Studies on the induction of macromutations through the reorganization of gene systems in rice (Oryza sativa L.)

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Populations of artificial autotetraploids of rice (Oryza sativa L. cvs. Nipponbare and Fukunishiki) were repeatedly irradiated with gamma-rays through several generations. Plants which did not differ in appearance from the original diploid plants occured occasionally in the populations. These plants were designated as diploid-like plants. Nine diploid-like plants were obtained so far, and their generations were advanced without irradiation in order to examine the mode of segregation of characters in their progeny. The results indicated that the diploid-like plants with multiple mutant characters could be obtained and that dominant characters, i.e. awned spikelet and colored apiculus, were included in the mutant characters. The observation of chromosomes revealed that the diploid-like plants had the same number of chromosomes (2n = 24) as diploid rice plants had. We failed in detecting microscopically the structural changes of chromosomes. We have been exploring the application of restriction fragment length polymorphism (RFLP) analysis to the problem.