Armillaria root disease causes mortality, growth repression and unstocked openings in juvenile stands in the southern interior of BC. The resulting loss of yield will adversely affect the forest sector and present serious challenges to forest resource managers when forecasting timber supply on diseased sites. Planting species of low susceptibility to killing by Armillaria ostoyae can reduce losses in new plantations. In this study, natural resistance mechanisms involving necrophylactic periderm formation and compartmentalization of infected tissue was studied in tissue samples collected from the roots of 20-30 year old western red cedar (Thuja plicata), western hemlock, (Tsuga heterophylla), and Douglas-fir (Pseudotsuga menziesii) trees infected with A. ostoyae. Following penetration by the fungus, a much higher frequency of resistance reactions were induced in western red cedar trees than hemlock and Douglas-fir. Unique resistance reactions involving a hypersensitive response consisting of rhytidome formation and the formation of traumatic resin ducts in the phloem were induced in cedar following invasion by the fungus. Effective compartmentalization following cambial invasion also limited the extent of girdling by the fungus in cedar roots, whereas in Douglas-fir and western hemlock compartmentalization was often incomplete. Surveys of juvenile mixed conifer plantations throughout the southern interior of BC revealed that annual mortality rates (percent of trees killed) in Douglas-fir were several times higher than in western red cedar. The frequency of western red cedar trees showing effective compartmentalization at the root collar was also significantly higher than in Douglas-fir. Results indicate that western red cedar is much more resistant to A. ostoyae than other conifers. The inclusion of cedar in higher proportions when planting infested sites may reduce the overall impact of Armillaria root disease. Extension work developed under this project included a one day field tour in August to demonstrate cedar resistance in the ICH and the preparation of a Decision Aid for Armillaria root disease and options for forest management for the southern interior region of BC. The decision aid includes a revised table of susceptibility ratings for conifers and a decision key that will enable foresters to make informed decisions with respect to Armillaria root disease impacts and minimize losses due to Armillaria in the regenerating stand.
B.J. van der Kamp and M.R. Cleary.
Van Der Kamp, Bart J., Cleary, Michelle R.. 2006. Reducing the impact of Armillaria root disease via mixed species plantations including western redcedar: final technical report. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), Armillaria, Ostoyae, Control
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