Application Potential of Wheat Root Endophytic Fungus G11: A Novel Biocontrol Agent Against Wheat Sharp Eyespot

Wheat sharp eyespot, mainly caused by Rhizoctonia cerealis, is a destructive soilborne disease that significantly threatens global wheat production, necessitating the development of sustainable control strategies. In this study, we isolated and identified an endophytic fungus, Penicillium oxalicum G11, from the roots of healthy wheat plants and comprehensively evaluated its antagonistic mechanisms and biocontrol potential against R. cerealis. In vitro assays demonstrated that G11 effectively inhibited R. cerealis growth through multiple mechanisms, including competition, antibiosis, and mycoparasitism. G11 exhibited strong antifungal activity, achieving average inhibition rates of 42.42% in confrontation culture, 45.96% via volatile metabolites, and up to 50.28% with fermentation filtrates. Microscopic analysis revealed that G11 hyphae coiled around R. cerealis hyphae, resulting in cellular degradation and further confirming its mycoparasitic behavior. Greenhouse experiments confirmed that G11 significantly reduced average disease incidence by 53.45% (solid fermentation product) and 49.07% (spore suspension) while promoting wheat growth and enhancing antioxidant enzyme activities. G11 inoculation increased catalase activity by 1,398.52 U·g −1 ·min −1 FW and peroxidase activity by 27,456.89 U·g −1 ·min −1 FW while significantly reducing malondialdehyde content by 18.47 μmol·g −1 FW, indicating improved cell membrane stability and stress resistance. Field trials further confirmed the biocontrol efficacy of G11, demonstrating a reduction in disease severity of 66.29% and an average wheat yield increase of 7.06% compared with nontreated controls. Additionally, G11 successfully colonized wheat roots, as verified by microscopic observation and molecular detection, highlighting its potential for long-term persistence and interaction within the wheat rhizosphere. This study represents the first report of P. oxalicum as a biocontrol agent against wheat sharp eyespot, providing a detailed mechanistic analysis of its antifungal properties. By integrating multiple suppression strategies—competition, antibiosis, and mycoparasitism—G11 demonstrates strong potential as a biocontrol alternative to conventional fungicides. Its effectiveness, combined with its environmentally friendly nature, suggests that G11 could serve as a promising microbial resource for sustainable disease management in wheat production, contributing to the reduction of chemical fungicide dependence and the advancement of eco-friendly agricultural practices.