Characterization of Species Collected from a Multiple Time-Point Sampling of Cucurbits in South Carolina.

Species of cause root and stem rot in cucurbits, but no formal surveys have been conducted in the United States to identify which species are responsible. The cucurbit hosts bottle gourd, cucumber, Hubbard squash, and watermelon were transplanted in May, July, September, and November into sentinel plots in four and five different fields in 2017 and 2018, respectively, in South Carolina. Eight of the nine fields were replanted in March 2019. Isolates (600) were collected and identified by sequencing DNA of the mitochondrial cytochrome oxidase I region. The four most common species were (45.6% of all isolates), (20.0%), (15.3%), and (12.8%). and were predominantly isolated in May, July, and September, whereas were predominantly isolated in November and March. Isolates of , , and were more virulent than isolates of and at 25°C. Representative isolates were screened in vitro for sensitivity to three fungicides: mefenoxam, propamocarb, and oxathiapiprolin. All isolates were sensitive to mefenoxam and propamocarb, but these same isolates were insensitive to oxathiapiprolin, except those classified taxonomically in clade I.