Delayed-leaf-senescence and heat-tolerance traits mainly are independently expressed in cowpea

Reproductive activity in cowpea [Vigna unguiculata (L.) Walp.] is characterized by two separate flushes of pod production. Grain yield from the second push strongly depends on extent of plant death due to soil pathogens after the first push is completed. A delayed-leaf-senescence (DLS) trait enhances the extent of plant survival but may reduce first-flush grain yield. Heat tolerance during reproductive development can increase first-flush grain yield and has been incorporated into cowpea but may reduce plant survival after the first push is completed. Interactive effects when combining DLS and heat-tolerance traits were evaluated. A cross was made between a DLS heat-susceptible line and a non-DLS beat-tolerant line. Evaluation and selection for these traits were carried out over several generations and a set of 40 lines with 10 each of the four combinations of DLS +/- heat tolerance and non-DLS +/- heat tolerance was developed. These lines were evaluated in contrasting field environments. Under senescence-inducing conditions, the DLS trait greatly increased plant survival and individual seed size, and it only caused a small reduction in first-flush grain yield that would have been off-set several fold by an enhanced second-bush gain yield. The heat-tolerance trait increased first-flush grain yield in very hot environments and only slightly enhanced the tendency for premature plant death in non-DLS lines with no effect on lines having the DLS trait. The DLS and heat-tolerance traits can be effectively incorporated into cowpea and would have beneficial effects on grain yield in specific circumstances with only small detrimental interactive effects.