Genetic Variability for Heat Tolerance in Cowpea.

Cowpea is a popular food crop in Texas and other Southern States of USA, and it is a good source of protein, minerals, vitamins, and antioxidants providing good nutrition as well as health benefits. It also contributes to improved soil fertility through atmospheric N-fixation. However, the cultivation of cowpea in the state is declining due to numerous production constraints including drought, heat, and pests. Therefore, a systematic program was initiated to develop improved cowpea varieties with tolerance to heat and drought, and resistance to aphid. A total of 41 cowpea varieties were planted at College Station on June 12, 2011. The temperature in July and August covering the reproductive phase of cowpea was above 100⁰F. This temperature range provided excellent opportunity to screen cowpea varieties for heat tolerance. The differences among varieties became clear after flowering when the heat susceptible lines droped flowers. Notes were taken on different yield components, and flower bud samples were also analyzed for pollen fertility. The results indicated major genetic differences among varieties. The most promising varieties with no damage due to heat were IT82D889-1, IT98K-1111, and IT98K-205-8 in the early maturing group, and IAR-48, IT98K-277-2, and IT98K-1092-1 in the medium maturing group with seed yields ranging from 27 to 52 g/plant. The most heat susceptible lines were IT98K-589-2 and IT86D-1010 in the early group, and Big John, UCR 288, IT98K 1069-6 and IT98K 476-8 in medium maturing group with seed yields ranging from 0 to 0.3 g/plant. All the heat tolerant lines showed normal fertile pollen, and heat susceptible lines had a range of sterile pollens indicating that heat causes pollen sterility and therefore reduced pod set.