Sphaeropsis sapinea morphotypes differ in aggressiveness, but both infect nonwounded red or jack pines.
Two morphotypes of S. sapinea [Diplodia pinea], designated A and B, occur in north central USA. Nonwounded seedlings of Pinus resinosa and P. banksiana were inoculated with conidial suspensions of isolates of each morphotype, obtained from hosts in Michigan, Minnesota and Wisconsin. Wounded seedlings were inoculated with water agar plugs colonized by these isolates. Both morphotypes penetrated both hosts without wounding. On nonwounded seedlings, the frequency of symptoms was 97 and 18% on P. resinosa, and 42 and 6% on P. banksiana for isolates A and B, respectively. On average, A isolates were more aggressive than B isolates on wounded seedlings of both Pinus species (A isolates causing needle necrosis 7.0 cm from the inoculation sites and B isolates 1.4 cm). Based on symptom severity (distance from the inoculation site at which necrotic needles were observed), A isolates were distinguished from B isolates on P. resinosa, but not on P. banksiana.