マツ属の生育におよぼすマツノザイセンチュウの影響

Abstract

マツノザイセンチュウは日本在来のクロマツやアカマツに大被害をあたえ, 外国産のマツ属にも被害をあたえている。さらに, マツノザイセンチュウは寄主を枯らさない場合でも, その生長が悪くなることがクロマツやアカマツなどで確認されている。本報告では, P. yunnanensis, 2F_l雑種 (P. thunb. × P. khasya. , P. thunb. ×P. tabulae.), 1F_2雑種 (P. thunb × P. masso.) の4種についてマツノザイセンチュウに対す抵抗性を, その接種により調査し, P. yunnanensisは弱感受性で, 他の3雑種は弱抵抗性であることを確認した。今までにマツノザイセンチュウに対する抵抗性を調査したマツ属のうちで, 生き残った個体 - 2F_l雑種を含む17種169個体の生育経過を測定し, マツノザイセンチュウの生育におよぼす影響を調査した。クロマツやP. thunb. × P. masso. (F_1) では, 他の種に比べてマツノザイセンチュウの接種は, 樹高生長に大きな影響をあたえ, 反面, P. taeda, P. elliottii, P. rigida, P. banksiana, P. sylvestris, P. pinasterでは, 接種は樹高生長に影響しなかった。クロマツでは, 接種された40個体のうち, 4個体で接種後3年自においてもその影響がみられたが, 4年目にはほぼ正常生長に回復していた。P. thunb. × P. masso. (F_1) も同様で, P. nigra, P. strobus, P. thunb. × P. tabulae. (F_1) では2年目まで, P. densiflora, P. tabulaeformis, P. taiwanensis, P. excelsaは接種の影響は翌年だけであった。マツノザイセンチュウは直径生長には, クロマツ, P. tabulaeformis, P. nigraの調査で, 接種後すぐにその影響があらわれ, 2年目にはほぼ生長は回復していた。P. taeda, P. elliottii (F_1) では樹高生長と同様に接種の影響はみられなかった。材積生長に対しては, 樹高生長, 直径生長にみられたようなマツノザイセンチュウの明らかな影響はみられなかった。

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 xylophilus, is widespread throughout Japan except for Hokkaido. Moreover, such pine wilt has been observed in many exotic pine species planted in Japan. It has been reported that, growth inhibition was observed in several pines, such as P. thunbergii, P. densiflora, P. massoniana and P. strobus which did not wither after the inoculation test of the nematode. The inoculation tests of the nematode carried out to four pines in July of 1983 were shown in Table 2, and the resistance or the susceptibility of these pines to the pine wood nematode was judged as following; [Figure omitted] On and after 1977, many pines were inoculated with about 2, 000 nematodes at the nursery in the Kamigamo Experimental Station and in the campus of the Kyoto University. The tested pines divided into two groups of the surviving and the withering because of the resistance or the susceptibility to the pine wood nematode. The growth of the surviving 169 trees belonging to seventeen pines (Table 1) including two F1 hybrid was measured for several years before and after the inoculation. The height growth of P. thunbergii and P. thunb. ×P. masso. (F1) among surviving species was more affected by the inoculation of the nematode than the other fifteen pines tested. On the other hand, the serviving trees of P. taeda, P. elliottii, P. rigida, P. banksiana, P. sylvestris and P. pinaster had grown healthy without the effects of the inoculation. In the third year after the inoculation, the suppressive effects of that still remained on the height growth of four among forty P. thunbergii. But in the fourth year after the inoculation, their growth was almost normal. In the same way, the effects of the inoculation remained in the third year after the inoculation on the height growth of P. thunb. × P. masso. (F1), and on P. nigra, P. strobus and P. thunb. × P. tabulae. (F1), its effects remained in the second year and on P. densiflora, P. tabulaeformis, P. taiwanensis and P. excelsa, the effects remained in the next year only. The inoculation of the pine wood nematode had suppressive effect immediately after the inoculation on the diameter growth of P. thunbergii, P. tabulaeformis and P. nigra, but its growth appeared to have recovered the normal growth in the second year after the inoculation. The diameter growth of P. taeda and P. elliottii was normal, too (Fig. 12). The effects of the inoculation to stem volume growth had appeared immediatley but were not so evidently as height and diameter growth.