| Selective gametocidal action of a chromosome of Aegilops
cylindrica in a cultivar of common wheat* T. Ryu ENDO Biological Laboratory, Nara University, Nara, Japan Preferential transmission of alien chromosomes has been reported in some alien chromosome addition (or substitution) lines of common wheat which had a certain chromosome derived from Aegilops species, such as Ae. triuncialis (2n=28, CCCuCu), synthetic triuncialis (2n=28 CCCuCu), Ae. caudata (2n=14. CC), Ae. longissima (2n= 14. SlSl), and Ae, sharonensis (2n=14. SlSl) (ENDO and TSUNEWAKI 1975, ENDO and KATAYAMA 1978, MAAN 1975). The preferential transmission of those Aegilops chromosomes was proved to be caused by selective fertilization or selective gametocidality in those addition lines, and the presence of the monosomic Aegilops chromosome itself was responsible for the selective gametocidality : Gametophytes to which a certain Aegilops chromosome was not distributed became difficult (or impossible in some cases) to develop normally, and those carrying the critical chromosome developed successfully into normal gametes. As the selective gametocidal action was effective on microspores as well as megaspores, self-pollination of the monosomic addition line gave rise to mostly disomic addition plants, which consequentially showed normal fertility. It was also demonstrated that differences in cytoplasm does not affect the selective gametocidal action. A chromosome of Ae. cylindrica (2n=28, CCDD) was found to be selectively retained in some cytoplasm substitution lines of common wheat. An F1 hybrid between Ae. cylindrica as female and a common wheat variety was repeatedly backcrossed to various kinds of common wheat in order to produce various cytoplasm substitution lines with different nuclei of common wheat. One of them, which had been backcrossed five times to a common wheat cultivar. Triticum aestivum cv. Jones Fife, was noticed to produce plants aberrant in appearance. The line was found to include in the chromosome complement a chromosome with a subterminal centromere which was suggested to be derived from Ae. cylindrica, since common wheat has no chromosome of that type. This line had a poor seed-set in every backcross generation, which indicated a relationship between partial fertility and selective retention of this cylindrica chromosome. The cylindrica chromosome was then transferred into a background of normal cytoplasm by reverse backcross to Jones Fife, using the cytoplasm substitution line as the pollen parent (this line has partial pollen fertility). A plant with 2n=43 was selected and crossed with Jones Fife's pollen or self-pollinated, producing 2n=43 plants and 2n=44 plants from the cross and selfing, respectively. The 2n=43 plants had this cylindrica chromosome and a meiotic configuration of 21"+1' (Fig. 1A). The 2n=44 plants had two such chromosomes and showed 22" at MI. In both addition lines, however, the chromosome pairing at MI was unstable, thus producing a trivalent and quadrivalent in some PMC's (Fig. 1B). The cylindrica chromosome may have had some effect on homoeologous pairing. |
| * The work was supported in part by a Grant-in-Aid (No. 476005) from the Ministry of Education, Japan. |
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