Effects of Treated Wastewater Irrigation on Chlorophyll Content, Leaf Color, and Gene Expression in Tomato (Solanum Lycopersicum L.)

Abstract

This study was investigated the effects of treated wastewater irrigation on physiological traits and gene expression in tomato plants (Solanum lycopersicum L.) during the early developmental stage. Two treatments which are control (tap water) and treated wastewater irrigation were compared. Physiological parameters, including SPAD values and leaf color, were assessed, while the expression of growth and stress-related genes (SlDREB2, SlARF9, and SlEXP1) was quantified using RT-qPCR with three biological replicates. Relative expression levels were calculated following the 2^−ΔΔCt method. The results demonstrated that treated wastewater irrigation significantly enhanced chlorophyll content (SPAD) in tomato leaves and shifted leaf coloration toward darker, greenish hues. At the molecular level, a pronounced upregulation of SlDREB2 was observed, whereas SlEXP1 expression was suppressed. Although SlARF9 expression showed an increase in relative to the control, this change was not statistically significant. Collectively, these findings suggest that treated wastewater irrigation can enhance photosynthetic capacity in tomato plants in the short term, while simultaneously activating abiotic stress signaling pathways and constraining certain growth-associated mechanisms.