Study on enhancing mutagenic efficacy by irradiating rice plant before ear differentiation

Rice plants were irradiated externally with 60Co γ-ray or internally with 32P β-beam at the time just before ear differentiation. The mutation frequency, shape of mutated sector, hereditary variation of the mutant of Japonica rice, hereditary pattern of the mutant characters and the application of useful mutants were investigated. The results showed: 1. the irradiation treatment at the time before ear differentiation can greatly raise the mutation frequency. The mutation frequency in creased to 21.67% for early maturity, 11.01% for dwarfness and 12.92% for late maturity respectively (counted on the basis of ear number) under the external irradiation of 60Co γ-ray. The mutation frequencies for early, late and dwarfness maturities irradiated internally by 32P β-beam were 15.5%, 61.6% and 26.34% respectively (counted on the basis of grain number), or 46.87%, 91.3% and 65.22% respectively (counted on the basis of ear number). 2. Mutants, that are rarely existed, of Japonica rice were obtained. 3. The segregation of posterity for some mutant characters was not in Mendel's regularity, the relationships between dominance and recessive for some mutant characters were reversed. 4. The prospect for the application of useful mutants in the rice breeding is encouraging