ナラ類の集団枯損にみられる辺材の変色と通水機能の低下  [in Japanese] Discoloration of sapwood and blockage of xylem sap ascent in the trunks of wilting Quercus spp. following attack by Platypus quercivorus.  [in Japanese]

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Author(s)

Abstract

近年日本海沿岸で増加しつつあるコナラ・ミズナラの集団枯損は常にカシノナガキクイムシの大量侵入を伴うため, この甲虫による被害であると認識されてきた。しかし枯損の原因は不明である。7月から10月まで, カシノナガキクイムシの穿入や葉の萎凋がみられる個体を伐到し, 樹幹断面を観察して萎凋の原因およびメカニズムについて検討した。穿入孔のある個体すべてに辺材部の褐変つまり傷害心材の形成が認められた。この変色部はすでに通水機能を失った組織である。変色範囲は穿入孔が多い樹幹下部で広い傾向があった。樹幹に色素液を注入して木部の通導を調べるとカシノナガキクイムシ穿入個体では吸入量が非常に少なく, 樹液の上昇が著しく阻害されていることが判明した。カシノナガキクイムシの孔道周辺の大径道管には菌糸の分布が認められ, この甲虫により持ち込まれた菌と推定された。葉の萎凋に先だって樹幹下部では変色が拡大し, 当年輪の大径道管にもチロースが形成されていることから木部の通水は停止していることがわかった。その位置より上部では水分欠乏により材の乾燥や形成層壊死, 葉の萎凋が起こるものと判断された。

Large mortality rates of oak trees (Quercus serrata THUNB. and Q. crispula BL.) during summer months has become a serious problem in districts along the Japan Sea. A specific fungus (being identified) has been detected in wilted oaks and mycangia of the ambrosia beetles (Platypus quercivorus (MURAYAMA)) which make deep pinholes into the sapwood from June onward. To explain the mechanism of wilting, we observed the reaction of tree tissues following beetle attack and fungal infection. The xylem had become widely discolored surrounding beetle's galleries. Vessels in such discolored areas are non-conductive. Conductivity of the vascular system, which was estimated by a dye injection at the base of the trunk, was markedly less in trees attacked by the beetles. Anatomical investigation of these tissue samples revealed that fungal hyphae were distributed in the vessels in the discolored areas especially in those open to the galleries. Tylosis formation was active in large vessels adjacent to the discolored areas. By the start of leaf curling or discoloration, the area of uncolored xylem decreased less than 20% of cross-sections near the base, and large vessels were plugged with tylosis even in the outermost rings. Above that area of maximum discoloration, cambial necrosis and xylem desiccation began for the complete blockage of sap-ascent.

Journal

  • Journal of the Japanese Forestry Society

    Journal of the Japanese Forestry Society 78(1), 84-88, 1996-02-16

    Japanese Forestry Society

References:  18

Cited by:  10

Codes

  • NII Article ID (NAID)
    110002830776
  • NII NACSIS-CAT ID (NCID)
    AN00198561
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    0021485X
  • NDL Article ID
    3927123
  • NDL Source Classification
    ZR21(科学技術--農林水産--林産)
  • NDL Call No.
    Z18-340
  • Data Source
    CJP  CJPref  NDL  NII-ELS  IR  J-STAGE 
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