Influence of 4-CPA and GA₃ on physiological, biochemical and yield attributes of tomato under high-temperature conditions

Abstract: The present research investigated the impact of plant growth regulators in mitigating the effects of heat stress in tomato (Solanum lycopersicum L.) genotype LST-6 and cultivar Punjab Varkha Bahar-4. In north India, the temperature in the summer season ranges between 25-45 ?C and temperature above 28?C leads to heat stress in plants and negatively affects the reproductive stage of plants. Considering this, we subjected the plants to varying concentrations of GA₃ (10, 20, 30 µg/mL) and 4-CPA (15, 45, 75 µg/mL). GA₃ application took place three weeks after transplanting, while 4-CPA was administered during the anthesis stage. We recorded observations from both control and treated plants, with a 10-day gap between each spray treatment. The application of plant growth regulators (PGRs) enhanced the plants’ ability to withstand high temperatures by improving photosynthetic efficiency, as evidenced by increased chlorophyll and carotenoid levels in the leaves. The level of different biochemical constituents (total protein, starch, total soluble sugars, phenol and proline content) also increased in PGRs treated plants. Application of GA₃ and 4-CPA also enhanced the membrane thermostability and reduced lipid peroxidation. The PGRs treated plants exhibited increased plant height, leaf area, pollen viability, fruit set, number of fruits per plant and fruit weight, ultimately improving yield. GA₃ and 4- CPA application also increased the total soluble solids, lycopene content and titratable acidity in tomato fruits. Thus, overall improvement was observed with the application of PGRs; however, 75µg /mL 4-CPA was most effective in imparting thermo tolerance.