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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Ash yellows ： ウィキペディア英語版 Ash yellows Ash yellows (Candidatus phytoplasma fraxini) is a disease in ash trees caused by phytoplasma, a specialized group of bacteria which lack a cell wall and attack the phloem of trees. This disease is relatively new so the disease cycle is mostly unknown, although it is thought that insect vectors are used as the mode of transmission. The disease is difficult to diagnose because some symptoms match those of stressed environmental conditions such as drought, flooding, or shallow soil. When trees become infected they can survive for many years or immediately die depending on the environmental conditions and health of the tree. The major symptom of this disease is witches broom which causes branches in tufts. Unfortunately, there are not many strategies for controlling the disease besides avoiding areas where it is more prevalent. ==Host and symptoms== Ash yellows is host-specific and it mostly attacks ash trees, specifically white ash (''Fraxinus americana'') and green ash (''Fraxinus pennsylvanica''). Although this disease mainly attacks ash trees, it has also been found to target lilacs. All ages and sizes of ashes are vulnerable to infection and symptoms will occur within three years of infection. Some of these symptoms include progressive loss of vitality, subnormal growth, and leaves that fail to reach normal size and are often light green to chlorotic.Additional symptoms include branch dieback, cracks in the bark, early color change in the fall, and premature death of trees. This disease is often diagnosed by the presence of a distinct symptom known as witches broom. Witches broom occurs when there is an overgrowth of the branches of the host, resulting in a clumps of branches that resemble the head of a broom. This usually occurs near the soil line but can occur higher up in the tree as well. 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「Ash yellows」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.