NEW FACTS ON HOST–PARASITE RELATIONSHIPS IN THE HYPOXYLON CANKER OF ASPEN

The isolation of Hypoxylon pruinalum (Klotzsche) Cke. from discolored wood beyond visible canker limits provided the first indication that this fungus invades xylem under sound bark of Populus tremuloides Michx. The strong inhibition of the fungus growth on bark meal agar and the active growth on wood meal agar is another demonstration of this particular host and parasite interaction. Further evidence for this behavior was obtained experimentally with living bark and wood of aspen. These studies have also shown that the fungus produces diffusible substances toxic to the living host tissues. It is concluded that H. pruinatum is a sapwood parasite.