Cold-hardy interspecific hybrid grape-associated Fusarium species are pathogenic on grapevines and barley.

Cold-hardy interspecific hybrid grapevines (CIHG; Vitis spp.) have expanded grape production in Northern regions of the United States, but mature vineyards in the upper Midwest are increasingly showing grapevine trunk disease-like symptoms, including cordon dieback, skipped spurs, stunted shoots, and vascular discoloration. Previous surveys recovered Fusarium spp. at high frequency from symptomatic CIHG tissues, but their roles as causal agents for vine decline remained unclear. In this study, we characterized Fusarium isolates recovered from symptomatic CIHGs in Iowa vineyards and evaluated their pathogenicity on grapevines and barley. Phylogenetic analysis of concatenated tef1 and rpb2 sequences resolved 88 CIHG-associated Fusarium isolates into 13 species-level lineages across four species complexes, with most isolates belonging to the F. sambucinum species complex and clustering within the F. graminearum clade. Representative isolates of F. graminearum, F. nanum, F. oxysporum, and F. sporotrichioides caused vascular lesions on both CIHG 'Itasca' and V. vinifera 'Chardonnay', with descriptively greater lesion lengths observed on 'Itasca', particularly at the later sampling time. Over 80 grapevine-associated Fusarium isolates were also evaluated on barley florets and/or seedlings. Approximately 40% of the isolates caused greater than 50% floret infection, and 70% exhibited seedling pathogenicity comparable to or greater than that of the positive control strain F. graminearum PH-1, indicating potential host overlap between grapevines and cereal crops. These findings support Fusarium spp. as causal agents of decline symptoms in CIHGs and suggest that Midwestern vineyards may be exposed to diverse Fusarium populations with relevance to both specialty and cereal crop systems.