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Defoliation-Induced Chemical Changes in Sugar Maple Roots Stimulate Growth of Armillaria mellea. Philip M. Wargo, Plant Pathologist, USDA Forest Service, Northeastern Forest Experiment Station, Hamden, Connecticut 06514; Phytopathology 62:1278-1283. Accepted for publication 17 May 1972. DOI: 10.1094/Phyto-62-1278.

Chemical changes induced in roots by artificially defoliating sugar maple trees in the field were examined for their effects on the growth of Armillaria mellea. Defoliation followed by production of new leaves caused a significant decrease in starch content of the roots and an increase in glucose and fructose in the outermost root wood but not in the root bark. Both total number and concentrations of some amino acids increased in the roots of defoliated trees, especially in the outer wood. The fatty acid content of the roots was low, and was not affected by defoliation. Growth of A. mellea was greater in all media amended with extracts of outer wood from defoliated trees, but not in all media amended with bark extracts. Defoliation may predispose sugar maple trees to attack by A. mellea by initiating in roots chemical changes that are favorable for the growth of the fungus.