WORLDWIDE DISTRIBUTION OF GENETIC-VARIATION AMONG ISOLATES OF BEAUVERIA SPP

Genetic variation among isolates of Beauveria spp. was defined by an analysis of electrophoretically demonstrable allelic variations of allozyme coding genes. One hundred and forty-six isolates from diverse geographical locations were assigned to forty-seven distinctive genotypic classes. Clustering analysis demonstrated that four morphological species (B. brongniartii, B. vermiconia, B. caledonica and Tolypocladium cylindrosporum) were genetically distinct from each other. However, with the exception of B. brongniartii, which clustered separately with B. amorpha, they were not clearly resolved from lines of B. bassiana. The level of genetic distance shown between cluster groups of B. bassiana indicated that it represents a species aggregate, components of which display overlapping genetic variability with isolates currently assigned to other species. All isolates were homozygous at each locus, consistent with haploidy, except for B. caledonica, which was heterozygous at one of the four loci. In spite of the maintenance of high diversity in B. bassiana, three geographically widespread genotypic classes were found to contain the majority of isolates. This suggests that, in many situations, B. bassiana exists with a clonal population structure. Various other aspects of the allozyme data (the magnitude of genetic distances between populations, gene diversity, and the pattern of distribution of genotypic classes) indicate that chromosomal recombination between different genotypes of B. bassiana spp. is rare or absent.