to in crease the concentration of solules and ultimalely cause a reduclion in Ihe osmotic potential of the cell (Kramer and Boyer, 1995). Fourthly, under moderate levels of slress, roots may still actively absorb inorganic ions (potassium, calcium, sodium, magnesium, chloride, and others) from the soil. Nutrients may not be utilised by the plant owing to drought-induced growth inhibition but instead, translocated ions may accumulate in the cell and induce substantial reduction in osmotic potential (Munns, 1988). Therefore, distinguishing between solute accumulation due to a concentration effect and true osmotica is a prerequisite before using solute accumulation as synonym to osmotic adjustment (Amede and Schubert, 1997). Parsons and Howe (1984) compared common bean (Phaseolus vulgaris) with Tepary bean (Phaseolus aculifolius) for their water relations, and conc1uded thal Tepary beans were more drought tolerant than common beans due to the higher osmotic adjustment pOlenlial they possessed. They, thus, suggested a transfer of osmotic gene from tepary beans to common beans to improve drought resistance. Mild drought favours root growth at the expense of shoot growth to enable roots to extend to the unexplored deeper part of the soil for available water. Adequate root density throughout the soil profile may increase Ihe diffusion area, thereby improving water availability and uptake. Maintenance of water status under water limitation can be partially attributed to rooting depth and root length density (Turner, 1986; Subbaro el al., 1995). Thus, root depth could be considered as an alternalive trait to screen drought resistant lines. Sponchado et al., (1989) compared two drought- tolerant bean genotypes (BAT 85 and BAT 477) with two drought- 6 ___________________________________________ ~C~op~m~g~w~lw·ffl~D~rQou~g~h~1 sensitive genotypes (BAT 1224 and A70) under drought-stress conditions at CIAT-Palmira to identify physiologica\ differences of drought resistance. Their results showed differences in drought resistance among genotypes were associated with rooting depth, but not with root length density, as roots of drought tolerant genotypes reached a depth of 1.3 m, while roots of drought sensitive ones reached a depth of only 0.8 m. Plants often maintain higher root length density than is required by the surface area of the shoot, mainly to minimize effects of other stress factors such as pests, and nutrient deficiency (Passioura, 1983). Water loss at the plant level largely depends not only on the size of the transpiring areas (mainly leaves) but also number and size of the sto mata, and the eonductivity of the cuticle. In crops, about 90% of total water loss is associated with stomatal transpiration (Monneveux and Belhassen, 1996) followed by water loss through the cuticle. The hydraulic conductivity of the cuticle depends upon thickness and the presence or absence, and the nature of cuticular wax embedded in or deposited on il. Plant transpiration loss could also be modified by the presence or absence of leaf traits such as leaf rolling ability, the colour of the transpirative organ or leaf refleetance. Moreover, early seedling establishment, early vigor, rapid canopy development in order to minimize evaporation, as well as leaf area maintenance have been suggested as potential drought resistance mechanisms of grain legumes (Subbaro el al., 1995). An experiment conducted to evaluate the effeet of drought on stomatal closure in beans and chick peas showed that in beans C02- fixation decreased by about 75% after 3 days of mild stress, while in chick peas C02-fixation was not affected by drought except for 25% reduction on the sixth day of stress (Amede, 1998). In other studies, O'Toole et al. (1977) showed that photosynthesis and transpiration rates in cornmon bean were near zero at plant water potentials of -0.9 to 1.0 MPa, showing that stomatal closure is one of the first steps of defenee against drought in beans since it is a more rapid and flexible process than other mechanisms like root growth or reduetion in leaf area. Thus, it could be eonsidered as an effective survival strategy for intermittent stress (Scenario III, Fig. 1) but not important for terminal stress (Scenario 1) since production of economic yield is the major goal at this stage of growth. CIAr ()ccasiº1!ªlP~b1icat.,."jo",n'LM=o.",3",8 ______ _ 7 4. DEVELOPING DROUGHT PROTOCOLS 4.1 Cnancterizatíon or Drought-prone environments In the Ea,t and Central Arriea Bean growing regions of Afriea receive different amount and dislribution oC raiofall (Worlman et al, 1998) and henee Ihe region experiences different drought scenarios. The BIWADA group identified four different drought sceoarios (Fig, 2), a) Seenario I represenls terminal drougbt. In Ibis case there could be enough water for early establishment and growlh, bul later phenological stages are exposed to soil water defici!. This is typically lhe case in relay cropped beans of lhe Rift VaHoy and in rice based systems of Africa (e,g, Madagascar), In practices of relay plantíng beans in the Maize field or in syslems wbere beans should follow rice, bean erop is commonly exposed to terminal droughí. 11 js also a common pbenomenon, in regions tbat fully depend on irrigation to produce the major .ash and food erops, lo grow beans on lhe residual moisture, Hen.e beans are exposed to terminal drought starting from early pod filling stages, Sudan and Egypt could be typical examples of tbis scenario, b) Seenario II represenls intermíllent drought: This is Iypical of regions with relatively good rainfaJl amount but paor distribution during Ihe growing period (Fig 2), There could be enough water for lbe érop througbout the IHe eyele excep! for so me shorl dry spells that may happen at any time of the year. This is very common in regions with extended growing period (e,g, Awassa in Elhiop;a and Norlbern and Eastern Tanzania), el Seenario 111 represents relatively prediclable drought. In Ihis case Ihe total amount of precipitation could be comparable lo good years, bul most of tbe rain falls within a short time of tbe growing season, Bean plants could be exposed lo stress at early stage of growlh but could receive enough waler at laler slages if lhe plantíng date is adjusted accordingly, This is a common phenomenon in mosl part of Ihe Great Rift ValJey of East Afdea, d) Seenario IV represenls dry semi-arid climates wbereby Ihe amount of rainfall is relalívely low lo cover the physiological demand of the orop al any stage of growlh despile ilS fair distributíon throughoUl the growíng period, Typical of this type of agroecology could be found in sQulhern and South-weslern Africa, 8 ____________________ 0:!ui!Jg wilh Droullln Fig 2. DifCerent scenanos oC drought In bean growing regions of Afríea Scenano nI ..... , \ \ \ Scenario II ~ e ID e' ID E w Scenario IV ~ Ol e ~.c: .;:: ~ :g,~ ID ~ ü: >'" \ \ \ ." >. re 'E ::l (J) - '" :; The following checklists were used to characteríse the drought prone bean growíng region. of Africa. • Altitude • Raínfall (Amount, distribution in 10 dars interval, ouset oC rainfal!, offset of rainfall aud duration) • Temperature (Min, Max, Avg) • Short and long dry spells within the growing season • Soíl characterístics (Type, lexture, pH, Soil Water Holding Capacity) • Frequency of drought (across seasons and years) • Length of growing period e/A T Occas:iona/ Publica/ion No. 38 9 • Length of maturity pefiod and maturity classe. available • Available bean maturíty cla.ses • Time of planting (sole and intercropping) • Types of companion ereps accompanying beaos • Traditiona\ drought eoping mechanísm. • Other observations Wortman etal., (1998) identified fourteen Afriean bean produetion envíronments, of which sil< could be categorised as drought-prone regions, as presented in Table l. 10 ____________________________________________ ~C~o~pl~n~g~w~1~·~~D~rQou~g~h~1 Table l. Charaeteristies of the major drought-prone bean growing environments in Afriea (Modified fram Wortman etal., 1998) Bean prod. Area Major soil Day length Water defieit Area (,000) Types E M L I Semi-arid highlands at low latitudes, > 1500 masl, < 400 mm moisture, unimodal Kenya East highlands 130 Be, Ne 12.1 M M M Rift valley 61 Be, Bk, Tm 12.1 H H H Kajiado 30 Ne 12.1 H H H Tanzania N. semiarid 43 Be, To 12. 