| Newly induced mutants of Triticum vulgare by
X-ray-treatments I. UCHIKAWA Laboratory of Cytogenetics, Biological Institute, Ehime University, Matsuyama, Japan The following types of mutants were newly found in X2 and X3 generation besides formerly reported speltoid, compactoid, lax-eared, dense-eared, short-strawed and bearded (Uchikawa, 1960). Treatments (75 kV, 20 mA, 315 r/m, dose 5-25 kr) were given to dormant seeds of T. vulgara containing 18.8% of water at 18C. (a) Dwarf-compactoids. These mutants include two cytogenetic types. All of these mutants are highly sterile and have remarkably short culms, broad and compact ears. The first type heterozygote had 41 chromosomes including three IX chromosomes, and the homozygote possessed 42 chromosomes involving four IX chromosomes; while the second type heterozygote had 40 chromosomes including one iso-IX chromosome, and the homozygote possessed 40 chromosomes involving two iso-IX chromosomes. From these findings it is assumed that the compactoid characters may be brought about by the duplication of one long arm or one whole IX chromosome which involves the gene Q locus, and that the dwarfness is caused by the lacking of other one or two chromosomes. (b) Dense-eared (Type II). This type differs from compactoids in the form of spikes and the arrangement of spikelets, and is also different from hitherto reported Type I dense-eared mutants in their chromosome constitution and appearance. This type plants are half sterile and have short culms and dense ears. The hetero- and homozygotes of this type had 42 chromosomes similarly, and at MI of PMC's the chromosome arrangement 19II + 1III + 1I was observed in the heterozygote and 19II+1IV in the homozygote. These facts show that the mutants of this type may be brought about by the duplication of a whole chromosome which bears the dense ear promoting gene, owing to chromosome substitution. (c) Disorder-eared. This type differs from so-called irregular eared. This type mutants are highly sterile and have disorderly ear forms caused by the prevention of shooting-out of ears due to hard embracing of top-leaf-sheaths. The heterozygote had 41 chromosomes including one fragment and the homozygote possessed 40 chromosomes. These facts show that this type mutants may be produced by the partial or whole deficiency of one chromosome bearing normal leaf-sheath embracing gene. (d) Spiral-leafed. This type mutants uniformly have twisted leaf-sheaths, spirally coiled leaf-blades and slightly twisted spikes. These are classified into three types by their ear forms. The first type having normal ears had 42 chromosomes, and usually chowed 19II + 1IV association at MI of PMC's. The second type having lax ears possessed 41 chromosomes in the heterozygote and 40 chromosomes in the homozygote. Both zygotes usually formed tetrapartite chromosomes at MI of PMC's. The third type possessing compactoid ear form commonly showed 19II + 1IV including one IX-iso-IX pair at MI of PMC's in the heterozygote. The homozygote usually showed 19II + 1IV including one iso-IX pair in PMC's. From these facts the author assumes that the spiral-leafed mutation is caused by the reciprocal translocation of two chromosomes, and that the ear forms are controlled by the aberration of other chromosomes. |
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