Abstract
The taxonomic status of Japanese tomato crown and root rot isolates ascribed to Fusarium oxysporum f. sp. lycopersici race J3 was determined on the basis of DNA-DNA reassociation kinetics. As compared with DNA homology among races of forma specialis lycopersici, isolates of race J3 showed relatively low homology (74-88%) with isolates of other races which caused typical vascular wilts of tomato, and shared high DNA homology (96-99%) within the race. By contrast, isolates of race J3 showed high DNA homology (95-100%) with an isolate of F. oxysporum f. sp. radicis-lycopersici, but exhibited low homology (69-87%) with isolates of other formae speciales of F. oxysporum. These results suggest that the causal fungi of tomato crown and root rot in Japan, previously proposed as race J3 of forma specialis lycopersici, should be designated as a different forma specialis: F. oxysporum f. sp. radicis-lycopersici (Jarvis and Shoemaker, 1978).
