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

High night temperatures during reproductive development can reduce yields of 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 available. An indirect screening technique was evaluated involving relative electrolyte leakage from leaf tissue sampled at the end of the dark period with incubation at temperatures that are hot for night-time conditions. This technique was tested with four different pairs of cowpea lines with similar genetic backgrounds but different heat sensitivities during reproductive development. Plants were grown in growth chambers at optimal temperatures. Additional tests were conducted with plants grown in moderately hot and extremely hot field environments. Three sets of three genotypes were used that are 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 differences in electrolyte leakage were obtained from plants grown in the growth chamber or field environments. Genotypes with heat tolerance during flowering 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 measure of leaf membrane thermostability, may provide an efficient indirect screening technique for reproductive-stage heat-tolerance genes that can be used with plants grown in a range of field nursery environmental.