Graduate Thesis Or Dissertation

Tree vigor and the susceptibility of Douglas-fir to armillaria root disease

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  • The main objective of this thesis was to determine the influence of tree vigor on susceptibility to Armillaria root disease. First, the effect of thinning, fertilizing and pruning on tree vigor of four young Douglas-fir (Pseudo tsuga menziesii var. menziesi,) plantations was explored. Tree vigor was calculated by measuring wood production per unit of leaf area per year. Then, the presence of Armillaria root disease was compared to tree vigor at plot and individual tree levels, to determine the relationship between tree vigor and the susceptibility to the disease. Mating tests, somatic compatibility tests, and isozyme analysis were used to determine the species and genets of Armi/aria occuring in the study sites. Tree vigor and growth were substantially increased by thinning, and neither fertilization nor pruning showed an important effect. Armi/aria ostoyae was the only Armi/aria species found causing tree mortality. Few, large genets characterized the population structure of this species, suggesting that vegetative spread over a long period of time was the dominant event in occupying the area. Armillaria ostoyae seemed to be aggressive enough to produce mortality where it was present, regardless of the vigor status of the host. It is concluded that increasing tree vigor as a strategy to reduce disease losses may not be a feasible option.
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