Sensitivity to Thiabendazole inFusariumSpecies Associated with Dry Rot of Potato

Abstract

Fusarium species associated with dry rot of potato tubers during 1992 and 1993 were characterized. We isolated fungi from wounds or preexisting lesions on randomly collected samples of seed, tablestock, and processing 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 pathogenic isolates of F. acuminatum, F. avenaceum, F. crookwellense, F. culmorum, and F. equiseti also were isolated. Using logistic regression analysis, significant relationships were found between the Fusarium species isolated and factors such as tuber use, method of isolation, year of isolation, and state of origin of the sample. Of the 200 Fusarium isolates, 82 grew at ≥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, and F. culmorum. TBZ-resistant isolates were obtained from most locations and all tuber types. The effective dose for 50% reduction in growth differed among isolates of F. sambucinum and F. solani, suggesting that there may be multiple beta-tubulin mutations that confer resistance.