Abstract
We previously proposed a new breeding scheme to develop hybrid wheat cultivars utilizing male sterility caused by the interaction between an Sv type cytoplasm and a 1BL-1RS chromosome (Toriyama et al. 1993). After this proposal, 13 Japanese cultivars were used to develop male-sterile lines and their maintainers. The donor of the Sv type cytoplasm of Ae, kotschyi was (Sv)-Norin 26, and the donor of the 1BL-1RS chromosome was 911-B-8-1O (abbreviation, st. 911). (Sv)-Norin 26 and st. 911 were repeatedly backcrossed with the 13 cultivars (cv. A is used to generalize a description). Then, the Sv cytoplasm-substituted lines [(Sv)-A] and the 1BL-1RS chromosome-substituted lines [mt. A] for 13 cultivars were developed as reported in our previous paper (Nonaka et al. 1993). During their breeding process, we observed the following phenomena other than the dose effet of the Rfv1 gene on restoration for pollen fertility. (i) Effects of the Sv cytoplasm on agronomic traits were negligible except on 1, 000 grains weight which may be compensated on grain yield by heterosis in F1 hybrids. (ii) Significant differences in some agronomic traits were observed between mt. A Iines and their original cultivars, though the effects of these differences on yield of F1 hybrids were not investigated. (iii) The pollen carrying the 1BL-1RS chromosome was inferior to the pollen carrying the 1B chromosome in gametic selection. (iv) Some mt. A Iines showed insufficient pollen shedding caused by non-opening or incomplete opening of glumes at flowering time. (v) Newly developed mt. A Iines had resistance to powdery mildew in addition to leaf rust. And, (vi) Male-sterile lines [ms(Sv)-mt. A] and mt. A Iines had white glume color instead of brown glume color of the original cultivars used.
