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

Abstract

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 (GA₃) was applied exogenously. After the 45 days of planting, tomato plants were sprayed with GA₃ at concentrations of 25, 50, 75, and 100 mg L^-1, whereas untreated plants were kept as control. Under both temperature conditions, shoot and root biomass was greatest in 'Roma' plants receiving 75 mg L^-1 GA₃, followed by 50 mg L^-1 GA₃. Maximum CO₂ index, photosynthetic rate, transpiration rate, and greenness index were recorded in 'Roma' plants cultivated at 25 °C, demonstrating good effects of GA₃ on tomato physiology. Likewise, GA₃ enhanced the proline, nitrogen, phosphorus, and potassium levels in the leaves of both genotypes at both temperatures. Foliar-sprayed GA₃ up to 100 mg L^-1 alleviated the oxidative stress, as inferred from the lower concentrations of MDA and H₂O_2, and boosted the activities of superoxide dismutase, peroxidase, catalase. The difference between control and GA₃-treated heat-stressed plants suggests that GA₃ may have a function in mitigating heat stress. Overall, our findings indicate that 75 mg L^-1 of GA₃ is the optimal dosage to reduce heat stress in tomatoes and improve their morphological, physiological, and biochemical characteristics.

Figure 1

Physiological variables of tomato as affected by temperature, genotype and exogenous application of GA₃. According to Tukey's honestly significant difference test, the same letters suggest that there is no statistically significant difference between treatments (p ≤ 0.05). Vertical bars indicate average ± standard error (n = 4, 5 plants per replicate).

Figure 2

Proline content of tomato as affected by temperature, genotype and exogenous application of GA₃. According to Tukey's honestly significant difference test, the same letters suggest that there is no statistically significant difference between treatments (p ≤ 0.05). Vertical bars indicate average ± standard error (n = 4, 5 plants per replicate).

Figure 3

Leaf minerals concentration of tomato as affected by temperature, genotype and exogenous application of GA₃. According to Tukey's honestly significant difference test, the same letters suggest that there is no statistically significant difference between treatments (p ≤ 0.05). Vertical bars indicate average ± standard error (n = 4, 5 plants per replicate).

Figure 4

Oxidative stress indicators of tomato as affected by temperature, genotype and exogenous application of GA₃. According to Tukey's honestly significant difference test, the same letters suggest that there is no statistically significant difference between treatments (p ≤ 0.05). Vertical bars indicate average ± standard error (n = 4, 5 plants per replicate).

Figure 5

Activities of antioxidant enzymes in tomato as affected by temperature, genotype and exogenous application of GA₃. According to Tukey's honestly significant difference test, the same letters suggest that there is no statistically significant difference between treatments (p ≤ 0.05). Vertical bars indicate average ± standard error (n = 4, 5 plants per replicate).

Figure 6

Correlation analysis among GA₃ treatments and various morphological, physiological, and biochemical variables of tomato cv. ‘Ahmar’ and ‘Roma’ under heat stress.

Figure 7

Weather conditions during the experiment.