Coix 属の改良に関する育種学的研究 (I) : 種間雑種ハトムギ×ジユズダマの F_1 植物について

1. Coix属は分類学上Zea属の近縁種である。Coix属を改良してZea属に代る飼料作物を育成する目的をもつて, 1956年以来Coix属内の種間交雑を開始した。即ち, ハトムギにジユズダマの越年性, 耐湿性等を導入する為に交雑試験を行つた。交雑は正逆2方向について行つたが, 結実率は夫々43.08%, 50.30%であり, 両者の交雑は比較的容易である。又交雑の方向により結実率に有意の差は認められなかつた。2. 種子の発芽試験の結果, ハトムギは83.93%の発芽率を示して最も高く, ジユズダマは45.31%で最も悪かつた。F_1はいづれも両親の中間の値を示し, 正逆交雑により夫々68.81%, 57.14%を示したが, 両者の間に有意差はなかつた。交雑の成功度として, 結実率との相乗積を算出すれば, 夫々2.96及び2.87で, 略々同様の結果を示した。3. 本交雑に於けるF_1植物は, 諸種の形質に関して著しくヘテローシスを表わした。即ち, 草丈, 分葉数, 葉数の3形質は, 生育の初期より旺盛な生育を示し, 特に分葉数は生育のごく初期に, 草丈及び葉数はその後期に増加程度が著しかつた。諸種の形質を成熟期に測定した結果, 草丈, 分蘗数, 葉数, 葉巾, 葉面積, 稈径及び生体重等は大きい値を示した方の親よりも更に増量したが, 就中草丈, 分蘗数, 葉巾, 生体重には有意の差を認めた。出穂期は両親の中間に分布し8月5∿10日であつた。刈取後の再生力は, 草丈, 分蘗数共に両親より強い傾向を示した。猶正逆交雑による2つのF_1の諸形質の間には有意差はみられなかつた。4. 花粉及び種子稔性は, 両親はいづれも良好であり, 略々90%以上の値を示した。之に対しF_1は正逆交雑共に両稔性の低下を示し, 花粉稔性に於いて60%以下, 種子稔性では30%前後に低下した。5. 両親の柱頭色は共に白色であるが, F_1のそれは鮮明な赤紫色を呈した。又種子形状はF_1はすべてジユズダマ型を示し, 卵形, 黒褐色, 硬質であり, ハトムギの長楕円形, 茶褐色, 軟質の特長は見られなかつた。育成したF_2個体の数が少なかつたが, その分離より, 之等はいづれも補促因子による作用と思われる。6. 成熟期に於ける風乾物の飼料分析の結果, 両親及びF_1の間には, 特に著しい増減がみられなかつたが, ヘテローシスによるF_1の収量の増加に併つて, 必然的に反当可消化養分収量は増大するものと思われる。7. F_1の全個体は圃場に於いて完全に越年した。即ち, ジユズダマの越年性がF_1に導入された為であり, 且つ越年後のF_1の生育は旺盛で, 再びヘテローシスを表わした。8. 本実験の結果, ハトムギとジユズダマの種間交雑に於いて, そのF_1植物の主要形質にヘテローシスを示し, 且つ, 越年性が附与され, 其他に形質の劣変化を認めなかつた事は, 飼料作物としてのCoix属の改良という見地より, 極めて有意義であると考える。1. The present paper deals with the results of investigations on the interspecific hybridization in genus Coix. This crossing was attempted between two Coix species : Hatomugi, Coix Ma-yuen ROMAN. (2n=20)×Juzudama, C. Lacryma-Jobi L. (2n=20) and its reciprocal combination. Now Hatomugi has been utilized for forage crops, but this crop is annual plant. On the contrary, Juzudama is perennial in growth and it has high resistance to bad conditions of environment. 2. In this interspecific hybridization the crossability in two crosses (Hatomugi×Juzudama and its reciprocal cross) were easy comparatively. That is, the percentages of seed set showed 43.08% and 50.30% respectively. The germinating percentage of F_1 seeds, obtained in this crossing, was inferior to Hatomugi (83.93%), but superior to Juzudama (45.31%). The percentages of F_1 seed germination were 68.81% and 57.14% respectively. 3. F_1 plants in this interspecific hybridization showed "Heterosis" for several characters. Namely, plant height, number of tillering, number of leaf, leaf width, leaf area, culm diameter and plant weight were vigorous as compared with both parents. Especially, in plant height, number of tillering, leaf width and plant weight the significant differences were recognized in statistically. In the early stage of development, all F_1 plants pointed out the heterosis. Heading date of F_1 plants was about 5th-10th August that is in the middle of the heading date of both parent plants. The ability of regeneration showed a more vigorous tendency in plant height and number of tillering than both parents. The significant differences were not recognized in statistically between the characters in both F_1 plants. 4. The pollen and seed fertility in F_1 plants were lower than both parents. That is, the fertility showed less than 60% in pollen and thereabout 30% in seed, in spite of the both fertility in parents showed more than 90%. 5. In this experiment, the inheritance in a few characters was observed. The stigma colour showed clear red-violet in all F_1 plants though both parents have white stigma. The character of seed riped on F_1 plant showed Juzudama type, that is ovate in seed shape, black-brown and hard seed coat. Although F_2 plants were scanty in this year, according to the segregation of F_2 plants, such phenomena will be explainable by complementary factors. 6. According to the chemical composition in dry samples at the ripenning stages, between the both parents and F_1 plants there were no difference remarkably. 7. All F_1 plants spent the rest of the year at the field. In the next year, the growth of F_1 plants was vigorously in compared with Juzudama that was perennial. 8. From these results mentioned above, it will be identified that the improvement of genus Coix as a forage crop is very significant, bacause the F_1 plants in this interspecific hybridization show heterosis and all F_1 plants show perennial type completely