Indian Journal of Plant Physiology

The effect of high temperature on CO₂ fixation was studied in four tomato genotypes, viz. Ailsa craig, Suncherry extra, UCA 204A and CLN 2026E. High temperature adversely affected the CO₂ gas exchange characteristics at the onset of flowering in all the four genotypes but magnitude of response differed. Photosynthetic rate was reduced significantly by heat-stress in genotypes UC 204A and Suncherry extra at early flowering stage (75 DAS) but it did not change in Ailsa craig and CLN 2026E. Significant reduction in photosynthetic rate due to heat-stress was observed during late flowering and ripening stage. The magnitude of reduction, however, was higher in genotypes Suncherry extra and UC 204A. Transpiration rate increased significantly in all the four genotypes at early flowering stage during heat-stress. However, we observed significant decrease in transpiration rate at later growth stages in Suncherry extra and UC 204A and this could be the possible reason for lesser adaptability of these genotypes at high temperature. The stomatal conductance followed same pattern, as of transpiration at flowering stage; however, stomatal conductance was not affected by heat-stress at ripening stage. The internal CO₂ concentration increased in all the four genotypes at flowering stage, however, no significant change in internal CO₂ concentration was noticed during ripening stage at high temperature.