The response of fungal community on citrus fruit surface to the application of Metschnikowia citriensis

Metschnikowia citriensis is an antagonistic yeast that was isolated from citrus systems, effectively controls postharvest green mold, blue mold, and sour rot in citrus fruits. This study explored its biocontrol mechanisms by treating citrus fruits with 1 × 108 cells mL−1 M. citriensis and analyzing fungal community dynamics via amplicon sequencing. The treatment significant reduced weight loss, disease incidence, and disease index of citrus fruits. Fungal diversity on order- and genus-level on fruit surfaces initially declined but recovered after 28 days, with M. citriensis-treated fruits showing higher species richness than controls. M. citriensis altered fungal community structure, specifically, there was a clear alteration of the microbiota characterized by higher Golubeviales levels in M. citriensis treated group individuals, but Capnodiales levels were significantly decreased. The genera Geosmithia, Lecanicillium, and Golubevia were more abundant in M. citriensis treated fruit, while genera Diploospora and Issatchenkia were more abundant in the Control group. Meira and Meyerozyma levels rose in M. citriensis-treated fruits during storage, though M. citriensis itself did not dominate. Furthermore, functional analysis of the fungal community revealed a significant presence of pathogens on the citrus fruit surface. These pathogens did not induce disease in the citrus fruit, suggesting that the surface microorganisms may regulate pathogen abundance below the pathogenic threshold through species interactions, such as competition or mutualism. Our result suggested that M. citriensis enhances biocontrol by modulating the structure and abundance of the fungal community, which may represent one of its mechanisms.