Basic studies on hybrid wheat breeding

Summary The nuclei of 12 common wheats (genome constitution AABBDD) were placed into the cytoplasms of Aegilops kotschyi and Ae. variabilis (both C^uC^uS^vS^v) by repeated backcrosses. Using these nucleus-cytoplasm hybrids, male sterility-fertility restoration relationship was investigated. Male sterility was expressed by these cytoplasms only in Slm, Splt and Mch. The other nine common wheat nuclei gave normal fertility against these cytoplasms. These cytoplasms were compared with the Triticum timopheevi cytoplasm that is now widely used in the hybrid wheat breeding program in order to investigate their effects on important agronomic traits of the 12 common wheats: The kotschyi and variabilis cytoplasms were as good as the timopheevi cytoplasm in this respect.The F₁ hybrid between (kotschyi)- or (variabilis)-Splt and CS showed normal fertility. Segregation of the fertiles and steriles in their F₂ generations followed the simple Mendelian fashion, i.e., 3 fertile1 sterile. Thus, the fertility restoration in this case is mainly controlled by a single dominant gene which will be designated as Rfv1. To determine its location, ditelo-lBS and -lBL of CS were crossed as male parents to male sterile (kotschyi)- and (variabilis)-Splt. The F₁ hybrids between the male sterile Spit's and CS ditelo-lBS became male fertile, while those between the male sterile Spit's and CS ditelo-lBL became completely male sterile. Thus, the location of the gene Rfv1 has been determined to be on the short arm of chromosome lB of CS. Furthermore, a close relationship between the fertility-restoring genes and the nucleolus organizer region was pointed out.Finally, the schemes of breeding the male sterile lines of a cultivar with these cytoplasms, and its maintainer line were formulated. The following two points were considered as the advantages of the present male sterility-fertility restoration system over that using the timopheevi cytoplasm in breeding hybrid wheat: (1) easier fertility restoration in F₁ hybrids, and (2) no need of breeding the restorer line.This work was supported by a Grand-in-Aid from the Ministry of Education, No. 386002. Contribution from the Laboratory of Genetics, Faculty of Agriculture, Kyoto University, Japan, No. 420.