Programa de manejo de residuos sólidos

This study has demonstrated the importance of maintaining local germplasm at a national level. Researchers in most countries do not fully utilise their locally adapted germplasm, due to a lack of important information associated with conserved germplasm (FAO, 2010). As an alternative, scientists use exotic germplasm from international genebanks, such as the International Institute for Tropical Agriculture (IITA), as in the case for cowpea in Malawi. The evaluation of local cowpea and the identification of genotypes with drought tolerance and other desirable attributes in this study will contribute to an improved utilisation of the conserved germplasm in Malawi.

Eco-geographic characterisation can assist in focussing the search for genotypes with stress tolerance from large collection of genetic resources from a diversity of ecologies (Redden, 2013). A study of peas from 804 accessions collected from different ecological sites in China (Li et al., 2013) identified drought tolerant genotypes from areas characterised by low rainfall and high temperatures. In addition, a geographic pattern of genetic variation was observed in 146 chickpea accessions, which indicated the adaptation of genotypes to specific geographic

and environmental conditions (Shan et al., 2005). In this study, none of the five drought

tolerant genotypes (Chapter 4) came from areas characterised by low rainfall and high temperature, represented by Cluster 4 (Chapter 3). The failure of the eco-geographic characterisation results to agree with the morphological and physiological characterisation of cowpea may be due to unbalanced sampling of genotypes from both wet and dry environments; and/or role of other factors contributing to the presence of drought tolerant genotypes in wet environments.

Application of key findings and opportunities for commercialisation and future directions for cowpea research in Malawi

Comparison of results from chapters 3 and 4 shows that all the drought tolerant genotypes came from clusters 1 and 2 of chapter 3. These results suggest that the wetter and cooler environments may be better sources of drought tolerance. The cooler sites may not have provided selection pressure against the trait or drought tolerance was maintained in wet environments because of occasional droughts which gave selective advantage in dry years to the available populations. Consequently, such environments may lead to retention of maximum genetic diversity. The presence of drought tolerant genotypes from wet environments suggests that adaptations for extreme conditions such as drought can often be found in wet and cooler environments.

On the other hand, lack of drought tolerant genotypes from clusters 3 and 4 of chapter 3 may be explained by three factors. Firstly, farmer-mediated selection in the hot and dry areas may lead to selection of short season landraces as an adaptation mechanism without necessarily

considering drought tolerance (Peleg et al., 2005). Secondly, the dry and hot areas may have

serious bottlenecks because just one or two consecutive drought seasons may lead to

extinction of most populations including drought tolerant ones (Blum, 2011; Penuelas et al.,

2013). Thirdly, complete loss of locally adapted landraces in drought prone areas may have

prompted farmers to acquire new germplasm adapted to wet conditions (Blum et al., 1989).

Therefore, to capture maximum diversity for drought tolerance, seed collectors and breeders should also target wet environments as potential sources of drought tolerant genotypes rather than concentrating in hot and dry environments only.

Despite the failure to identify drought tolerant genotypes from areas with low rainfall and high temperature, the eco-geographic characterisation (Chapter 3) has identified geographic gaps in cowpea germplasm (places with no or limited locally available germplasm). These

identified gaps could be filled by either conducting fresh collection missions, or the repatriation of cowpea from international genebanks that collected cowpea samples prior to the establishment of the National Genebank of Malawi in 1992. The International Institute for Tropical Agriculture genebank alone holds more than 400 accessions of cowpea collected from Malawi (Bioversity International, 2011). Repatriation of this germplasm may cost less than conducting collection missions. In addition, materials collected many years back may represent true landraces, as they were collected before the introduction of improved varieties, which may have crossed with the landraces. However, these repatriated materials may be characterised by arrested evolutionary processes, compared to newly collected germplasm,

which may have evolved within changing environments on farms (Hammer et al., 2003).

Therefore, the filling of gaps using both options is ideal for the conservation of a wide diversity of cowpea germplasm as long adequate storage facilities are available at the National Genebank to accommodate the new germplasm.

On-farm conservation of germplasm is an in situ conservation strategy, which recognises

farming communities as custodians of local crop diversity (Maxted et al., 2002). The

advantage of this strategy is that it enhances the adaptation of germplasm to local conditions. Eco-geographic characterisation identified sites which could enhance the adaptation of cowpea to drought conditions (Chapter 3). On-farm conservation initiatives in Nsanje and Chikwawa districts areas characterised by low rainfall and high temperature would enhance the adaptation of cowpea and other crops to drought conditions. Consequently, the Malawi Plant Genetic Resources Centre (MPGRC), in collaboration with other organisations, should consider the establishment of on-farm conservation in these areas. The establishment of such conservation sites now would ensure the future availability of germplasm that is adapted to low rainfall and high temperature.

Application of key findings and opportunities for commercialisation and future directions for cowpea research in Malawi

Eco-geographic characterisation has improved the quality of passport data of the available germplasm. In most genebanks, details of environmental conditions describing collection

points are scarce (Hijmans et al., 2001). In this study, rainfall, temperature and the altitude of

the collection points of cowpea germplasm have been acquired through the use of DIVA- GIS, a tool specifically developed for the management of plant genetic resources and freely

available climatic data (Hijmans et al., 2005). Taking advantage of the available tools, eco-

geographic characterisation should be considered as a key genebank management operation, more especially in genebanks where germplasm is not properly described by environmental conditions. The acquisition of climatic variables of the available germplasm would assist in the search for genotypes adapted to specific environmental conditions.