Heat stress mitigation in tomato (Solanum lycopersicum L.) through foliar application of gibberellic acid.

Phytohormones mediate physiological, morphological, and enzymatic responses and are important regulators of plant growth and development at different stages. Even though temperature is one of the most important abiotic stressors for plant development and production, a spike in the temperature may have disastrous repercussions for crop performance. Physiology and growth of two tomato genotypes ('Ahmar' and 'Roma') were studied in two growth chambers (25 and 45 °C) when gibberellic acid (GA) was applied exogenously. After the 45 days of planting, tomato plants were sprayed with GA at concentrations of 25, 50, 75, and 100 mg L, whereas untreated plants were kept as control. Under both temperature conditions, shoot and root biomass was greatest in 'Roma' plants receiving 75 mg L GA, followed by 50 mg L GA. Maximum CO index, photosynthetic rate, transpiration rate, and greenness index were recorded in 'Roma' plants cultivated at 25 °C, demonstrating good effects of GA on tomato physiology. Likewise, GA enhanced the proline, nitrogen, phosphorus, and potassium levels in the leaves of both genotypes at both temperatures. Foliar-sprayed GA up to 100 mg L alleviated the oxidative stress, as inferred from the lower concentrations of MDA and HO and boosted the activities of superoxide dismutase, peroxidase, catalase. The difference between control and GA-treated heat-stressed plants suggests that GA may have a function in mitigating heat stress. Overall, our findings indicate that 75 mg L of GA is the optimal dosage to reduce heat stress in tomatoes and improve their morphological, physiological, and biochemical characteristics.