POPULATION-STRUCTURE OF GIBBERELLA-PULICARIS (ANAMORPH FUSARIUM-SAMBUCINUM) FROM POTATO-TUBER DRY ROT IN NORTH-AMERICA AND EUROPE

Gibberella pulicaris is the sexual stage of Fusarium sambucinum, the major cause of potato tuber dry rot in North America and Europe. In a previous study 42 strains from dry-rotted tubers in North America were analyzed for genetic diversity by mating type and vegetative compatibility group (VCG) tests. In the present study, an additional 96 strains from North America, 21 strains from Europe, and six strains from other geographic areas were analyzed. Both mating types, MAT1-1 and MAT1-2, occur widely outside North America. In contrast, all but two, Canadian, strains of the 138 North American strains analyzed to date are MAT1-1. VCG analysis provides additional evidence that genetic diversity of G. pulicaris from potato tubers is high in Europe but low in the United States. These results suggest that the potential for pathogen change due to sexual recombination is low in the United States, but may be higher in Europe. Limited genetic diversity of G. pulicaris in the United States indicates that there are likely to be few barriers to heterokaryon formation and asexual recombination in the field. Thus, the potential exists for rapid spread and persistence of advantageous mutations throughout the G. pulicaris population, which may have contributed to the recent proliferation of strains resistant to the fungicide thiabendazole which has been widely used to control tuber dry rot.