Studies in Forest Pathology: Xxiv. Polyporus Tomentosus Fr. As a Major Factor in Stand-Opening Disease of White Spruce

Abstract

Stand-opening disease in Saskatchewan spruce forests is characterized by the occurrence of patches, often of an acre or more, of declining and dead trees. Polyporus tomentosus Fr. is a major cause of the disease, which develops slowly, with 20 to 30 years elapsing between initiation of attack and death of the trees. Extensive root decay develops before the above-ground symptoms become apparent. Inoculation experiments have shown that P. tomentosus grows about 1.5 in. per year, and that the fungus is parasitic on white spruce.Polyporus tomentosus may enter healthy roots at a point of contact with infected roots; no evidence was found that it entered through root tips or directly from the soil. The fungus remains viable in infected roots for at least 16 years. The disease is commonly associated with injury caused by root-tunnelling weevils in the genus Hylobius. Host vigor did not appear to influence infection or disease development. In culture, the optimum temperature for P. tomentosus was 20 °C and the optimum pH was 4.5. At lower temperatures P. tomentosus appeared to have a competitive advantage over fungi isolated from dying rootlets. Small seedlings grown in agar with P. tomentosus were killed in 8 months. Under these conditions P. tomentosus was much less virulent than Rhizoctonia, solani Kühn and Phytophthora cactorum L. and C. Schroet.

The Effect of Decay on Growth Rate in a White Spruce Plantation

“…This is particularly true of A. mellea, and even of P. tomentosus and to a certain extent of S. galactinum, three of the four main fungi isolated in this study. Whitney (1962) reported that spruces dying from P. tomentosus infection had 20°/0 or less of the roots still living, and that by then the fungus had decayed the sapwood for short distances around the root collar and had gone one to two feet up the trunk. This was the decay pattern found on many trees in our study.…”

“…It does not evaluate the possible losses due to tree mortality caused by these fungi even though P. tomentosus, the fungus responsible for two thirds of the decay measured, is known to kill trees (Whitney 1962). In addition, Lavallee (1972), after a detailed inspection of all trees on the sample plots, reported that 22% of the spruces living in 1962 were dead in 1972.…”

Site and soil characteristics related to the incidence and spread of Inonotus tomentosus

“…al., 1988;van Groenewoud, 1955;Whitney, 1962;Whitney, 1980). By causing tree mortality, this root rot fungus has an important role as a natural disturbance agent.…”

“…Inonotus tomentosus can be active for several years before any above ground symptoms are evident . These include reduced height growth, chlorosis, and decrease in needle longevity (Merler, 1984;Whitney, 1962). Fruiting bodies are also not reliable indicators of disease because their production is weatherdependent (Kendrick, 1992).…”

“…The study discussed in Chapter II was completed before soil pH was related to I. tomentosus infection (Chapter III) since suggestions have been made in previous literature that some root disease fungi are able to ~ ter the pH of nearby soils (Harley, 1971;Whitney, 1962).…”