Basic studies on hybrid wheat breeding using the 1BL-1RS translocation chromosome / Aegilops kotschyi cytoplasm system - 1. Development of male sterile and maintainer lines with discovery of a new fertility-restorer

The Aegilops kotschyi cytoplasm and a 1BL-1RS translocation chromosome that consists of the long arm of wheat chromosome 1B and the short arm of rye c hromosome 1R were transferred to six spring common wheat cultivars by repea ted backcrossing. Resistance to leaf rust race 21B conditioned by the Lr26 gene and a secalin subunit encoded by the Sec-1 gene, both on the 1RS arm, were used as the selection markers of the translocation chromosome. Five of the six cultivars used were converted to complete male steriles, whereas t he remaining one, cv. Kitamiharu 48, retained normal fertility, after trans fer of both the 1BL-1RS chromosome and Ae. kotschyi cytoplasm. Conventional gene analysis suggested that Kitamiharu 48 carries an incompletely dominan t fertility-restoring gene. The F-1 hybrids between the male steriles and o rdinary common wheat cultivars recovered fertility only at a low level, ind icating that a single dose of the Rfv1 gene on the 1BS arm of wheat is insu fficient for full fertility restoration under spring-sowing condition. Our results are in clear contrast to complete fertility restoration under fall- sowing condition reported by Nonaka et al. (1993). Combination of the 1BL-1 RS chromosome / Ae. kotschyi cytoplasm system with a new fertility-restorin g gene discovered in Kitamiharu 48 may provide a breakthrough for spring-ty pe hybrid wheat.