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POSTERS: New and emerging diseases

Pathogenicity, phylogenetics, and cucurbit susceptibility to a soilborne disease complex of winter squash (Cucurbita maxima) in Oregon
Hannah Rivedal - Oregon State University. Kenneth Johnson- Oregon State University, Javier Tabima- Oregon State University, Alexandra Stone- Oregon State University

Winter squash (Cucurbita maxima cv. ‘Golden Delicious’) grown in Oregon for edible seed has experienced yield losses due to an undiagnosed soilborne disease. Fusarium solani, F. culmorum, F. oxysporum, Plectosphaerella cucumerina, and Setophoma terrestris were associated with symptomatic tissues in field surveys. Phylogenetic analyses of ITS and EF1? gene regions of 241 isolates of these species confirmed their identity. Fusarium solani isolates clustered with F. solani f.sp. cucurbitae race 1. In pathogenicity trials, F. solani produced the most severe symptoms, followed by F. culmorum, F. oxysporum, P. cucumerina, and S. terrestris. Mixed fungal species inoculum produced symptoms greater than F. solani alone. While these trials indicate the disease is primarily caused by F. solani, the complex of F. solani, F. culmorum, F. oxysporum, and P. cucumerina enhances symptoms. To understand the host range, 35 cultivars representing seven cucurbit species were grown at four commercial farms in 2015 and 2017. Farms with a history of cucurbit production had higher disease severity than farms with no cucurbit history. Winter squash and cantaloupe (Cucumis melo) had the highest disease severity, and cucumbers (C. sativus) and a squash hybrid (C. maxima x C. moschata) had the lowest severity. Though winter squash had high severity overall, cultivars ‘Sweet Mama’ and ‘Winter Sweet’ exhibited resistance to the disease and could be grown as alternatives to industry standards.