SPHAEROPSIS SAPINEA MORPHOTYPES DIFFER IN AGGRESSIVENESS, BUT BOTH INFECT NONWOUNDED RED OR JACK PINES

Two morphotypes of Sphaeropsis sapinea, designated A and B, are recogn ized in the north central United States. Nonwounded seedlings of red ( Pinus resinosa) and jack pine (P. banksiana) were inoculated with coni dial 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 p enetrated both hosts without wounding. On nonwounded seedlings the fre quency of symptoms wits 97% for A isolates and 18% for B isolates on r ed pine and 42% for A isolates and 6% for B isolates on jack pine. On average, isolates of the A morphotype also were more aggressive than B isolates on wounded seedlings of both pine species (A isolates causin g 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 could be distinguis hed from all B isolates on red pine, but not on jack pine. These obser vations indicate the potential importance of distinguishing between S. sapinea morphotypes encountered in nurseries, plantations, and natura l stands.