Is apomixis a key to future seed production?
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CTA. 1991. Is apomixis a key to future seed production?. Spore 36. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/45629
Apomictic plants are generally little known, although they are common in developing countries and have a biological characteristic which could be used to improve agricultural production: they reproduce even though they have only the female...
Apomictic plants are generally little known, although they are common in developing countries and have a biological characteristic which could be used to improve agricultural production: they reproduce even though they have only the female characteristics. If seeds are selected from highly productive stock then the same levels of performance can be expected from the following harvest. Farmers in developing countries rarely, if ever, produce selected seed. They keep back part of the harvest for the next season's sowing, but the next generation may be less productive and different in character from the previous one. Furthermore, in tropical countries it is often difficult to employ modern agricultural techniques: chemicals are expensive and can cause pollution; the land does not tolerate frequent or deep ploughing, nor do intensive growing methods cope well with the climate or pest attacks. If attempts are made to improve local seed varieties by selection then their hardiness and adaptability are often lost. For these reasons agronomists are always seeking new methods of developing improved crop varieties. Apomixis means fatherless plants Some scientists claim that the use of apomictic plants would be an excellent solution: of the thousands of plants which come under this heading, many species are tropical. The plants themselves, which include species of millet, maize and citrus, do not differ from others except that they have a particular gene which affects the means of reproduction. In sexually reproduced plants the offspring have the characteristics of both parents, but in apomictic lines the plants resemble only the female. Knowledge of the specific characteristics of these plants has, until now, been confined to agronomy textbooks since it has been generally thought that to use them in the field would be too complicated and too expensive. However, apomixis as a reproductive method virtually eliminates genetic changes. All that is necessary in order to have identical seedlings the next season is to take seeds from prolific stock. The process is simple: the male pollen does not fertilize the ovule of the female plant but only reaches the albumen in which the ovule develops. The embryo plant is therefore 100% maternal in character. Apomictic reproduction, as with propagation by cuttings or cloning, gives rise to little or no genetic change The seedlings of the next generation are identical to each other and to the female parent plant. It would be perfectly feasible to use these plants in developing countries. Most tropical Gramineae have apomictic species among their genera. 'Thus among the 200 or so species of millet, more than three quarters are apomictic,' explained Yves Savidan, a research scientist with ORSTOM, whose specialty is apomixis and who has just set up a research network. 'Often it is impossible to cultivate them as they produce very few seeds but prostrate stalks instead. But it is the apomictic gene which is of interest in millet. Hybridization permits the transfer of this gene from one plant to the other. Once the grower has harvested his first crop of prolific and apomictic millet, he has only to extract the seeds from the best heads to have a field full of them, and nothing but, the next year.' A safe way of increasing yields This method of seed production has a twofold advantage: firstly it avoids major changes to farm-saved seed for growers who cannot afford to take risks. Secondly, as Yves Savidan puts it, 'apomixis ensures homogeneity in reproductive terms, but gives a heterogeneous range of plants' - in that the grower selects his seed from the best heads but from different varieties. This means that the resulting millet plants will be uniformly productive but in countries where to have only one variety means vulnerability to climate, disease and pests, some can be drought-resistant, some pest-resistant, and some immune from certain viruses. This gives enormous advantages. All that is needed to determine whether a variety is apomictic and to establish the ease of reproduction of the hybrids is a simple, optical microscope. But scientists remain cautious about the future implications of this biological characteristic: 'This will not mean a revolution in tropical agriculture,' warned Yves Savidan. 'It exists as a possibility as yet untried, but which could yet be a factor in bringing about great improvements.' The new network that has been established by Yves Savidan is APONET. Its objectives are to promote and coordinate basic research on apomixis to make this reproductive process a major tool in modern plant breeding and a tool for development. Also to manipulate apomixis and sexuality in order to improve apomictic species, and to transfer a gene or genes which control apomixis to crops that reproduce sexually. APONET, International Network for Apomixis Research, Yves Savidan ORSTOM Mission Mexico, Homero 1804-1002 Col. Los Morales, 1150 Mexico City, MEXICO