The Influence of the Endophytic Grapevine Microbiome on Pierce’s Disease Development

Pierce’s Disease (PD) of grapevine, caused by the xylem-limited bacterium Xylella fastidiosa (Xf), is a major threat to the grapevine industry. In vineyards that are under high PD pressure, there are interesting examples of vines exhibiting either no symptoms or very mild PD symptoms (disease-escaped). These differences are likely not attributed to the genetics of the plant because all vines in a vineyard are clonal. We hypothesize that the microorganisms inhabiting the xylem in these disease-escaped vines are inhibitory to Xf and subsequently reduce disease severity, due to their shared ecological niche. We have characterized the microbial communities residing in PD-infected vines and compared them to disease-escaped vines and identified a subset of beneficial organisms that are antagonistic to Xf. We characterized the fungal and bacterial endophytic communities using an Illumina MiSeq platform targeting the ITS and 16S rRNA genes, respectively. Pseudomonadales was the most abundant bacterial taxonomic group, and Pleosporales was the most abundant fungal taxonomic group. Some bacterial and fungal phylotypes correlated either positively or negatively with PD severity. Furthermore, we cultured a subset of the endophytic microbes that possessed strong anti-Xf properties and suppressed PD symptom development in greenhouse bioassays. We are also currently assessing the role that members of the grape microbiome play in stimulating plant immunity. We envision harnessing these microbes to construct a beneficial synthetic phytobiome that can be deployed into grapevines during the nursery propagation process.