Linking Conservation And Plant Breeding

To serve the two broad crop improvement systems, the formal and the informal, different approaches are needed in the conservation and supply of the diversity for current and future genetic advance. As a generalization, ex situ methods were developed primarily to meet the needs of the formal crop improvement system. The importance of in situ conservation of crop wild relatives was recognized, but, until recently, there were very few programs that specifically targeted wild relatives of crops. Within the informal system a more holistic approach has been advocated and activities aimed at supporting the conservation of traditional crop cultivars in situ have been initiated. As discussed earlier, there is a great need and opportunity to promote an integration of these approaches.

Conservation per se is rarely a conscious objective of farmers; however, in applying selection pressures for particular traits, traditional farmers are generally aware of the need to maintain high levels of "background" diversity. The ways in which traditional farmers manage their genetic diversity have dual effects of conserving within the gene pool many of the adaptive features of their crops either individually or as coadapted gene complexes, while at the same time allowing that gene pool to evolve in other respects to meet new needs.

Plant breeding in the formal sector depends on four main sources of diversity: wild relatives (and increasingly nonrelated taxa), mutation (often artificially induced), landraces, and modern cultivars. Of these four, the variability in landraces, or farmer varieties, is probably the most underexploited. Isozyme and molecular analyses show that landraces and wild relatives remain the main reservoirs of genetic diversity in crop gene pools (Miller and Tanksley, 1990). In addition, much of that diversity may not be obvious even through traditional genetic manipulations, but may be located and successfully used by employing molecular analyses (Tanksley and McCouch, 1997). Genetic erosion of these reservoirs continues, in some cases at alarming rates and for various reasons, and it is imperative that efforts to conserve them be strengthened. Ex situ gene banks alone are not sufficient, and it is in the best interests of both the formal system as well as the traditional farming communities themselves that the dynamic "cauldron" of genetic diversity be maintained in situ, and be allowed to continue to evolve.

Formal breeding, for economic reasons, has tended to neglect crops of only local importance and the needs of farmers in diverse marginal environments. However, for farmers in marginal areas, such crops may be the basis of their survival. They have to depend on their own efforts and can rarely expect assistance from the formal system. It is highly unlikely that formal breeding will ever fully meet their diverse needs.

The need to produce more food for the ever-growing world population requires increased productivity from all sectors. Both formal and informal systems of crop improvement have a vital role to play; yet each tends to operate independently of the other. While there is a flow of materials from the informal to the formal system, its genetic diversity remains inadequately exploited by professional breeders. Ways must be found to link these valuable sources of diversity more closely to professional breeding efforts.

Qualset et al. (1997) suggest ways that both farmers and professional breeders can link their plant-breeding efforts in breeding for "locally based conservation and improvement" of crop plant genetic resources. In a joint breeding effort, farmers would continue their tradition of improving their own material within the limits of their resources. Formal breeding programs would contribute by introducing new selection criteria and techniques that would improve performance but not change the basic character of the crop. Single gene traits which could, for example, improve disease resistance could also be introgressed and be made available to farmers in the genetic background of the material they are already using. Sperling et al. (1993) successfully involved farmers in Rwanda in breeding and selecting segregating populations of beans.

Integration of formal and informal breeding efforts are increasing and will stimulate the flow of genetic resources and information in both directions. Additional ways in which the formal system can assist the informal include the following (Hawtin et al., 1996):

• Strengthening links between farmers and gene banks to ensure adequate long-term conservation of landraces, with systems to facilitate the restoration of landraces to communities that have lost them;

• The provision by gene banks of adapted materials collected from one location to farmers in other, environmentally similar locations for local testing and adaptation;

• The provision to local communities of segregating populations and other breeding products derived from their own landraces;

• The introduction into local landraces of specific genes of relevance to local circumstances;

• The provision of a broad range of elite lines, within and from which farmers can select according to their needs; and

• Training farmers in crop improvement techniques that are relevant to their own circumstances.

As already mentioned, more participatory breeding approaches are being developed and tested in which formal sector breeders are working closely with farming communities. Through a greater understanding of the needs and aspirations of such communities, and through working in partnership, scientific expertise can best be brought to bear on the problems faced by those farmers that have been the most neglected up to now. Such approaches are expected not only to contribute to rural community development, but may also help to ensure that the large gene reservoir managed by the farmers continues to exist and to evolve, and remains a resource for all crop improvement efforts in the future.

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