Chaetoglobosin A Contributes to the Antagonistic Action of Chaetomium globosum Strain 61239 Toward the Apple Valsa Canker Pathogen Cytospora mali

Apple Valsa canker (AVC) weakens apple trees and significantly reduces apple production in China and other East Asian countries. Thus far, very few AVC-targeting biocontrol resources have been described. Here, we present a thorough description of a fungal isolate (Chaetomium globosum, 61239) that has strong antagonistic action toward the AVC causal agent Cytospora mali. Potato dextrose broth culture filtrate of strain 61239 completely suppressed the mycelial growth of C. mali on potato dextrose agar, and strongly constrained the development of AVC lesions in in vitro infection assays. ultra-performance liquid chromatography (UPLC) and HPLC-MS/MS investigations supported the conclusion that strain 61239 produces chaetoglobosin A, an antimicrobial metabolite that inhibits C. mali. Using genome sequencing, we discovered a gene cluster in strain 61239 that may be responsible for chaetoglobosin A production. Two of the cluster's genes-cheA, a PKS-NRPS hybrid enzyme, and cheB, an enoyl reductase-were individually silenced, which significantly decreased chaetoglobosin A accumulation as well as the strain's antagonistic activity against C. mali. Together, the findings of our investigation illustrate the potential use of Chaetomium globosum for the management of AVC disease and emphasize the significant contribution of chaetoglobosin A to the antagonistic action of strain 61239.