Genetics and Heritability of Shoot Drought Tolerance in Cowpea Seedlings

Abstract

ABSTRACT Phenotyping a large population of breeding lines for drought tolerance is time consuming and often unreliable due to multiple possible mechanisms involved. In cowpea ( Vigna unguiculata L. Walp), a box‐screening method was used to accelerate phenotyping of shoot drought tolerance in cowpea seedlings. This reduces the confounding effects of adaptive root traits by restricting root growth and provides a homogeneous soil moisture environment across genotypes. Nonetheless, multiple mechanisms of shoot drought tolerance have been reported which further complicate phenotyping. The objective of this study was to determine the most reliable indicators of shoot drought tolerance using the box screening method and to explore genetic basis and heritability of two mechanisms of shoot drought tolerance previously reported in cowpea. Trifoliate necrosis was found to be the most reliable indicator of overall shoot drought tolerance in cowpea seedlings. Stem diameter was highly correlated with unifoliate and trifoliate necrosis but not well correlated with resistance to wilting, suggesting that carbohydrates stored in the stem may help to mitigate water stress. A unifoliate stay‐green trait was discovered that segregates as a single recessive gene. However, it did not cosegregate with resistance to trifoliate necrosis, therefore it is unlikely to confer drought tolerance, and it does not appear to be related to the single dominant gene for drought tolerance previously reported.