Biofortification with selenium and melatonin improves seed yield and quality of Phaseolus vulgaris L. under drought stress by enhancing physiological and antioxidant responses

BACKGROUND: Beans are one of the main crops in Eqlid County, northern Fars Province, where they were cultivated more than 18,000 hectares. To investigate the effect of melatonin (Mt) and selenium (Se) on biofortification, seed yield, and yield components of common bean under drought stress, a two-year experiment was conducted using a split-plot factorial arrangement within a randomized complete block design with three replications at the Agricultural and Natural Resources Research Station of Eqlid County in northern Fars Province. The main factor included three levels of drought stress (T1: no stress, T2: irrigation after 80 mm evaporation from a Class A pan as moderate stress, and T3: irrigation after 100 mm evaporation from a Class A pan as severe stress). The first sub-factor comprised three levels of Mt (Mt1 = 0, Mt2 = 100, Mt3 = 200 µM), and the second sub-factor involved foliar application of Se as sodium selenite at two levels (Se1 = 0, Se2 = 5 mg/L). Recorded traits included seed yield, number of pods per plant, 100-seed weight, protein, proline, superoxide dismutase, catalase, phenylalanine ammonia-lyase, total phenol, and selenium concentration in seeds. RESULTS: Results showed that seed yield (T1 = 2591.1 > T2 = 1850 > T3 = 877.8 kg/ha), pod number/plant (T1 = 9.33 > T2 = 7.21 > T3 = 6.54) and 100-seed weight (T1 = 38 > T2 = 35.7 > T3 = 33.9 g) declined under waer deficit stress but improved with increasing Mt and Se concentrations (T1 = 4023.3, T2 = 3513.3, T3 = 1837.8 kg/ha, T1 = 14.8, T2 = 14.3, T3 = 12 and T1 = 45.7, T2 = 43.9, T3 = 40.9 g). Additionally, antioxidant enzymes activity (Superoxide dismutase and Catalase) increased in stressed plants with higher Mt and Se levels compared to control (by 179 and 58% for T1, 248 and 69% for T2), indicating an enhanced defense response. Although the highest seed yield and yield components were obtained under water deficit stress conditions, considering drought-induced yield reduction, the application of 200 µM Mt and 5 mg/L Se may be cost-effective. CONCLUSION: Overall, the results suggest that the use of Mt and Se could serve as an effective strategy in managing water deficit stress and improving crop performance in agricultural environments with challenges.