Estimation of Optimum Temperature for the Determination of CELL Membrane Thermostability in Corn and Bean.

Identification of plant tolerance to heat requires novel strategies for measuring plant responses to this stress.  Leaf electrolyte leakage is an indirect method that can be utilized as a selection criteria for heat tolerance in plants, but it has to be adapted to each species.  The objective of this study was to measure heat-induced leaf electrolyte leakage in corn and bean in order to determine heat tolerant genotypes and also to establish the optimal developmental stage for use of electrolyte leakage as a selection criteria.  This study included two genotypes of corn (Zea mays L.) and two genotypes of bean (Phaseolus vulgaris L.) measured during both vegetative and floral stages.  Heat treatments included 40, 50, and 60°C applied to leaf discs for a duration of 60 minutes.  Electrolyte leakage estimated as Percent relative cell injury (RCI) was used as a criteria for cellular membrane thermostability.  Results showed that the greatest amount of membrane electrolyte leakage occurred during flowering for both corn and bean and the amount of leakage correlated with genotype tolerance to heat.  The temperature which caused the greatest electrolyte leakage depended on the species, 50°C for bean and 60°C for corn.  Our results indicate that use of membrane thermostability measured as electrolyte leakage is an effective criteria for identifying genotypes tolerant to heat damage during flowering in a genetic improvement program.