A survey of canker-associated pathogens in declining cold-hardy interspecific hybrid grapevines in Iowa

Grapevine decline is an emerging concern for cold-hardy interspecific hybrid grape (CIHG) cultivars grown in the Midwest, with the fungal taxa associated with this decline remaining poorly characterized. In this study, we conducted surveys across Iowa vineyards in 2023 and 2024, collecting symptomatic samples from multiple cultivars and tissue ages. As a result, over 1,300 fungal isolates were isolated and characterized. Among these, Fusarium, Pestalotiopsis, and Cytospora, generally recognized as pathogens of grapes or other woody plants, were prominently detected. Further analysis showed that the incidence of Fusarium and Pestalotiopsis increased with tissue age, while Cytospora remained consistent. Phylogenetic analyses placed Fusarium isolates within two major species complexes, including well-studied plant pathogens of cereal crops, and identified Pestalotiopsis and Cytospora species related to those reported on grapevines and other woody hosts. Co-occurrence of these fungi was common, with significant variation in incidence and co-occurrence patterns across cultivars, suggesting that host genotype influences fungal colonization dynamics. For example, fewer samples from the cultivar ‘La Crescent’ showed simultaneous detection of Fusarium and Pestalotiopsis compared to other cultivars. While the pathogenic roles of these fungi in CIHG vine decline remain to be confirmed, these results provide a first step for future pathogenicity testing and the development of targeted management strategies to mitigate grapevine decline and its economic impact on CIHG production in the Midwest.