1 H H H 2. Semiarid high1ands at mid latitudes, >1500 mas1, <400 mm moisture, unimodal Ethiopia Rift valley 64 Xh 12.4 L M H Lesotho Foot hills 7 We, Be 13.6 L M L South Afriea High veld 45 Le 13.5 L M L 3. Semiarid at mid altitudes & low latitude, 1000-1500 masl, < 400 mm moisture, bimodal Kenya East,mid-alt 60 Lf 12. I M H H Rwanda Eastern 60 Fo 12.1 M H H Tanzania N&E mid-alt 14 Nd, To 12.1 M H M 4. Semiarid mid-altitude & mid-Iatitude, 1000-1500 masl, <400 mm moisture, unimodal Angola Mid-alt 30 Lf, Fo 12.6 L M M Ethiopia Haragrhe 20 Bd, Be 12.6 L M M Zimbabwe Mid-veld 3 Lf 13.2 L H H 5. Semiarid mid-altitudes on aeid soils, 1000-1500 masl, <400 mm moisture, unimodal Madagasear L M H Following riee 10 Je 11.0 Zambia N, eentral,NW 14 Fr 12.8 L M H Swaziland 2 Ne, Le, Fr 13.0 L M H 6. Partly arid, supplemental irrigation, residual moisture, < 1000 masl, Unimodal Sudan, Northern 20 Je 12.5 L M H Egypt, Nile delta 20 Je 12.6 L M H Morroeo, N 7 Le 12.9 L M M CIAT Occasíonal Publícatíon No. 38 .... __ 1_1 Key: Be = Chromic cambisol, Ne= Eutric nitosol, Bk= Calcic cambisol. Tm= Mollic andosol, To= Oehric andosol, Xh= Haplic xerosol, Le= Chromic luvisol, Lf= Ferrie luvísol, Fo= Orthic fenalosol, Nd= Dystríc nitosol, Bd= Dystric cambisol, Je= Euric fluvisol, Fr= Rhodic ferralsol, Jo= Calcaríc f1uvisol E= early stage, M= early floweríng, L= low, M= medium, H=high L= later stages Table 2. Agroecological traits of selected East and Central African bean growlDg areas h-:-:-:; K Y A : Length of 90-100 DRC <90 days SUD TZA : 90 days, low 90-100 days tcmp ETH 90-100 · Growing : season ¡ ! Maturity · period 100-150 90-120 90-100 <90 days 120 days, k . climhers I PlanÚng time l' Oct/Nov Early · . March/ . March •.... _--~ [SeveritY : Apríl __ +! -;-;--.--+-----+--;:;---;----j~~~­ March Associate crops Coppíng rneasures 2 4 Maizc, pigeonpea, cowpea 2-3 i 1-2 Maize, cassava i Early Early planting, planting, contour mulch wilh cultivation crap -planting , residue in furrows : '()Iher----+-- ! Water ohservatians ¡rrigatíon practices : i . harvesting not adopted I Long Supplement nil irrigation al irrigation interval in rice (15-60 days) svstem Key: KYA= Kenya, DRC= Democratic Republic of Congo, TZA= Tanzania, ETH= Ethiopia i 12 _____ Coping witlt Drouglt1 As presenled in Tables 1 and 2, camman bean is exposed príncipally lO terminal drougbt partly because it is grawn as a secondary crop following maize or rice, and partly fertile soil. of higher waler holding capacily are commonly allocated to cereal •. Sinee terminal drought oflen coincides with lbe most drougbt sensitive growth stages of beans (f1owering, pod formalien and seedlpod fílling) stress effects on photosynthesis and assimilate translocatíon could significanlly affect yíeld. The mosl important effecI of drought on bean yield i. nol only through affeeling photosynlhesis but also through hindering assimilatíng transporl from the souree lo the sink. Physiologieallmorphological meehanísms Ihat may make the plant maintain tissue plant water potential and turgor Ihal sustains assímilation, Iransloealion and partitioning, are therefore of paramount importance. In regíons with extremely low amounl of raínfall «300 mm) aceompanied by high temperature, heat stress could aggravate water stress effeets. Heat stress is known lo affeel Ihe physiological integrity of the planl regardless of planl water pOlentíal 5.2 Experimental methods in drought research Differenl experimental methods could be used lo compare beau genolypes al different growth stages and al different level of drought intensity. The most commonly used methods are field experímentation, pot experiments, chamber house experimenls, nulríeol salulions, rain-out shelters, rhizotron experiments and petridish experíments. The potenlial advantage Or disadvantage of Ihese experimenlal methDds is presenled in Table 3 CIAr Occasional Publication NO.38 13 Table 3. Comparison of differen! experimental methods used lO conducl drought stress research Advantage Dísadvantage I Melhod 'L Fi.~ld~-------+--~G~I~·v-e-s-a--r~e~al~i-st~i~C-g-r-o~u-n~d~--'I~---'H~i'd'd'e~n-hCa~l~f~(~r'o'o~ts~)~a~re~--" : experiments - Effeotive under ,difficult lo quanlify 1I. Pot experiments lII. Chamber houses : IV Nutrient ! solutíon i - characterised environments Resulta are compJicated Large no. of materials by otber factors (soi! could be tested heterogeneity, soíl Relatívely eheap moisture variability, and Best to compare based on temperature variations rain íeld alon Ihe da Uniform management of : Labour intensive 1, _ treatments possible in , Limited no. of treatments terms of soil fertilíty, could be tested water '- Pot size restricts root Easy to determine plant growtb water statul Does not sustain plant Relatively cbc.p demand till maturíty Bes. to com are biomass Temperature, relative :"--¡--'L~í'm::O:ít'e-"d;-::sp'áce (few humidily &. radíalion can treatmenlS could be be controlled testcd) Exact comparison possible Veryexpensive Best to measure gas excbang._. ___ .. _~,..... ____ +- Relalivoly faSl results could be obtained Bes! to evaluate nutrient/water stress i nteraction Les, precise (m.y nol refrecl realíly) Complications may arise due lo stres,or effeel. (Polyethylene glyeol or Ab,eissic aeid) Labour intensive V~, ~R~a~i-n-o-u-I------4----';R:-e-;f"le-e-l:-s-r"e-a-;l"i""ty---------!"'-~l:!n~d~u~c"e'-S';h:O';a~1 '!.sé'tr"e'-s-s-----I .heIter, Many malerials could be Higber relative humídíty , VI, Rhízotron ¡ experiments VII. Petr; dish experimenls tesled (slow induction of 'tress) 1- Effeclive to compare yleld I - Leaking effeets ! nnder parlially conlrolled . conditions Side by síde compar;son I :~ó'nly few trealmenl, could of treatments possible be tested Effectlve lo follow-up Bulky, labonr intensivo root growtb, depth and_--4:I ___ ===-.:c distribution ........ . '-"SIlOrt term (minutes lo Should be"'supplemented honrs) by fi.id or PO! Economical experiments ,_~ __ -,fI,fay n 0l..':.ef!.e"Ue a Ji I Y ___ • 14 __________________________________________ ~C~o~p~in~~~w~il~h~D~r~o~u~e~ht 5. INDICATORS OF DROUGBT RESISTANCE In the literature, traits that may endure drought resistance of crops are advocated based on theoretical modules, laboratory experimentation, or mathematical correlation between the presence of the trait and yield under drought, without sufficient attempt to demonstrate whether and how the particular trait contri bu tes lO final yield. Proline accumulation is a good example of such a trait, wilhout any proof of its value as an indicator of drought resistance (Ludlow & Muchow, 1990). Sorne of the most probable indicators are presenled in Tables 4&5. Table 4. Potential mechanisms ol drought resistance in common beans grown in intermittent or terminal stress (Amede, 2001) Intermittent stress Terminal stress • Synchrony of fast growth • Synchrony of flowering/early stages to water supply pod filling to water suppJy • Early vigour • Mobilization of assimilates • Stomatal regulation from source to sink • Developmental plasticity • Rooting depth • Root depth and density • (Osmotic adjustment of roots • Leaf are a maintenance and shoots) • Other survival strategies rabie 5. Sorne indicators and methods of detecting Drought resistance in Beans (Ronno, 2001). Indicators or Drought Resistance Resistance Mecbanism Detection Metbod al Morpbololdcal l. Continued leaf Drought a voidanee Determination of leaf area expansion of primary and toleranee. following mild and and seeondary moderate drought stress; trifoliate at lowered determination of leaf water soil water potential potential (LWP) for 50% (SWP) reduetion. 2. Formation of rapidly Drought avoidanee Determination of root length growing deep and and volume under moderate extensive roots system drought stress. CM T Occasíonal Publicalion No. 38 15 I b. Pbysiological I ~. Decreased Stomat.l Drought avoidance Determination of SWP and transpiration at critica~ , LWP for 50% reduction of SWP transpiration, Capabílily lo Drought tolerance ¡ Determina¡ion of SWP and 1 o.moregulat. ' LWP at decrea.lng relative resulting in water content IRWC). maintenance of turgor i , 3. Capabílity to be Drought avoídanee Subjeel plants to akornate "hardened" and tolerance drying and re-watering lo drougM stress followed by subsequent testing of changes in morphological. physiological, , bíoehemíeal and physícal • drought responses. 