The investigation of the metabolites from different cocultures of Nigrospora oryzae and Irpex lacteus in solid medium revealed two new squalenes (1 and 2); one new azaphilone (3); two new tremulane sesquiterpenes (4 and 5); and three known compounds, conocenol B (6), conocenol C (7), and 4-(4-dihydroxymethylphenoxy)benzaldehyde (8). The antagonistic relationship was examined by studying metabolite production. The production of compounds 6 and 8 by I. lacteus after the induction of coculture indicated significant selectivity for antifungal activity against phytopathogenic N. oryzae, with MICs of 16 μg/mL; compounds 6 and 8 also exhibited antifungal activities in vivo against Cerasus cerasoides infected by N. oryzae at concentrations of 100 μg/mL. New compounds 2 and 4 showed antifungal activities against Colletotrichum gloeosporioides, with MICs of 8 μg/mL, and compound 4 showed antifungal activity against Didymella glomerata with an MIC of 1 μg/mL. These results indicate that the mutually antagonistic relationship in the coculture of the phytopathogen and the endophyte can result in antibiotics that inhibit the phytopathogen and downregulate the production of phytotoxins by phytopathogenic N. oryzae. New compound 5 from I. lacteus showed weak activity against acetylcholinesterase (AChE), with an inhibition ratio of 16% at a concentration of 50 μM.
Keywords: Irpex lacteus; Nigrospora oryzae; antifungal selectivity; coculture induction; metabolite; mutual antagonism.