Allelochemicals found in plants are gaining favor as biostimulants and alternative growth regulators in agriculture. Withania coagulans and Cassia fistula are known to produce numerous secondary metabolites, such as phenolic compounds, that can regulate seed germination and seedling growth. This study investigated the allelopathic effects of aqueous extracts from Withania coagulans seeds and Cassia fistula fruits on turnip germination and seedling growth. Laboratory experiments were conducted using extract concentrations of 0, 2.5, 5, 10, 20, 40, and 80 g/L. Therefore, this paper hypothesized that low concentrations would induce growth in a hormetic manner, whereas higher levels would inhibit it. Results revealed a hormetic response, where lower concentrations of W. coagulans extract (2.5 and 5 g/L) significantly increased root length (41.5% and 24.3%, respectively), root fresh weight (by 72.5% and 63.5%), and shoot fresh weight (by 59.5%), while reducing mean emergence time, and time to 50% emergence compared to the control. Higher concentrations (10-80 g/L) inhibited germination, with complete inhibition observed at 40 and 80 g/L. C. fistula extracts exhibited more complex interactions, with the 40 and 80 g/L concentrations enhancing shoot length and fresh weight, and 80 g/L also increased germination percentage. Phenolic compounds such as quercetin, ferulic acid, gallic acid, and p-coumaric acid identified in both extracts may contribute to these effects. This study demonstrates the hormetic effect of the W. coagulans and suggests that low concentrations (2.5-5 g/L), particularly (2.5 g/L), may serve as a natural growth enhancer to improve turnip growth and yield.
