マツ生立木に対する線虫Bursaphelenchus sp.の接種試験 Inoculation Experiments of a Nematode, Bursaphelenchus sp., onto Pine Trees

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九州一円のマツ枯死木から, 線虫の一種Bursaphelenchus sp.が普遍的に検出されることは既報のとおりである。本試験では, マツ生立木にBursaphelenchus sp.を接種してその影響を調べたのであるが, 接種木の多くが枯死し, 本線虫に強い加害性のあることが明らかになった。その概要はつぎのとおりである。1)マツ生立木に対し線虫を1本あたり約600,30,000,1,500,000頭の3段階で接種すると, 30,000頭以上で枯死が起こった。2)接種懸濁液中の線虫, Pestalotia菌および両者を取り除いた洗浄濾液を個々にマツに接種した結果, 線虫を含む接種液のみが強い加害性を示した。3)線虫をマツの一次枝, 主幹地際, 根株などの木質部内に有傷接種すると, 60〜100%の異常, 枯死が起こった。樹皮からの接種では, 無傷区は枯れず, 有傷区では10本中1本だけが枯れた。しかし, 根株の周囲に線虫培養円板を埋めたものは, 接種した5本すべてが枯死した。4)微害, 中害, 激害型の3林分で線虫を3月に接種すると, 激害型林分では異常木, 枯死木の発生時期が早く, 枯死率が高かったが, この傾向は6月接種区では認められなかった。5)月別の接種では, 2月接種区で50%, 3〜8月接種区で70〜100%の枯死が起こり, 9〜10月の接種では枯死はまだ起こっていない。夏期に線虫を接種されたマツの多くは15〜30日で樹脂滲出量が著しく低下し, 2〜3か月後に枯死した。なお, 接種時期の遅速にかかわりなく, マツの枯死は7月以後に起こった。6)本線虫はクロマツ, アカマツ, リュウキュウマツに対して強い加害性を示したが, テーダマツ, バンクスマツ, プンゲンスマツおよびスギ, ヒノキにはまったく加害性を示さなかった。

Epidemic occurrence of a virulent blight of pine trees throughout the southwestern part of Japan, especially in Kyushu district, has long been noticed among Japanese foresters. A large number of pine trees in many stands declined and finally died off ; for instance, about 39-million trees or 380-thousand cubic metres in volume were damaged in 1968. The cause of this damage has been attributed to the attack of bark beetles up to the present time. In the previous paper (TOKUSHIGE & KIYOHARA) the authors reported preliminarily that a species of nematode, Bursaphelenchus sp., was commonly detected in the wood of dead pine trees collected from many localities in Kyushu. To determine the effect of this nematode onto healthy pine tree, several series of inoculation test were conducted in certain pine stands (Table 1). From these experiments the authors came to the conclusions that Bursaphelenchus sp. detected from the dead pine tree is considered as one of the causal agents for the death or pine trees and it plays an important role in the deterioration of pine forests throughout the southwestern part of Japan. Results obtained are summarized as follows : (1) When about 600 nematodes were injected into the heartwood at the base of stem, amounts of oleoresin exudation from the punched wound gradually reduced but the inoculated trees did not die after all ; whereas almost all of pine trees inoculated with the nematodes at the rate of more than 30,000 per tree were finally killed (Table 2). Therefore, pine trees were usually inoculated with 30,000 nematodes per tree in the other inoculation series. (2) Nematodes used as inoculum were multiplied on the colony of Pestalotia sp. isolated from dead pine wood. As inoculum suspension was prepared by washing the Bursaphelenchus-Pestalotia culture, it contained nematodes and conidia of the fungus. However, conidia of Pestalotia and filtrate from the mixed suspension proved to be harmless to healthy pine trees. Only inoculum containing nematodes, pure suspension of Bursaphelenchus sp. and mixed suspension of Bursaphelenchus-Pestalotia, manifested the ability to kill healthy pine trees (Table 3). (3) Inoculation of nematodes into the xylem resulted high mortality rate of the trees, regardless the part of the tree where it was injected ; primary branch, base of stem, or thick root. Negative result was obtained from the inoculation on unwounded bark, and low mortality rate was recorded in the inoculation to wounded one. Five trees, to which disks of pine wood colonized with the nematode and the fungus were placed and burried around their root without wound, were all killed (Table 5). (4) The following results were obtained from the monthly inoculation experiments from February through October : Highest mortality resulted in the inoculation made from June to August, wherein the latent period, from the injection of inoculum nematodes to the stop of oleoresin exudation or to the appearance of wilt symptom, shortened by 15〜30 days or 2〜3 months. In the trees inoculated in the spring season, the latent period was lengthened and their death did not occur before summer. Mortality in this case was lower than that in the summer inoculations. No dead tree was observed up to December 20th in the case of inoculation carried out from September to October (Tables 4,6). (5) Two inoculation series were given in the three pine stands showing different rates of natural infestation. In the inoculation series carried in March, pine trees of the highly infested stand tend to die more rapidly and in higher rate than those of the moderately or slightly infested stands. On the other hand, no such tendency was recognized among three stands in the inoculation series carried in June (Figure 1). (6) It seems certain, from the inoculation test on the various pine species and certain other conifer genera, that Pinus thunbergii, P. densiflora and P. luchuensis are highly susceptible to this nematode, Bursaphelenchus sp., wh

収録刊行物

  • 日本林學會誌

    日本林學會誌 53(7), 210-218, 1971-07-25

    一般社団法人日本森林学会

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各種コード

  • NII論文ID(NAID)
    110002833439
  • NII書誌ID(NCID)
    AN00198561
  • 本文言語コード
    JPN
  • 資料種別
    Journal Article
  • ISSN
    0021485X
  • NDL 記事登録ID
    8404694
  • NDL 雑誌分類
    ZR21(科学技術--農林水産--林産)
  • NDL 請求記号
    Z18-340
  • データ提供元
    CJP引用  NDL  NII-ELS  IR 
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