Variation Among Isolates ofSphaeropsis sapineain the North Central United States

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Abstract
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 .times. 12.6-12.8 .mu.m. Isolates designated as type B produced white to black mycelia closely appressed to the agar surface with conidia 33.5-34.3 .times. 11.6-12.1 .mu.m. 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 idntifcal 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 on declining host tissues.