An initial assessment of genetic relationships among populations ofFusarium circinatumin different parts of the world

Fusarium circinatum Nirenberg & O'Donnell, the fungus responsible for pitch canker disease, is a destructive pathogen of Pinus spp. Pitch canker was first described in 1946 in the southeastern United States, and since 1987 has been reported in numerous other locations including California, Mexico, Japan, and South Africa. To make a preliminary assessment of relationships between populations of F. circinatum in these different locations, we compared allele and genotype frequencies based on eight polymorphic regions of DNA from 76 isolates of the fungus. Patterns of relatedness indicate that the California and Japanese populations of the fungus share lineages with the southeastern U.S.A. population. Genetic diversity is highest in Mexico, implicating it as the center of origin for the fungus. The association of multiple vegetative compatibility groups with a common multilocus genotype suggests that vegetative compatible group diversity may be generated by mutation, rather than through recombination resulting from sexual reproduction.