The combination of AM fungus <i>Rhizophagus intraradices</i> and endophytic fungus <i>Metarhizium robertsii</i> enhances the resistance of wolfberry to root rot disease

Wolfberry (Lycium barbarum) is an important economic crop with extremely high medicinal value; however, root rot disease leads to a serious decline in the yield and quality of wolfberry. In this study, we used one-year-old wolfberry seedlings as test material to explore the control effect of single or combined inoculation with arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices and endophytic fungus Metarhizium robertsii on wolfberry root rot and preliminarily probed the related disease resistance mechanisms. The results showed that both R. intraradices and M. robertsii could successfully colonize the roots of wolfberry, and the combined inoculation significantly increased the colonization rate of R. intraradices and reduced the incidence of wolfberry root rot, with a control effect of 68%. Combined inoculation enables plants to absorb nitrogen and phosphorus more effectively by increasing the nutrient uptake area and activity of wolfberry roots, which helps to increase chlorophyll content and promote plant growth. It also improved the resistance of wolfberry to root pathogens by regulating endogenous hormones (significantly increasing the contents of salicylic acid, indole-3-acetic acid, gibberellin A3, and decreasing the content of abscisic acid) and enhancing defensive enzyme activities (superoxide dismutase, peroxidase, and ascorbate peroxidase). In terms of soil, the combined inoculation significantly increased the nitrogen content and enzyme activities (sucrase, urease, and catalase), creating a more favorable growth environment for wolfberry. In conclusion, AM fungus R. intraradices combined with endophytic fungus M. robertsii can effectively enhance the disease resistance of wolfberry to root rot and has certain biocontrol application potential (Graphical abstract).