Abstract:Physiological and mutagenic effects of sodium azide alone and in com- bination with gamma-rays were studied in rice under laboratory and field conditions.The physiological damage and mutagenic effect of M_2 were investigated.The results are as follows: 1.Sodium azide could induce physiological damage in M_1 generation and mutations of chlorophyll,plant height and heading date in M_2 gene- ration.The damage and mutation frequencies increased with increasing con- centrations of sodium azide. 2.Physiological and mutagenic effects were found to be pH dependent. In comparison with treatments at pH 7.0,sodium azide caused more M_1 damage and induced more mutation in M_2 at pH 3.0. 3.Sensitivity of rice to sodium azide increased after presoaking treat- ments.24h-presoaking,howoever,could alleviate injury by sodium azide at pH 3.0. 4.Treatments of gamma-rays together with sodium azide resulted in increased M_1 damage and M_2 mutation frequencies,and the combinative ef- fect was more conspicuous when azide was used at pH 3.0.An expanded mutation spectrum was also observed in the combined treatments. 5.Number of the initial cells in the embryo of main panicles was esti- mated to be 2—3,according to the segregation ratio of chlorophyll mu tants in M_2. The combined treatments of gamma-rays(15—30kR)together with so- dium azide(0.5—1mM)at pH 3.0 were recommended for rice mutation breeding programm.