Experimental field trials model how the climate crisis will alter phyllosphere and carposphere fungal communities of <i>Vitis</i> sp. L’Acadie blanc across growth stages

The climate crisis is changing temperature regimes worldwide, threatening global viticulture and wine production, as temperature is a primary driver of grape development. In Atlantic Canada, temperatures are projected to increase, inducing premature grape ripening. This can impact their biochemical profiles and, consequently, the quality of the vines, in terms of plant health and fruit yield, and therefore the quality of the wines produced. Temperature is also a key factor in determining the composition fungal communities on the leaves (phyllosphere) and fruits (carposphere) of grape vines. Therefore, to better understand how these communities might change under potential future temperature regimes, we experimentally manipulated grapevines (Vitis sp. cv. L’Acadie blanc) in the field. We used on-the-row mini-greenhouses to increase the temperature at different developmental or phenological stages of the fruits, and across the whole season. Phyllosphere and carposphere were sampled at four developmental stages, their DNA was extracted, and the fungal communities were identified via ITS metabarcoding. We found that phyllosphere and carposphere had significantly different community composition, which remained relatively stable throughout plant development. Increased temperature treatments had the most significant effect on fungal phyllosphere communities; we observed that phyllosphere samples exposed to higher temperatures before the onset of ripening maintained fungal communities with higher species richness throughout development. Our analysis showed that the increase in fungal diversity among phyllopshere communities corresponds to enrichments in potential phytopathogenic fungal taxa. However, this increase in phyllosphere fungal diversity was not conserved at other growth stages when the leaves developed at higher temperatures for the whole season. The results of this study will contribute to better understanding the impact of the climate crisis on grapevine phyllosphere and carposphere fungal community composition and assembly. This will allow producers to better adapt to climate variability and to better understand the role that these communities could play on grapevine health.