Effect of Foliar Application of Melatonin on Some Morphological and Physiological Traits of Sour Orange Rootstock in Salinity Stress Conditions

Soil salinity is one of the major environmental stresses which reduces the growth and yield of crops by affecting wide spectra of physiological and biochemical processes in plants. In this study, effect of foliar application of melatonin levels (0 and 200 μM) under salt levls (0, 30, 60, 90 and 120 mM NaCl) on sour orange rootstock was investigated. The experiment was carried-out as factorial arrangements in completely randomized design with four replications in 2020-21 at the research farm of Sari Agricultural Sciences and Natural Resources University, Sari, Iran. The results showed that most of morphological and physiological characteristics were affected by salinity and foliar application of melatonin. Salinity × foliar application of melatonin interaction effect was significant on most of studied traits including leaf length, leaf width, flush number, flush length, root length, leaf moisture and dry matter contents of leaf, ion leakage, stomatal conductance, transpiration rate, of assimilation rate, vapor pressure deficit and photosynthetic quantum yield. Foliar application of melatonin increased leaf moisture content, flush number, assimilation rate, stomatal conductance and photosynthesis quantum yield, while leaf ion leakage decreased. The highest photosynthetic quantum yield was recorded in 200 µM melatonin and salinity free treatment. Foliar application of melatonin under salinity stress conditions improved most of the physiological parameters. Foliar application of melatonin at different salinity levels caused significant increases in length and width of flush leaves compared to the control. Overall, the results of this study showed that foliar application of melatonin reduced negative effects of salinity stress on growth and physiology of sour orange rootstock, therefore, it can be considered as an effective approach to mitigate the adverse effect of soil and water salinity on sour orange rootstock.