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The Role of Yeasts in the Cranberry Fruit Rot Complex

Zachary Zalewski: University of Wisconsin Madison

<div>Cranberry (<em>Vaccinium macrocarpon</em>) is an economically important fruit crop in North America. Cranberry fruit rot occurs before and after harvest and is believed to be caused by a complex of filamentous fungi. After searching for potential bacterial or yeast pathogens, however, we discovered two pathogenic yeast species (<em>Hanseniaspora uvarum</em> and <em>Candida railenensis</em>). In the 2017 season we sampled 10 dry-harvested and 20 water-harvested berry samples from various locations to (i) further explore the potential role of bacteria and yeasts in the fruit rot complex; (ii) determine the prevalence and diversity of pathogenic yeasts; and (iii) assess the effect of harvest method on presence of yeasts and bacteria. In the dry-harvested samples 0-5% of berries yielded yeasts in the absence of pathogenic, filamentous fungi on PDA, whereas 10-68% of berries in water-harvested samples yielded yeasts in the absence of filamentous fungi. Isolates are being identified and tested for pathogenicity. Because <em>H. uvarum</em> and <em>C. railenensis</em> were initially discovered in the presence of cycloheximide, we also performed a disc diffusion assay to test their sensitivity to three fungicides used on cranberry (azoxystrobin, chlorothalonil, and prothioconazole). Both yeasts showed high tolerance to the fungicides at doses exceeding field doses by more than 1000-fold. These data give us important insights into the transmission and control of these new players in cranberry pathology.</div>