Identification of races of Colletotrichum orbiculare on muskmelon in South Carolina.
This paper presents the results of a study conducted, using cucumber cultivars Marketer and H19 and watermelon cultivars Black Diamond and Charleston Gray, to determine the races of C. orbiculare present on muskmelon currently grown in South Carolina, USA. In 2013, one muskmelon isolate from Barnwell was identified as race 1, another muskmelon isolate from Barnwell was race 2, and the muskmelon and watermelon isolates from Charleston were race 2. A third muskmelon isolate from Barnwell appeared to be race 2, although significantly more disease developed on H19, which is resistant to race 2, than on the water control. Some watermelon seedlings collapsed due to lesions at the base of the hypocotyl. As a result, mean severity of race 2 isolates was significantly greater on Black Diamond and Charleston Gray (>80%) than on Marketer (19-42%). In 2014, the 8 muskmelon isolates from Barnwell were identified as race 2B, as severity on Black Diamond (mean of 58.6%) and Marketer (16.5%) was greater than on the water controls (0.01-0.2%), Charleston Gray (0.7%) and H19 (1.8%). Some cotyledons on Black Diamond collapsed due to lesions at the point of attachment to the hypocotyl. Thus, for 7 isolates, severity was significantly greater on Black Diamond than on Marketer. This is thought to be the first report of C. orbiculare race 2B from South Carolina.