Reproductive-stage heat tolerance, leaf membrane thermostability and plantmorphology in cowpea

High night temperatures during reproductive development can reduce yields o f cowpea [Vigna unguiculata (L.) Walp.]. Screening whole plants for degree of flowering and pod set in hot environments has been effective in breeding for heat tolerance, but suitable screening environments often are not avai lable. An indirect screening technique was evaluated involving relative ele ctrolyte leakage from leaf tissue sampled at the end of the dark period wit h incubation at temperatures that are hot for night-time conditions. This t echnique was tested with four different pairs of cowpea lines with similar genetic backgrounds but different heat sensitivities during reproductive de velopment. Plants were grown in growth chambers at optimal temperatures. Ad ditional tests were conducted with plants grown in moderately hot and extre mely hot field environments. Three sets of three genotypes were used that a re either heat susceptible during both early flowering and pod set or heat tolerant during early flowering and heat susceptible during pod set or heat tolerant during both early flowering and pod set. Similar genotypic differ ences in electrolyte leakage were obtained from plants grown in the growth chamber or field environments. Genotypes with heat tolerance during floweri ng and pod set had less leaf electrolyte leakage than either genotypes with heat susceptibility during flowering and pod set or genotypes having heat tolerance only during early flowering. Leaf electrolyte leakage, as a measu re of leaf membrane thermostability, may provide an efficient indirect scre ening technique for reproductive-stage heat-tolerance genes that can be use d with plants grown in a range of field nursery environmental.