Characterization of the causal agents, epidemiology and biological control of white haze on apple.

White haze, caused by an extensive fungal colonization of the apple surface, is an emerging issue in several European apple production areas. It results in compromised quality and decreased marketability of the fruits, leading to economic losses. In this study, fungal strains were isolated from apple in Northern Italy and the species diversity was assessed using molecular and phylogenetic tools. Moreover, the ability of the isolated species to reproduce symptoms on healthy apples artificially inoculated was tested. Six species belonging to different basidiomycetous genera (Entyloma, Golubevia, Tilletiopsis) were identified. The most frequently isolated strains were inoculated on healthy apple fruit, showing to be able to reproduce symptoms on red-skin apples, fulfilling Koch’s postulates. Metabarcoding was used to characterize both epiphytic and endophytic microbial communities of apple fruit across six time points from early fruit development up to the end of shelf life. Golubevia was the most abundant epiphyte (2–4%) from BBCH 81 (1–7% relative abundance) to the end of shelf life. Moreover, two Aureobasidium pullulans strains were tested against white haze of apple. An efficacy comparable to the chemical control treatment was demonstrated at the end of shelf-life. This work provides new insights to increase knowledge about aetiology and epidemiology of white haze on apple. In addition, biocontrol of white haze with antagonists was tested for the first time.