Induction and Selection of Rice Mutants for Salt Tolerance

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The first aim of the present study was to elucidate physiological properties responsible for the NaCl tolerance of a rice variant which was considered to be salt tolerant variant after screening mutants induced by the N-Methy-N-Nitroso Urea (MNU) treatment of the fertilized egg cells of rice Oryza sativa L. cv. Kinmaze. Sodium (Na) concentrations of shoot and root of the tolerant variant, on a dry matter basis, were determined after salination. Na content of the shoots was lower than that of Kinmaze. On the other hand Na content of root was high compared to that in the shoot. Similarly salt tolerant variety, Nona Bokra, showed Na contents in shoot and root. From these results it appeared that the tolerant variant was more effective in excluding Na from the shoot as observed in Nona Bokra. Therefore, it was concluded that the rice variant showing such salt tolerance response should be collected for providing genetical resources for improving salt tolerance. Since the degree of NaCl tole … More rance in the rice variant obtained so far was not enough, the second a aim of the present study was focused on screening variants with improved salt tolerance from rice mutants derived from MNU treatment of fertilized egg cells of Indica rice variety, IR 36. The salt tolerance response of the M3 seeds was examined in the same salinized nutrient culture solution as carried out in the case of Kinmaze. However, no tolerant plants could be obtained because the salinization conditions were not proper for IR 36. Therefore, the seedlings at 4 leaf stage were used for salt tolerant screening. The nutrient solution was salinized with 120 mM NaCl instead of 85 mM NaCl, and further the response to salinity was determined by comparing seedling growth of variants to that of IR 36 after 3 week salinization. Seedlings with good growth compared to IR 36 were considered as tolerant. Tolerant plants were grown to maturity in normal nutrient solution. The 405 strains were screened for salt tolerance and 28 strains (50 individuals in total) were obtained. These salt tolerant variants wil be given further screening for production of genetical resources of rice improved salt tolerance. Less