The effect of melatonin and salicylic acid applications on plant growth of Diyarbakır sürme watermelon (Citrullus lanatus) and crimson sweet cultivar under salt (NaCl) stress

This study investigated the responses of the local Sürme genotype (Citrullus lanatus) and the commercial Crimson Sweet watermelon variety to salinity stress and treatments with melatonin and salicylic acid. The experiment was conducted in April 2023 under soilless cultivation conditions at the Faculty of Agriculture, Dicle University, using a randomized complete block design with three replicates. Melatonin (50, 100, 200 µM) and salicylic acid (0.5 and 1.0 mM) treatments were applied, followed by the induction of salt stress using 150 mM NaCl. Various morphological and physiological parameters, including plant height, root length, leaf area, chlorophyll content, and proline levels, were measured. Results showed that salt stress significantly reduced growth parameters such as plant and root length, leaf number, and biomass. However, melatonin and salicylic acid treatments partially alleviated these negative effects. Notably, the application of 200 µM melatonin improved plant growth and dry weight in both Crimson Sweet and Sürme genotypes, bringing them closer to control levels. Proline content, which increased under salt stress, was reduced by melatonin and salicylic acid treatments. Furthermore, changes in reflectance ratios and other physiological parameters highlighted the plants' adaptive responses to stress conditions. In conclusion, melatonin and salicylic acid applications were effective in enhancing the salinity tolerance of watermelon genotypes. These findings suggest potential for the cultivation of watermelon varieties in saline soils in Diyarbakır region and provide valuable insights for future breeding programs. Additionally, supporting these genotypes with biostimulant agents offers an important resource for developing new salt-tolerant cultivars.