Heat-stress effects on dry matter partitioning, pollen viabilityand fruit yield in tomato genotypes

Heat-stress is one of the most important limiting factors for crop productivity under sub-tropical conditions, mainly because of its adverse effects on photosynthetic efficiency and pollen fertility. However, induction of heat shock proteins during heat-stress helps the plant to tolerate high temperature. In the present study, we evaluated four tomato genotypes viz. CLN 2026E, UC 204A, Suncherry extra and Ailsa Craig for their heat-stress response at different growth stages. The mitochondrial small heat shock proteins (MT-sHSPs) were expressed in leaves of all the four genotypes when the plants were exposed to 38°C for 4 hours. The flowers of CLN 2026E and Suncherry extra started accumulating MT-sHSP within one hour of exposure to 38°C, however, we observed expression of MT-sHSP in CLN 2026E flowers under heat-stress (35/27°C, day/night temperatures) conditions. The genotypes CLN 2026E and Ailsa Craig had significantly higher cell membrane thermostability at high temperature. These genotypes also showed comparatively less reduction in fruit yield at 35/27°C day-night temperatures. Significant reduction in pollen fertility of genotypes UC204A and Suncherry extra was observed during heat-stress. These genotypes did not show in vitro pollen germination at 35°C, indicating their sensitivity to high temperature. On the other hand pollen of genotypes CLN 2026E and Ailsa Craig germinated well at 35°C and also even at 40°C little germination was observed, providing the evidence of thermotolerance.