SENSITIVITY TO THIABENDAZOLE IN FUSARIUM SPECIES ASSOCIATED WITH DRY ROT OF POTATO

Fusarium species associated with dry rot of potato tubers during 1992 and 1993 were characterized. We isolated fungi from wounds or pre exis ting lesions on randomly collected samples of seed, tablestock, and pr ocessing tubers, primarily from the northeastern United States. Of 154 samples, 99 yielded one or more Fusarium isolates, 98% of which were pathogenic on potato tubers. The most frequently recovered pathogenic species were F. sambucinum, F. solani, and F. oxysporum, but pathogeni c isolates of F. acuminatum, F. avenaceum, F. crookwellense, F. culmor um, and F. equiseti also were isolated. Using logistic regression anal ysis, significant relationships were found between the Fusarium specie s isolated and factors such as tuber use, method of isolation, year of isolation, and state of origin of the sample. Of the 200 Fusarium iso lates, 82 grew at greater than or equal to 5 mg/liter of thiabendazole (TBZ) in V8 agar and were considered resistant to TBZ. These included isolates of F. sambucinum, F. solani, F. oxysporum, F. acuminatum, an d F. culmorum. TBZ-resistant isolates were obtained from most location s and all tuber types. The effective dose for 50% reduction in growth differed among isolates of F. sambucinum and F. solani, suggesting tha t there may be multiple beta-tubulin mutations that confer resistance.