Studies on the interspecific and intergeneric hybridizations between Lolium and Festuca

For the purpose of creating new forage crop suitable to warmer region of Japan, the authors intended to raise the interspecific and intergeneric hybrids using four main graminae harbacious plants, perennial ryegrass (Lolium perenne L.), Italian ryegrass (L. multiflorum Lam.), tall fescue (Festuca aruudinacea Schreb.) and meadow fescue (F. pratensis Huds.). For the first step, we studied on the crossability between these species, comparison of the morphological characteristics and cytological analysis of hybrid plants. The results obtained are as follows. 1. Intergeneric hybridization was not so hard, although the results were different in cross combinations, namely, we could get the hybrid plants more easily when Lolium sp. were used as maternal plants than reciprocal crosses. The interspecific hybridization was much easier than the intergeneric hybridization. But, back crosses to F_1 plants by parental species were very hard, and we got only three hybrid seeds which did not germinate. Furthermore, we could not get any seeds by sib-crossing between different F_1 plants or selfing in all hybrid plants tested. The percentage of seed setting by selfing differed in species and it was about 30% in tall fescue against 1.6% in perennial ryegrass. The results were compiled in Tables 1-5. 2. General appearance of hybrid plants resembled more to Festuca sp. than to Lolium sp., although dimentions of such characters as culm length, ear length, number of ears per plant, number of rachis per ear and number of nodes per ear were intermediate or resembled more to either parental species. Hybrid seeds were very light compared with parental seeds, and interspecific hybrid seeds were pretty heavier than intergeneric ones. In general, the degree of variation was large in hybrid populations. All hybrid plants delayed somewhat in the date of heading and flowering than parental species and showed long duration of flowering time. About 24% of the hybrid plants had completely degenerated anthers and the other showed very high pollen sterility ranging from 0.1 to 1.1%. The data on measured characters were presented in Figs. 1-3, Plate 4 and Tables 6-10. 3. As haploid chromosome number was 7 in Lolium sp. and 21 in Festuca sp., genus hybrid plants contained 28 chromosomes in somatic cells. In the meiotic division of the hybrid plants, it was not so easy to distinguish complete configurations, then we counted the number of univalent chromosomes for convenience. The frequency of univalent chromosome varied widely from 0 to 11 in either cell of the same anther or different plant. But, the average number of univalents did not differ so widely in cross combinations, ranging from 3.10 in L. mult.×F. prat. to 3.86 in L. mult.×F. arund. Such irregularities as chromosome bridges, laggards and fragments were also frequently observed in later stages of reduction division. From these analysis we supposed that the genome of Lolium sp. is semi-homologous to some genome of Fastuca sp. The results of cytological studies were compiled in Tables 11-14 and some microphotographs are presented in Plates 5 and 6. 4. We are now going to produce fertile amphidiploid plant by colchicine treatment or r-ray irradiation of hybrid seeds or F_1 plants.1. 本研究はLoliumとFestucaの属間雑種から,両者の勝れた形質を兼ね備えた,わが国暖地向き牧草の育成の可能性を検討する目的で,九州大学農学部育種学教室で着手された成果を報告するものである. 2. 交配にはLolium perenne L.,L.multiflorum Lam.,Festuca arundinacea Shreb.,F.pratensis Huds.の4種を用い,これら4種間における種・属間交雑の難易性,形態的特性の比較,細胞学的研究の3方面から検討された. 3. LoliumとFestucaの交雑成功率は,交雑の方向によつて異なり,染色体数の少ないLoliumを母にした場合によい成果があげられ,かつ,perenneの場合がmultiflorumの場合よりも成功率は高かつた. 4. 種間交雑の場合は,属間交雑に比して,着粒率,発芽状態,雑種個体の作出などすべての点で勝れていた. 5. F_1植物に1両親を戻し交雑した結果では後代植物を得ることはできなかつた. 6. 両親は一般に他殖性作物とされているが,かなりの自殖種子が得られ,とくにF. arund.では29.4%の自殖率がみられたが,F_1植物の自殖では全く種子が得られなかつた. 7. F_1植物の外観は,全般的にはFestucaに近い中間性を示し,とくに花序は円錐花序を呈し,葉はFestucaよりも繊細になり,またすべてのF_1植物が永年性となつた. 8. F_1植物の稈長はLoliumに近いかやや劣り,変異の幅が広く穂長は両親より短く,穂数はFestucaに近い値を示した. 9. F_1植物の1穂全小穂数,花序の節数および1次枝梗数は,いずれも両親の中間値を示した. 10. F_1植物の花粉母細胞における1価染色体の出現頻度は0から最高11まで観察され,組合わせで若干の相違がみられたが,1細胞当りの平均では3.10～3.86で著しい差はなかつた.両親では1価の出現頻度は極めて少なく,1細胞当りの平均で0.18～0.40で,ほとんど正常な2価対合がみられた. 11. F_1植物では第1および第2分裂後期において遅滞染色体,染色体橋,断片染色体等の異常が観察され,第1分裂終期および4分子期にかなり高頻度の小核が見られた. 12. F_1個体の24%では葯が退化して花粉が認められなかつたが,残余のF_1植物でも花粉稔性は0.1～1.1%と著しく低かつた,親植物では25%から95%までの広い個体変異がみられた. 13. 戻し交雑の結果からF_1植物は雄性不稔であるばかりでなく,雌性不稔と推定した. 14. LoliumのゲノムはFestucaのゲノムと部分相同性を示し,両属間に系統発生的な関係が存在するものと推定した. 15. LoliumとFestucaの属間雑種から新らしい牧草を育成する仕事を推進するためには,さらに広汎な戻し交雑の採用とF_1植物から複2倍体植物を育成する必要がある旨を論議した