Heat tolerance of upland cotton during the fruiting stage evaluated using cellular membrane thermostability

Abstract

Excessively high temperature during the reproductive stage significantly reduces yield in cotton. The cellular membrane thermostability (CMT) assay indirectly measures integrity of cellular membranes through quantifying electrolyte leakage following heat treatment. Higher CMT has been related to heat tolerance and higher yields in several crop species, but its utility and relationship with seed cotton yield (SCY) is not well established. Experiments were carried out in the greenhouse and in the field under optimum and high temperature regimes, to assess the response of upland cotton to CMT. Upland cotton cultivars as well as hybrids differed significantly ( P<0.01) for CMT. Although the temperature regimes modified the relative ranking of the cultivars and hybrids, heat-tolerant and susceptible groups remained quite stable. Cultivars FH-900, MNH-552, CRIS-19, and Karishma emerged as relatively heat-tolerant (thermostable) and FH-634, CIM-448, HR109-RT and CIM-443 as heat-susceptible. Exposure to high temperature prior to the CMT test produced better distinction between heat-tolerant and heat-susceptible cultivars and hybrids. The relationship between CMT and SCY was stronger among cultivars than among hybrids. The regression analysis indicated higher SCY due to higher CMT in the presence of heat stress. CMT was positively related to SCY under supra-optimum greenhouse conditions as well as early and late field regimes. Under optimum (non-stressed) greenhouse conditions, however, CMT was negatively related to SCY, indicating that susceptible cultivars and hybrids produced higher yields in the absence of heat stress. This also implied that in upland cotton these two traits were independent of each other, the presence or absence of heat stress determined their relationship. The differential ability of cotton cultivars and hybrids to adjust to CMT under heat-stressed conditions points towards physiological adaptation to heat stress or heat hardening in upland cotton. It was concluded that CMT could be a useful technique for differentiating heat-tolerant and susceptible cottons, however, its indirect selection on the basis of SCY under non-heat-stressed environments must be implemented with caution.