マツノザイセンチュウ接種マツ属の生育、とくに接種後3年間の生育について

Abstract

マツノザイセンチュウは, マツ属に侵入して, 枯死させるばかりでなく, 生存個体にも生育阻害をおこすことが, とくにクロマツでみられ, 本報告は, クロマツ, アカマツのほか5種類の外国産マツ属を用いて, マツノザイセンチュウ接種後の3年間の生育経過を調査した結果をとりまとめたものである。供詰マツ属は, P. thunbergii, P. densiflora, P. massoniana, P. pinaster, P. strobus, P. banksiana, P. rigida の7樹種で, 京都大学農学部附属演習林上賀茂試験地および本部試験地の苗畑で調査した。マツノザイセンチュウ接種後, 生き残った個体で, とくにクロマツの樹高生長に接種翌年の生長減退が目立ち, 減退の激しい場合, 接種前の伸長量の約20％しか伸長しなかった個体もみられた。反面, 80％またはそれ以上の伸長量を示し, 影響のすくない個体もみられた。クロマツを平均すると40 - 60％で, 他樹種と比べて, その生長減退は目立った。クロマツの接種翌年の新梢に展開した針葉が, 新梢長に比べて多数みられ, 生長減退が激しい新梢ほど針葉密度が大きい現象がみられた。しかし, 接種の翌々年には, 新梢の生長減退が続いても, このような高密度の針葉の展開はみられなかった。アカマツおよびP. massonianaでは, 最も生長減退の大きかったものでも50％で, 生長減退がみられない個体もみられ, 平均すると約80％になる。P. pinaster, P. strobus, P. banksiana, P. rigida では, 平均値で90％を越え, とくに, P. banksiana, P. rigida では, すべての個体で伸長生長に, マツノザイセンチュウの影響はみられなかった。肥大生長には, クロマツで, マツノザイセンチュウ接種年および翌年に生長減退がみられたが, 2年目には回復していた。マツノマダラカミキリの次世代幼虫の繁殖は, 新成虫の後食, マツノザイセンチュウの侵入によって, 9月下旬までに枯れた樹体にみられ, それらの幹の枯死年の生育は, 春材だけであった。秋材が形成されていた幹にはカミキリは繁殖していなかったが, 10月以後の枯死木で, 秋材がすこしみられる幹にも, 数匹の幼虫が生息しているものが, 少数例みられた。

The withering of Japanese black and red pines, P.thunbergii and P.densiflora, which has been attributed to the attack of the Japanese pine sawyer, Monochamus alternatus, and the pine wood nematode, Bursaphelenchus xylopilus, is widespread throughout Japan except for Hokkaido and. Aomori Prefectures. Moreover, such pine wilt has been observed in many exotic pine species planted in Japan. Growth inhibition was observed in pines, such as P.thunbergii which did not wither after the inoculation tests. In 1979 and 1980, 257 trees belonging to seven pine species, P.thunbergii, P.densiflora, P.massoniana, P.pinaster, P.strobus, P.banksiana and P.rigida, were each inoculated with about 2, 000 nematodes, at the nursery in the Kamigamo Experimental Station and in the campus of the Kyoto University (Table 1 and 2), and their growth was measured for three years after inoculation. The height growth and the shoot elongation of P.thunbergii among the surviving pines was more affected by the inoculation than the six other pine species examined. That is, the height growth of some P.thunbergii in the year after inoculation was only about 20% of the mean growth during the two years before inoculation. There were also a few P.thunbergii whose height growth during the year after inoculation was 80% or more than that during a year of healthy elongation. On the average, these values were within the between 40% and 60% of the normal growth (Fig.6). Furthermore, in the second year after inoculation, the height growth of P.thunbergii was more than that in the year after inoculation, but suppressive effect of the inoculation still remained (Fig. 7). In P.densiflora and P.massoniana, the minimum in the height growth during the year after inoculation was about 50% of the growth of healthy trees in one year. On the average, the height growth of both pines was about 80% of that of healthy trees (Fig. 6). No effect of the inoculation could be detected on the height growth of P.banksiana and P.rigida (Fig. 6). In the case of P.thunbergii, the inoculation of the pine wood nematode had a suppressive affect on the diameter growth immediately after the inoculation, but in the height growth it exerted a great influence during the year after the inoculation. The diameter growth of P.thunbergii appeared to have recovered to normal growth in the second year after inoculation (Fig. 8). In P.thunbergii, the needle density, that is, the number of fascicles per unit length of a shoot elongated in the year after inoculation was larger than that of the healthy normal shoot. This phenomenon was not clearly observed on the shoot of the other six pines. In the second year after inoculation, the needle-density of P.thunbergii was nearly normal even when the shoot elongation of the inoculated trees was suppressed (Fig. 9) Observations of withering pines in Tokuyama Experimental Station have shown that the Japanese pine sawyer can not lay eggs on the pines hibernatedly withering, and on the pines withering from April to June in the year after the parasitism of the pine wood nematode. The propagation of the next generation of Japanese pine sawyer has been observed on the withering pines which had not produced the summer wood. These pines withered rapidly before the end of September after the parasitism of the pine wood nematode through the maturation feeding of Japanese pine sawyer. Most of the withering pines produced the summer wood was not infested with the next generation of Japanese pine sawyer.