| Meiotic irregularities in intervarietal hybrids of
common wheat Y. WATANABE Laboratory of Wheat Rust Resistance, Division of Upland Farm Crops, Tohoku National Agricultural Experiment Station, Morioka, Japan Meiosis in PMC's of the F1 hybrids between spring and winter types was studied in comparison with that of spring x spring or winter x winter hybrids. As spring wheat varieties, NORIN No. 3, Sapporo - Haru - komugi No. 1, Saitama No. 27, Konosu No. 25, and as winter wheat varieties, Aoba-Komugi, Nanbu-Komugi, Fultz No. 1, Kanred were used respectively. As is clearly seen from this table, the univalent frequency of F1's is very high compared with that of the parents, and there seems to be no definite relation between the univalent occurrence and the growth habits of parental varieties concerned in the crossing, unlike the results of HOWARD et JOSHI (1951), as shown in oats. Anyway, one can see that the irregularities of meiosis, above all, the univalent formation, are promoted by hybridization, whether it may be made between spring and spring or winter and winter or not. Especially in the cross combinations in which Konosu No. 25 or Aoba-Komugi were concerned, the univalent were formed in abnormally high frequency of 30%, rarely over 70%. The number of univalents observed is usually two, often 4 to 6 being encountered. Multivalent chromosomes such as trivalent or tetravalent were also observed. However, Sapporo - Harukomugi No. 1, though this variety itself shows low value in both the univalent frequency and the percentage of irregularity, resulted in an excessive number of multivalent chromosomes in the hybrids with which it was concerned. In such hybrids, the mode of chromosome configurations is in 1VI+19II, and 1VI was often observed, 1X being rarely met with. This is because it contains at least a translocation in the homozygous condition. The failure of chromosome pairing or the formation of multivalent chromosomes has been often observed so far even in the pure varieties of common wheat. This is because there exists semi-homology between chromosomes of three different genomes constituting T. vulgare Vill. And the degree of semi-homology is perhaps different in different varie ties, in spite of their possessing the identical genome formula. Moreover, there are chromosomes which are structurally differentiated. Therefore, when two gametes, male and female, different in the degree of chromosome differentiation, were united with each other through fertilization, the F1 plant thus produced would come to reveal its intrinsic disharmony by taking the form of meiotic instability. By examining the amount of such irregularities in F1 hybrids, the relative affinities among their parental varieties may be determined. |