Seed priming - induced drought tolerance in Castor: Unravelling the physiological and molecular mechanisms

Castor is an essential nonedible oilseed crop with significant applications in the cosmetic and chemical industries. It is cultivated primarily in rainfed regions, where drought is a common abiotic stress factor. Seed germination, the critical initial stage, is particularly affected by drought. Seed priming with radical scavenging chemicals such as salicylic acid, melatonin, hydrogen peroxide and ascorbic acid has been explored to increase germination under water deficit conditions. This study aimed to evaluate the effects of different concentrations of these chemicals on the physiological and antioxidant enzyme activities of castor under drought stress. Two water regimes were applied in the study. Among the treatments, seed priming with 80 ppm salicylic acid significantly improved key parameters, including the germination % (71 %), speed of germination (4.1 %), vigour index (3141), chlorophyll content (28.3 SPAD units) and relative water content (63 %). It also increased the antioxidant enzyme activities such as CAT, POD, SOD and APX, along with the overexpression of the drought-responsive gene RCECP63 under water deficit conditions. These findings highlight that seed priming, particularly with salicylic acid, offers a promising strategy to enhance castor resilience under prolonged drought stress, providing a practical approach for improving crop performance in drought-prone regions.