Resistance of Pinus ponderosa to Endocronartium harknessii in Pennsylvania. W. Merrill, Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. N. Wenner, Research Assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802, and B. Towers, Forest Pathologist, Pennsylvania Department of Environmental Resources, Middletown 17057. Plant Dis. 70:317-320. Accepted for publication 5 September 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-317.

Incidence and severity of infection by Endocronartium harknessii on Pinus ponderosa from 49 seed sources were measured in central Pennsylvania. Levels of infection varied more within than among seed sources. The greatest variation in resistance was among seed sources from the northern portions of the range of P. ponderosa in Montana, Wyoming, South Dakota, and Nebraska. Some seed sources recommended for reforestation of strip mine spoil banks contained high percentages of susceptible individuals and should not be used where this pathogen occurs.