The increased occurrence of drought in Malawi requires concerted efforts to strengthen agricultural strategies including exploring the potential of local germplasm of cowpea which can adapt to such conditions. The local germplasm with desirable adaptation mechanisms would augment the international efforts of breeding drought tolerant genotypes by with meet needs and preferences of local farmers in Malawi. This literature review has identified key areas for consideration as a first step in the identification of drought tolerant genotypes of cowpea maintained at the Malawi Plant Genetic Resources Centre. Eco-geographic characterisation of the available germplasm would help to identify potential accessions with drought tolerance and identify potential sites for on farm conservation to enhance adaptation to drought. Classification of the available germplasm into appropriate response categories of drought avoiders or drought tolerators’ adaptation mechanisms by using both morphological and physiological traits would help to establish drought tolerance breeding populations to
complement the efforts by the international community. Leaf wilting remains a fundamental trait in screening for drought despite the associated scoring challenges. The revision of the scoring system for wilting would address some challenges associated with the current scoring systems. Once the drought tolerant genotypes are identified and confirmed, further tests on agronomic performance and farmers’ preference would provide insights for direct benefits at farm level. Most breeding efforts in Malawi are thwarted by poor adoption, poor seed distribution and marketing of improved varieties. To accelerate adoption of future improved cowpea varieties, early involvement of farmers in the selection of breeding germplasm, efficient seed distribution and marketing are inevitable.
Chapter 3
: Eco-geographic characterisation of the locally adapted cowpea
germplasm
Abstract
The availability of germplasm in genebanks is a rich resource for future agricultural development. However, utilisation of the conserved germplasm is limited by the lack of associated useful information, including eco-geographic information describing collection sites. This study characterised 66 cowpea accessions from Malawi using geographic and climatic variables, in order to identify potential genotypes adapted to drought conditions, identify gaps for future collection missions, and identify sites for on-farm conservation efforts. A distribution map of the 66 accessions was used to extract online eco-geographic variables of annual mean temperature; mean temperature of wettest quarter; mean temperature of warmest quarter; annual precipitation; precipitation of wettest month; precipitation of wettest quarter; and precipitation of warmest quarter from WORLDCLIM database (www.worldclim.org). The extracted variables were used in a cluster analysis to classify the accessions into distinct groups. The distribution map showed that, out of the total 27 possible districts in Malawi, the accessions were collected from 19 districts only, with Chikwawa registering the highest number (15). The eight other districts and areas with few accessions represent gaps, which require germplasm collection or repatriation of germplasm from international institutions holding cowpea germplasm from Malawi. The cluster analysis grouped the 66 accessions into Cluster 1 with 29 accessions, Clusters 2 and 3 with 16 accessions each and Cluster 4 with 5 accessions. Accessions in Clusters 3 and 4 may represent potential candidates for drought tolerance, as they were collected from dry and hot zones. On farm conservation of cowpea in hot dry zones, such as Chikwawa and Nsanje, denoted by Cluster 3, could enhance adaptation of germplasm to drought conditions. Further morphological and physiological studies are recommended, in order to identify the drought tolerance levels of the local germplasm.
Eco-geographic characterisation of the locally adapted cowpea germplasm
3.1 Introduction
Landraces or traditional local varieties of different crops have been collected from a wide range of environments and conserved in genebanks. For instance, 50,000 accessions of cowpea germplasm are conserved at a global level (Bioversity International, 2011) and the Malawi Plant Genetic Resources Centre (MPGRC) has collected 66 accessions of the locally adapted cowpea landraces from local farmers around the country. Although a wide range of diversity is available in these genebanks, its utilisation is limited by the lack of detailed passport data including geographic and climatic variables (FAO, 2010; Hazekamp, 2002; Li
et al., 2013). Therefore, research which improves the availability and accessibility of detailed passport data would help to avail the potential of the currently collected germplasm.
Eco-geographic characterisation is one of the key steps which are often ignored in most genebanks, due to limited capacity. Eco-geographic characterisation involves a description of germplasm based on characteristics of collection site habitats. This is considered as a first step in identifying genotypes that are well adapted to particular habitats. The importance of eco-geographic characterisation is based on the premise that environmental conditions at the collection point impact the evolution of the population (Allard, 1996). Several studies have demonstrated the importance of eco-geographic characterisation when identifying plant eco- types. For instance, eco-geographic variables correlated with heading days, ripening days, height of plant, harvest index and volumetric weight in barley landraces (Endresen, 2010). In barley and wheat landraces eco-geographic parameters correlated with reaction to net blotch
and stem rust diseases, respectively (Endresen et al., 2011). Horsegram landraces collected
from varying altitudes in the Himalayan region showed significant genotypic variations,
following altitudinal gradients (Gupta et al., 2010). These variations of different traits, with
environmental conditions for their survival; and this pattern could be further explored during identification of unique germplasm for crop improvement.
Although eco-geographic variables have a direct effect on crop adaptation, data availability is limited in most genebanks, including the Malawi Plant Genetic Resources Centre. The
development of DIVA-GIS software for the management of germplasm (Hijmans et al.,
2001; 1999) and the availability of climatic data from www.worldclim.org (Hijmans et al.,
2005) have accelerated the extraction of both geographic and environmental data that are not readily available in the collections. Although such tools are available, their application in classifying germplasm has not been fully explored, due to limited capacity in most genebanks. This study characterised cowpea germplasm from Malawi, based on both geographic and environmental conditions at the collection points. The aims of the study were:
a) To identify potential germplasm adapted to drought conditions;
b) To identify gaps in the collection for future targeted collecting missions;
c) To identify potential sites for on-farm conservation of cowpea.