POSITIVE AND POTENTIAL NEGATIVE EFFECTS OF HEAT-TOLERANCE GENES IN COWPEA

Hot weather can cause reductions in crop yield. Cowpea [Vigna unguicul ata (L.) Walp.] is sensitive to high night temperature during reproduc tive development, but genotypes with heat tolerance have been develope d. Positive and potential negative effects of the heat-tolerance genes were evaluated in contrasting field environments. Six pairs of cowpea lines with differences in heat tolerance during reproductive developm ent but similar genetic backgrounds mere grown in eight field environm ents with average night temperatures ranging from cool (17 degrees C) to very hot (28 degrees C). Heat susceptible genotypes exhibited a 12% decrease in first-flush grain yield per degree centigrade increase in average night temperature above 20 degrees C because of decreases in pod set and harvest index. Heat-tolerance genes progressively enhanced first-flush grain yields by increasing pod set on main-stem nodes and enhancing the overall partitioning of carbohydrates into grain with i ncreases in average night temperature above 20 degrees C. Heat-toleran ce genes (or closely linked genes) also had a progressive dwarfing eff ect, mainly resulting from shorter main-stem internodes and involving reduced shoot biomass production, with increases in average night temp erature above 15 degrees C. Heat-tolerance genes slightly enhanced the extent of premature plant senescence occurring just after the first f lush of pods was produced. Second-flush grain yields mere positively c orrelated with the percentage of plants that survived after producing the first flush of pods. The value of the heat-tolerance genes is disc ussed with respect to their positive effects on reproductive developme nt and solutions to potential negative effects due to dwarfing are con sidered.