Sexuality, Distribution, and Dispersal of Heterobasidion annosum in Pine Plantations of Vermont

Abstract

Mating experiments with monosporous isolates of H. annosum from red pine plantations in Vermont demonstrate that the fungus is heterothallic and unifactorial. Clamp connections are present in tissue isolates from basidiocarps and in mycelia formed from compatible matings. The distribution of clamp connections within these mycelia is irregular and the features of this character are described in detail. The incompatibility factor is multiallelic and 40 alleles were identified in our collections from 53 basidiocarps. These alleles were used as naturally-occurring genetic markers to examine the distribution of the fungus within plantations. The distributional data are used to contribute information regarding dispersal. The genetic evidence suggests that centers of infection within a plantation are not due to the extensive vegetative spread of single clones, but that multiple inoculations are common in the development of infection centers. Nevertheless, the vegetative growth of mycelium does occur across the root systems of adjacent trees.