| 概要 |
Local varieties of Cryptomeria are divided into two main types, the native cultivar and the improved one. The former is furthermore classified into two types the one that have been regenerated by laye...ring or seeding in the natural stands as Urasugi type, and the other that have been cultivated for a long time by cuttings through repeated selection in the districts where the intensive culture have been carried out. The improved cultivar, rather new varieties, which have been propagated by cuttings selecting excellent individual trees from the planted forests originated by seedlings. The native cultivar grows slowly in the early stage of the plantation, it is characteristics, however, that the cultivar keeps constant growth for a long time until the matured stage, and many of the varieties are also fine quality. While the growth of improved cultivars are excellent from the early stage of the plantation. And forest fertilization brings a great effect on the improved cultivars, especially the fertilization in the early stage of the plantation causes to the close stand. Generally the improved cultivar by cuttings is very effective for increasing the growth and improving the tree form and quality, the plantation in mono clone, however, makes the scope of plantation smaller and brings unexpected damages caused by tyhoon, snow, disease, insects, etc., and moreover the plantation of the improved cultivar in excellent growth tends toward the application of short rotation system. And it is apt to decrease the productivity of soil. Furthermore the viability will be decreased by the aging due to repetition of cuttings in mono clone, and the disappearance of many genes will be caused by the breeding of clone. As described above, it is necessary to develop the intensive works under the consideration of various deffections. And furthermore, the study on the breeding of new varieties should be performed by applying the hybrid vigor or establishing gene bank.
スギの地方品種は大別して在来品種と育成品種の二つにすることができる.前者はさらに,ウラスギ型にみられるような天然林において,伏条や天然下種更新がくりかえされた結果,自然淘汰によって成立したものと,集約的栽培が営まれている地域で,古くから自然的人為淘汰が行なわれた結果として成立したものとに分けられる.育成品種は比較的新しい品種で一般には実生の林分(天然林,人工林を問わず)から形質や生長において,すぐれた個体が人為的に選択され,さらにさし木などによる遺伝子固定がなされて増殖されたものである. 古くからの在来品種は,概して初期の生長は遅いが,後年に至るまでよくその生長を持続する傾向があり,材質も比較的すぐれたものが多い.育成品種は,造林初期から生長の速いものが多く,しかも林地施肥の効果が大きく,特に,幼令期の肥培は林分の閉鎖を早めることができる.一般にさし木による育成品種は,生長量の増大,樹形や材質の改良をはかるうえに大きな効果が期待されるが,単一クローンの植栽は,適地の範囲をせばめ,風雪害や病虫害の異常発生を招きやすい.しかも,初期生長の速い品種の植栽は,短伐期作業への傾向を強める一因ともなり,したがって地力の減退を招来する恐れがある.他方では,同一クローンのさし木の繰りかえしは,Agingによる生育能力の低下が予想されまた,クローンの育成は他の多くの遺伝子を消滅させる原因ともなりかねない. したがって,集約栽培をすすめるにあたっては,このような種々の欠点を常に考慮におく必要がある.さらに一方では,遺伝子保存林の設定や,雑種強勢の利用などによる新品種創成への努力が払われなければならない.続きを見る
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Mendeley出力
