Enhancing salinity stress tolerance and phenylalanine ammonia lyase gene activity using osmolytes in Moringa seedling production

The salinity of irrigation water is one of the major abiotic stresses that have a variable reaction to soil structure, which has detrimental impacts on seedling development and quality. The osmolytes can help lessen these adverse effects on the establishment of Moringa oleifera seedlings. Therefore, this study was conducted in Egypt (30″53′30, 87″ N and 30″41′29, 77″ E) using polyethylene bags during May – July 2020 and 2021. Three factors in a factorial split –split plot experiment were arranged in randomized complete block design. The main plots were soil structure; sand:clay 2:1 (V/V) and sand 100 %, whereas the subplot treatments were salinity levels; tap water as a control 0.5, 1.5, 4, and 6 dS m⁻¹, and sub–subplot osmolytes; tap water as a control, and glycine betaine, mannitol, proline, and sorbitol all at 0.2 g L⁻¹ as a soil drench. This study aimed to evaluate the effects of osmolytes and soil structure on growth parameters and phenylalanine ammonia lyase (PAL) gene expression in Moringa seedlings. The study concluded that Moringa seedlings in sand:clay performed significantly (P ˂ 0.05) better than those in the sand. With increasing salinity levels, osmolytes enhanced all seedling growth parameters and PAL gene expression compared with the control in the two soil structures. The order of tolerance to salinity stress was sorbitol ˃ proline ˃ mannitol ˃ glycine betaine ˃ control. Moringa seedlings produced in sand:clay treated with 0.2 g L⁻¹ sorbitol and salinity at 4 or 6 dS m⁻¹ were superior in most growth parameters and PAL gene expression.