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Response of Western Coniferous Seedlings to Infection by Armillaria ostoyae Under Limited Light and Nitrogen. J. A. Entry, Graduate research assistant, Forest Science Department, College of Forestry, Oregon State University, Corvallis 97331; K. Cromack, Jr.(2), E. Hansen(3), and R. Waring(4). (2)(4)Associate professor, professor, respectively, Forest Science Department, College of Forestry, Oregon State University, Corvallis 97331; (3)Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 81:89-94. Accepted for publication 22 August 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/Phyto-81-89.

During the first 16 mo of growth, seedlings of five western coniferous species were subjected to one of three physiological treatments: balanced light and nutrients, light limitation and adequate nutrients, or nitrogen limitation and adequate light. Four-month-old seedlings were inoculated with one of three isolates of Armillaria ostoyae. After 1 yr, disease severity was significantly greater when light or nitrogen were limited than when they were balanced. Seedlings responded to light or nitrogen limitation by lowering the concentration of phenolic compounds and/or raising that of sugar in root tissue. Such changes lower the ratio of the energy required for phenol or lignin degradation (Epd and Eld, respectively) to the energy from available sugar (Eas), which may indicate decreased disease resistance in seedlings. Decreasing Epd:Eas ratios were correlated with increasing disease severity and may be important in explaining why pathogenic species of Armillaria preferentially invade stressed seedlings.

Additional keywords: phenolic:sugar ratio, thermochemical budgets.