VIEW ARTICLE

Ecology and Epidemiology

Variation Among Isolates of Sphaeropsis sapinea in the North Central United States. M. A. Palmer, Research plant pathologist, North Central Forest Experiment Station, St. Paul, MN 55108; E. L. Stewart(2), and M. J. Wingfield(3). (2)Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108; (3)Plant pathologist, Plant Protection Research Institute, Private Bag X5017 Stellenbosch, 7600 South Africa. Phytopathology 77:944-948. Accepted for publication 16 December 1986. 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, 1987. DOI: 10.1094/Phyto-77-944.

Isolates of Sphaeropsis sapinea ( = Diplodia pinea) from naturally infected Pinus spp. in the north central United States differed in cultural characteristics and virulence. Isolates designated as type A produced fluffy white to gray-green mycelia on a variety of media. Conidia of these isolates produced in culture were 34.3–39.4 x 12.6–12.8 ?m. Isolates designated as type B produced white to black mycelia closely appressed to the agar surface with conidia 33.5–34.3 x 11.6–12.1 μm. Type B isolates produced conidia on sterile pine needles incubated in the dark at 25 C, whereas type A isolates sporulated only in light. Type B isolates also produced spermatia-like spores in dark and light. Type B isolates generally grew more slowly than type A isolates at 20 and 25 C, although optimum growth for most type A and B isolates occurred at 25 C. Type A and B isolates had identical isozyme banding patterns for four of six enzymes. Greenhouse inoculations demonstrated that a representative type B isolate required wounds to infect young shoots, whereas the type A isolate did not. Once wounded, host tissue showed no difference in the extent of discoloration between isolates, as demonstrated by field inoculations. In the north central United States, type B isolates are apparently opportunistic and colonize wounded or declining host tissues.