2倍体

生態

育種

交雑

f_1×m_2 H: index of heterosis, m_1:mid-parent value of the number of days until blooming, f_1:F_1 hybrids value of the number of days until blooming, m_2:mid-parent value of the plant height, and f_2:F_1 hybrids value of the plant height. It was clarified, through the comparisons of the index numbers with all the crosses raised, that the F_1 hybrids took the value under 1.0 were rather scarce, and the hybrids showing above 1.1 index attained to 76% of the crosses examined. Moreover, the index numbers of 45% of all the hybrids attained to above 1.2. 5. Top-crosses were tested to make clear the efficiency of the cross-combinations, revealing that the "Ball's Supreme Red" was much more suitable than the "Lucky Strike" in inducing heterosis in the earlier flowering, though the later variety was, in turn, more suitable than the former in the plant height. Thus it becomes to be interesting for the practical purpose that the "Lucky Strike" can develop much more steady stem than the "Ball's Supreme Red". 6. Larger number of foliage leaves could be produced on the stems corresponding to the increase of the plant height, excepting only few examples not accompanying any noticeable heterotic expressions. 7. The growing thickness of stems and the number of florets were usually no less influenced under various environmental conditions, so that with these characters there could not ascertained any definite heterotic tendencies. 8. The characters such as the flowering time, the plant height, and the number of leaves developed, did not show any significant differences between the reciprocal crosses. Also there could not observed any different heterotic tendencies between the reciprocal crosses, with some rare exceptions. These situations have been ascertained exclusively with both the 2x and the 4x forms used. Coefficients of variance with those characters varied only slightly between the reciprocals and also behaved quite similarly under various environmental conditions. 9. It may be one of the most urgent requisites for the future breeding techniques of raising F_1 hybrid varieties that we could endow each of their desirable characteristic the definite progressional direction of the development of heterosis. For this purpose, the pedigree selections of "Lucky Strike" were entertained by the author, succeeding at last in raising 3 genotypically distinct strains, i.e., the early bloomer with medium height, the medium bloomer with medium height and the late bloomer with tall height, respectively. And F_1 various hybrids were raised, through the crosses using each of those three different strains as the mother parent, revealing certain facts about heterotic phenomena, i.e., these F_1 hybrids, raised through the crosses with a certain male parent strains, took quite resembling appearance or, in some cases, more heterotic one to any one of their mother strains with the individual characteristics concerned. And this fact will suffice to give a valuable suggestion for utilizing an effective cross-combination towards the future well-planned breeding programs. And moreover, it was made clear through there F_1 crosses that the former two strains, which were quite different in their appearances from each other, behaved, in turn, genotypically quite similarly. Thus the gene analysis of the unknown forms will be duly accomplished, to some extent, through the artificial raising of F_1 hybrids between those forms. 10. The grade of seed-fertility through cross-pollination was somewhat lower than that through self-pollinations. Mother strains showing higher fertility by the selfing cod produce higher yield of seeds. F_1 hybrids could obtain, in general, a good yield of seeds, reading even to 2-3 times of the amount of seeds set per capsule by the selfing. Such circumstances will give a clear insight towards the utilization of the double-crosses as a fruitful breeding technique, and the further progress of introducing superior F_2 form will become to be quite practicable in our grading. Throughout the F_2 generations of the 2x hybrids the higher seed-fertility could be still maintained to some extent.