The Ameliorative Effects of Foliar Amino Acid Applications on Tomato (Solanum lycopersicum L.) Growth and Pigment Content under Salinity Stress

Abstract

Salinity can restrict tomato growth, particularly under arid and semi-arid growing conditions. This greenhouse pot experiment evaluated whether foliar application of a commercial amino acid (AA) mixture could improve growth and pigment responses of tomato (Solanum lycopersicum L. cv. Falcon) exposed to 100 mM NaCl. Six treatments were arranged in a completely randomised design with four replications: control, 100 mM NaCl, 100 ppm AA, 200 ppm AA, NaCl+100 ppm AA, and NaCl+200 ppm AA. Treatments were applied weekly for seven weeks, after which plant height, fresh and dry weights, root length, chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents were measured. Salt stress significantly reduced plant height and root length relative to the control. Foliar AA application modified plant responses, with the 200 ppm dose generally performing better than 100 ppm under salinity. The NaCl+200 ppm AA treatment produced higher plant height, plant fresh weight, plant dry weight, and root length than NaCl alone. Pigment variables showed numerical differences among treatments, but these differences were not statistically significant. Correlation analysis, principal component analysis, and radar chart evaluation indicated treatment-dependent relationships among growth and pigment parameters. Overall, foliar application of 200 ppm AA may support vegetative growth of tomato under 100 mM NaCl, although further validation is required to clarify pigment-related and physiological mechanisms.