Grapevine leaf epiphytic fungal and bacterial communities are influenced more by spatial and temporal factors than powdery mildew fungicide spray programs

Authors: Yang, Hui-Ching; Rodriguez Ramos, Jean; Hale, Lauren; Naegele, Rachel

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2023
Publication Date: 8/11/2023
Citation: Yang, H., Rodriguez-Ramos, J.C., Hale, L.E., Naegele, R.P. 2023. Grapevine leaf epiphytic fungal and bacterial communities are influenced more by spatial and temporal factors than powdery mildew fungicide spray programs. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-02-23-0012-R.
DOI: https://doi.org/10.1094/PHYTOFR-02-23-0012-R

Interpretive Summary: Grapevine powdery mildew is the most important grape disease in California. Fungicide sprays have been widely applied to manage the disease, but their impacts on other microorganisms that can contribute to vine health have not been sufficiently studied. Therefore, in this study we investigated the non-target effect of the fungicide sprays on grapevine leaf microorganisms. We collected leaf surface microorganisms throughout the growing season from two California vineyards, each treated with identical fungicide spray programs. We used genetic markers ITS2 for fungal and 16S rRNA V4 region for bacterial compositions and diversity analyses. We found that location (vineyard) and time significantly affected bacterial and fungal community compositions, while spray treatment did not, suggesting that the shifts of grapevine foliar microbial communities may be driven mainly by spatial and temporal factors rather than specific fungicide applications.

Technical Abstract: Synthetic fungicide treatments for management of 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. The phyllosphere’s microbiome can influence plant health by minimizing disease through surface competition and affect yield and quality of fruit. 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, while spray treatment did not. Plant pathogenic fungi was the dominant fungal guild in both locations and, in one location, its dominance increased significantly as the season progressed. Botrytis, an important post-harvest 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.