Abstract
BACKGROUND: The imbalance between Egypt's water requirements and supply necessitates the use of unconventional water sources, such as treated sewage water (TSW) and agricultural drainage water (ADW), to combat water scarcity. This study investigated the effects of foliar glycine betaine (GB) on vegetative growth parameters, physiological characteristics, photosynthetic pigments, leaf element contents, anatomical leaf structures, and antioxidant activity. The experiment was conducted in two successive seasons (2021/2022 and 2022/2023) using Kapok seedlings irrigated with ADW and TSW at different mixing ratios with normal irrigation water (NIW) (25%, 50%, 75%, and 100%), combined with foliar spraying of GB at concentrations of 0.0 and 50 mM. RESULTS: The results revealed that irrigation with 100% TSW or ADW significantly decreased vegetative growth parameters, physiological characteristics, photosynthetic pigments, leaf element contents, leaf thickness, and the contents of the leaf mid-vein, N, P, K, and Ca. In contrast, the levels of free proline, total phenolic content, Na, Cu, Ni, Mn, Zn, Pb, and antioxidant activity increased. Additionally, GB significantly improved all parameters, while reducing the contents of Na, Cu, Ni, Mn, Zn, and Pb in the leaves. CONCLUSIONS: Irrigation of Kapok seedlings with TSW or ADW mixed with NIW at 25% and 50% resulted in better performance, similar to irrigation with NIW alone for most parameters. Combining GB and water treatments by mixing TSW or ADW with NIW at a 50:50 ratio and spraying with 50 mM GB produced better results than control seedlings irrigated with 100% NIW. Antioxidants also play a defensive role in plants against various stress factors. Therefore, GB may have a protective effect on peroxidation-linked membrane deterioration, scavenge free radicals, and provide osmotic protection.