Yeast-like fungi and yeasts in withered grape carposphere: Characterization of Aureobasidium pullulans population and species diversity

Yeast-like fungi and yeasts residing on carposphere of withered grapes for Italian passito wine production have been scarcely investigated. In the present study, isolates from single berries, both sound and damaged, of Nosiola, Corvina and Garganega varieties were analyzed at the end of the withering process. Great variation of cell concentration among single berries was observed. In sound berries, yeast-like fungi were significantly more frequent than yeasts. Species identification of isolates was carried out by BLAST comparative analysis on gene databases and phylogenetic approach. All yeast-like fungi isolates belonged to Aureobasidiwn pullulans. They displayed different culture and physiological characteristics and inhibitory capacity against phytopathogenic fungi. Moreover, PCR profile analysis revealed high genotypic similarity among these strains. A total of 35 species were recognized among yeast isolates. Ascomycetes prevailed over basidiomycetes. To the best of our knowledge, Naganishia onofrii and Rhodosporidiobolus odoratus were identified for the first time among yeasts isolated from grapes, must or wine. Hanseniaspora uvarum and Starmerella bacillaris were the most frequent species. Most species were found only in one grape variety (nine in Nosiola, 10 in Corvina and five in Garganega). The sanitary state of withered grapes could have an important impact on the structure of these epiphytic populations.