The Effects of Genotype and Irrigation Regime on PSII Heat Tolerance in Cotton

Abstract

Aims: Differences in tolerance to drought and heat stresses exist among cotton species and between modern and obsolete genotypes. However, it is not clear if increases in thermostability under water deficit are associated with genotypic differences in drought tolerance. Therefore, the objective was to identify differences in heat tolerance and physiological acclimation of contrasting cotton genotypes under water-deficit stress and recovery conditions. Study Design: The experimental design was a randomized complete block design with five replications. Treatments consisted of three cotton genotypes, DeltaPine (DP) 0912 B2RF, Pima 32, and Siokra L23 and two water regimes, a well-watered control and a water-stressed treatment. Place and Duration of Study: The experiment was conducted in 2012, and repeated in 2013, at the Altheimer Laboratory, University of Arkansas in Fayetteville, Arkansas. Methodology: Heat tolerance was assessed through maximum quantum yield of Photosystem II at temperatures 25°C to 45°C and measurements of stomatal conductance were also performed. Results: Differences (P = .05) in heat tolerance and physiological acclimation exist among the genotypes under water-deficit stress and recovery conditions. Pima 32 showed higher heat tolerance and improved stomatal conductance at recovery. Siokra L23 was relatively heat sensitive and showed moderate recover in stomatal conductance after plants were re-watered. DP 0912 was the least heat tolerant. Conclusion: Thermostablity under water-deficit stress was associated with drought tolerance of genotypes, with Pima 32 having the highest heat tolerance acclimation in response to water-deficit stress, followed by Siokra L23 and DP 0912.