Variation among isolates of Sphaeropsis sapinea in the north central United States.
Isolates of Sphaeropsis sapinea (Diplodia pinea) from Pinus spp. differed in cultural characteristics and virulence. Isolates designated as type A produced fluffy white to grey-green mycelia on a variety of media. Conidia of these isolates produced in culture were 34.3-39.4×12.6-12.8 µm. Isolates designated as type B produced white to black mycelia closely appressed to the agar surface with conidia 33.5-34.3×11.6-12.1 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°, although opt. growth for most type A and B isolates occurred at 25°. Type A and B isolates had identical isoenzyme banding patterns for 4 of 6 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. In the north central United States, type B isolates are apparently opportunistic and colonize wounded or declining host tissues.