Mechanism of induced disease resistance in the bark and sapwood of western redcedar

Samples of sapwood and bark of western redcedar were collected at 3 day to 6 week intervals after injury and extracted with water, chloroform and acetone. Extracts were tested for the presence of some common heart-wood compounds and in vitro fungi toxic properties. Extracted samples collected 6 weeks after injury were inoculated with a decay fungus, and the resulting weight losses determined. No heartwood compounds were detected in any extracts, and no extracts were fungi toxic in vitro. Weight losses following decay of extracted chips indicated that decay resistance was initiated in the bark and sapwood. Thus, these tissues possess a mechanism of disease resistance induced by injury. It is concluded that this resistance results from the deposition of a toxic substance that is unextractable with water, chloroform, or acetone. The alteration of sapwood, if not the bark, is analogous in certain respects to the formation of reaction zones in the sapwood of various trees, since these zones are induced by injury and are characterized by abnormal toxin formation. However, the toxins formed in other trees are normal heartwood constituents, and in this respect apparently not parallel to the toxic substance induced in western redcedar.Forestry, Faculty ofGraduat