Chilling Tolerance during Emergence of Cowpea Associated with a Dehydrin and Slow Electrolyte Leakage
- A. M. Ismail,
- A. E. Hall and
- T. J. Close
Seeds of annualw arms eason 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°C) compared with more favorable (28°C) 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−, 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-11 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.
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