4. Response to applíed i Drougbt avoidanee Determination of effeet on ABA ' and tolerance membrane leokage. ..... - ¡ c. Biocbemical i l. Maintenanee of high Drougbt avoidance i Determination--·O·f NRA in most nitrate reductase activity and tolerance reeently expanded leaf al , (NRA) at lowered SWP decreasiog SWP and LWP at whieh NRA falls to 50% of unstressed level 2. Laek of proline Drought avoidance Determination of SWP and synthesis and and tolerance LWP at which prolíne accumulation at lowered accumulation begins SWP d. Cytological and : ultrastructural Maintenance of nuclear Drought avoídan.e Determination of nuclear area and nueleolar dry and tolerance and dry mass in epidermal masses and areas at cells from drought stressed lowered SWP Inlants. el Pbvsical Maintenance of i Drougbt tolerance ' Determination of Iclease of Membrane integrity u\travíolet absorbing solutes (Iaek of leakiness) at (220 nro from leaf dises ! lowered tissue WP i subjeeted to 50% fresh weight level. In General Pos session of varying Drought tolerance Determination of RWC and-';-;:- low criticaJ WP for non LWP below which plants wjll recovery upon rCM not recover watering , 2. Maintenane. of ,Drought avoidanco Determinatíon of SWP ··"'bieh cotyledonary fUDction at I and tolerance coryledonary abscission lowered SWP beain. ______ -'"Cc~()'¡¿pl!L'n"'IlJ!Owilh DroUllht Low Soil Water Incident Light Intensity U Synehronlzation of pi.nt dewlopment and water availabmty e.rtiness of dlIvelopment PI.stidty 01' Q'OWIh Synchronization of plant developmant to season ef the year with moderate Hght inteosity MaJntenance of high tissue water potenUa¡ w Efficieney of water acqulsltlon Mutual $haoíng ptllnts within 11 unopy t.e.Ve;I 0t'I índividuII¡ p/IInts Control of lioht ab$orption ift.g, Increne o, rootlng depth IInd diftnsity, ; ItJ<:té(t$e af hydrilJllc amductivity ! ~ Efficient conservabon oftissue water •• (J. OeaNSII al _1 surfactl by ro/linfJl RedUdion of IMf refl«tltnct: (ltuJf hairs, w.x) AdaptaUon of leaf orientation i shlrinkafla Oecruse of cuticular w.mr los (wax deposits) Efffdent lYtfIUlation of stmufUtl ~re Abiltty Ior óSmotic adjustmw w..,at, .. L In _ ceIIu., leveI AblOrption of excitatlon enet9y (ChroIophy/l c:onlent) Thermal dlss1pation of excitatlon eMrQY (e,g_ xilnthophyll cyde) Harmles$ utílisation of r.dox equivalents (NAD{P}H) e·l1· ~thesls, P/totorespirWDn Activa oxyg:en forrnation (e.g. Oz -1, 02) F,... radical SC8vanolng defente mechaniSf\"\$ (MZymatlc ami non~tic IIntiOKidants) Free radlca/s ~ In excess Drought-Induced Photooxidative damaqe Excltatlon eNrgy In _ cetluJar level Píg 3. Causes, effeets and resístanee mechanísms of photooxidatíve stress in crop plants (After Mueller, 1998), When erops are exposed to high light íntensity in general and in combinatíon wíth drought or mineral nutdent defidency in partícular, the electron flow in Ihe photosynthesis complex could disrupted, which may lead to irreversible damage of Ihe photosynthelic apparatus as indicated by ehlorosís and necrosis of the leaves (photooxidation). Bean varieties that could decrease Iight absorption or dissipating energy through reflecting Iight and heat, changing leaf angle or possess physiological mechanisms to detoxify harmful oxidative agents could perform better under Iight stress candítions. CM T Occasjonal Puhlicalírm No, 38 5.1 Processes in Identification of Drougbt Resistance Indicative Traits 17 The following checklists were used to mooitor tbe type of drought environmenl Iha! we are working with, and to identify plant Irail. tha! could be used by researchers in identifying drought resistant materials. The ultimat. goal will be to develop beao varieties equipped with drought resiSlance Iraits and adaptable lo Easlern aod Ceotral AfrieRn conditions, The most important questions to consider during Ihe process of identificalion of important traits Ihat are to be used for development of drought resistant bean varieties were whether: • There is a relationship between the Irai! in question and drought resistance • The trait is expressed mainly wheo the crop is exposed lo stress • The liming of the trait expression coincides with the most drought sensitive stages of Ihe crop • The trait is responsive 10 changes in soil water slatus • The Irail is highly correlated to biomas. production and grain yield • The trail is easily measuranle or observable • The trail lS highly correlated lo otber drought resislance indicators • The trait has a regional value lO be con.idered in standard protocols About 18 potential indicators were included in the process as suggested by different authors (Turner, 1986, Singh etal, 1994, Amede, 1998). The proposed trait. to be íntegrated into bean breeding programmes for droughl-prone regíon. are assessed in terms of potential contributions to productivity. survival under drought, stability across years, and practicat usage of the trait under lhe existing laboratory and capacíty conditions, as presented in Table 6. Tabl. 6, Potential indieators as identified based on sets of criteria for use in improving drought resislance in beans ---- ------~---- Rcsponds to Híg¡:¡IY-l Easily --- o(".gi';'no1 Correlation Drought Resistan.e between Ihc changes in corre)ated to measurabJe value for Indicators Irait and soil water biamas I or observable standard Total Rank drought status produetion or ¡ protocol Sum reslstance I g;rain vi.ld Plant WP 3 3 2 I 3 12 9 O.motie potential 3 3 2 3 3.5 14.5 1 RWC 3 3 3 3 2.25 14.3 2 RGR 2 3 2.5 3 2 12.5 8 Biomass 2 2 2 2.5 2 11.3 10 Vigour 2 3 3 3 3 14 4 , Root deptb 2 2 2 1 1 8 l3 Roo! density 3 3 1 1 1 9 12 Pods/planl 2,5 2 3.5 3 3 13.8 6 Seeds/pod 1 1 3 3 2 10 10 Seed weight 1 1 1 3 1 7 14 Grain yield 2 2 3.5 3 3.5 14 4 Earlv maturitv 3.5 2 3 3 3 14.3 2 Duration of f10wering 2 3 2 3 3 13 7 Periad of seedJillíng 2 2 3 3 2 12 9 Degree of 2 2 13 3 2 12 9 translocation "" .... l'.r"duclion '-f¡¡oiency 2 3 3 3 2 13 7 ~~!!~!~iyityj~4f;lx 3 2 2 3 3 13 7 Where: O ¡rrelevant, 1 ~ Low, 2 = medium, 3 High, 3.5=Very high '- "º ~~ :t CIA T Occasional Publica/ion No. 38 6. Determination nf Drougbt Resistanee Indieators 6.1. Indicators of plant water status 6. L l. O,motie potelltial 19 The commonly used techniques to measure osmotic poteolial of plana are cyroscopíc, psychometríc and pressure chamber (Turner, 1981), freezíng poinl depressíon (osmometer), íneípíent plasmolysís, and solutíon equílíbriurn. Tite osmometer method s depend on the change ín the freezing point while psyehometric method depends on Ihe change ín the relatíve vapour pressure. To measure osmotic potentíal, the turgor pressure must be reduced to zero usually by kíllíng the tí.sue by freezíng or by healing. An effective and relatívely eheap techníque for determíníng the osmotie pOlenlial of tíssues is the solulíon equílibrium method, which employs relative weight gaín of samples from water uptake when placed in solutíons of variahle osmotic pOlential. The sah solution is used to calculate the osmotic potential of the solution (van'l Hoff relations). The pressure chamber technique involves Ihe reduction of turgor pres.ure to zero, not by killing the tissue and liberatíng the solutes, but by applyíng pressure to the 1eaves and obtaining Ihe osmolie potentíal from Ibe pressure - volume relationship of Ihe intaet cells. Once the turgor pressure reaches zero, the volume of water in the cell is related lo applied pressure as follows: l/Pe = Vs - V/RTN Where P, = Pressure in the chamber, Vs = volume of símplistic water in the lurgid leaf, V= volume of the simplistic water expressed, R gas constant, T = Kelvin tcmperature and N = Moles of solute in the leaf, a plot of l/P, against V should be linear when the turgor pressure !