Isozyme Variation within and among Host-Specialized Varieties of Leptographium wageneri

Abstract

Isozyme variation of 76 isolates representing the three taxonomic varieties of Leptographium wageneri was studied using starch gel electrophoresis. Of 21 enzymes tested, 10 were polymorphic, having from two to six electromorphs. Only 14 combinations (electrophoretic types) of the 29 electromorphs of the polymorphic enzymes were found, each restricted to a single variety. Within each variety, one electrophoretic type was abundant and broadly distributed, and populations of additional types were geographically isolated or restricted. Ordination of genetic distances (D) among the electrophoretic types revealed three non-overlapping, well separated clusters that corresponded to the three varieties. Gene diversity (H) in each variety was low (0.017 to 0.040), but genetic differentiation between varieties was high, with a coefficient of gene differentiation (GST) for the species of 0.860. These results suggest that the designation of the three host-specialized, morphologic variants as varieties is justified and suggest the rarity or lack of genetic recombination in nature.