GROWTH INHIBITION OF Botrytis cinerea BY NATIVE VINEYARD YEASTS FROM PUGET SOUND, WASHINGTON STATE, USA

Commercial grape production in Washington State, USA relies on the use of fungicides to combat grape pathogens. However, increasing incidence of fungicide resistance is of concern to the wine industry and members of the public. Here, we extend previous studies on the biocontrol potential of native Washington yeasts from Central Washington to yeasts and Botrytis cinerea from the Puget Sound, where Botrytis bunch rot is endemic. Field isolates of native yeasts and B. cinerea were collected from diseased grapes from two vineyards in 2017 and 2018. Multi-locus sequence analysis showed that the Botrytis isolates were related to each other and to B. cinerea accessions in GenBank, but one isolate was more closely related to B. eucalypti. For dual plate inhibition assays, five B. cinerea isolates were selected from different grape cultivars. Ten native yeasts, isolated from the same cultivars, were selected for their ability to inhibit B. cinerea in preliminary screens. The yeasts were identified as Candida californica, Hanseniaspora uvarum (5 isolates), Pichia kluyveri (2 isolates) and Metschnikowia pulcherrima based on sequences of the D1-D3 regions of the nuclear large ribosomal RNA gene. These nine yeasts inhibited up to three of the five pathogen isolates, and inhibition was not identical for the five H. uvarum strains. Furthermore, the Botrytis isolates showed differential sensitivity to the panel of yeasts. The last yeast inhibited all pathogen isolates and resembled Aureobasidium pullulans in morphology and inhibition pattern. As in the previous study, which focused on Mt. pulcherrima and Mt. chrysoperlae, in vitro inhibition was found to be dependent on the genotypes of both the native yeast strain and Botrytis isolate. The present findings indicated that native yeasts can exert inhibition on bunch rot pathogens co-occurring at the same locality, and the development of biological control needs to account for genotypic differences in yeasts and pathogens.