The effect of foliar potassium silicate, glycine betaine and salicylic acid application on drought resistance, yield and quality of black magic grape variety under limited water application

This thesis was conducted to investigate the effects of glycine betaine, potassium silicate, and salicylic acid applications on mitigating drought problems in vineyards caused by limited water resources due to climate change induced by global warming. The study examined the effect of foliar applications of potassium silicate (0.1% and 0.2%), glycine betaine (25 mM and 50 mM), and salicylic acid (1 mM and 2 mM) on grape yield, quality, and ecophysiological characteristics in the Black Magic grape variety. These applications were performed twice: at fruit set and at the beginning of veraison under non-irrigated (Rainfed-only receiving rainfall) and deficit irrigation (50% of full irrigation) conditions. According to the findings, the 50% irrigation treatment generally resulted in the highest yield (9451 g/vine), cluster weight (295.4 g), cluster width (11.93 cm), cluster size (216.3 cm²), berry length (26.66 mm), berry width (17.94 mm), berry size (478.7 mm²), and berry detachment force (326.3 g). The highest total soluble solids (TSS) and acidity values (18.27% and 0.424 g 100 mL⁻¹, respectively) were obtained from the non-irrigated treatment. Among the biostimulant applications, all treatments except for the 2 mM salicylic acid application resulted in higher yield and cluster weight compared to the control. The highest TSS was observed with the 0.2% potassium silicate treatment, while the highest maturity index was recorded with the 1 mM salicylic acid treatment. Leaf water potential measurements during the ripening period showed that all biostimulant applications resulted in higher values than the control (-13.71 bar). In terms of the interaction between irrigation and biostimulant applications, the highest yield and cluster weight (11146 g/vine and 348.3 g, respectively) were obtained with the 50% irrigation + 1 mM salicylic acid combination, while the highest berry detachment force (337.5 g) was observed with the 50% irrigation + 0.1% potassium silicate combination. In conclusion, the combination of 50% irrigation and biostimulant applications was found to be effective in enhancing drought tolerance. It is suggested that future studies should explore the effects of different biostimulants and their varying concentrations.