CHILLING TOLERANCE DURING EMERGENCE OF COWPEA ASSOCIATED WITH A DEHYDRIN AND SLOW ELECTROLYTE LEAKAGE

Seeds of annual warm season crops are sensitive to chilling temperatur es during emergence often encountered during spring sowings in subtrop ical regions, Mechanisms for genotypic differences in emergence of cow pea [Vigna unguiculata (L.) Walp.] seedlings were investigated under c hilling field and controlled growth chamber conditions. Rate of emerge nce was slower and extent of maximal emergence was less under chilling (15 degrees C) compared with more favorable (28 degrees C) soil tempe ratures. Under chilling conditions, deeper sowing (7.5 vs. 2.5 cm) res ulted in slower as well as less maximal percentage emergence. Reducing seed moisture content to 50 g kg(-1) resulted in decreased percentage emergence and faster electrolyte leakage from seeds compared with see ds at moisture contents of 120 and 150 g kg(-1), which had similar eme rgence. In all studies under chilling conditions, cowpea line 1393-2-1 1 consistently attained greater maximal percentage emergence than the genetically similar line 1393-2-1. A 35-kDa dehydrin protein [late emb ryogenesis abundant (LEA) D-ll family] was found in 1393-2-11 seeds th at was absent in 1393-2-1, and leakage of electrolytes during seed imb ibition at low temperature was slower from 1393-2-11 seeds. Studies wi th reciprocal hybrids indicated nuclear inheritance and a dominant eff ect for the gene controlling the presence of the dehydrin, and a mater nal effect on the extent of electrolyte leakage from seeds at chilling temperature. An additive model was developed for the dependence of th e chilling tolerance of 1393-2-11 on the presence of the dehydrin (pos itive nuclear effect) and the extent of electrolyte leakage from seeds (negative maternal effect), which accounted for 96% of the variation between observed and calculated percentage emergence values of the hyb rids.