Phosphorus fertilizer and arbuscular mycorrhizal fungi application improves bitter melon fruit yield and some phytochemical compounds under irrigation deficit stress

Drought stress is among the most effective limitations of the yield and quality of agricultural products, and the application of arbuscular mycorrhizal fungi (AMF) is a proposed method for increasing plant resistance to adverse effects of water deficit stress. A two-year field trial was implemented using a split factorial design within a randomized complete block framework with three replications. Three irrigation levels, including irrigation following 20 %, 50 %, and 80 % available soil water discharge (ASWD), were distributed randomly in the main plots, and a factorial combination of phosphorus (P) fertilizer (with and without P) and AMF (Glomus mosseae, Glomus intraradices, and non-inoculation) were placed randomly in the sub-plots. Investigations determined that by decreasing irrigation at a level of 80 % ASWD, the number and weight of total fruit, chlorophyll, and leaf P compared to 20 % ASWD showed a decrease and electrolyte leakage (EL), MDA, enzyme antioxidants (CAT, APX, PPO), and non-enzymatic (carotenoid, flavonoid, anthocyanin), and fruit secondary metabolites (rutin, momordicin, charantin) increased. AMF inoculation and P fertilizer, although decreased MDA and EL, increased enzyme and non-enzymatic antioxidants and secondary metabolites of fruit. Bitter melon fruit weight improved under inoculation with AMF and P (with and without P fertilizer) at all irrigation levels. Reduced irrigation increased the momordicin and charantin, but the combination of AMF and P had no significant effect. This method offers valuable innovation in improving yield, enhancing secondary metabolites, reducing the need for P fertilizer, and optimizing water and soil resource management, which is especially important in the sustainable production of medicinal plants in water-deficit areas.