Armillaria luteobubalina is a bifactorial heterothallic fimgus with multiple alleles at the incompatibility loci. Genotypes and clones of the fungus in eucalypt forests in central Victoria were differentiated by pairings of single basidiospore isolates to determine the identity and distribution of mating alleles or by utilizing intraspecific antagonism between genetically distinct forest isolates. Both methods gave similar results although neither could distinguish between closely related genotypes. Forty-nine patches of forest vegetation infected by A. luteobubalina from c. 24 m2 to 3.5 ha in extent were mapped and isolates obtained from hosts within the patches. Of infected areas, 71% were occupied by a single genotype and the maximum number found in any one patch was three. In multiple genotype patches the different genotypes occupied separate sectors. Clones of some genotypes had a locally discontinuous distribution while others were restricted to a single location. Within areas occupied by a single genotype all hosts were infected by that genotype. Forty-four distinct genotypes were identified. Attempts to artificially inoculate stumps with basidiospores of A. luteobubalina failed. A. luteobubalina is present in these eucalypt forests as a community of genetically distinct mycelia. The size, distribution and development of clones are consistent with the hypothesis that the fungus is dispersed by both basidiospore infections and vegetative growth through host root systems.

Armillaria species cause Armillaria root rot on a wide range of plant species throughout the world. Based on morphology and sexual compatibility, various species of Armillaria have been reported from Australia and New Zealand. These include A. hinnulea, A. fumosa, A. pallidula, A. novae-zelandiae and A. luteobubalina from Australia In New Zealand, A. limonea, A. novae zelandiae, A. hinnulea and a fourth undescribed but morphologically distinct species are recognized. To determine the phylogenetic relationships between Armillaria spp. from Australia and New Zealand, the ITS region (ITS l, S.8S rRNA gene and ITS2) of the rRNA operon was amplified and the DNA sequences determined for a collection of isolates. The ITS sequences of A. ostoyae (from USA) and A. sinapina (from USA) were included for comparison. Phylogenetic trees were generated using parsimony analysis. Armillaria hinnulea was found to be more closely related to Armillaria spp. occurring in the Northern Hemisphere than it was to the other Australian and New Zealand species. The remainder of the Australian and New Zealand Armillaria spp. included in this study formed a monophyletic clade and confirmed separation of species based on morphology and sexual compatibility.

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