Diversity of wild yeasts in a central Washington vineyard

Tyler Baldwin Bourret

The yeast flora of wine grapes (Vitis vinifera) is likely to affect the character of wines, both through activity in the vineyard and during vinification. This study is the first to characterize the yeasts associated with grapes in Washington. Yeasts were isolated from grapes collected from an experimental vineyard at the Washington State University Irrigated Agriculture Research and Extension Center, located at Prosser, WA. Grape flowers, berries and bunches of cultivars ‘Chardonnay’ and ‘Riesling’ were collected on four dates between June 30 and October 26, 2010. Dilutions of cell suspensions made by rinsing flowers and berries and from fresh must were incubated at 18 – 21°C on Wallerstein Labs Nutrient Agar (WLNA) supplemented with 100 ppm streptomycin sulfate. Isolates were characterized on the basis of culture morphology and cell morphology. The first and second domains (D1/D2) of the nuclear ribosomal DNA (rDNA) large subunit (LSU), 5.8S rDNA and internal transcribed spacers (ITS) sequences were obtained from 121 isolates. Species determination was based on cultural features, microscopic morphology, physiological tests and phylogenetic analysis of sequence data. 53 species were found distributed among five fungal subphyla, which was more than expected based on similar published studies. Within Saccharomycotina, 13 species in the genera Candida, Hanseniaspora, Metschnikowia, Meyerozyma, Pichia, Wickerhamomyces and Yamadazyma were determined. Isolates within the Metschnikowia pulcherrima clade appeared to possess considerable diversity. Pucciniomycotina was represented by 12 species, in Curvibasidium, Rhodosporidium, Rhodotorula, Sporidiobolus and Sporobolomyces. Five phylogenetically distinct species in the subphylum could not be determined. Isolates in Ustilaginomycotina were placed in Pseudozyma except for a single strain determined to be Rhodotorula bacarum. Within Agaricomycotina, 17 species in the genera Cryptococcus, Cystofilobasidium, Hannaella, Holtermanniella and Mrakiella were determined. Seven species of yeast-like fungi were found, representing Pezizomycotina classes Leotiomycetes, Dothideomycetes and Sordariomycetes. Sixteen species were previously unreported from wine grapes and 17 species were unreported from North America. Several strains appear to represent undescribed species. These findings suggest that the diversity of naturally-occurring yeasts in this region may offer previously unexplored tools for producing premium wines of distinctive character.

Diversity of wild yeasts in a central Washington vineyard

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