Advancing the Generation of Sugi, <i>Cryptomeria japonica</i> D. Don by Greenhouse Cultivation

An experiment to advance the generation of a Sugi clone (G-5), Cryptonzeria japonica D. Don, which is heterozygous for a lethal recessive gene producing light green seedlings was made by greenhouse cultivation. Firstly, in 1965, outcrossing and selfing were made on G-5. In December 1965, the seeds were sown in a wooden box (55×30×13cm³) in a greenhouse, and they were promoted to grow to have a sufficiently large plant size for gibberellin treatment. In the summer of 1966, gibberellin treatment was made to induce flower bud differentiation. In the spring of 1967, these F₁ plants were back-crossed with the pollen of G-5 and the mature cones were collected in the fall. Thus one generation was advanced by full two years.<br> Eighty four F₁ plants (66.4%) out of the outcrossed progeny had cone (s). Meanwhile, 36F₁ plants (59.0%) out of 61 selfed F₁ plants had cone (s). Number of mature cone per plant ranged between 1 and 10, and their mean values were a little more than 3 in both progeny groups. In the selfed progeny, mean 1000-seed-weight, mean number of the seeds per cone were significantly lower than those of the outcrossed progeny.<br> After a germination test, mean germination percentage of the selfed progeny was significantly lower than that of the outcrossed progeny. On the other hand, selfed seeds of G-5 in 1965 and back-crossed seeds of the selfed progeny showed the same level of germination at ca. 27%.<br> Observed genotypic frequencies of both progeny groups were as follows: in the outcrossed progeny; dominant homozygote vs. heterozygote was 35:27, and in the selfed progeny; dominant homozygote vs. heterozygote was 9:12. They showed good agreement with the expectation of 1:1 in the former, and 1:2 (hetero) in the latter, respectively. By the back-crossing of G-5 to the heterozygous F₁ plants, segregation of the seedlings in the ratio of normal vs. light green is 3:1 is expected. Meanwhile, smaller number of light green seedlings were segregated in the outcrossed progeny.<br> In this back-crossed F₂ generation, more than 2000 seedlings were raised from 83 F₁ plants. In the practical Sugi breeding works with an advancement of the generation, it may be important to use individuals or strains which have abilities to bear a plenty of flowers of both sexes by gibberellin treatment and have higher cross- and self-compatibilities in addition to their specific traits for, for examples, fast growth, disease- and cold resistances. Moreover, development of early progeny testing techniques for respective breeding purposes is essential.