Cowpea, Vigna unguiculata (L.), is an important grain legume grown in the tropics where it constitutes a valuable source of protein in the diets of millions of people. Some abiotic and biotic stresses adversely affect its productivity. A review of the genetics, genomics and breeding of cowpea is presented in this article. Cowpea breeding programmes have studied intensively qualitative and quantitative genetics of the crop to better enhance its improvement. A number of initiatives including Tropical Legumes projects have contributed to the development of cowpea genomic resources. Recent progress in the development of consensus genetic map containing 37,372 SNPs mapped to 3,280 bins will strengthen cowpea trait discovery pipeline. Several informative markers associated with quantitative trait loci (QTL) related to desirable attributes of cowpea were generated. Cowpea genetic improvement activities aim at the development of drought tolerant, phosphorus use efficient, bacterial blight and virus resistant lines through exploiting available genetic resources as well as deployment of modern breeding tools that will enhance genetic gain when grown by sub-Saharan Africa farmers.
Abstract. Water deficit is the main yield-limiting factor across the Asian and African semiarid tropics and a basic consideration when developing crop cultivars for water-limited conditions is to ensure that crop water demand matches season water supply. Conventional breeding has contributed to the development of varieties that are better adapted to water stress, such as early maturing cultivars that match water supply and demand and then escape terminal water stress. However, an optimisation of this match is possible. Also, further progress in breeding varieties that cope with water stress is hampered by the typically large genotype  environment interactions in most field studies. Therefore, a more comprehensive approach is required to revitalise the development of materials that are adapted to water stress. In the past two decades, transgenic and candidate gene approaches have been proposed for improving crop productivity under water stress, but have had limited real success. The major drawback of these approaches has been their failure to consider realistic water limitations and their link to yield when designing biotechnological experiments. Although the genes are many, the plant traits contributing to crop adaptation to water limitation are few and revolve around the critical need to match water supply and demand. We focus here on the genetic aspects of this, although we acknowledge that crop management options also have a role to play. These traits are related in part to increased, better or more conservative uses of soil water. However, the traits themselves are highly dynamic during crop development: they interact with each other and with the environment. Hence, success in breeding cultivars that are more resilient under water stress requires an understanding of plant traits affecting yield under water deficit as well as an understanding of their mutual and environmental interactions. Given that the phenotypic evaluation of germplasm/breeding material is limited by the number of locations and years of testing, crop simulation modelling then becomes a powerful tool for navigating the complexity of biological systems, for predicting the effects on yield and for determining the probability of success of specific traits or trait combinations across water stress scenarios.
This is author version post-print archived in the official Institutional Repository of ICRISAT www.icrisat.orgTerminal drought tolerance implies that plants have enough water to fill grains. Water saving traits, measured in tolerant and sensitive cowpea lines, showed that tolerant lines have developed several constitutive mechanisms, closely related to one another, which reduces the rate of water use and delay drought effects. This opens the possibility to decipher their genetic basis towards the development of drought tolerant cowpea cultivars. conditions and restricted TR more than sensitive lines under high VPD. Under WS conditions, transpiration declined at lower FTSW in tolerant than in sensitive lines. Tolerant lines also maintained higher TR and CTD under severe stress than sensitive lines. TE was higher in tolerant than in sensitive genotypes under WS conditions. Significant and close relationships were found between TR and TE, CTD, and FTSW in both environments under different water regime conditions. In sum, traits that condition how genotypes manage limited water resources discriminated tolerant and sensitive lines. Our interpretation is that a lower canopy conductance limits plant growth and plant water use, and allows tolerant lines to behave like non-stressed plants until the soil is drier and maintains a higher transpiration under severe stress. A lower TR at high VPD leads to higher transpiration efficiency.
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