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Aspen trunk rot is a fungal disease that causes stem decay heart rot of living aspen trees. The pathogen that causes this disease is the fungus ''Phellinus tremulae''. Most of the symptoms of this disease are internal, with the only external signs of a diseased aspen being fruiting bodies called conks. A single conk found on an aspen can indicate advanced decay of up 82% of the tree volume.〔Pscheidt, J. W., and C. M. Ocamb. "Aspen (Populus Tremuloides)-Aspen Trunk Rot." ''Pacific Northwest Pest Management Handbooks''. Oregon State University, 2014. Web. 21 Oct. 2014.〕 Internal decayed wood of freshly cut aspens is spongy, yellow/white colored, surrounded by black zones of discoloration, and contains a distinct wintergreen smell. The fungus is spread via airborne spores released from the fruiting body which can infect through dead branches, branch stubs, or wounds in the tree. Although no direct management control is known, harvesting aspen stands that have been damaged or harvesting stands before decay becomes advanced minimizes tree loss. Aspen wood is white, malleable but strong, and heat tolerant and therefore has many commercial uses including matches, packing paper, lumber, plywood, pulp, and animal beds. Aspen trees diseased with aspen trunk rot decrease the economic value of the lumber. ==Hosts and Symptoms== Aspen trunk rot affects only living aspen and occasionally a variety of poplar trees. Trembling Aspen ''Populus tremuloides'' and Large-tooth Aspen ''Populus grandidentata'' are two major hosts of trunk rot.〔Volk, Tom. "Phellinus Tremulae, One of the Causes of Heartrot, in Honor of Valentine's Day. Tom Volk's Fungus of the Month for February 2004." N.p., 14 Feb. 2004. Web. 22 Oct. 2014. 〕 In all infected species, the most obvious sign of rot is a conk on the stem of the tree. A conk is the woody fruiting body of the fungus that forms a triangular shape. Conks are perennial and can survive for up to twenty years. They form about five years after the initial infection.〔USDA. "Aspen Trunk Rot." ''Forest Health Protection Rocky Mountain Region''(2011): 1-2. Web. 21 Oct. 2014.〕 As the decay progresses, rot within the heartwood occurs. The rot appears as a yellowish-white spongy material with black zone lines surrounding it.〔Basham, J. T. "Decay of Trembling Aspen." ''Canadian Journal of Botany'' 36 (1958): 491-505. NRC Research Press. Web. 11 Oct. 2014.〕 The main body of rot occurs in the trunk and stem but basal rot can occur as well.〔Ostry, Michael E., and James W. Walters. "How to Identify and Minimize White Trunk Rot of Aspen." United States Department of Agriculture, 1983. Web. 22 Oct. 2014〕 The decayed wood has a distinct wintergreen aroma that signifies trunk rot. At the initial stages, the decay may appear discolored but continue to be hard and firm while at later stages, the rot may becomes brownish and the tree may lose structural strength and snap due to a wind gust or other damaging factor.〔Hebertson, Liz. ''Management Guide for Aspen Heart Rot'' 13.6 (2005): 1-6. ''Forest Health Protection''. US Forest Service, May 2005. Web. 11 Oct. 2014.〕 Aspen trunk rot affects older (50–60 years) trees more than younger trees. Older trees tend to have more wounds and damage. ''Phellinus tremulae'' can maintain a resting state for 20 years, so older trees have a greater chance of being infected.〔Yukon Forest Health, n.d. ''Yukon Energy Mines and Resources''. Web. 22 Oct. 2014.〕 Older trees become diseased and die more quickly than younger trees. Stem wounds also increase the opportunities for infection no matter the age of the tree.〔 In order to diagnose aspen trunk rot, conks are the first sign to look for. Perennial conks with concentric growth rings indicate severe decay because each growth ring signifies a season of disease. It takes many years to build up the concentric rings to indicate severe decay. The conks can appear to have a triangular shape and the lower surface is covered in pores.〔Worrell, James J. ''Decay and Discoloration of Aspen''. N.p.: US Department of Agriculture-Forest Service, 2009.〕 Knots and stem wounds/scars also indicate decay within the aspen tree while cavities and cracks display the inner decay.〔 Aspen trunk rot is a white rotter because the lignin is broken down within the tree, giving the diseased trunk a white appearance. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Aspen trunk rot」の詳細全文を読む スポンサード リンク
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