>ecome zero. Extrapolation of Ihe straight line, V = O given lhe osmotÍe potenlial at full turgor; and osmo¡ic potential at zero turgor in the poínt at which the water potential and osmotic potentíal are equa!. If tbe total volume of water in tbe leaf (VI) is determíned from inítial turgid weight (TW) and dry weight (nW) Vt = TW - DW Assumptions of Ihe method are that the reflection coeffleient of tbe membranes is close to unity and Ihat solutes do no! move frQm the cells to the xylem under the imposed pressure. ~ .... Coping withDrought 6.1.2 Plant Water Potential Measurements of LWP are made between IOOOhr and 1200 hr 2 weeks after germination and tbe weekly until flowering. To me. sur e lbe LWP, one elegant and eheap metbod is a pressure chamber (Seholander probe. Seolander et al., 1965). This technique is based on Ihe assumption that tension in the xylem stream is equilibrated wilh Ihe water potential of the Icaf rissue. A young fully expanded trifoliate leaf is cut quickly using a sharp razor bl.de. Wrap with • gluing foil and place in lhe chamber of lhe pressure bomb with cut end of the petiole just protruding from the chamber through a rubber plug which is used to seal the chamber. Pressure inside thé chamber is gradually increased by using compres sed gas from a eylinder until the sap .xudes to the CUI end of the xylem vessels. Detectían of exudation of water at tbe end poínl is made using a band lens. This operation should generally take less than 2 minutes. Al least three samples are measured per plol. lhe readings are in bar and could be converted into Mega Pascal (MPa) units (10:1). The amount of pre8sure needed to pres8 the sap out of the vessel is proporlional lo Ihe water potenlial of plant tissue. 61.3 Turgor Pntential lt is Ihe physieal pressure exerted by the water in the vaeuole against Ihe cytoplasm aud Ihe ceH wall on the internal content of Ihe cell by Ihe walls of the turgid ceHs. The turgor potenti.1 can be measured directly by pressure probe technique. It can also be calculaled from the difference belween lhe total osmotie potential and water potential, if measured from the same sample at similar conditions. Replicate samples eould be t.ken from the plant .nd one replicate can be placed immediately lO lhe scholander probe for determinatíon of water potential while lhe olher replicate is frozen in liquid nitrogen for determination of osmolÍc potential. Plant sap is pressed from lhe frozen and tba.wed sample for delermination of osmotica. 6.1 4. Relative Water Content (RWC) Conventionally, RWC is determined as simple caleulation of water eontent, a weight ratio between dry and wet biomass. However, there was an understanding among seienlÍsts that simple ratio of dry & wet biomass is nol sensitivo 10 evaluate eellular water relations. Instead, water content should be ealculated as RWC by comparing the eurrent hydration of a lissue to its maximum pOlential hydration. Five leaf dises. 7 mm in diameter are punched oul from lhe recently most expanded Icaf on each of the lhree plants selecled in each plol. After weighing immedialely using an eleelronie balance to determine fresh weight (FW), the discs are placed in a vial eontaining de-ionised water for 16h in a refTigerator at 5°C (Turner 1981. Runkulantile el al. 1993) in order lo regaín turgor. (YA T Occasianal Publication No. 38 21 The discs are then removed from the vials, gently wiped usíag a blotting paper snd tben re-weigbed to obtain turgid weigbts (TW). E.eh sample is again immediately replaced back in tbe empty vial and oven dried al 70°C for 48 br (to a constanl weight) to oblain dry weight (DW). Estima!!,. of RWC are determined between 1000 and 1200 h (midday). The first estimate is done 15 DAE and at bud formation. Tbe estimate of water content in eaeh plan! is calculated as follows' RWC [(FW - DW)I(TW - DW)] " 100 6.2. Indi~ators of Drought escape The moSI effective strategy of a drought-resistant crop should be lo match the most sensitive phenological growtb stage to the peak soH water availability (Ricbards, 1996), and drougbt escape eould be one of tbe mos! reHable strategies of drought resistanee for speeifíc environments. However, drougbt escape in beans is strongly assocíated with low yield. A yíeld trial from CIA T on forty two bean genotypes with varying maturity period from 52 lO 83 days showed thal differences in matudty was strongly assocíated with a yíeld difference of 2000 kg ha"' (While, 1988). Low yie1d in early maturíng genotypes eould be justifíed solely by reduced períods of photo-assímilatíon but also due to shortened remobílizatíon/translocation períod. 6.2.1. Dayo lO 50% Flowering (DTF) Tbis parameter is measured as the difference in number of days from date of plantíng to date when 50% of the plants in eaeh plot bad one or more fírst flowers. Tbís stage coincides with the ínitiatíon of developmenlal stage R6 (CIAT, 1987). The plantíng date sbould coincide wíth avaílability of suffieíent soil moísture to allow germination of seeds. Drought escaping varíetíes eould be identifíed through determination of day. lo flowering. 6.2.2. Duratioo af Flowering (DF) Tbis parameter ís determined as the average Dumber of days between the first open flower and the last open flower per plart ín a plol. The population beíng assessed should be fairly stable and nol segregating. Five randomly selected planls ín eaeh plol could be used for monítoring purposes. 6.2.3. Day. to Maturity (DTM) This is determined as the number of days from date of planting to date when 50% of plants in eaeh plOI attained physiological maturíty R8 (CIAT, 1987). Al tbís stage, pods are dry and browD. 22 ___________________________________ ~ _____ ~C~O~P&m~g~wÜhD[Q#gW As in DTF, the plantíng dale should coíncide with av.i1abilíty of sufficient soí! moisture lO allow germinatíon of seeds. 6.3. Indieaton of Growth & ProduClivity under Drought 6.3.1 Delermination of Grain Yield Plols are harvested when 95% of the pods are dry and brown (R9). Harvest areas must be identified and determined befare harvest. Border rows and plants within the h.rvest plot. must be c1early marked. Harveot afe' is determined as: Harvest plot (m') = Total length of h.rvested rows (m) x space between rows (m). After harvesling, the seed from eaeh plat is weighed using an electronic balance Ihat has an aceufacy of al Jeast 0.1 g and reearded. Grain yieJd io then delermined as: Grain yield (g/m') = (Seed weight/Harvest area) 6.3.2. Phu!t vigour E.eh plot io assessed for general growth VigOUf al four weeks after germination. Scoring wiJJ be made on a seaJe of 1 to 5, whereby 1 = very poor, 2 = poor, 3 average, 4 = good, 5 = very !lood. 6.3.3. Pods per Plan! Determine Ihe average number of pods per planl by randomJy harvesting 5 plann in a plot, eoun! Ihe number of pods al physiological maturity (R9) and divide by 5. 6.3.4. Production Effidency (PE) This parameter ís determined as: PE = (DSDIDVP) x Grain yield Where DF = Duration of seed development (days belween 50% flowering and PhysioJogical malurity (R8). DVP = Duralion of vegetative pedod (days between germination and 50% flowedng -R6). 6.3.5. Sensitivity Index (SI) The SI deveJoped by Fisher and Mauer (1978) gives a robust and extendahle opportunity lo compare multipJe trials. This SI i. therefore recommended for use in BIW ADA trials. CIA T Qccasiona/ Publicat/on NO. Jtl SI = [1 - (D/C)]I [1 - (Dm/Cm)] Where D Drought yield, C = Control yield, Dm = Mean yield across all Iines under drought Cm = Mean yield across all lines under control 23 The following parameters were considered as secondary indieators eHher because lhey may need lahoratory facilities and training or are no! sensitivo enough to show differences among trealment. 6.3.6 Relative Growtb Rate (RGR) To obtain the ROR values, dry weight at seedling, pre-f1owering, f10wering and pod development are obtained by cutting the shoots at the ground surfaee. Five plants are randomly seleeted in eaeh plol. The shoots are then oven-dried to a constant weight at 70"C. The average value per plant represents the mean for eaeh plol. The RGR is calculated as: RGR ((1/w) x (ow/ot)} Where, w ~ average plot dry weight (g) ów = ehange in dry weight (g) ot = time between each harvest date. 6.4 Indi(ator. of Developmental Plasticity In comparíson to drought escaping Iypes, genolypes wíth a potenlial developmenlal plastícity would be mueh preferable. Developmenlal plasticity means Ihe ability of a genotype to adjust the duratíon of different growth phases and canopy development pattern to suít moisture availabilily duríng tbe growing season (Subbaro el al., 1995). For ínstance, peg initiation and elongation of groundnut plants ceaSes when soil moisture is depleled to 80% of the plant- available water, and recommences when soH water is adequate (Chapman el al., 1993). Pod setting and filling at lower nodes during Ihe early growlh of sorne chick pea genotypes ensured that at leas! sorne seed se!ting occurred in case of recedíng soil mois!ure (Saxena el al., 1993). 