Exogenous Melatonin Alleviates NaCl-Induced Salinity Stress in Forage Pea (Pisum sativum L.): Concentration...

Background/Objectives: Soil salinity is a major constraint on legume productivity worldwide, threatening forage pea (Pisum sativum L.) cultivation in semiarid regions. This study evaluated the effect of exogenous melatonin in attenuating NaCl-induced salinity stress across diverse forage pea genotypes. Methods: A three-factor factorial experiment was conducted under greenhouse conditions, testing three NaCl levels (0, 100 and 200 mM) and four melatonin concentrations (0, 100, 150 and 200 µM) across 13 genotypes with three replications (468 pots). Nine vegetative traits were measured and analyzed by factorial ANOVA and Tukey's HSD test. Results: Increasing NaCl from 0 to 200 mM reduced plant height by ~28% and node number by ~32%. Application of 100 µM melatonin under 100 mM NaCl reduced canopy temperature from 28.1 °C to 23.7 °C and restored SPAD values from 21.7 to 26.5 under 200 mM NaCl. By contrast, 200 µM melatonin under severe salinity paradoxically suppressed SPAD to 8.9 and reduced root length. Emirbey and Kirazlí showed the greatest vegetative growth, while Özkaynak exhibited the highest chlorophyll content. Conclusions: 100 µM melatonin emerged as the optimal concentration for alleviating moderate salt stress in forage pea, and genotype selection is critical when deploying melatonin as a biostimulant under saline conditions. Direct measurement of biomass, yield, and forage quality under field conditions remains an essential next step before agronomic deployment.