| Dense-eared mutants derived from X-ray induced lax-eared
wheat. I. UCHIKAWA Laboratory of Cytogenetics, Biological Institute, Ehime University, Matsuyama, Japan In the progeny of X - ray induced lax - eared mutants with 41 chromosomes the author newly found two cytogenetic types of dense - eared mutants besides already reported three types of dense - eared mutants of common wheat (UCHIKAWA, 1960, '61). These newly found two types were called Type IV- and Type V dense - eareds by the author. The arising percentage of the former was 1.23 and that of the latter 0.95. These two types of dense - eared mutants generally showed condensation of rachis, rounding of glumes, shortening of culms, diminution of germinating percentage and seed fertility, and augmentation of ear density, as shown in Table 1, Type IV heterozygous dense - eared mutants gave normals, heterozygotes, homozygotes, lax - eareds, and short slender plants with normal ear form in the ratio 1 : 1.1 : 0.1 : 0.6 : 0.1 in the following generation; and the heterozygotes had 42 chromosomes including one iso - chromosome. In meiosis of their PMC's the chromosome associations 20II + 1I + 1isoI (51.7%) and 20II + 1 unequal pair (47.2%) were mostly observed, though in rare occasions 19II + 2I + 1 unequal pair (0.7%) and 19II + 3I + 1 iso - chromosome (0.4%) associations were seen. One partner of the unequal pair or one of the two univalents was a middle sized chromosome with submedian attachment, and the other partner was an iso - chromosome which consisted of two long arms of this chromosome. The iso - chromosome usually showed horse - shoe shape or small bivalent form by pairing itself with interstitial chiasmata. Both the unassociated iso - chromosome and its partner frequently lagged in their behaviors and were eliminated forming micronuclei at the outside of the daughter nuclei. The results of crossing experiments between these heterozygotes and Type I subcompactoids with 42 chromosomes including one iso - chromosome showed that the iso - chromosome of this dense - eareds differed from that of subcompactoids in size and form and that they did not pair each other. The homozygotes possessed 42 chromosomes, too, but two iso - chromosomes were included in this case. In meiosis of PMC's of them, almost all PMC's had 20II + 1 isoII (53.0%) or 20II + 2 isoI (45.3%) associations. |
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