Effects of Exogenous Melatonin on the Morphological, Physiological and Biochemical of Prunus Rootstocks Under Drought Stress

Abstract Drought is a major constraint on the growth and yield of horticultural crops, especially stone fruit trees. This study explored the effects of melatonin on drought tolerance in seven peach–almond hybrid rootstocks (GN2, TT, 34.2, 50.10, 35.1, GF677, and GN). Melatonin was applied foliarly at three growth stages using two concentrations (0 µM and 100 µM), while drought stress was induced at three levels: control (100% field capacity, FC), moderate stress (60% FC), and severe stress (40% FC). Key traits assessed included growth parameters, leaf abscission, leaf area index, relative water content (RWC), proline and malondialdehyde (MDA) levels, and peroxidase enzyme activity. The results indicated that under drought stress, growth traits and RWC of the leaves declined, whereas leaf abscission rate, proline, and MDA content increased. Under severe drought stress, rootstock ’50.10’ exhibited the highest proline concentration (127.8 µmol g–1 fresh weight), while ‘TT’ under non-stress conditions with melatonin showed the lowest (51.95 µmol g–1 fresh weight). MDA levels peaked in ‘50.10’ (47.54 nmol g–1 fresh weight) and ‘34.2’ (46.67 nmol g–1 fresh weight), with ‘TT’ recording the lowest (12.69 nmol g–1 fresh weight). Peroxidase activity increased under moderate drought (60% FC) in ‘GF677’, ‘TT’, and ‘GN2’, but declined under severe stress (40% FC); in contrast, ‘GN’, ‘34.2’, ‘35.1’, and ‘50.10’ showed reduced activity under both stress levels. ‘TT’ and ‘GF677’ demonstrated superior drought tolerance, while ‘50.10’, ‘34.2’, and ‘GN2’ were more sensitive. These results highlight the potential of foliar melatonin treatment to mitigate drought-induced damage in stone fruit rootstocks.