6.4.1 Rool lenglb and density The oldes! system of studying root system was lo excavate them, an expensive attempt in terms of labour and time. Currently the rhizotrons (2-3 mts long) became popular for having large underground observation tunnels, and windows large enough to follow the development of tap and fine roots. Rhizotron study is possibly one of the most reliable method lo determine root leng!h density in plants in situ, Another locally available method for determining tap root (TRD) and root dry weight (RDW) is a trough 24 Copinf{ wifh DrQUghf following procedures used by Ronno (I999). Troughs constructed using baked are filled with ficld .oil. Each trough .hould measure at leas! 1.5 m bigb. AII troughs are fully irrigated to field capacity prior to planting. The procedures for calculatíng the amount of water required per trough are adopted from Doorenbos and Pruítt (1977). Q (m') ~ IOIEa (P x SOl) x D x A Where Q ~ amount of irrigatíon requíred Ea = applícation effíciency (as.umed a! 65%) P fraction of total available soil water permitting evapotran spi ra tion S9 = total available soil water D = rooting depth (m) A = trough size in hectares Appropriate soí! fertility .nd crop protection methods must be taken lO maíntain a healthy crop TRD and RDW are monítored on two occasíons namely seedling and f10wer initíation developmenl .tages. At each sampling date, troughs are well-watered about 6 hours prior to sampling to allow easy removal of the bricks without interferíng with the roots. At sampling time the bricks bordering one si de of each trough are carefully removed exposing Ihe rOOI •. Each plant is then carefully dug out and immersed in a container of water to soak and remove the soil surrounding the roo1S. Roo!s 50 washed are measured for length by using a ruler and subsequently severed at the stem base and oven dried to determine root weight. Five planls in each plot are harvested to obtain these measurements. 6.4.2 Biomas. adjustments Grain yield is a converted functioo of biomass accumulation, whích is linearly related to cumulative transpiration (Tanner and Sinclair, 1983). Higher grain yield in legumes is positively correlated with higher plant biomass but negatively with drought resistauce (Slim and Saxena, 19(3). Amede et al (1999) showed that in faba beans, drought sensitivity increases with increasing plan! height and Ihe correlatinn was very high (r=+ 0.93). Thus, high yieldíng genotypes were drought sensitíve and vice versa. Since genotypes that are water saving are commonly low-yielding, growíng those genotypes in favourable years would lead to a considerable yield loss (Slim and Suena, 1993). However, for agroecologies with terminal drought, as in seenario 1 (Fig )), genotypes witb smaller biomass production may perform better under drought as the water requirement of sucb material s will be low. CIAr Qccasional Publicatíon No.j8"--__ _____________ -",2",,5 6.4.3 Translocation efficiency Screening many Iínes in the ficld hased on rooting depth or root length density is laborious and normally impraetical. The simples! method suggested for sereening drought-resístant lines in the field is delayed sowing (Singh el al., 1994). Sinee legumes grown in semi-arid regians commonly eneounter terminal drought, sowing a month later than normal in the spring has be en effective in differentiating between drought-resistant and sensitive lines (Singh el al., 1994). As translocation is less affected by drought than photosynthesis and respiration (Boyer, 1976), late sowing may help to evaluate the ahílity of the genotype to transloeate reserves lo the sink during Ihe onsel of terminal drought. The assimilales could aet as a buffer against the efreels of water defieils on curre nI assimilalion (Ludlow and Muchow, 1990). The assimilates could originate from pro-anthesís or post-anthesis periods dependíng up on lhe time of stress and the amount of reserve available in the stem. Varietal differences in heans for lhis lrait has been observed (I.M. Rao & S. Beehe, CIAT, Personal communication). 6.4.4 Stomatal regulation Stomatal conduetance could he measured by parornel.rs. The commonly used diffusion porometers are smaJl cuvetles lhal can be attached to leaves that monitor humidity in the cuvette over lime The null pororneters measure steady-state rate of transpirarion of the enclosed leaves. 7. Indicators of drougbt beyond the plant: Tlle soi! water In agricultural studies, annual or seasonal preeipiralion is oflen used as an index of planl waler availability, allhough this index suffer. from not laking the soil influences into consideration. Several physieal characterislics of soHs affecl lhe quality and quantily of water available lo plant •. Soil texture dictate. lhe amounl uf water lo be retained in root zono and lhe funclional response between soil waler potential and soil waler conten!. Following precipitaríon, water will drain lhrough a soil profile rapidly in sandy soils, leavíng little capillary waler behind compared lo clay soils. On lhe other hand, the soil solulion will have higher water availability in sandy lhan elay soils. As a response, many researchers preÍer to measure sol! water contenl as an index of plant water availability. Soil water canten! can be mea su red by pereent of dry weight, lensiometers, neutron probes, psehrometery, or time domain refleetomelery. 26 ______________ --"c"'QP'i!.J!L·nIK-l:. with Droughl 8. BREEDING FOR DROUGHT TOI,ERANCE Breeding for drought toleranee is an important objective for most market-driven regional bean improvement programmes. However, mos! of tbe activities have been limited to screening for drought under field condítions. Although breeding strategies ha ve been developed for most importan! biotic .nd abiotic constr.ints, efforts made to develop similar appro.ches for drought tolerance have been limited. This seelion discusses Ihe prerequisites and slrategies in breeding for drought toleranee. 8.1 Prerequisites in breeding ror drougbt toleran~e Certain requiremenls should be met if worthwhile progress is lo be made in breeding for droughl toleran ce. These are' l. A large-seale simple and rehable sereeniog tecnnique to dístínguish belween resistant and susceptible plants/progenies should be available. 2. A suitable ratíng seale should be available. 3. Sourees of resistance should be identified. 4. Knowledge of genetics of resistance can help the breeder decide the breedíng methods which can be employed 5 Knowledge of the mechanisms of resistance ;s useful in handling breeding material. 