Anthracnose is a destructive foliage and fruit disease of cucurbits worldwide, particularly on cucumber, watermelon, and cantaloupe. Three fungal taxa have been implicated in the cucurbit anthracnose complex [Colletotrichum orbiculare (CO), C. magna (CM), and the putative teleomorph Glomerella cingulata var. orbiculare (GC)]. In the past 7 years we have assembled a large geographically diverse collection of cucurbit isolates that have been characterized for virulence, vegetative (heterokaryon) compatibility, and mitochondrial and nuclear DNA RFLPs. All isolates that are pathogenic on cucurbit foliage are CO, belong to one of the four VCGs, and belong to a single mtDNA RFLP haplotype. Three races of CO (1, 2, and 2B) can be distinguished by their disease reactions on cucumber (`Marketer' and `H19') and watermelon (`Black Diamond' and `Charleston Gray') differentials. Race 1 (cucumber pathogen) and race 2 (watermelon pathogen) were the most common. Examination of virulence on cucurbit fruit indicates that CM and GC are more aggressive than CO, indicating that they could primarily be fruit-rot pathogens. Race 1 and 2 have been used effectively for screening disease resistance in cucumber and watermelon. Isolates of CM, GC, and Colletotrichum spp. recovered from fruit lesions were not pathogenic or were weakly virulent on cucurbit foliage and were diverse with regard to VCGs, nuDNA, and mtDNA RFLPs. However, CM and GC were more virulent on cucurbit fruit than CO.
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