Fruits and perspectives of mutation breeding

In Japan, since late 1950's the studies on mutation breeding have developed rapidly. The efficiency of obtaining mutation was found to vary with the kind and dosage of mutagen, the method of treatment, external and internal factors before, during and after the treatment, the species, ploidy and genotype of plants, and the developmental stage at the time of treatment. The spectrum of mutation was also found to be influenced by the kind and dosage of mutagen, the genotype of plants, and the stage of plant development and DNA replication. For the effective selection of mutation, in self-multiplying crops, some theoretical approaches were made on the procedure of raising successive generations following mutagenic treatment, the size of population in each generation, and the time and intensity of selection. As for vegetatively propagating crops, the methods to eliminate chimeras were intensively examined, and some useful techniques such as internal disbudding and successive cuttingback were established. The number of the new varieties produced by mutation breeding in Japan is 47, and 14 kinds of crops as of June, 1981, of which 29 varieties were bred through the direct use of induced mutation. Characteristically, many varieties having short stalks and/or early maturity have been bred by this method. The most successful new variety of short stalks was the rice variety Reimei. The remaining 18 were indirectly produced from induced mutants, and most of them were rice varieties. (Kaihara, S.)