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ABSTRACT
Diploid isolates of Armillaria were collected from a 50 × 25 m plot at each of two sites in the White Mountains, New Hampshire. All living and dead trees were examined for rhizomorphs, mycelial fans and decay. Isolates were identified to species using diploid-haploid pairings, and clones were delineated using somatic incompatibility and six isozyme markers. At a predominantly spruce-fir site, only A. ostoyae was identified and evidence suggested that at least 25 trees (10%) were pathogenically colonized. Isolates from 39 trees were divided into six somatic incompatibility groups; the largest somatic incompatibility group had colonized at least 17 trees. At a mixed conifer-hardwood site, three species of Armillaria were identified. Six somatic incompatibility groups of A. ostoyae were identified among isolates from 32 of 281 trees; the largest somatic incompatibility group colonized 14 trees and was at least 25 m in diameter. At least 14 of the 32 trees from which A. ostoyae was identified were pathogenically colonized. Armillaria gemina (31 trees) and A. calvescens (29 trees) were isolated mostly from epiphytic rhizomorphs on hardwoods, were apparently pathogenic on four of the trees, and were each divided into two somatic incompatibility groups. Two juxtaposed somatic incompatibility groups of A. ostoyae had identical isozyme electromorphs, but each of the other somatic incompatibility groups had an unique combination of electromorphs. The distribution pattern of the somatic incompatibility groups and correspondence with isozyme electromorphs supported the hypothesis that the somatic incompatibility groups represent asexually spreading clones. At both sites, there was little intermingling of clones of the same species; however, at the mixed conifer-hardwood site clones of the different Armillaria species overlapped considerably.
