6-Pentyl-2 H -pyran-2-one from Trichoderma polysporum DCR2 Confers Southern Blight Resistance in Dendrobium catenatum : Pathogen Inhibition and DcCOMT1 -Associated Phenylpropanoid Metabolism

Abstract Dendrobium catenatum, a valuable edible-medicinal orchid, is threatened by southern blight, predominantly caused by Sclerotium delphinii. An endophytic fungus, Trichoderma polysporum DCR2, was previously found in our study to effectively suppress S. delphinii P1 growth and reduce southern blight incidence in D. catenatum. Here, we integrated multiomics, compound antifungal bioassays, and functional validation to reveal how DCR2 enhances D. catenatum resistance against P1. 6-Pentyl-2H-pyran-2-one (6-PP) from DCR2 was identified as a key antifungal metabolite against P1 and enhanced southern blight resistance in D. catenatum. Furthermore, DcCOMT1 was identified as a key gene in the phenylpropanoid biosynthesis pathway that responded to the 6-PP and P1 treatments. These results uncovered the mechanism that 6-PP improves the resistance of D. catenatum to S. delphinii through the regulation of DcCOMT1-mediated phenylpropanoid metabolism. These results advance understandings of mechanisms underlying orchid–endophyte interactions and disease resistance by Trichoderma, providing strategies for biological controls of southern blight.