VIEW ARTICLE

Ecology and Epidemiology

Sources of Inoculum of Sphaeropsis sapinea in Forest Tree Nurseries. M. A. Palmer, Research plant pathologists, Forest Service, U.S. Department of Agriculture, North Central Forest Experiment Station, St. Paul 55108, Present address: Pacific Northwest Forest and Range Experiment Station, Corvallis, OR 97331; R. E. McRoberts(2), and T. H. Nicholls(3). (2)Mathematical statistician, Forest Service, U.S. Department of Agriculture, North Central Forest Experiment Station, St. Paul 55108; (3)Research plant pathologist, Forest Service, U.S. Department of Agriculture, North Central Forest Experiment Station, St. Paul 55108. Phytopathology 78:831-835. Accepted for publication 1 February 1988. 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, 1988. DOI: 10.1094/Phyto-78-831.

Inoculum potential of tissues colonized by Sphaeropsis sapinea was determined by studying inoculum potential and spore dispersal from cones, seedlings, and litter of red pine. Cones from red pine in nursery windbreaks, cones from beneath windbreaks, and diseased nursery seedlings had the greatest inoculum potential. Conidia of S. sapinea were dispersed throughout the growing season from all sources, but most spores were disseminated from April through June, when second- and third-year seedlings were most susceptible to infection. The number of spores produced by individual cones differed among and within windbreaks, and the period of peak spore production by individual cones differed among cones. Disease gradients in seedbeds of first-year red pine at the Wilson Nursery, WI, indicated that most inoculum originated from windbreaks bordering the west end of the seedbeds. The inoculum potential of cones and the pattern of disease distribution in the seedbeds suggest that cones on windbreak trees are the primary inoculum source in seedbeds of first-year red pine.