Severity of Endocronartium harknessii in Two Provenance Stands of Pinus ponderosa in Michigan. C. S. Thomas, Graduate Research Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. J. H. Hart, Professor, Departments of Botany and Plant Pathology and Forestry, and C. E. Cress, Professor, Department of Crop and Soil Sciences and Agricultural Experiment Station Statistician, Michigan State University, East Lansing 48824. Plant Dis. 68:681-683. Accepted for publication 23 April 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-681.

Transplants (2-1 stock) representing 73 seed sources of Pinus ponderosa were planted at two sites 74 km apart in 1968 in southwestern Michigan. Before being planted in Michigan, 0.5% or less of the stock became infected with Endocronartium harknessii at a Nebraska nursery. In 1982, disease severity (number of galls per tree) was recorded for each tree and mapped. P. ponderosa var. scopulorum was more severely diseased than P. ponderosa var. ponderosa (P = 0.05). Within P. ponderosa var. scopulorum, two southern ecotypes, Colorado Plains and Southern Rockies, were more severely diseased than others (P = 0.001). Resistant and susceptible seed sources occurred within ecotypes of both varieties.