林木のさしきに関する研究 : とくに, 植物ホルモンのバランスと発根との関係

Abstract

本報告はさしきの研究の一端としてホルモンと発根との関係を主として発根の容易なポプラおよびメタセコイアについてしらべた結果と, それによってえられた知見をもととしておこなった発根困難樹種アカマツに関する実験結果をとりまとめたものである｡ I. ホルモンと発根 (1) メタセコイアの樹冠の上部と下部とからとったさしほのホルモンをアベナ ･ テストによってしらべ, 発根のすぐれている樹冠下部からのさしほが発根のわるい樹冠上部からのさしほよりも生長促進物質量が多く, 生長抑制物質量がすくないことをみとめた｡ また, スギやメタセコイアのさしきでは採穂母樹の年令がわかいほどよく発根する傾向があるが, これらの樹種では年令のわかい母樹からのさしほほど生長促進物質の生長抑制物質にたいする量的な比率 (ホルモンの比率) のたかい傾向があった｡ (2) ホルモン処理によってホルモンの比率を適当にたかめると発根が促進せられたが, その効果はさしほの内的条件や環境条件によって左右せられる｡ (3) ホルモン処理の効果はもともと発根に非常に適している場合や不適当な場合には小さく, 無処理でおよそ30%の発根率を示すようなさしほでもっとも大きかった｡ II. アカマツのさしき 約10 ~ 13年生のアカマツの側枝を切断処理して発達させた萠芽枝の発根に関係すると考えられる内的条件と普通枝のそれとを比較検討した｡ (4) 萠芽枝は普通枝よりもホルモンの比率がたかかった｡ (5) 萠芽枝は普通枝よりもCの含有量がすくなく, Nの含有量は多かった｡ したがって, C-N比は萠芽枝のほうがひくかった｡ (6) 萠芽枝と普通枝との水浸出液にはポプラのさしきの発根を阻害する作用はみとめられなかった｡ (7) 萠芽枝からとったハタバは普通枝からとったハタバよりもさしつけ後しばらくのあいだの水分収支の均衡がよくたもたれていた｡ 要するに萠芽枝は普通枝よりも発根に適した内的条件をそなえているようであった｡ そこで, 萠芽枝のさしきの発根の良否をしらべた｡ (8) 5月中旬に母樹の側枝を切断処理して発達させた萠芽枝を処理当年の秋と翌春にさしきし, 普通枝よりもかなりよく発根することをみとめた｡ 秋ざしと春ざしとでは春ざしのほうがよかった｡ (9) 萠芽枝は母樹を処理する時期によって生長に差を生じ, 5月中旬頃までに処理した場合には処理年内に十分な生長をとげたが, 6月以降に処理した場合にはその年内に十分生長しなかった｡ 処理年内に十分生長した萠芽枝はよく発根したが, 未発達の萠芽枝はあまりよく発根しなかった｡ (10) 萠芽枝のさしほの芽の数を調節した結果, もっとも小さい芽1個だけつけたさしほがもっともよく発根し, 次いで全部の芽をとってしまったさしほがよく, 全部の芽をつけておいたさしほがもっともわるいことをみとめた｡ (11) 萠芽枝のさしきのホルモン処理はかなり効果があった｡ とくに, 1個だけ芽をつけておいたさしほにおいてもっとも効果があった｡ 次に環境条件について実験した結果を要約すると次のとおりであった｡ (12) さしき用土中の有機物量は多いほどわるく, さしほの枯死腐敗率がたかくなり, 発根率が低下した｡ (13) 75%以上の庇陰下に常時さしつけておくとさしほの枯死率がいちじるしくたかくなり, 発根率が低下した｡ 25 ~ 50%の庇陰を常時あたえると全く庇陰をあたえなかった場合よりもさしほの枯死は多少すくなくなったが, 発根はいくぶんわるくなった｡ (14) 発根に必要なさしき床の温度はおよそ23 ~ 30℃前後であろうと考えられた｡

This report deals with some results of the experiments the authors carried on, as a part of studies on the cuttings of forest trees, with an intention to clarify the relationship between the rooting responses of cuttings and their phytohormones. To make these problems clear, the authors experimented in the first place with the rooting behavior by the method of water culture, using the cuttings obtained from the mother trees of Populus nigra and Metasequoia glyptpstroboides. In the second step the knowledge derived from the first experiment was to apply the experiment on Pinus densiflora cuttings, which was recognized as very difficult material for rooting. 1. Relationship between the rooting responses of cuttings and their hormones. 1) In Metasequoia, the cuttings taken from the lower part of the crown contained more growth inducing substances and less growth inhibiting substances than that from the upper part. In the cuttings of Cryptomeria japonica and Metasequoia, the growth inducing substances seemed to increase, and the inhibiting substances to decrease, in accordance with the advance of age. The rooting was most favorable when the hormone ratio (the ratio of the volume of growth inducing substances to the growth inhibiting substances) was high. 2) Rooting of cuttings was induced when the hormone ratio was adjusted by hormone treatment. The effects of the treatment seemed to vary with the degree of rooting ability of cuttings. The effect, however, was remarkable on the cuttings having a rooting ability of 30% (rooting percentage) in a non-stabilized state, and the effects decreased as the rooting ability rose or decreased from this figure. 2. Cuttings of Pinus densiflora In order to improve the ability of the cuttings to root in P. densiflora, the part of the top part of the lateral branches of the 10--13 years old mother trees were cut out, and from the section developed adventitious branches. 3) The adventitious branches showed a higher hormone ratio than the ordinary ones, and the former contained more nitrogen and less carbon than the latter and showed a smaller C--N ratio. 4) The water exracts of P. densiflora cuttings had no apparent restraint on the rooting of Populus nigra ones. 5) The cuttings of leaf-bunddles obtained from the adventitious branches kept the waters balance for some time being planted compared with the ordinary ones. From these results the authors thought that the adventitious branches provide more excellent conditions of inner part than the ordinary ones for the rootings. 6) When the top parts of lateral branches of the mother trees of 10--12 years old were cut off in the middle of May, the adventitious branches developed. The cuttings of these (adventitious ones) were planted in the autumn of the same year and in the next spring they rooted much better than the ordinary ones. 7) When the top parts of lateral branches of the mother trees were cut off in the middle of May, the adventitious branches reached the full growth within the same year, and the cuttings obtained from these showed good rooting. When the branches of the mother trees were treated, the rooting was not good. 8) The rooting of the cuttings of adventitious branches, which contained only one bud, was best. The rooting of those from which all of the buds was cut off was good in the second place and for those on which all of the buds were left was feeble. 9) Hormone treatment took effect for the cuttings of adventitious branches: the cuttings which retained all of the buds showed a high percentage of the dead cuttings and the rooting percentage was not improved by the treatment. But both the number of roots, and the total length of main roots per rooted cuttings were fairly increased. The cuttings which retained a single bud and the ones from which all of the buds were cut off were both encouraged by the hormone treatment in regard to the percentage of rooted cuttings, the number of main roots, and the total length of main roots per rooted cutting. Therefore, the hormone treatment was especially effective on the cuttings which retained only a single bud. 3. Environmental conditions 10) The percentage of the dead and decayed cuttings became larger in proportion to the amount of organic materials in the cutting medium. 11) Under the shade of 75 ~ 90%, the percentage of rooted cuttings was very small, while that of the dead cuttings was high. In the shade of 25 ~ 50%, the percentage of the dead cuttings was smaller than that of the cuttings which were not given any shade (open) at all. However, it seemed to more or less slow down for the rooting. 12) It seemed that the favorable temperature for a cutting medium ranged from 23℃ to 30℃.