Melatonin seed priming enhanced drought tolerance in rapeseed (Brassica napus L.) cultivars

Drought stress poses a major challenge to sustainable agriculture, and seed priming with melatonin has shown potential to mitigate stress damage in crops. However, the effects of melatonin priming (MP) on drought tolerance in rapeseed (Brassica napus L.) remain underexplored, particularly under field conditions. In this study, two rapeseed cultivars, Shiraali and Pakola, were primed with melatonin and tested under irrigated and drought stress conditions. Results indicated significant cultivar differences for most parameters, except for plant number, peroxidase (POD), catalase (CAT), 1000-seed weight, and harvest index. MP outperformed hydro priming (HP) for most traits, except for branch number, harvest index, and seed protein content. Drought stress significantly affected all parameters, except for POD, branch number, and 1000-seed weight. Shiraali exhibited higher plant density, plant height, chlorophyll a, protein, and erucic acid content, while Pakola showed superior ascorbate peroxidase (APX) and CAT activities, chlorophyll b, carotenoids, oil content, and glucosinolates, as well as higher yield. MP enhanced antioxidant activity and pigment accumulation compared to HP. Under drought conditions, a reduction in plant pigments, yield, and protein content was observed, while oil, glucosinolates, erucic acid content, and antioxidant activities increased. Pakola outperformed Shiraali in 1000-seed weight, yield, and oil content under both irrigated and drought conditions following MP. Our results indicated that melatonin may contribute to drought tolerance through integrated physiological, biochemical, and antioxidant interactions in rapeseed.