| II. Records ABSTRACTS OF THE 16th WHEAT GENETICS SYMPOSIUM OF JAPAN Kihara Institute for Biological Research Oct. 26, 1980 Wheat Genetics Symposium of Japan has been held every two years to exchange ideas in the field of wheat genetics. In the 16th Symposium, Drs H. Kihara and S. Sakamoto were invited as guest speakers. Dr. Kihara spoke about "Nucleus-Cytoplasm Heterosis in Wheat". Dr. Sakamoto participated in "the survey of emmer wheat in Spain" supported by FAO in 1980. He talked about "Collection of Spelta Wheats in Spain". Followings are the abstracts of papers presented in the general session of the 16th Wheat Genetics Symposium. A strain of tetraploid wheat With homoeologous chromosome pairing derived from the Aegilops speltoides-Triticum boeoticum amphiploid Jun'ichi SANO and Masatake TANAKA Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University Muko, Kyoto In order to understand the relationship between the gene Ph (suppressor of homoeologous chromosome pairing) on chromosome 5B of polyploid wheats and the promoter(s) of homoeologous chromosome pairing present in Aegilops speltoides, transfer of the promoter(s) into tetraploid wheat was attempted as the first step. For this purpose an F2 plant with somatic chromosome number 2n=30 derived from the cross Ae. speltoides-Triticum boeoticum amphiploid x T. dicoccum (TANAKA et al. 1979, Rep. Pl. Germ-plasm Inst., Kyoto Univ. 4: 1-11) was backcrossed to T. dicoccum. Among the resulting B1F2, three plants, designated A, B and C, had 2n=27, 28 and 29, respectively. These plants were crossed by Ae. sharonensis (2n=14) whose genome is not homologous to those of the tetraploid wheat, and triploid hybrids were obtained. The occurrence of the homoeologous pairing in these hybrids was tested by examining the amount of chromosome pairing at MI of PMC's. Homoeologous chromosome pairing was observed in all cross combinations between A, B, or C and Ae. sharonensis. Sixteen hybrid plants of B x Ae. sharonensis were classified into four pairinglevel groups in terms of the mean number of chiasmata per cell, i.e. five plants in Level I (2.4-3.8 Per cell), seven in Level II (4.7-6.4), three in Level III (7.5-8.4) and one in Level IV (11.1). These results suggest that the plants in Level I have the gene Ph but do not have the promoter, those in Level IV have the promoter but do not have Ph, and those in the Levels II or III have both or neither. From the frequency distribution of individuals in the four pairing-levels, it seems probable that the gene Ph and the promoter segregate independently. In contrast with this, out of 1 6 hybrid plants of C x Ae. sharonensis, 13 fell into Level III, which suggests that the plant C had a pair of homologous chromosomes causing homoeologous pairing. Then these chromosomes will show regular meiotic pairing and one of them may be transmitted to almost all the hybrid plants, causing homoeologous pairing. They may explain the hypertetraploid chromosome number (2n=29) of plant C. The plants A, B, and C had one to two multivalents and several univalents per cell on the average. The multivalent formation is probably due to homoeologous pairing. The mean chiasma frequency per cell in plant C was higher than both A and B. |