Biological Species ofArmillaria Melleain North America

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Abstract
SUMMARY Armillaria mellea consists of at least ten reproductively isolated groups, the equivalent of “biological species.” Each biological species possesses bifactorial heterothallism with compatibility discernible by the gross mycelial morphology of paired monosporous isolates rather than the presence or absence of clamp connections and dikaryotic cells. Monosporous testers were obtained from 97 fruiting bodies in North America. Pairings of testers from different fruiting bodies indicated that each isolate belongs to one and only one intersterile group, i.e., intersterility between groups is complete. Nutritional selection applied to confronted auxotrophic strains from two of the biological species revealed no prototrophy (genetic complementation) between the strains of these groups, whereas prototrophy was revealed by the same method within groups. Members of several of the biological species are distributed widely in North America. Isolates may be collected from a broad range of host species or also as saprophytes. The 10 biological species are not clearly distinguishable by unique geographical ranges or substrate specificities. Armillaria mellea is considered to be a complex of morphologically distinct species. This study shows that the taxon is divided into genetically isolated distinct biological species.