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The effect of high temperature on ability of cowpea [Vigna unguiculata (L.) Walp.] to set pods was investigated under field conditions and in controlled environments. During hot weather in the Imperial Valley, Calif., the cowpea strains TVu 4552, PI 204647, and ‘Prima’ produced substantial numbers of pods, while 55 other strains produced no or few pods, even though they produced numerous open flowers. Studies in growth chambers demonstrated that TVu 4552 has greater tolerance to high night and high day temperatures at flowering than the California cultivar, ‘California Blackeye No. 5’ (CBS), whereas Prima is intermediate. Susceptibility to high temperatures was associated with low pollen viability and indehischent anthers for CB5 and with anther indehiscence for Prima. Artificial pollination demonstrated that pistil viability of all three genotypes was not significantly affected by high temperature. Thus, the flower abscission observed with CB5 and Prima at high temperatures was mainly caused by male sterility. In addition, substantial levels of embryo abortion were observed with CB5 and Prima at high day temperatures. Apparently, Imperial Valley provides a suitable field environment during the summer for screening cowpeas for heat tolerance. This environment is presently being used to screen the segregating populations from crosses designed to incorporate the heat tolerance of TVu 4552 and Prima into genetic backgrounds suitable for the tropics and subtropics.

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