Effect of irrigation water quality and foliar-sprayed glycine betaine on photosynthetic pigments, water status, and element content of kapok seedlings

This study aims to examine the main and interaction effects of irrigation with treated sewage water (TSW), agricultural drainage water (ADW) and foliar spraying with glycine betaine (GB) on physiological parameters and chemical composition of kapok (Ceiba pentandra L.). Therefore, a pot experiment was conducted during the summer seasons of 2021 and 2022 in a private farm in Beni-Suef Governorate, Egypt. The experimental layout was a split plot in a randomized complete blocks design with three replications. Kapok seedlings were irrigated with Nile irrigation water (NIW) either directly (100%) or mixed TSW or ADW with NIW (25, 50, and 75 %) in addition to glycine betaine (GB) was applied at (0.0 mM and 50 mM). Results showed that irrigation with TSW (100%) and ADW (100%) decreased pigments content (Chl a, Chl b, and carotenoids), membrane stability index (MSI), relative water content (RWC), relative chlorophyll content (SPAD value), leaf thickness, N, P, K and Ca content, but increased Na, Cu, Ni, Mn, Zn, and Pb content. Moreover, GB significantly increased Chl a, Chl b, carotenoids, MSI, SPAD, RWC, N, P, K, and Ca content and antioxidant activity, as well as reduced Na, Cu, Ni, Mn, Zn and Pb content in leaf. Irrigating kapok seedlings with TSW or ADW and NIW at 25, 50% give better results similar to those irrigated with NIW for all parameters. GB and water treatments interaction give better results at 50 mM GB, and TSW or ADW mixed with NIW at rates of 25%, and 50%, respectively. Therefore, spraying of GB (50 mM) and irrigation with TSW or ADW mixed with NIW at the rate of 50% improved physiological parameters, chemical constituents, and nutrient content compared to control conditions.