Factors influencing infection and initiation of decay by the Indian paint fungus (Echinodontiumtinctorium) in western hemlock

Abstract

Sporulation by the Indian paint fungus was maximal during cool, wet periods in the fall. Basidiospores were viable throughout the year, but maximum germination occurred only after temperatures had fallen below 0 °C. It is postulated that infection of western hemlock (Tsugaheterophylla) occurs in spring when a single basidiospore comes in contact with the stub which remains after shade-killed branchlets, about 1 mm in diameter, are broken off at their base. Anatomical studies of branch stub formation showed that this stage is reached around age 40 and that residual stubs must be exposed almost 2 years before they can serve as infection courts. After stub closure, the fungus becomes dormant and can survive in the medullary tissues for up to 50 years or more without causing decay. The possibility is discussed that conditions associated with large branch stubs and other deep-seated injuries, such as logging scars, broken tops, or frost cracks, are responsible for reactivating dormant infections and initiating the decay process. Clarification of the infection mechanism explains observed variations in severity of decay caused by E. tinctorium in different forest associations and provides a simple method, based on host age and stem-ring patterns, for estimating the decay threat in individual trees and stands, without extensive, destructive sampling.