Previously unrecognized diversity within fungal fruit rot pathosystems on Vitis vinifera and hybrid white wine grapes in Mid-Atlantic vineyards

Abstract

Fruit rot diseases are among the most economically important challenges facing the rapidly growing wine grape industry in the Mid-Atlantic region of the United States. Although diverse fungi are associated with fruit rots, most are considered secondary pathogens. Surveys in fall 2015 and 2016 recovered seven species of hyphal fungi from diseased berries, in which Aspergillus japonicus and Colletotrichum fioriniae were the dominant species recovered from Vidal blanc clusters, and Alternaria alternata and Colletotrichum fioriniae were the most common species recovered from Chardonnay. Two species not previously described as pathogens, Aspergillus japonicus and Pestalotiopsis telopeae, could initiate fruit rot in intact Chardonnay berries (incidence: 5–17.5% of berries); all other species were weak pathogens and likely function as secondary colonists. Introduction of inoculum into a mechanical wound significantly increased disease incidence for all species (P < 0.001). The hybrid white cultivar Vidal blanc, grown primarily for fruit rot-resistant traits, was found to be highly susceptible to the newly described pathogen A. japonicus, as well as the ripe rot pathogen C. fioriniae (P = 0.01). This is one of the first studies to evaluate fruit rot pathosystem diversity in Mid-Atlantic vineyards, and to assess the relative susceptibly of a hybrid cultivar to fruit rot diseases. This information will be used to develop diagnostic resources and to further research and outreach efforts for improving fungal fruit rot management.