8.2 Screening techniques The fírst seetions of Ihis report have discussed the merits and demerils of the various techniques, and finally recommended a prolocol that should be followed. Lack for su eh a protocol in the past made it difficult to compare results from various sites. A few additional i.sues related to management of drought nurser;es need to be eonsidered Sites whieh are representative of lhe region should be selecled. They should assure adequate drought and permit proper trial managemen!. A useful way to evaluate the represenlativeness of sites is lo implement cluster analy.is as sugge.ted by White and Singh (1991). Sites that are very similar would appear in the same cluster (based on relative yield) and, thus, should be avoided sinee no new ¡nformalion is .xpeoted from Ihe additional site. Experimental designo work al CIAT -Colombia and elsewhere has shown lhat lattice design. are superior to randomized complete block designs. In mosl cases at eIAT, latlices with three replieates have been found effective to delect the desired levels of difference. For non-Iattiee designs, four replicates are used. For unreplicated nurseries with large numbers of entries, augmented designs (Lin and Poushinsky, 1983), and moving averages (Knott, 1972) have been found more effeetive. CIAr Occasianal Publica/ion No. 38 _______________________ ~1 PlOI size: With relatively uniform plant populations and soils, experience al CrAT has shown thal the minimum useful plot size is about 10 m', with a harvestable area of 4.5 m ' Where uniformity is a problem, plot sizo should be increased. Replicates (and blocks within lattíces) should be distributed ín relatively square formals, taking into consideration known gradients, lo minimize within- block variation. Planting dates: These should be chosen ín such a way thal a 20-day stress period occurs 30 days after planting and coincides with flowering and early pod fill. In cases where occurrence of drought is doubtful, replicates of a single trial at different planting dates sbould be considered. A 13-day difference was used at CIAT- Colombia lo general e variable rainfall patterns and yield. Trial management: In hreedíng for drought tolerance, agronomic managemenl should provide condilions símílar to Ihose in farmers' fields and, at the same time, assure an appropriale aud reliable Jevel of stress for screening. Where available, irrígation provides a valuable tool 10 protect agaínsl faílures caused by insufficient moisture and to producing a graded level of stresses according to tbe selection pressure needed at a given stage of genetic advancement (Wbile and Singh, 1991). Irrigalion al so helps to dístinguish between truly drought-susceptible genolypes (witb excellent yields under irrigalion and Jow yields under drought) and those, whích are jusI poor materials (Iow yíelds under al! conditions). Identificatíon of such. a susceptible check ís an easy way to evaluate stress levels of nurseries and will slrengtben conclusions from drought tolerance studies. Data from irrígated and control plol' provide a means for calculating stress indices such as arithmetic mean, geometric mean, response, percent reduction, and Fischer and Maurer stress indexo Al CIAT, preference has been to use Ihe geometric mean to avoíd serious biase. associated witb the olher four índíces. 8.3 Ratlng scale CIAT has developed standard I -9 ratíng scale for drought toleran ce, where 1-3 ís tolerant, 4-6 intermediate and 7-9 ís susceptible. No betler screening criterio tban yield under drought have becn found Yield values ín stress and control plots are used to calculate Ihe geometric means. Slability analyses may be used where data from more than Ihree or four Iríais with the same en!ríe. ís available, 8.4 Sonrces of resistanee Improvemenl of character depends on avaílabilíty of useful sourees of resist.ncc. Modest efforts have been made lo ídentify sourees of drought resíslance at CIAT. Several lines have been used in breeding for drought toleran ce in beans. These ínelude A54, A170, A195, BAT 336, BAT 477, BAT 1289, Bayo Criollo del Llamo, Bayo Río Grande, Durango 5, Dur.ngo 222, Chiapas 7, Apelito, 28 ____ ____________ m(;gpjI15Lwith]Jrought G1502, Rio Tibagi, Gordo, Mulalinho Vagem Roxa, Rim de Po reo, Favinha, San Cristobal 83, ICA Linea 17 aud V8025. More germplasm from Ihe gene bank and experimental lines is being ,creened lO identify new aud better SQurces of droughl tolerance. However, many researehers feel Ihal genelic variability for drought toleranee in be.n is low. They have suggested u,ing genes from related species. The prime choice is tepary (Phaseolus aculifolius) whose superiority has beco demonstrated. Although interspecific erosses with p, vulgar;'; and p, aculifolius have been obtained, only resistance to common bacterial blight has becn transferred to lhe common bean, Reeent studies showed that hybrids using lepary bean showed good drought tolerance in Honduras, Drought toleran ce has also been reported in pinto bean. It will be necessary lO sereen breeding populations, landraces, advanced breeding lines and other accessions in Ihe region to identify reliable sourees for resistan ce lt will be pruden! to e"pIoil sources identifled by CIAT -Colombia and use Ihem in erossing programmes with lepary and local materials. Sereening in adapted cultivars and advanced breeding populations should be given priorilY heeause they already contain resistaneos to diseases and pest, quality trails and adaptation characteristic s. 8.5 Genetic. of drought resistance Little is known about the inheritance of droughl tolerance in comman bean, This is probably a reflection af the laek of rehable sourees, sereening eriteria and partly lack of interest among researcher,. It is, perhaps. also an indieation of the eomplexity of tnis traic Drougbt tolerance is associated witb many morphological, physiologieal and chemical traits, wbich are probably controlled by different groups of genes. Resistance to tempera!ure-drought stress was determined by a single dominan! gene in P.1.297079 and by two complementary genes in P ,1. J 5 J 062 (Bouwkamp aud Summers, 1982), All three genes were inherited independently, Menosso el al (1978) found that low eontent of free proHne (which accumulates in leaves of many crops under drougb! stress) was partially dominant, and about four genes were involved in its inheritance. However, Amede etal (1998) concluded tha! massive proline accumulation was a symptom of asevere internal water stress, and this aeeumulation had no survival value during drough!. Therefore, proline accumulation is considered to be of nO practical value in breeding for drought toleranee. Mode of inheritance of early flowering varies from monogen;c, digenie to polygenie. Root charaeteristics show quantitative inheritance. It appears lhat, for breeding purposes, drought toleran ce should be treated as a multi- faceted quantitative trait, The ohjective in a breeding prograrnme is to increase Ihe frequency of alleles eonferring improved performance under drought stress. CIAr Occasional Publkª!io1lJnuM'!f,o/,.,.3~8L-______________ -"",29 8.6 Breeding Methods Although bean breeders have been studying drought toleranee sinee the 1930's, hardIy any commercially important variety has been deveIoped specifically for drought tolerance. However, seIeclion in stress environments has resuIted in improved performance. In Kenya, GLP 1004 and GLP-X 92 have been reported to be droughl tolerant while GLP 806 is tolerant to both heat and drought (Mulgai, 1983). In breeding bean for moisture-stress environments, it should be appreciated that the objective is not so mueh to maximize yield but to assure a reasonable yield, whieh cover. production costs and provides .some additional return to farmers. Harvestable yield and its reliability from year to year, rather than mere plant .urvival, are critieal to farmers (White and Singh, 1991; Parsons, 1979) In addition, breeding for drought toleran ce should not be seen in isolation. Growers will rejeet drought resistant cultivars ir il is partieularly susceptible to other m.j or stresses on theír f.rms. Barnes (1983) defíned drought tolerant cultivars to those possessing economic levels of disease, insect, and nematode resistanee; toJerance to soil, water and air problems; and ínsensítívity to normal temperature and photoperíod fluctuations. Breeding methods, which can be employed for rapid incorporation of specific mechanísms of drougbt tolerance, sueh as early maturity, deep roots, small foHage, thick lea ves and trichomes, inelude pedigree and inbred-backcross. In addition, three-way and modifíed douhle eross may be used to rapidly increase lhe frequency of desirahle genes. A recurrent selection program using 821S3 (equivalent to F3/F4) yield tests has also been .tarted al CIAT for improvement of drougbt toleranee in eommon beans. Gamete se[ection proeedure for simultaneous improvement of both qualítative and quantitative traits has been used effeetively al CIAT. This procedure may be employed to improve drought tolerance and other traits. 