Graduate Thesis Or Dissertation
 

Population structure and incidence of Heterobasidion annosum in grand fir and Douglas-fir on the Nez Perce National Forest, Idaho

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  • Annosus root disease (Heterobasidion annosum (Fr.) Bref.) is causing notable conifer mortality in grand fir habitat types in central Idaho. The most significant mortality is occurring in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco.) trees of all age classes. This project was designed to study some aspects of the general biology of H. annosum in central Idaho. Study sites were selected on the Elk City and Clearwater Ranger Districts of the Nez Perce National Forest, Idaho. The specific objectives of the study were: 1) characterize the population structure of H. annosum on three sites with grand fir habitat types on the Nez Perce National Forest, including identifying the intersterility group(s) present; 2) determine if the relative incidence of the disease on these three sites has significantly increased with clearcutting; and 3) determine if the relative incidence of H. annosum varies between species of trees, and between sizes of trees and stumps on these three sites. Three pairs of stands in the grand fir series habitat types were intensively examined during the summers of 1990 and 1991. Each pair consisted of a 10 to 30-year-old clearcut and an adjacent 80+ year old uncut stand. Basic stand data were collected from 1/125th-hectare (1/50th-acre) plots. These plots were then rated for root disease severity using the following guidelines: 0= no evidence of root disease; 1= H. annosum fruiting bodies and/or decay present; and 2= symptomatic trees present. Plots from each of these ratings were then selected for intensive sampling. Intensive sampling was done on 1/5Oth-hectare (1/20th-acre) plots. Samples were collected using three techniques: 1) stumps were sawed to ground level and wood samples and/or H. annosum fruiting bodies were collected; 2) trees 12.7 cm (5 inches), diameter at breast height (dbh) or larger, were drilled above two major roots with a gas powered drill and the resultant chips were collected; and 3) trees less than 12.7 cm (5 inches) (dbh) were excavated and two roots were collected. All isolations were placed on a selective medium for H. annosum. Vegetative compatibility (vc) plate pairings between isolates were used to describe the vc groups of H. annosum in the study areas. All possible pairings within stands were performed, as well as all possible pairings between adjacent stands. Forty-one vc groups were identified with this plate pairing method. Thirty-three were unique, represented by single isolates. The other 20 isolates fit into eight multiple isolate vc groups. Isozymes from seven enzyme systems were then used to discern differences within multiple isolate vc groups in order to identify possible clonal groups. Four of the eight multiple isolate vc groups had identical banding patterns within each vc group, so were considered clones. Two other multiple isolate vc groups came from the same tree, so were assumed to be clones, although the isozyme work was incomplete. The last two multiple isolate vc groups were separated by a great distance, and proved to have different isozyme banding patterns, and were thus determined to be separate individuals. The largest distance between isolates from the same clone was approximately 136 meters (446 feet). The intersterility group(s) of all collected isolates were identified by examining selected enzyme systems. All isolates belong to the S intersterility group. The most noteworthy conclusions from the incidence work done in this study are as follows: clearcutting stands in the grand fir series habitat types without treating stumps significantly increases the frequency of H. annosum; uncut stands in the grand fir series habitat types are infected with H. annosum, although at relatively low frequencies; and Douglas-fir and grand fir (Abies grandis (Dougl.) Lindl.) have very similar disease incidence rates and are likely very similar in their susceptibilty to infection by H. annosum. The following additional conclusions have been made: 1) Spore infections are apparently the major means of introduction of annosus root disease into these uncut and clearcut stands. Vegetative spread is secondary in importance; and 2) H. annosum is rarely the only root disease present in stands in the grand fir series habitat types in central Idaho. It is often found in combination with other root pathogens including Armillaria sp., Phaeolus schweinitzii ((Fr.) Pat.), and Perenniporia subacida ((Pk.) Donk).
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