Characterization of Fusarium oxysporum f. sp. radicis-cucumerinum attacking melon under natural conditions in Greece

A severe root and stem rot disease of melon was observed during the 2001 growing season on four glasshouse crops in Heraklio, Greece. A total of 43 isolates of F. oxysporum, obtained in Crete from glasshouse‐grown melon and showing fusarium wilt or root and stem rot symptoms, were characterized by pathogenicity and vegetative compatibility. The majority of these isolates was also fingerprinted via amplified fragment length polymorphic (AFLP) analysis. Of the total number of isolates, 22 were identified by pathogenicity tests as F. oxysporum f. sp. melonis, 20 as F. oxysporum f. sp. radicis‐cucumerinum, while one isolate was nonpathogenic on cucumber, melon, sponge gourd and pumpkin. All 22 isolates of F. oxysporum f. sp. melonis were assigned to vegetative compatibility group (VCG) 0134, and all 20 isolates of F. oxysporum f. sp. radicis‐cucumerinum to VCG 0260. Isolates of F. oxysporum f. sp. radicis‐cucumerinum were incompatible with isolates of F. oxysporum f. sp. melonis. AFLP fingerprinting allowed for the clustering of the isolates of the two formae speciales of F. oxysporum along two separate phenetic groups: f. sp. melonis to AFLP major haplotype I, and f. sp. radicis‐cucumerinum to AFLP major haplotype II. Overall, pathogenicity, vegetative compatibility grouping and AFLP analysis were correlated and effectively distinguished isolates of F. oxysporum from melon. This appears to be the first report of natural infection of melon by F. oxysporum f. sp. radicis‐cucumerinum worldwide.