Graduate Thesis Or Dissertation
 

Distribution and variation of Armillariella mellea clones in relation to vegetative cover and severity of root rot in Ponderosa pine

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  • Root rot due to Armillariella mellea (Vahl. ex Fr.) Karst. is unusually severe in ponderosa pine near Glenwood, Washington. Isolate relations, clonal variability, vegetation patterns, and climate were examined in relation to severity of disease in this area. Ninety-one isolates from 70 infection centers were examined. Pairings of neighboring isolates showed that 52 clones exist in the area investigated. A survey of vegetation allowed each sampling site to be placed in one of three vegetation types of habitats (ponderosa pine, mixed species, or Douglas fir/grand fir). Examination of clones and vegetation patterns together revealed that some clones were continuous from one vegetation type to the next. Mycelium growth rates, rhizomorph growth rates, and colony dry weights on MDP and malt extract media were measured for all isolates. Differences in these measures between clones and between isolates in different vegetation ii types were statistically analyzed. Significant (p < .001) differences between clones and nonsignificant differences between vegetation groups were found for all measures. Significant (p < .001) differences were found between media for all measures, with MDP being superior for all isolates. Other morphological characteristics (color and density of aerial mycelium, presence of pseudosclerotium, tufts, exudations, and aerial rhizomorphs, and color and form of submerged rhizomorphs) did not differentiate between clones or vegetation groups. These findings indicate that severity of Armillaria root rot in ponderosa pine in Glenwood may be due, not to morphologically or spatially unique clones in the ponderosa pine cover type, but to high pathogenicity of the biological species of A. mellea as a whole in Glenwood and/or to high susceptibility of ponderosa pine in this area. Measurements of A. mellea clones involving more than one infection center showed that the average age of these clones was 466 years, based on a 1.0 m/yr. rate of spread. The age of the largest clone found was calculated to be 1,126 years.
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