| II. Record Proceedings of the 18th Wheat Genetics Symposium of Japan The 18th Wheat Genetics Symposium of Japan was held at Tottori Mycological Institute, Tottori. Japan on Oct. 14 and 15, 1984. The followings are the abstructs of the contributed presentation. In addition to these constribution, a film demonstration was presented by the Institute. An Aegilops longissima chromosome causing chromosome aberrations in common wheat T. Ryu ENDO Nara University, 1230 Horaicho, Nara, Japan 631 A chromosome of Aegilops longissima, (2n=14, SlSl), which was spontaneously substituted for wheat chromosome 4A in a common wheat (Triticum aestivum, 2n=42, AABBDD) cultivar 'Selkirk', was found to render the wheat gametes without it functionless, thus being exclusively transmitted to the offspring (Maan 1976). In order to produce the longissima chromosome substitution line in another common wheat cultivar 'Chinese Spring', 'Chinese Spring' monosomic 4A was crossed as female with the monosomic longissima chromosome addition line of 'Chinese Spring'. The somatic chromosome constitution in root-tip cells of the offspring was examined by a chromosome banding technique, N-banding which could identify 16 of 21 'Chinese Spring' chromosomes and the longissima chromosome. Unexpectedly, obvious chromosome aberrations, such as deletion, translocation, and ring chromosome, were found in many of the effspring ; nineteen out of 34 plants examined had one or more of such aberrations. The same addition line was crossed as male to euploid 'Chinese Spring', and a part of the offspring (four out of 12 examined) showed at least one chromosome aberration. However, no chromosome aberration was detected in any of the offspring (19 plants were examined) from the self-pollination of the disomic substitution line of 'Chinese Spring', in which a pair of 4A chromosomes were substituted with a pair of the longissima chromosomes. It was hardly suspected that the chromosome aberrations had occurred in the gametogenesis of the monosomic addition line because its pollen meioses had been perfectly normal. From these facts, it was suggested that the longissima chromosome in the monosomic condition itself caused the chromosome aberrations in common wheat, though the genetic background might affect the frequency of the occurrence of the aberrations. The aberrations seemed to occurr in any chromosome, including the longissima chromosome, and in any chromosome region, and were demonstrated to last to meiosis, though only a few plants were examined with the pollen mother cells. A few plants showed clear karyotype mosaics ; different roots from the same seedling had different chromosome aberrations. This fact implied that the aberrations had occurred in early embryogenesis. Besides Ae. longissima, Ae. sharonensis (2n=14, SlSl)and Ae. speltoides 2n=14, SS) were so far proved to have a chromosome causing chromosome aberrations like the longissima chromosome. Such chromosomes might not be rare in Triticum and Aegilops and at least partly responsible for the karyotype differentiation in those genera. |