A Microbiome-Based Approach to the Management of Grape Powdery Mildew

This report describes the progress we made during the first year of a two-year project that aims to describe the microbial communities (?microbiomes?) that are naturally associated with grape leaves and berries in vineyards. We are interested in these communities because we think they contain strains of bacteria, fungi and/or yeast that can be exploited to delay or predict the establishment in the vineyard of the fungal pathogen Erysiphe necator, which causes grape powdery mildew. Such strains are relevant to grape growers, because they can be incorporated into existing management practices or forecast models for powdery mildew in an effort to reduce the use of fungicides. To identify said strains, we are using a novel DNA-based method called pyrosequencing that is superior over older methods in revealing the identity and relative abundance of members that make up these microbial communities. So far, we have collected over 350 leaf and berry samples from 7 different vineyards in 2 states (California and Oregon), from 5 different clones of Pinot Noir and Chardonnay, and from 6 different stages of grape growth, ranging from flowering to harvest. This large number of samples is necessary to increase our chances of being able to pick out, from the huge number of microorganisms that are naturally present on grape leaves and berries, those that show a negative or positive correlation with the occurrence of E. necator and thus have true potential as challengers or foretellers of the establishment of this fungus in the vineyard. From the surfaces of all leaves and berries we collected, we have isolated bacteria, fungi, and yeasts and have quantified their abundances. We also extracted their DNA for pyrosequencing analysis which is currently underway. A preliminary analysis of a subset of DNA samples provided us with an early view into the bacterial diversity that is associated with Chardonnay leaves and berries. Clear from this analysis is the fact that leaves and berries differ in the types of bacteria that they carry on their surfaces. Does this difference correlate with levels of E. necator on the same leaves and berries? If so, what bacterial types underlie this difference, and can they be used for our purpose? These are some questions that will be addressed in the second year of the project. Our preliminary data set from the first year is the start of a database that will grow during the course of the second year into a depository of DNA-based information which we can use to identify strains with protective or predictive value against grape powdery mildew. The long-term goal of this research is to present grape growers with ?microbiome?-based options for management decisions relating to disease in their vineyards and quality of their product.