Influence of High Temperatures on Gas Exchange Rate and Growth of Eight Tomato Cultivars under Controlled Heat Stress Conditions

Eight tomato cultivars of different origin were evaluated for heat tolerance. Plants were grown in growth chambers under two temperature regimes (37/27 degrees C or 37/22 degrees C day/night). Variations in leaf gas exchange rate as well as the vegetative growth and reproductive development in response to heat stress were investigated. Heat tolerant cultivars showed higher photosynthetic rate under heat stress conditions at the different growth stages in comparison to the heat sensitive ones. Photosynthetic rate increases from the vegetative stage, peaks at the flowering and declines at the late fruiting stage. The reproductive processes in tomato were more sensitive to high temperatures than the vegetative ones. Number of pollen grains, fruit set percentage and fruits fresh weight produced by the heat tolerant cultivars were higher than those produced by the heat sensitive ones. Night temperature had an effect on the number of pollen grains produced and released and fruit set percentage. A positive correlation between the photosynthetic rate and fruit set was observed.