8.7 Strategies in Breeding Bean for Drought Toleranee Three strategies can be followed in breeding beans for drought toleranee: improvement of parental sources of drought tolerance, breeding for drought tolerance per se, and breeding drought tolerance ¡mo commereial cultivars. In absence of a better criterion, seleetion for drought toleranee .houId be based on yield performance Strategy 1: Improvement oC parental sourees Parental lines with reliable drought toleranee eharaeteristics are required in a breeding programme. Available germplasm should be _______ .... __ .... Copil¡gwith Droughr sereened al primary and secondary sites as identified in the protocol suggested in Ihis report. The germplasm should inelude landraces, drought toleran! lines identified by CIAT-Colombia, commercial cultivars available in the region and advanced Iines held by varicus national and regional programmes. In assembling Ihis germplasm, care should be taken to include materials from race Durango from the highlands of Mexico aud other centres of diversity, which have evolved under drought stress conditions. A eritieal evaluation of parental sources for their response to temperature extremes, major diseases and pest, in this region should be made. Drought tolerant parents defíeient in major constraints can be further improved by ineorporating genes through "n inbred-backcfosS method or its modifications, About 100 hybrid plants should be used as male parents from the fírst (F 1 BC tl and subsequent backcrosses. Two backcrosses with recurrent parents followed by two generations of inbreeding are often adequale before begínning single plan! seleclions aud progeny testíng This strategy will produce Iines with multiple resistance, which can be tested in on-farm Irials, and the best Iines eventually released. Alternatively, it will provido drought tolerant parental lines for further breeding aClivities, Strategy 2: Breeding ror Drought tolerance per se This is a medium to long term breeding programme specifieally for drought tolerance. It can be justified on the basis of Ihe large areas affected by drought in Ea't, Central aud Southern Afríca, causing severe yield losses, Predícted clima!ic changes further justify a strategic regional breeding programme for drought toleran ce, This approaeh involves making erosses among different sources of drought tolerance and relaxed selection for plant types, grain types and other features. The erosses should assure maximum recombination of different traíts, mechanisms, sources and genes associated with drought tolerance, Genes for large root volume and deeper root growth, early maturity, tolerance to heat, poor soíl fertility, small foliage, low canopy temperature, and other traits associated with drought should also be intercrossed with drought- tolerant parents, Whén the parents are genetically very diverse, for .xample for seed size, maturity, growth habit and adaptation, stratogies su eh as recurrent seleclion, baekerosses, three-way erosses or modified double erossos should be used to in crease Ihe frequency of desirable genes (White and Singh, 1991). The approaeh followed at CIAT is shown in Table 7. CIAT Occasiona[ Publication NO.38 31 Table 7. Early generation yield test used at CIAT, Colombia ror breeding drought toleranee in hean. Montb , Generation Aetiyities , lanled ~=e.::;---+~-:~,-~-I ....... _._-- December : Parental Intermate among March : seleeted arents Parental and. Intermate among FI . seleeted parents and erosses. Saye F2 seed from seleeled single June __ += __ --,,-_,-+,er088e s. Parental and Inlermat. among F, seleeled parents and CTesses. Saye F, seed frem s.IDeled crosses .'-D;:-e-c-e-m-cb:-e-r---j F ¡------+G~ro w ou I and sa y e June : IDecember F, ! : ¡ Juoe ! F. rDeeember F, June F. December F7 L ! seed from seleeled eros ses : Yield-test all crosses in replicated trials Save F, single pod bulks from seleeted erosses Yield test and save F4 single pod bulk from seleeted : crosses Yield-test and save F, bulk from seleeted erosses : Spaee-plant and i make single plant selection Progeny test and seed increase i Yield-test selected ! lines for oational : programmes and • other ourseríes and I speeifie pbysiologieal studles Source. Wh.te and Slngb (1991) : Loeation and 'selectian ressure Palmira : i Nane Palmira Nane Palmira None ~.~ Palmira None Palmira None Quilichao Drought, common bacterial blight, angular leafspot, fertility, roo! rols Popayan Drought, anthracnose, root rols Palmira Drought, roo! rots ..... - , Quílichao : Same as F3 Palmira, Quilichao and Popayan s,m ... ;,:] and F, ....... . .... 12~ ..... ___ _ Copillff wifh Droughl. Strategy 3: Incorporation of drougbt tolerance iu commercial cultivars Thi •• trategy differs from breeding for drought tolerance per se because, in additíon to drought, other yield-limiting factors su eh as diseases and pest resislance musl be simultaneously bred inlo commereíal cultivar •. The main steps Ihal can be followed are: l. Idenlify Ihe regionally importanl base cultivars lO be improved 2 Identify Ihe major production constraints e.g. drought, angular leafspot, anthracnose, COmmon bacterial blight and rus! 3 Determine the type of new cultivar to be developcd and characteri.ties it should have. 4. Idenlify three to six sourees of resistance to eaeh constraim. 5 Intermate the base cultivars to produce single cros,es. 6. From single cros.e., intermate lo ereate backcrosses, three-way and double crosse •. 7 Inlermate donor parenls to combine two Of more traÍ1 •. 8. lntermate the three-way and double eros'es with eross.s from donors to create F, with eombined trait,. Base parents erosses are used as females. F, may be backcrossed to maintain substantial conlributions from regional base cultivars or advanced to F2. 9 F, yield trial under optimum management al one loeation to identify high-yielding erosses. Harvest best populations as single pod bulks. 10. F,: yíeld-test under moderate drought pressure, low soíl fertility, common bacterial blight and angular leafspo!. Seleel and harvest single pod bulh. 11. F4 : Selected populalions are grown in a replicated trial under pr.ssure of anthracnose and drougb!. Harvest single pod bulks. 12. F,' The bulks are ,creened under drought pressure. Make single plant seleetions. Note tbat by tbe time single plant selection commences, early segregaling generatians will have been exposed to climatic, soil and biolÍc stresses oecurring at three contrasting sites. This allows only survíval and identifieation of genotypes, which combine desirable traits in successive generatians. When the number of trails desired in cultivars is large, extreme pressure for any single trait, especially quantitatively inherited ones in early gencralions, is .voided. 13. F6-F7 bulk families or lines from F7 onward are yield tested under drought and non stress environments and evaluated in separate eomplementary nurseries for anthracnose, common blight, angular lenfspot and otber constrainls. Because relatively liltle has been done on breeding bean for drought tolerance, BIWADA and regional pragrammes will have lo iniliate an effeetive programme perhaps following lbe experienees and suggestíons outlined above. BIWADA may focus initially on str.tegy I .nd follow the protocoI outlined in this repor! Strategy 2 and 3 may be carried out as part of the regional strategic aetivity. CIAr Occasionq{ Publicatíon.No, 38 .... ~~ ... , ... ~ .... ~~ __ .... ~_~3u.3 Tbere is need to study the inberitance and mechanisms of inheritance and incorporate farmer partícípatory approaches in all strategies, Table 8. Site activilies and standard experimental protocols for testing materials for drought resistance [It:t~~itLI~untries Indícators s 0]1---lo be Characters measured I Primary KENY A AlIf- SOiTiype . Seree.ing ETHIOPIA PH I UGANDA SWHC TANZANIA N. P and SUDAN K Secondary MADAGASCAR 5 best Soil type Screening DRC Indicators pH MALAWI SWHC ZAMBIA i (30% bes! N. P "nd i On-farni- SOUTH AFRICA materiat'L _ K ALL COUNTRIE YieId Soil type (brooding Maturity pH studies) (lO Farmerl . Díseasel SWHC country) I pest N. P and K ~- ----- (S-IObesl) Wealher parameters ---Max & Min Temperature 10 Year average seasonal rajufall Max~& Min --- Tcmperature 10 Year average seasonal rajnfall Max & Mio Temperature 10 Year average seasonal rainfall ----- Duration of experíments 2 scasons 2 seaSODS 3 seasons lJ'Jll-m f,-cr--o f --l-p -fOí--g i i-e Rcplications ! 