Exploitation of a New Breeding System by the Use of Mutator in Rice

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A mutator and a recessive slender-glume genes were simultaneously induced from gamma-irradiated seeds of a rice variety Gimbozu. The mutator is activated by a reverse mutation of a slender-glume gene, inducing various kinds of mutations at many loci. The objective of this study is to exploit the way of introducing the mutator into practical breeding program. 1. A number of M_3 Progenies of non-slender-glume plants (M_1) which had appeared in slender-glume lines, possessing the mutator, were examined for their agronomic characteristics. The results showed that the genetic variations induced in agronomic characters were quite large and often had the directions peculiar to the mutator. It was noted that high-yielding mutants were rather easily obtainable. 2. A number of heading-time mutants induced by the mutator were compared with gamma-ray induced heading-time mutants for several agronomic characters. The mutator as well as gamma-ray proved to induce not only single-character mutation but also plural-character mutation. 3. Allelism tests between the mutant genes and marker genes revealed that the mutator induced mutations at least at the loci on seven different chromosomes 1, 2, 3, 4, 5, 9 and 11.4. A number of F_3 slender-glume lines derived from the crosses between a slender-glume line and three varieties were examined for the appearance frequency of nonslender-glume plants as a criterion of mutator activity. As a result. mutator activity is kept also in various kinds of genetic backgrounds other than that of the original variety Gimbozu. 5. From the above findings, it was concluded that the mutator is a new mutagen having the power comparable with that of gamma-ray.