Improving salt tolerance threshold in common bean cultivars using melatonin priming: a possible mission?

Abstract

Common bean (Phaseolus vulgaris L.) is mostly cultivated on marginal soils where salinity is a key stress. The focus of the present study was to evaluate the efficiency of melatonin priming and hydro priming on germination, growth parameters, antioxidant defense system and tolerance threshold in seven common bean cultivars grown under different levels of salinity stress. The experiments were conducted as a factorial arrangement based on a completely randomized design with six replicates. The results showed that salinity levels decreased radicle and hypocotyl lengths, seedling vigor index, and salinity tolerance threshold under Petri dish conditions. However, melatonin priming alleviated the inhibitory effects of salinity and enhanced salt tolerance threshold of all the cultivars. The highest tolerance thresholds of Dorsa, Almas, Koosha, and Pak cultivars were obtained under 100 µM melatonin treatment, while in Sayad, Shekoofa, and Derakhshan, 20 µM melatonin caused higher thresholds. Results of the greenhouse experiment showed that melatonin priming increased salt tolerance threshold, but it reduced malondialdehyde content and hydrogen peroxide accumulation. It also induced a higher increase in relative shoot dry weight of the cultivar Dorsa than the other cultivars. The cultivars Dorsa and Shekoofa treated with 100 and 20 µM, respectively, maintained a lower MDA content and Na+ concentration and a higher K+/Na+ ratio in shoot and root, N concentration and salt tolerance threshold than the other cultivars under salinity stress. These results suggest that seed priming with melatonin enhances salinity tolerance by stimulating antioxidant activities, alleviating oxidative damage and enhancing plant dry weight.