Chilling tolerance during emergence of cowpea associated with a dehydrin and slow electrolyte leakage

Seeds of annual warm season crops are sensitive to chilling temperatures during emergence often encountered during spring sowings in subtropical regions, Mechanisms for genotypic differences in emergence of cowpea [Vigna unguiculata (L.) Walp.] seedlings were investigated under chilling field and controlled growth chamber conditions. Rate of emergence was slower and extent of maximal emergence was less under chilling (15 degrees C) compared with more favorable (28 degrees C) soil temperatures. Under chilling conditions, deeper sowing (7.5 vs. 2.5 cm) resulted 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 seeds at moisture contents of 120 and 150 g kg(-1), which had similar emergence. In all studies under chilling conditions, cowpea line 1393-2-11 consistently attained greater maximal percentage emergence than the genetically similar line 1393-2-1. A 35-kDa dehydrin protein [late embryogenesis abundant (LEA) D-ll family] was found in 1393-2-11 seeds that was absent in 1393-2-1, and leakage of electrolytes during seed imbibition at low temperature was slower from 1393-2-11 seeds. Studies with reciprocal hybrids indicated nuclear inheritance and a dominant effect for the gene controlling the presence of the dehydrin, and a maternal effect on the extent of electrolyte leakage from seeds at chilling temperature. An additive model was developed for the dependence of the chilling tolerance of 1393-2-11 on the presence of the dehydrin (positive 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 hybrids.