A comparison of different methods for the identification of genets of Armillaria spp.

In a previous study, somatic incompatibility (SI) was used to map the genotypes (or genets) of three Armillaria species (A. ostoyae, A. gallica, A. cepistipes) at four forest sites. A total of 109 genets was identified among 764 isolates of the three species. The object of the present study was to compare SI with three other methods of distinguishing genets: Random Amplified Polymorphic DNAs (RAPD), mating-type alleles, and isoenzyme analysis. RAPDs and mating-type alleles were used with 73 isolates belonging to 36 genets identified on the basis of SI reactions. A few isolates were assayed for isoenzyme polymorphism. RAPDs, mating-type alleles, and SI were equal in their ability to distinguish genets in the populations tested. In three cases, isolates distinguished by SI reactions included two subgroups with different RAPD phenotypes. In two cases groups distinguished by different SI reactions shared the same set of mating-type alleles. Isoenzyme analysis showed interspecific differences and a few differences between the genets of the same species. These results validate the use of SI as a routine method for epidemiological studies of Armillaria spp. The EcoR I fragment profiles of mitochondrial DNA of the same group of isolates were also assayed. The analysis regrouped the genets into 'mitochondrial types' sharing a common cytoplasm and possibly closely related to one another through sexual reproduction. Each mitochondrial type consisted of one to five different genets.