Genotypic variation in growth, single leaf physiology, and acclimation potential of thylakoid processes in cotton exposed to high temperature extremes

Abstract

The cotton crop already experiences yield-limiting high temperatures during the growing season, which are predicted to worsen in a changing climate. This makes the identification of heat tolerant cultivars that can acclimate to high temperature conditions a necessity. The objective of this study was to assess the effects of growth temperature and genotype on plant growth, single-leaf physiology, and thermotolerance of thylakoid processes for cotton exposed to optimal and supra-optimal temperature conditions. A diverse collection of cotton cultivars was selected based on previously documented differences in thylakoid-specific thermotolerance, and they were exposed to optimal (30/20 C) and two supra-optimal growth temperatures (35/25 and 40/30 °C). There was a significant interaction between genotype (G) and growth temperature (T) for all growth measures (leaf area, mainstem node production, and plant dry weight), photosynthetic rates, nighttime respiration and stomatal conductance, and thermotolerance of photosystem II. Greater relative growth (plant dry matter) under high temperature was strongly and positively correlated with leaf area and strongly and negatively correlated with nighttime respiration and stomatal conductance. In contrast, photosynthetic parameters were not significantly associated with genotypic variation in growth-specific thermotolerance. Thermotolerance of the thylakoid reactions was not consistently associated with more thermotolerant growth. We conclude that genotypes with heat tolerant vegetative growth have higher relative leaf area and lower relative values for nocturnal respiration and stomatal conductance under high temperature conditions.