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Cowpea varieties for drought tolerance
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Success in breeding for cowpea with drought tolerance has not been as pronounced as for many other traits. This is partly due to lack of simple, cheap, and reliable screening methods to select drought-tolerant plants and progenies from the segre gating populations and partly due to the complexity of factors involved in drought tolerance. Measuring drought tolerance using physiological parameters is expen sive, time consuming, and difficult to use for screening large numbers of lines and segregating populations. Since several factors and mechanisms (in shoots and roots) operate to enable plants cope with drought stress, drought tolerance appears as a complex trait. However, if these factors and mechanisms can be separated and investigated individually, they may be easier to manipulate by breeders. We have developed a simple "box screening method" for shoot drought tolerance in cowpea, which eliminates the effects of roots and permits nondestructive visual identifica tion of shoot dehydration tolerance. Alongside this, we have also developed a "root-box pin-board" method to study the two-dimensional root architecture of individual plants. Using these methods, we have identified two mechanisms of shoot drought tolerance in cowpea, which are controlled by single dominant genes as well as major differences for root architecture among cowpea varieties. Combin ing deep and dense root systems with shoot dehydration tolerance offers the opportunity to breed and select for highly drought-tolerant plants.