西瓜の蔓割病(麥凋病)に關する病理學的研究. VII. : 一般考察; 水分通導組織の局部的崩壞説の提唱
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Among the theories offered to explain the cause of wilting produced by the vascular pathogene, these followings are the prominent ones which have been established under experiments. (snip) In his earlier reports, the author denied the theories of embolism of vessels by mycelia, by tyloses or by gas and other different substances produced in the vessel. As to the toxin theories, it was also claimed that the poisonous substances excreted by the fungus or produced within the destructed root tissue are not the direct cause to bring the host plant to wilting. In the former part of this paper, some considerations we r e given to these theories mentioned above. Also, the embolisum theory of DASTUR and injury theory of ROSEN were criticized not to be the cause of wilting. In the latter half of this paper, after giving general discussion to his former reports, the author presented his hypothesis to explain the cause of wilting of the disease; that, is, wilting is the consequence of "the local destruction of water conductive tissue by actual fungal invasion." The fungus which entered at the top of the host plant, soon gains it position in the stele and multiplies there. Then, by the aid of migration of microconidia, new growths are formed in the upper parts of the water conductive tissues. Thus the fungus invades the living tissues surrounding the vessels, so that their power to conduct the ascending sap is lost44). Because, the ascending of conductive water will be performed under perfect border of the vessel wall, when it is ruled by transpiration force rather than by root pressure. If such damages happen on many of the vascular bundles connecting with each other, then the wilt symptom of the affected plant will be resulted. As to the poisonous substance produced by the pathogene, it is suggested that it will prevent the formation of remedial tissues of the host plant, as it precedes the actual hyphal ivasion and weakens the surrounding elements. So that the diseased parts, however they may be at first of the inner local necrotic lesions, are led to unfaborable prognosis; the diseased area will become larger, and at last some partial or whole wilting of the affected plant will take place. In addition to this hypothesis, the rootlet destruction theory and leaf parenchyma destruction theory are also endorsed by the author to explain some cases of wilting. These three theories coincide with each other at the respect that the destruction of the affected tissue by actual fungal invasion is the cause of the wilting of the fungal wilt disease.植物の麥凋病に於ける麥凋現象發現の原因に關し實驗の結果提唱せられ且つ現今支持せられてゐる諸説を著者の方式によつて分類した。これらの多くの諸讀の當不當は著者從來の報告によつて夫々批評せられてゐるのであるが, 本文に於ては一應更に總合的に之等を顧慮したる後, 從前の報告に於て批評を加へなかつたものについて述べた。後半に於ては, 著者の從前の實驗に對する一般的考察をなし, 西瓜の蔓割病に於ける麥凋現象登現の原因は主として菌自體の侵害による水分通導組織の局部的崩壞にありとしたのである。根端又はその附近より侵人したる病原菌は寄主の幼根の心柱内に侵入し, ここに於て繁殖後の轉流によつて水分通導組織の上位部に點々新菌叢の發生を見るに至り, かくてその部に繁殖したる菌は, 水分通導組織の周壁を構成せる生細胞組織を侵害する結果, 遂にその被害部の導管は水分通導機能を喪失するに至る。かかる導管群の被害が一莖中比較的廣範圍に亙つて而も相互略々聯絡して發生するが如き場合に於て麥凋現象が發現するのである。而して本菌の分泌する毒物については, これが影響は寄主の側に於ける防禦組織の形成を抑歴する結果となり, 病患部は増惡し容易に治癒することなく, かくて被害植物の局部的又は全般的麥凋次いで枯死となるのである。著者は自説以外に, 細根の腐敗説及麥凋局部の柔組織の菌自體による侵害説も麥凋現象の發現の原因であるとし, この三者を一括して被害局部の崩壞となし, これが植物麥凋病に於ける凋の原因であるとした。
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