Biocontrol of Monilinia fructigena, causal agent of brown rot of apple fruit, by using endophytic yeasts

In this study; an isolate of Monilinia fructigena the causal agent of apple fruit brown rot was isolated from rotten apple fruits cv. Golden delicious. In the in vivo pathogenicity assay, it presented significant disease incidence on the inoculated apple fruit, thus confirming its virulence. Five endophytic yeasts were isolated from healthy apple fruits; identified according to their microscopic characteristics as; Schwanniomyces vanrijiae, Galactomyces geotrichum, Pichia kudriavzevii, Debaryomyces hansenii, and Rhodotorula glutinis. The first three isolates showed appreciable inhibitory potential against M. fructigena by in vitro test; moreover, they caused a significant inhibition of germination of pathogen conidia by 67.6-89.2%. Identification of these three potent yeasts in addition to M. fructigena isolate was confirmed by PCR analysis through amplification of ITS region. In in vivo assays, fruits were inoculated with each of the 5 BCAs and M. fructigena simultaneously; 24 h before, and 24 h after pathogen inoculation, showing a noticeable reduction of disease incidence by 84.02-89.5%, 80.1-86.9%, 56.3-86.9% respectively, compared with the controls. By in vitro plate assays, BCAs were able to produce fungal cell wall hydrolyzing enzymes such as: chitinases, pectinases, beta-1,3-glucanase, and protease, in addition to the production of a killer toxin. At 10 mg/L of Fe+3 in PDA, the three BCAs recorded significant in vitro inhibition of M. fructigena growth. The three potent BCAs do not express human pathogenicity traits. The aims of the current study were to isolate and characterize yeasts able to inhibit the growth of M. fructigena during apple storage.