Genetic variation for stomatal conductance in upland cotton as influenced by heat-stressed and non-stressed growing regimes.

摘要

Stomatal conductance is an important heat avoidance mechanism and its association with higher yield and heat resistance has been established in Pima cotton. Experiments were carried out on upland cotton (Gossypium hirsutum) under heat-stressed and non-stressed greenhouse and field regimes in Faisalabad (Pakistan) to understand the impact of heat-stressed and non-stressed environments on the genetic and combining ability variations for stomatal conductance. The experimental material comprised 8 upland cotton cultivars and their 15 F1 cross combinations obtained in a line x tester mating arrangement. The results showed high genetic variability for stomatal conductance in a single environment, but low genetic variability across environments, due to higher magnitude of the environmental interaction, especially that caused by temperature regimes. The interaction effect of temperature regimes also substantially modified general and specific combining ability variations for stomatal conductance. The relative contributions of general and specific combining abilities to total phenotypic variation for stomatal conductance also underwent a great change across field temperature regimes. The non-stressed regime favoured the expression of genes causing the additive type of genetic variability. The heat-stressed field regime, however, favoured the expression of both additive and non-additive types of genetic variation for stomatal conductance in upland cotton. Recurrent selection for the accumulation of favourable genes for general combining ability under non-stressed conditions was suggested for improving stomatal conductance in applied cotton breeding programmes.