2 1 10 (EACH FARMER IS A REP) 45cm X 15cm 2 rows, 3m Local spacing 4 rows. 4m long -Lo"cal spacing Rows 5m long Plot size at leasl 25 M' w ... () _a i* ¡- Coping with Drought 35 9. REFRENCES Amede, T. and S. Schubert (1997): Solute pool enl.rgement in Drought sensitive or-Iolerant grain legumes. Con central ion effee! or osmotic adjustment ? Planl nutrition for sustainable environment, Kluwer Academic Publishers, Japan. 165-167 Amede, T., E. von Kittlitz and S. Schuberl (1999): Differenti.l droughl responses of Faba be.n (Vicia faba L.) Inbred lines. J AgroDomy and Crop science 183, 35-45. Arnede, T. (1998): Analysís of drought resistance in grain legumes: The case of Vicia faha, Pisum sativum, Phaseo{us vulgaris and Cicer arietinum. VERLAG ULRICH GRAUER publishing, Sluttg.rt, Gerrn.ny. 135 p. Bouwkamp, J.e. and W. Summers, 1982. lnherilance resistan ce to temperature- drought stress in lhe snap beans. J. Heredity 73:385-386. Boyer, J.S. (1976): Photosynthesis at low water potenlials. Philos. Trans. R. Soco London Ser. B. 21:501-512. Ch.pman, S.C., M.M. Ludlow, P.P. Blarney .nd K.S. Fiseher (1993). Effect of drought during early reproductive development on growth of cultivars of ground nut (Arachis hypogaea L.) 11. Biomass production, pod developrnent .nd yield. Field Crops Res. 32: 211-225. Fischer, R. and R. Maurer (1978): Drought resistanee in spring wheat cultivars, 1. Grain yield responses. Aus!. J. Agrie. Res. 29897-912 Hanson, A.d., C.E. Nelsen, A.R. Pedersen & E.H. Everson (1979). Capacity for proline accurnulatíon duriog water stress in b.rley and its implications for breeding for drought resistance. Crop SeL 19: 489-493 Knott, D. (1972)' Effects of seleelion fm F2 plan! yield or subsequent generations in wheat. Can. J. Plant Sei 52: 721-726 Kramer, P. J. and J. S. Boyer (1995): Water relations of plants and soils. Academie Press, UK. 480p. Lin, C.S. and G. Poushinsky (1983): A modified augurnented design for an early st.ge of plant seleelian involving a large number oftest lines withoul replications. Biometries 29: 553·561 Ludlow, M.M .• nd R.e. Muchow (1990): A critical evaluation of trails for improving crop yields in water-lirníled environments. Advanees in Agronomy, Vol. 43: 107-153. Menouo, O.G., C. Vioríra, A. Br.garena, and J.e. Siva, (1978): Hereditariedade de toor de prolina em folhas turgidas e desidratadas de fejveiro (Phaseolus vulgaris). Turrialba 28: 340-342. Monneveux, P. and E. Be1hassen (1996): The diversity of drought adaptation in lhe wide. Planl growth regul.tíon 20. 85-92. 38 __ _ __________ ...... _ ... Cppillg with Draught APPENDIX l. Analy.i. of lhe strengths and weaknesses of participating countries with regard lO drought research .ctivilies. IKENYA I I :c.;S,;"Tc=R::.oE,,;N,-:,G::..;T:..:H~~S,,- _ -_ -_ -~ -_ -_ -_ -_ --: -_ -_ -_ -_ -_ -_ -_tc\-;W~~E.:.:Á~K";N"7E,,,S::S..-.E ... Sc;-_ ~, • Drought prono environmenls Unreliable weather -.-~c;--;----+ eo n d i t ion s - d sk'll '1 k f ee filca expertence an 1 s In ,Re o screenJng eqUlpmen research : --..... _-----~------..... _---- , Linkage with IARCs eg CIA'f, Limited financial and human! , ICRlSAT reSOUfces Poor co-ordination and communication Democratie Republie of Congo ~ ..... (dry Drought prone environment ! : spots) --...... _---~"perienceíñdrOUght research in Types of drought badJy ! a>sociation-CIAT defined i ...... _ .... ~---- ... _ .... _----- . . . : Laek of equipment ~--.. Poor cornmunication ! Li mited fi naneial resources , .... _---, -----~--~. _____ -,-': ~on:~~:~:~: weath:~ ____ ] -- .. ·····-··f-I-·····---- ~ ! TANZAl\IA D h! raug prone enV1fon me t 'Low h a capae't n um n 1 y In FExperi~nce people indrought area Drought activities Laek of equipments Good networkíng with CIAT, Badly defined drought prone ICRISAT areas Bad communication Limíted resources . Unrellable weather ~=:-'C c;-----..... -.--------ri ~co.!ldition.~ __ _ SUDA.:cN~ ____ _ Two differen! systems (irrígation & .... : Human capacíty residue moisture) Same as Tanzania Limi!ed machinery develo men! f,L;-;-in-; .. k-.a-g-e-w-Ci_--;thC-OI~CccAc;R=D"CA:-7¡-;C"C¡;-A;-T;;:----'-: ~L"'a':";:c.~. of e ui men! Fluctuation of floods from sea son to sea son '---------------.. ·--r,Limited germplasm (early ! i r ---- ____ ...... __ .. __ ___ ...... _+..;Jll¡¡tu rínS) Limited resources ~'="'-----1 CIAr Qccasional Publication No.38 ETHlOPIA I Wide experience in drought : behaviour ~ .. Limited germplasm for beans Human capacity (Senior and Graduate) Environment - drought prone areas I REGIONAL ASPECT [liasic information available on i characterízation of drought prone u~nvironment i A critical mass of capadties in , drought research Inlerregional Networking is good i Informallon aVRllable to Ilmtted , level I exlent 39 i : Lack of germplasm with I environmenlal plasticit~ Limited ¡¡;ermplásm , Limited research facilities I . Poor consideration. by I seientist and policy makers I , Lack of uniform protocols I I Limited research on drought in relation lO other areas I ' Limiled germplasm al region : level 1 I Lack of equlpmenl : L i m i t ed human é-a-p-a-c""'i-t y~i-n--I ¡--.. _ --------------i-' ~d'-'ro"'u"'g...,hl research : I Early warning system for'l bean productlOD 18 laebng - Drought coefficient is 1-____________ .. ____ ¡.)acking. : I Absence of reliable I ' iodicators I Lack of sereening metbodologies !I Reluctance to invest in droul1;ht re8earch I i Lack of commitment from , . ____________ -Li-!"policy & donors ~ l' Lack of infrastructure to~l _.. . combat drougbt I Absence of defined L' technology from farms of , . ________ ..Jldifferent eategories I COOi1!f:wilh Droyght ___________________ ~3u.7 Tanner, C,B" and T.R. Sinelair (1983), Efficient water use in erop productíon: Research or Re-search, In H, Taylor el al, (eds) Limítations lO effieienl waler use in crop productíon, pp 1-28. American sodety of Agronomy, Madison. Tardieu, F, (1996); Drought pereeption by plants, Do eells of droughted plants experience water stress. Plan! growlh regulation 20,93-104, Turner, N.C, (1986): Adaplations lO water deficÍls: A changing perspective. AuSI, J, Plant PhysioL, 13: 175-90. White, J,W and J, Izquierdo (1991): Physiology of yield potential .. nd .sah stress. In: A. Van Schoonhoven, O. Voysesl, eds, Common beans: research for erop improvement. Wallingford, UK. CAB International & Cali, Colombia, CIAT, 287-382, While, J, W., J. Kornegay, J. Castillo, C,H, Molano, C. Cajiao, G, Tejada, 1992. Effecl of growth habíl on yíeld of large seeded bush bean cultivars of common bean, Fíeld Crops Res 29: 151-162, Whíle, J.W. and S, Singh, 1988, Breeding for drought resislance in beans, In White,J,W, Hougenboom, G" F, Ibarra and S.P, Singh (eds.), Bean drought workshop, CIAT, CaJí, Worlmann, c., R, Kirkby, C. Eledu and D,Allen (1998), Atlas of common bean production in Afríca, CIAT publicalion no. 297. Cali, Colombia, LQ. __ ~ ____ ~ . ...... _~~. _______ ...• _~ Comngwilh Drought APPENDIX 1. Analysis of Ihe strengths and weaknesses of participating countrie, with regard lO drought research activilies. KENYA STRENGTHS Drought prone environments Technic.1 experience and skill. in research Linkage with IARCs eg CIAr, ,lfRISAT ----~ --._---~_ .. _---- WEAKNESSES Unreliable weather : conditions ! Lack of sereening equípment I Limiled financial and human ! resources Poor co-ordinatían and communication I I i Democrátíc Republíc of Cong:,-0c-~~+ _______ ~~~_ ... ----l : Drought prone envíronment (dry I i s~ots) ... ! Experience in droughl research ín •• ssoei.tion-CIAT ! Types af drought badly : defined Lack of equipment Poor cornmunicatíon Limited fiollncíal resollrcesJ Unreliable we.ther i conditíans TANZANIA 1 Draught prone environment Low human capacity í: DrollAht aClivities ~.- Ex ~~rienc..e QeaElein drought area • Lac.k of equipments 1 Go~d networkmg w1th CIAT, ,Badly deflned drought prone ! lCRISAT ____ ..... _ ~~~ __ -,-;I a~r-"e",a,,-s .... _ .. -c~-----j : Bad communication ! , Limited resourees Unreliable weather I eandition rIUDAN--~-~-~~'~---+==='----~---i ¡ Two differen! systems (irrigation & • Human capacity [reSidue maisture) l' i Same as Tanzania Limíte'(j machinery-----i . . dev~opment : Linkage with ICARDA-¡.,-;:C"'I-:A-;;T,----t-I L~ac:" .. .k; afe9,,,u.:Ji "im~e:.:.nt,--;---;-___ , I I Fluctuatíon of floads from ! season to season ,Limited germplasm (early I maturíng)