GENETIC EXCHANGE AND RECOMBINATION IN POPULATIONS OF THE ROOT-INFECTING FUNGUS ARMILLARIA-GALLICA

Genetic individuals, or genets, of Armillaria and other root-infecting basidiomycetes are usually found in discrete patches that often inclu de the root systems of several adjacent trees. Each diploid individual is thought to arise in an unique mating event and then grow vegetativ ely in an expanding territory over a long period of time. Our objectiv e in this study was to describe the population from which such genetic individuals are drawn. In a sample including 274 collections represen ting 121 genetic individuals of A. gallica (synonym A. bulbosa) from t wo sites in each of four regions of eastern North America, genotype fr equencies at seven nuclear loci were not significantly different from Hardy-Weinberg expectations. Furthermore, allele frequencies at the se ven loci were not significantly different between regions. Additional allelic data from four non-contiguous regions of mitochondrial DNA sho wed little or no population subdivision over the four regions. Analysi s of the distribution of multilocus mtDNA haplotypes revealed some clo nal transmission of mtDNAs between genets and nonrandom mating within sites. Despite the sharing of mtDNA types by some individuals, the ove rall sample contained a high level of genotypic diversity. The apparen t linkage equilibrium between some pairs of loci and the high level of phylogenetic inconsistency among all four loci suggest the occurrence heteroplasmy and recombination among mtDNAs of A. gallica in nature. In laboratory matings of two haploid strains with different mtDNA type s, a low frequency of recombination in mtDNA was detected.