Worrall James J
USDA Forest Service, Rocky Mountain Region, Forest Health Management, 216 N. Colorado St., Gunnison, CO 81230, USA.
Plant Dis. 2009 Mar;93(3):293-298. doi: 10.1094/PDIS-93-3-0293.
Dieback and mortality of Alnus incana subsp. tenuifolia in the Southern Rocky Mountains apparently began by the late 1980s and have become a concern to land managers. A survey of alder including 68 transects from southern Wyoming to northern New Mexico indicated that, of 6,503 standing stems, 37% were dead, 29% had dieback, and 34% were healthy. Transects intercepted 1,479 m of live and 1,177 m of dead alder canopy. A second, more localized survey with 32 transects in the upper Gunnison River watershed of Colorado yielded similar results. Abundance of live sprouts was inversely related to amount of dieback and mortality in a genet, suggesting that affected genets are dying and not replacing themselves. Damage did not vary substantially by geographic area and was not related to elevation, animal browsing, or distance to nearest road. Distance to nearest stream was weakly, inversely related to severity of dieback and mortality. Symptoms were not consistent with disease of alder caused by Phytophthora alni in Europe, and isolations for Phytophthora species were negative. Cytospora canker, caused by Valsa melanodiscus (anamorph Cytospora umbrina), is the proximate cause of the dieback and mortality.
落基山脉南部灰桤木亚种薄叶桤木的枯死和死亡现象显然在20世纪80年代末就已开始，这已成为土地管理者关注的问题。一项对桤木的调查包括从怀俄明州南部到新墨西哥州北部的68条样带，结果表明，在6503株立木中，37%已死亡，29%有枯死现象，34%健康。样带截获了1479米的活桤木冠层和1177米的死桤木冠层。在科罗拉多州甘尼森河上游流域进行的第二项更具局部性的调查，有32条样带，也得出了类似结果。一个无性系中活萌条的数量与枯死和死亡数量呈负相关，这表明受影响的无性系正在死亡且无法自我更新。损害在不同地理区域间没有显著差异，也与海拔、动物啃食或到最近道路的距离无关。到最近溪流的距离与枯死和死亡的严重程度呈微弱的负相关。症状与欧洲由桤木疫霉引起的桤木病害不一致，对疫霉属物种的分离培养结果为阴性。由黑盘拟茎点霉（无性型为暗孢壳囊孢）引起的壳囊孢溃疡病是枯死和死亡的直接原因。
