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.