ツシママツの遣伝と変異に関する研究 (II) : 母樹別ミショウ系統における幼苗の変異性

Abstract

本研究は有名マツの一つであるツシママツの母樹別家系を育成して, 一連の実験・調査を行ない, 林木育種に関する基礎資料を提供することを目的としている。本報は母樹別家系の幼苗期における諸形質の表現型変異に関する資料をとりまとめたものである。母樹別実生系統について苗畑における3年間に子葉数, 子葉長, 胚軸長, 本葉形成所要日数, 1年生苗の冬芽数, 苗高, 2年生苗の根元直径, 主軸高, 最高軸高, 枝数, 越冬時の形態, 3年生苗の根元直径, 苗高, 枝数, 頂部の越冬形態などの変異を調査し, つぎのことがわかった。1) 2年生苗の越冬時の形態を成葉および幼形葉のつきかたにより成形, 部分幼形, 幼形の3型に分けたところ, 一般に成形がもっとも多く, 部分幼形がこれにつぎ, 幼形は少なかった。これら3つの型に属する幼苗のそれぞれの百分率に関し母樹別系統間に差異が認められた。3年生苗の頂部の越冬形態をAa (主軸が側軸より高い), Ab (側軸が主軸より高い), Ba (Aaと同型であるが針葉をつける), Bb (Abと同型であるが針葉をつける) の4型に分けたところ一般にAaが多く, Bb, Ab, Baの順になるが, 各系統間に顕著な差は認められなかった。2) 量的形質における変異の大きさは, 形質によって大きいものと小さいものがあり, また系統間にも差異が認められた。子葉数は6のものが多く, 系統によって多少の差が認められた。子葉長は系統閲の変異が大きく, 系統間に有意差のある組みわせがかなり多く認められた。胚軸長には特に顕著な差はみられなかった。本葉形成所要日数は系統によってかなり差があることが判明した。冬芽数の変異は大きく, 系統間の差異が顕著であった。1年生苗高, 2年生直径とも系統間では大きな差異は認められず, 2年生苗高を主軸高と最高軸高とに分けてみたが両者の頻度分布はほとんど変わらず, 系統間の差も少なかった。枝数は2, 3年生とも系統間に大きな差は認められず, 3年生の根元直径にも同一傾向が認められた。3) 各形質問の相関の高いものとして胚軸長と主軸高, 主軸高と最高軸高, 2年生直径と3年生苗高, 3年生苗高と3年生直径があり, いずれも1％水準で有意の相関が認められた。冬芽数, 苗高, 根元直径と他の形質間には正の相関を示す傾向が多く認められ, 本葉形成所要日数は3年生枝数を除き, 他の生長に関連するすべての形質との相関係数は負の値を示す傾向があることがわかった。4) 以上述べた表現型形質のなかで母樹別系統間に有意差のある形質は, 母樹系統の育種上選抜の対象となりうる可能性がある。今後, 生育経過と比較検討することにより, これら幼苗形質のうち成木時の形質との相関をみることにより, 早期検定に適切な形質を具体的に指摘できるようになろう。

This work was carried out to investigate variation in the seedlings within or among the half-sib families obtained from twenty mother trees of Pinus densiflora, local variety Tsushima-matsu. One- to three-year-old seedlings grown in the nursery of Kyoto University Forest were used for this purpose. As characters for investigation the followings were chosen: number and length of cotyledonary leaves, length of hypocotyl, days for appearance of adult-form leaves, number of winter buds, growth height, length of main axis, number of branching, main-stem diameter at the base (soil level), wintering form of the top part, and so forth. Results obtained were as follows. 1) Depending on the state whether the young shoot (s) of the top developed adult-form leaves or not, the wintering form of two-year-old seedlings could be classified into three, i.e., adult-, partially juvenile- and juvenile-form. The proportion of seedlings belonging to these forms becomes smaller in the above-stated order, and significantly differs among the half-sib progenies. Several types were also distinguished in the wintering form of the top part of three-year-old seedlings, but remarkable difference among half-sib families was not discernible in regard to the appearance ratio of such variations. 2) Amount of variation within or among the half-sib families differed much or less in each observed quantitative character. Branching number of the three-year-old seedlings had maximum coefficient of variation, i.e. from 31.72 to 45.61, though the distribution somewhat resembled Poisson's. Minimum coefficient of variation was found in the number of cotyledons, i.e. from 5.74 to 10.16. Length of cotyledon and number of days for appearance of adult-form leaves had also small variation. By analysis of variance, it was recognized that some characters had significant difference among the half-sib families. Above all, number and length of cotyledonary leaves, number of winter buds and height of the three-year-old plants showed statistically significant differences in many combinations of two progenies. These characters might be useful for studies on quantitative genetics and breeding of forest trees. 3) Characters of the two half-sib families, which obtained from the trees chosen as "elite", showed no conspicuous differences as compared with those of the other eighteen families. 4) Correlations between characters were varied according to the characters examined, and the partners which showed significant correlation were considerably few. There were positive correlations between height or diameter growth and some of the other characters. Between length of hypocotyl and length of main stem, length of main stem and growth height of plant, stem diameter of the two-year-old seedlings and growth height of the three-year-old ones, stem diameter and growth height in the three-year-old seedlings, the correlations were significant at 0.1% level.