外国産マツ属の虫害に関する研究 : 第7報 マツノザイセンチュウにより枯死したマツ属について

Abstract

マツノザイセンチュウに起因するクロマツ, アカマツの集団枯損は, 関東以西の西日本に大きな被害をあたえ, さらに拡大している。また, わが国に植えられている外国産マツ属にも被害をあたえている。本報告は, 主として, 京都大学農学部附属演習林上賀茂, 白浜および徳山の3試験地に植えられている外国産マツ属のマツノザイセンチュウによる枯損を調査した結果をとりまとめたものである。枯損マツ属は, P. thunb. × P. masso. のF_1雑種を含めて20種に達し (表-2 - 6), 一般に, マツノザイセンチユウに対して抵抗性があるとみなされている P. taeda, P. elliottii, P. palustris, P. massonianaの枯損も観察された。枯死マツの枯死年の樹高生長は, アカマツ・クロマツ型の伸長をするものでは, 大部分が正常であったが, テーダ・スラッシュマツ型のものは, 前年の伸長量に比べてすくなかった。直径生長も前年生長量よりすくなく, マツノマダラカミキリの次世代幼虫が繁殖している幹には, 春材のみで秋材がみられなく, カミキリが繁殖していない幹には秋材が形成されていた。マツノザイセンチユウに対するマツ属の感受性 (抵抗性) を, 前報の接種試験と本調査の結果から, 前報で未分類であった樹種を加えて4段階lこ分類すると表-7のようになった。

It is well-known that the most severe damage of Japanese black and red pines, P. thunbergii and P. densiflora, which have been attributed to the attack of Japanese pine sawyer, Monochamus alternatus, and the pine wood nematode, Bursaphelenchus xylophilus, are widespread throughout to southwestern Japan. The withering damage of the exotic pines by the pine wilt in Japan had been observed in the pine stands from 1977 to 1981 mainly at the three Experiment Stations of Kyoto University Forest, Kamigamo in Kyoto prefecture, Shirahama in Wakayama prefecture and Tokuyama in Yamaguchi prefecture. The withering of twenty pines including F1 hybrid of P. thunb. × P. masso. by the pine wood nematode had been certified and the propagation of the next generation of Japanese pine sawyer had been observed in about half of the withering pines. In such a case, generally, there was spring wood only in the radial growth of the withering year. The summer wood had been produced in the withering pine stem not infested with the larvae of the pine sawyer. On the case of pine species of densi･thunbergii type, uninodal, on the height elongation, the elongation of these pines was normal in the withering year, too. But on the pines of taeda･elliottii type, multinodal, the height growth of the withering year was less than the year before the withering. The pine wood nematodes were mostly recovered from the stems of these withering pines. The withering pine species observed by these investigations were as follows; Subsect. Gerardianae----P. bungeana, Leiophyllae----P. leiophylla, Sylvestres ----P. nigra, P. pinaster, P. sylvestris, P. massoniana, P. thunb. × P. masso. (F1), P. khasya, Australes ----P. palustris, P. taeda, P. elliottii, Ponderosae----P. ponderosa v. scopulorum, P. engelmannii, P. rudis, P. michoacana, P. pseudostrobus, Oocarpae ----P. radiata, P. muricata, P. greggii, P. ooearpa, Judging from the previous inoculation test and these investigations, the susceptibility or resistance of the pine species to the pine wood nematode was showed in Table 7.