Maureen Moroney* and Mark Gleason
*Iowa State University, 2213 Pammel Dr, Ames, IA, 50011 (mmoroney@iastate.edu)

Hanseniaspora uvarum, a non-pathogenic, weakly fermentative, and aroma-releasing epiphyte, is the predominant yeast on winegrapes at harvest and during early fermentation. We isolated H. uvarum from cold-hardy hybrid winegrapes in Iowa, developed methods to quantify its growth on the surface of grapes, measured sugars in exudate from those cultivars, and characterized H. uvarum’s carbon utilization and fungicide sensitivity. La Crescent and Marquette grapes were collected July and August 2021. Yeasts were isolated by shaking fruit clusters in water, then plating on selective media. From 70 preserved isolates, eight collected in late August were confirmed as H. uvarum by ITS sequencing. Preliminary phylogenetic analysis of the collected H. uvarum isolates, plus reference isolate YB-505 from USDA-ARS, did not indicate genetic clustering based on source cultivar. Table grapes were used to develop methods for surface sterilization, H. uvarum inoculation and incubation on grape skins, and yeast recovery and quantification. Ames isolates were inoculated onto La Crescent and Marquette berries in August 2022. Most Marquette berries split during incubation and were discarded, while growth on La Crescent was highly variable and showed no significant difference among isolates. Glucose plus fructose was measured in grape exudate from La Crescent and Marquette in August 2022, with large variation among berries, but no significant cultivar difference. Phenotype microarrays were conducted on YB-505 to evaluate its utilization of carbon sources and its chemical sensitivities. Notable for viticulturists and winemakers are its sensitivity to copper sulfate, metabolism of sorbate and pentoses, and low utilization of Saccharomyces cerevisiae-fermentable sugars such as raffinose, galactose, and maltose. This work confirms that H. uvarum is present on winegrapes in Iowa before harvest; preliminary work suggests it is also present on mummies in early spring. It also highlights substantial intracluster variation in the chemistry, morphology, physiology, and biotic interaction of individual berries.

Funding Support: Midwest Grape and Wine Industry Institute