Control of Neofusicoccum parvum-induced fruit rot in Rosa roxburghii using osthol: from laboratory efficacy to field application

Rosa roxburghii Tratt., a vitamin C-rich edible and medicinal fruit native to southwest China, plays a vital role in poverty alleviation and economic development in mountainous regions. In this study, Neofusicoccum parvum was identified for the first time as a pathogen causing fruit rot in R. roxburghii . Koch's postulates were fulfilled by re-isolating the fungus from artificially inoculated fruits, confirming its pathogenicity. Morphological and molecular analyses further validated the pathogen's identity. The optimal growth conditions for N. parvum were determined to be 28–30 °C and pH 5, with D-fructose and NH 4 Cl as the preferred carbon and nitrogen sources, respectively. Continuous light exposure was found to maximize mycelial growth. Among six tested plant extracts, osthol, Scutellariae Radix extract, and matrine exhibited notable antifungal activity, with osthol showing the highest efficacy (EC 50  = 30.57 μg/mL). Field trials demonstrated that 1% osthol emulsion in water (EW), applied at 300–500-fold dilution, achieved 60.68%–77.57% control efficacy against fruit rot after 21 d of the second application. This performance was comparable to the chemical fungicide 10% difenoconazole water dispersible granule (WG) (67.58%–81.04% efficacy at 5000–7000-fold dilution). This study provides a scientific basis for the biocontrol of N. parvum -induced fruit rot disease in R. roxburghii .