Yilinuer Adili, Wenjing Zhang, Yinliang Guo, Guangmu Tang, Wanli Xu, Di Feng
Soil salinization severely restricts the sustainable production of watermelon globally. To exploit the application potential of agricultural residues and alleviate salt stress in watermelon seedlings, this two-factor experiment explored the influences of watermelon leaf extract (WLE) on seedling growth and physiological characteristics. Two NaCl concentrations (0 and 50 mmol L −1 ) and three WLE dosages (0%, 5%, 10%) were set in this study. Salt stress drastically suppressed seedling growth. Under the 50 mmol L −1 salt condition, 5% WLE significantly elevated plant height by 11.54%, stem diameter by 27.31%, root fresh weight by 50.55%, total root length by 66.83% and root surface area by 72.39%. Simultaneously, proline content, superoxide dismutase and peroxidase activities rose by 20.21%, 21.85%. The concentrations of abscisic acid and jasmonic acid increased by 66.33%, whereas indole-3-acetic acid content declined by 31.34% ( P < 0.05). The effect of 10% WLE was insignificant, with even mild inhibitory trends observed. Under non-salt conditions, WLE generally restrained root and physiological traits. Collectively, 5% WLE effectively improves watermelon seedling salt tolerance via coordinated regulation of vegetative growth, osmotic homeostasis, antioxidant defense and hormone balance. This pot experiment provides preliminary theoretical support for the in-situ recycling of watermelon crop wastes. Field trials can be carried out in subsequent research to verify its practical effects and translate this technology into a low-cost scheme for improving crop salt tolerance.