Grapevine Leaf Epiphytic Fungal and Bacterial Communities Are Influenced More by Spatial and Temporal Factors than by Powdery Mildew Fungicide Spray Programs

Synthetic fungicide treatments for managing grapevine powdery mildew have been widely applied in vineyards for decades, yet their ecological impacts on microorganisms in the phyllosphere have not been sufficiently studied. To investigate the impact of fungicide sprays on the grapevine leaf microbiota, grapevine leaf epiphytes were collected throughout the growing season from two California vineyards, each treated with identical spray programs. Each spray program was designed to control grapevine powdery mildew and contained five rotating synthetic fungicides. Leaf samples were collected before the first spray and between subsequent spray applications. Amplicon sequencing of ITS2 and 16S rRNA V4 regions was used to compare leaf epiphytic fungal and bacterial/archaeal diversities, taxonomic compositions, and differential abundances of taxa among treatments, locations, and sampling time points. Location (vineyard) and time significantly affected bacterial and fungal community compositions, whereas spray treatment did not. Plant-pathogenic fungi were the dominant fungal guild in both locations, and, in one location, their dominance increased significantly as the season progressed. Botrytis, an important postharvest pathogen in grapes, was significantly higher in relative abundance in one of the locations in the late season and acted as a hub genus in a co-occurrence network. In summary, the overall impact of the different spray programs on microbial community compositions was not significant, suggesting that the shifts of grapevine foliar microbial communities may be driven mainly by spatial and temporal factors rather than specific fungicide applications. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .