Screening cotton varieties (Gossypium hirsutum L.) for heat tolerance under field conditions

Fifteen upland cotton Gossypium hirsutum L., were evaluated for heat tolerance based on agronomical and physiological characteristics under field conditions where temperature exceeded 40°C in July and August. Genotypes showed statistically significant differences for stomatal conductance, photosynthetic yield, fluorescence, photosynthetically active radiation (PAR), seed cotton yield, plant height, boll weight, seed cotton weight, number of seeds per boll and 100 seed weight. In the study, relative cell injury level (RCIL), ranged from 54.56 to 79.44% and stomatal conductance ranged from 264.86 to 570.50 mol m-2s-1. Associations between investigated traits indicated that there were some positive correlations. These data indicated that photosynthetic yield, fluorescence, chlorophyll content (SPAD value), cell membrane thermostability (CMT), plant height and number of bolls per plant can be used for improving seed cotton yield. However, among these measurements CMT, SPAD value and fluorescence were more practical in large breeding trials. The results showed that AGC 375 and AGC 208 cotton varieties had lower relative cell injury level (higher cell membrane thermostability) and higher seed cotton yield and photosynthetic yield than other investigated varieties