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Tolerance of Half-Sib Families of Red Maple to Verticillium Wilt. Alden M. Townsend, Research Geneticist, Shade Tree and Ornamental Plants Laboratory, North Central Region, Agricultural Research Service, U. S. Department of Agriculture, Delaware, Ohio 43015; Winand K. Hock, Research Plant Pathologist, Shade Tree and Ornamental Plants Laboratory, North Central Region, Agricultural Research Service, U. S. Department of Agriculture, Delaware, Ohio 43015. Phytopathology 63:673-676. Accepted for publication 12 December 1972. DOI: 10.1094/Phyto-63-673.

Seedlings representing six half-sib families of red maple were inoculated with Verticillium dahliae. After inoculation, differences among families in foliar symptoms and in the suppression of height growth were highly significant. Illinois and Arkansas sources showed the least foliar symptom development and growth reduction, and Pennsylvania and Minnesota sources the most. Twenty-five percent of the Illinois seedlings showed less than 10% foliar symptoms after two inoculations. All of the Pennsylvania and Minnesota seedlings showed more than 10% foliar symptoms after two inoculations. Isolation of the pathogen from seedlings showing less than 5% foliar symptoms indicated tolerance rather than resistance to the fungus.