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Genetics

Population Structure and Genetic Analysis of Field Resistance to Thiabendazole in Gibberella pulicaris from Potato Tubers. Anne E. Desjardins,Mycotoxin Research, National Center for Agricultural Utilization Research, USDA-ARS, 1815 North University Street, Peoria, IL 61604; Elizabeth A. Christ-Harned(2), Susan P. McCormick(3), and Gary A. Secor(4). (2)(3) Mycotoxin Research, National Center for Agricultural Utilization Research, USDA-ARS, 1815 North University Street, Peoria, IL 61604; (4)Department of Plant Pathology, North Dakota State University, Fargo 58105. Phytopathology 83:164-170. Accepted for publication 22 October 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/Phyto-83-164.

Forty-two strains of Gibberella pulicaris (anamorph: Fusarium sambucinum, synonym F. sulphureum) were obtained from dry-rotted potato tubers collected in North America between 1963 and 1991. Twenty-four of 25 strains collected in 1990 and 1991 were resistant to the fungicide thiabendazole (TBZ), which is widely used to control potato dry rot. The 17 strains collected between 1963 and 1986 were all very sensitive to TBZ. In laboratory tests, most TBZ-resistant and TBZ-sensitive strains were virulent on potato tubers and produced trichothecene mycotoxins in liquid culture and in potato tubers. All 42 strains were characterized for sexual compatibility by crosses with tester strains and for vegetative compatibility by complementation of nitrate-nonutilizing mutants. Twenty-one (50%) of the strains belonged to one widespread vegetative compatibility group (VCG 01). Twelve strains (26%) belonged to two additional overlapping groups (VCG 03 and 04). Forty strains were mating type 1. Two strains were mating type 2 and belonged to a unique group (VCG 02). All TBZ-resistant strains were vegetatively compatible with TBZ-sensitive strains collected in previous years. Genetic analysis indicated that TBZ resistance was stable and inherited as a single gene or as closely linked genes, and that resistance mutations of independently isolated field strains were allelic. These results suggest that TBZ-resistant strains are competitive and have the potential to spread and persist in the G. pulicaris population that causes potato tuber dry rot in North America.