Arbuscular Mycorrhizal Fungi For Vegetable (Vt) Enhance Resistance To Rhizoctonia Solani In Watermelon By Alleviating Oxidative Stress

The beneficial effects of arbuscular mycorrhizal fungi (AMF) vary depending on the species of fungi and host plants. In this study, we tested 8 mycorrhizal consortiums to explore the best AMF conformation for watermelon plants. The results showed that colonization with mycorrhiza for vegetable (VT) resulted in the highest biomass accumulation, photosynthetic rate, and dependence in watermelon seedlings. VT increased the photosynthetic rate and dry weight by 68.6% and 63.4%, respectively, compared with non-AMF plants. Dose trial on inoculum density for VT revealed that 300 spores per plant caused the highest dry weight, photosynthetic rate, and dependence. Notably, different inoculum density differentially affected endogenous hormone levels, whereas 300 spores/plant caused the highest accumulation of abscisic acid, indole acetic acid, and gibberellic acid. When VT inoculated plants were infected with soil-borne fungal pathogen Rhizoctonia solani, they showed only 18.4% disease incidence with a 59.7% control effect compared with the 45.7% disease incidence in control plants without VT inoculation. R. solani decreased the photosynthetic rate, chlorophyll a, chlorophyll b, and carotenoid content by 38.8%, 20.5%, 63.4%, and 33.6%, respectively, while VT colonization significantly improved those indexes. Moreover, VT significantly reduced the relative electrolyte leakage, H2O2 accumulation, and lipid peroxidation, and increased the root activity and antioxidant enzymes activities and their transcripts in roots, suggesting mitigation of oxidative stress caused by R. solani. Our results suggest that VT at optimal dose could enhance watermelon resistance to R. solani and thus can be considered as a biological control agent for R. solani management in cucurbits.