Abstract
Following the construction of the Gamma Field at the Institute of Radiation Breeding in 1960, mutation breeding was accelerated in Japan. The facility is used, with a radiation dose up to 2 Gy/day (ca. 300,000 times that of natural background), to induce mutations at a higher frequency than occurs in nature. There have been 318 direct- use mutant cultivars representing 79 species generated through irradiation of gamma-rays, X-rays, ion beams and chemicals and somaclonal variation. Approximately 79% of these direct-use cultivars were induced by radiation. There have been 375 indirect-use mutant cultivars, including 332 rice, of which 162 cultivars (48.8%) were derived from the semi-dwarf mutant cv. 'Reimei'. The economic impact of these mutant cultivars, primarily of rice and soybean, is very large. Some useful mutations are discussed for rice, such as low digestible protein content, low amylose content, giant embryo and non-shattering. Useful mutations in soybean such as radiosensitivity, fatty acid composition and super-nodulation have been identified. Japanese pear and apple resistant to Alternaria disease have also been identified. The achievements of biological research such as characterization and determination of deletion size generated by gamma-rays, the effect of deletion size and the location, and a mechanism of dominant mutation induction are identified. Similarly, genetic studies on mutations generated through the use of gamma-ray induced mutations, such as phytochrome response, aluminium tolerance, stay-green (Mendel's gene) and epicuticular wax have also been conducted. Mutation breeding is a very useful technology for isolating genes and for elucidating gene functions and metabolic pathways in various crops.
Mutation Breeding in Ornamentals