VIEW ARTICLE

Physiology and Biochemistry

Response of Douglas-Fir to Infection by Armillaria ostoyae After Thinning or Thinning Plus Fertilization. J. A. Entry, Graduate research assistant, Department of Forest Science, Oregon State University, Corvallis 97331; K. Cromack, Jr.(2), R. G. Kelsey(3), and N. E. Martin(4). (2)Associate professor, Department of Forest Science, Oregon State University, Corvallis 97331; (3)Research scientist, U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station, 3200 Jefferson Way, Corvallis, OR 97331; (4)Scientist, USDA, Forest Service, Intermountain Forest and Range Experiment Station, 1220 S. Main, Moscow, ID 83843. Phytopathology 81:682-689. Accepted for publication 10 January 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-682.

Second-growth stands of Douglas-fir (Pseudotsuga menziesii) were thinned to a 5- × 5-m spacing (TT); additional plots were thinned and fertilized once with 360 kg of N (as urea) per hectare (TF). An unthinned, unfertilized stand (UT) served as a control. Ten years after treatment, trees were inoculated with two isolates of Armillaria ostoyae. Trees receiving the TF and TT treatments produced greater diameter growth, leaf area, and wood production per square meter of leaf area per year than did those under the UT treatment. Rates of infection by A. ostoyae were highest in trees that received the TF and lowest in trees that received the TT treatment. Concentrations of sugar, starch, and cellulose in root bark tissue were highest in trees receiving the TF treatment and lowest in trees receiving the TT treatment. Concentrations of lignin, phenolics, and protein-precipitable tannins were highest in root bark from TT trees and lowest in root bark from TF trees. Biochemical parameters of root bark tissue were regressed with incidence of infection; coefficients of determination (r²) ranged from 0.07 (starch) to 0.57 (phenolic compounds). Ratios of the energetic costs of phenolic and of lignin degradation to the energy available from sugars (E_pd:E_as and E_ld:E_as) were correlated with incidence of infection (r² = 0.77 and 0.70, respectively). Thinning combined with fertilization may predispose P. menziesii trees to infection by A. ostoyae by lowering concentrations of defensive compounds in root bark and increasing the energy available to the fungus to degrade them.