Foliar Application of a Mixture of Exogenous Substances Induces Tolerance to Drought Stress in Tea [Camellia sinensis (L.) O. Kuntze] Plants
摘要
Drought is one of the main factors limiting the yield and quality of green leaves in tea plants. Our study aimed to investigate the effects of various exogenous substances on the modulation of the physiological and biochemical responses to drought stress in tea plants cv. Kashef. To mimic the rainfalls recorded in the Guilan province (north of Iran), drought stress was applied for 40 days (June 3—July 11, 2022). The effects of the foliar application of exogenous substances, including melatonin (300 µM), nutrients (2% potassium chloride + 0.1% zinc sulfate + 0.1% magnesium sulfate + 0.025% boric acid + 0.05% amino acid arginine), carboxymethyl chitosan (100 mg L−1), melatonin + nutrients, carboxymethyl chitosan + nutrients, and salicylic acid (0.02%), were investigated and compared to the control condition (i.e. drought stress, without any foliar application) to determine the tolerance of 15-year-old tea plants cv. Kashef to drought stress. The results showed that under drought stress conditions, foliar application of melatonin significantly increased the relative water content of leaves, chlorophyll and carotenoid content, proline content, and antioxidant enzyme activities of catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) compared to the control. On the contrary, it significantly decreased malondialdehyde levels compared to the control. Furthermore, foliar application of melatonin + nutrients increased green leaf yield total protein content, antioxidant enzyme activity, and chlorophyll stability index in response to drought stress. Our data show that foliar application of melatonin or melatonin + nutrients can be a suitable strategy to increase the growth and yield of tea plants under drought stress.