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Heat and Chilling Tolerance during Germination and Heat Tolerance during Flowering Are Not Associated in Cowpea

Dep. of Botany and Plant Sciences, Univ. of California, Riverside, CA 92521-0124

Awatif A. Mohsen

Dep. of Botany, Faculty of Science, Tanta Univ., Tanta, Egypt

^* Corresponding author (E-mail: anthony.hall{at}ucr.edu).

Warm season crops can be stressed by either chilling or hot temperatures; however, breeding may overcome these problems. Studies were conducted to determine whether cowpea [Vigna unguiculata (L.) Walp.] genotypes differing in heat tolerance during flowering also differed in germination at chilling or hot temperatures. Genotypic differences in germination were detected at 15.5 ± 0.5°C and 38.5 ± 0.5°C. Leakage of electrolytes, carbohydrates, and amino acids were quantified during germination at chilling and at intermediate (25°C) and hot temperatures. Six closely related pairs of lines differing in heat tolerance during flowering did not consistently differ in either chilling or heat tolerance during germination. Genotypic differences in germination ability at chilling and hot temperatures were not associated. With chilling, genotypes differed in rate but not in maximal percentage germination, and rates of germination and leakage were negatively associated. With hot temperature, genotypic differences were in maximal percentage germination and these differences were not associated with differences in leakage. Leakage rates of electrolytes, carbohydrates, and amino acids were positively correlated and were very high under chilling and only slightly higher under hot compared with intermediate temperature. The mechanisms and presumably the genes involved in tolerance to chilling and heat during germination appear to differ and be different from the genes that confer heat tolerance during flowering. Consequently, it should be possible to breed cowpea cnltivars with both chilling tolerance during germination and heat tolerance during flowering for use in subtropical zones and different cnltivars with heat tolerance during both germination and flowering for use in tropical zones.

Received for publication March 8, 1996.