Morpho-physiological improving effects of exogenous glycine betaine on tomato (Lycopersicum esculentum Mill.) cv. PS under drought stress conditions

Drought stress reduces the yield and production of tomato (Lycopersicum esculentum Mill.). Tomato does not naturally accumulate glycinebetaine (GB) in the cells under natural conditions. Effects of exogenous glycinebetaine on some morpho-physiological characteristics of Lycopersicum esculentum Mill. cv. PS was evaluated at different levels of drought stress. The experiment was conducted in a factorial design based on completely randomized block design (RCBD) with four replications. Seeds were germinated and arranged in pot conditions. Plants were watered weekly, bi-weekly and tri-weekly once as drought stress and irrigation was based on 100% of field capacity (FC). Exogenous glycinebetaine was applied as foliar at three levels (0, 5 and 10 mM) in three stages with 10 days interval. Root length, leaves number, total leaf fresh weight, total leaf dry weight, leaf area index, relative water content (RWC), and stress tolerance index (STI) were analyzed in the vegetative stage. Moreover, flowering number, fruit number and fruit weight were recorded during reproductive period. Results showed that the vegetative growth parameters [shoot height (maximum; 59.75 cm, minimum; 40.25 cm), root length (highest; 58.25 cm, lowest; 38.25 cm), leaf number (largest; 47.50, lowest; 16.50), leaf area (most; 819.21 mm, least; 305.63 mm)] and physiological characteristics [total shoot fresh weight (maximum; 52.68 g, minimum; 48.23 g), total shoot dry weight (maximum; 51.18 g, minimum; 36.67 g), relative water content (highest; 47.08, lowest; 25.95) and stress tolerance index (highest; 1.220, lowest; 0.548)] decreased with the increment of drought stress. In addition, all the above mentioned traits increased (70%, 73%, 187%, 193%, 168%, 9%, 72% and 122%, respectively) by exogenous application of glycinebetaine, significantly. Reproductive growth parameters [the number of flower (largest; 46, least; 23), fruit number (largest; 45, least; 22) and weight of fruit (maximum; 34, minimum; 20)] decreased under drought stress and increased significantly by 86%, 115% and 125%, respectively under exogenous application of glycinebetaine. Based on studied reproductive growth parameters in two levels of drought stress, the 10 mM exogenous glycinebetaine was the best treatment and recommended to alleviate effects of drought condition.