水稲F_2における株保存の育種学的意義

To secure the quantitative characters of the individuals as truely expressed genotypes in the primary generation of hybrids, against the effects of the modification, we tried to induce the "clonalization" of F_2 plants in rice.
The F_2 plants of "Kameji No.1" × "Norin No.8" were cultivated in 1955, and after harvesting their underground parts were transplanted in glass-house for wintering and propagating clonaly. In May 1956, the seedlings newly sprouted in the stocks were separated one by one, and were transplanted to the nursery, and next to the field. Most of clonal lines were consisted of 5-8 plants.
(1) Table I shows that the heading date varies pretty widely among the clonal lines, on the other hand, the ear length and the stem length less.
(2) The correlatioh coefficient of the heading date, the % of the damaged ears by stem maggot and the stem length between F_2-individuals and F_2-clones, are significantly high (Table III), and their variations as a whole are less in clonal lines than in individuals (Table II). These characters are the ones known as to have strong heritabilty in the recent studies of the bulk method of plant breeding.
(3) In our later studies about the resistance of rice varieties against the injury of stem maggot, we have already known that the % of the damaged ears depends upon the headihg date, i. e. the relationship between both is expressed as a straight line. Examining the results in the F_2 clonal lines from this standpoint, we can recognize that F_2 of the strong variety (Kameji No.1) × the weak (Norin No.8) are grouped into strong (G_1), medium (G_2) and weak (G_3) groups as the ratio of 1 : 2 : 1 (Fig. II), otherwise, in the case of F_2 individuals we couldn't do it.