ISOLATE TYPES OF SPHAEROPSIS-SAPINEA ASSOCIATED WITH MAIN STEM CANKERS AND TOP-KILL OF PINUS-RESINOSA IN MINNESOTA AND WISCONSIN

Isolate types of Sphaeropsis sapinea associated with main stem cankers and top-kill of Pinus resinosa were identified as type A and type B. S. sapinea was cultured from recovering, dying, and dead trees of different ages and with different disease histories from five plantations and one natural stand in Minnesota and Wisconsin. The occurrence of a particular isolate type was related to plantation or stand location but not to symptoms, tree condition, isolation location, or canker size. In general, S. sapinea was isolated more frequently from recovered trees that became diseased in 1985 than from recovered trees that were diseased earlier. In all locations, trees were predisposed to disease by drought, hail, or frost. Cambium was killed only during the year of infection, and S. sapinea colonized only the wood extant when infection occurred. Both type A and type B isolates were facultative pathogens causing an annual canker of P. resinosa.