Synergistic effects of melatonin and chitosan in alleviating drought stress in saffron: (Crocus sativus) insights into plant growth and biochemical responses

Saffron (Crocus sativus L.) is recognized as a strategic crop with high economic, nutritional, and cultural value in Iran; however, in recent years, its yield has significantly declined due to climate change, particularly drought stress. This study was conducted to evaluate the combined effects of drought stress at three field capacity (FC) levels (100%, 70%, and 40%), melatonin (100, 200, and 400 mg/L), and chitosan (100, 150, and 200 mg/L) on saffron performance over two years. The measured traits included leaf dry weight, leaf length, stigma dry weight, fresh flower weight, flower number, total corm weight, photosynthetic pigments, catalase activity, proline, electrolyte leakage (EL), and relative water content (RWC). Our results showed that the FC40 DS level had the most pronounced effects, significantly reducing RWC and pigment content, increasing EL, and ultimately leading to considerable reductions in leaf dry weight, leaf length, stigma dry weight, flower number, and total corm weight across both years. In contrast, the combined application of melatonin and chitosan significantly alleviated these adverse effects. The synergistic action of these two compounds helped maintain RWC, reduce EL, and enhance catalase activity, thereby mitigating reductions in both vegetative and reproductive performance particularly under FC70 and FC100. A strong positive correlation between stigma dry weight and flower number (R2 = 0.79) indicated a close relationship between improved physiological processes and reproductive performance. Moreover, multivariate analysis using principal component analysis clearly distinguished the applied treatments and associated traits. “PC1 and PC2 explained 74.8% and 18.9% of variance respectively, clearly separating drought and biostimulant combinations based on physiological traits.” These findings confirm the synergistic application of melatonin and chitosan as an effective strategy to enhance saffron resilience under drought stress conditions.