Studies on the application of alteration in genome size to rice breeding

为了获得核DNA含量改变的二倍体水稻植株，对水稻（Oryza sativa L. cv.）的人工同源四倍体群体进行了研究。Nipponbare和Fukunishiki)几代人都反复暴露在伽马射线下。在群体中偶有与原始二倍体植株外观无差异的植株。目前已获得9株二倍体植株。这些植物在没有辐照的情况下进行了代前试验，以研究其特征的分离和核DNA含量的变化。实验结果表明，四倍体辐照获得的突变株核DNA含量的变异范围比二倍体辐照获得的突变株（Norin 8）或日本品种的变异范围更大。此外，与原始品种（日本basare和福岛）相比，突变株的DNA量变化方向都是方向性的，而对二倍体植株（Norin 8）辐照后获得的更多ns使其DNA量减少。在对突变性状的研究中，发现通过四倍体辐照技术可以在同一株植株上同时诱导多个定性和定量遗传性状的突变。我们研究了这些突变性状之间的相关性以及DNA数量与性状之间的相关性。众所周知，株高与穗粒数、粒重等农艺性状同时变化。据报道，这些发现被解释为突变基因的多效性，而这些副作用通常是负面的。然而，目前的结果表明，这些性状可以通过四倍体辐照技术独立地改变。突变性状与DNA量无关。研究结果表明，基因突变对表型的影响比基因组大小更显著。我们认为基因系统在改变DNA量的过程中也通过染色体重组发生改变。进一步的调查将揭示其中的机制。少

In order to obtain the diploid rice plants with altered nuclear DNA content, populations of artificial autotetraploids of rice ( Oryza sativa L. cv. Nipponbare and Fukunishiki ) were repeatedly exposed to gamma-rays through several generations. Plants which did not differ in appearance from the original diploid plants occurred occasionally in the populations. So far, 9 diploid plants were obtained. These plants were advanced their generations without irradiation in order to examine the segregation of characteristics and the variation of nuclear DNA content.In the experiments, it was revealed that the mutant strains obtained through tetraploid-irradiation technique had wider range of variation in nuclear DNA content than the mutant strains obtained by irradiation of diploid plant (Norin 8) or Japanese cultivares had. In addition, the direction of changes in DNA amount from those of original cultivares (Nipponbasare and Fukunioshiki) was both directional, whereas many of the mutant strai … More ns obtained by irradiation of diploid plants (Norin 8) reduced their DNA amount.In the investigation of mutated characters, it was indicated that several mutations of qualitatively and quantitatively inherited characters were induced in a single plant simultaneously through the tetraploid-irradiation technique. We examined the correlations among those mutated characters and also between DNA amount and the characters. It is well known that the plant height changes simultaneously with several agronomic characters such as number of spikelet per panicle, grain weight and so on. It is reported that these findings were interpreted as pleiotropic effect of a mutant gene, and these side effects were usually negative. The present results, however, suggest that these characters can be altered independently by using tetraploid-irradiation technique.The mutated characters were not correlated with DNA amount. The findings suggest that the genic mutations have more marked effects on phenotype than the genome size have. We considered that the genic systems are also altered through chromosome rearengement in the process of changing DNA amount. Further investigations will reveal the mechanisms involved. Less