Mutagenic Effects of Sodium Azide in Rice1

Seeds of rice (Oryza sativa L. spp. japonica) cultivar ‘M5’ were presoaked in distilled water and treated for 2 or 3 hours with 0, 0.12, 0.50, 0.75, 1.0, 1.25, 1.50, and 1.75 mM sodium azide solutions prepared in 0.1 M phosphate buffer (pH 3). After treatment the seeds were rinsed for 1 hour in 15 C tap water. Seeds receiving a 2‐hour azide treatment were redried in a fume hood at room temperature for 24, 48, 72, and 96 hours prior to planting to develop treatment procedures suitable for transporting dry, treated seeds rather than growing seedlings. Although the scope of this study did not permit field evaluation of the redried treated seeds, it was found that seeds treated for 2 hours with I mM azide and redried for 96 hours had more injury than seeds treated for 3 hours with I mM azide without redrying. Thus, a 1 mM azide treatment for 2 hours with redrying may be near the maximum permissible for sufficient field viability of the M1. Seeds with a 3‐hour azide treatment were planted immediately after rinsing. The seedlings were transported by air to the California test site and transplanted for the mutation study. Criteria used to assess the biological effects of azide on rice were germination, seedling height, and seed sterility in the M1 generation, and chlorophyll‐deficient seedlings and viable mutations in the M2 generation. In general, an increase in azide concentration, along with an increase in the post‐treatment redrying period, resulted in a decrease in M1 germination and seedling height. Azide treatment also induced sterility, the highest concentration producing maximum (62.2%) seed sterility. The same treatment induced chlorophyll mutations in 98.5% of the M1 panicle progenies and in 14% of the M2 seedlings. The viridis type of mutation was most frequent. The highest frequency of viable mutations scored in the adult plant stage was 4.64% on an M2 plant basis. All azide concentrations were mutagenic. Short‐culm and dwarf mutant types were more frequent than the early‐flowering mutant types in the azide‐induced mutation spectrum. Azide should prove useful as a mutagen for the genetics and practical breeding of rice.