Abstract
Five alkylating agents, ethylenimine (EI), ethyl methanesuifonate (EMS), N-nitroso-N -ethyl urea (NEUA), N-nitroso-N-methyl urea (NMUA) and N-nitroso-N-methyl urethane (NMUT), were compared on the mutagenic effectiveness and efficiency in a few agronomic characters of rice. The modes of dose-response of seedling height, survival rate of seedlings and seed fertility in M1 generation were remarkably different with the different agents used : Methylating agents brought about more toxic effects on M1 plants than ethylating agents. The data obtained in M2 indicated that ethylating agents induced the mutations in chlorophyll, heading date and culm length more easily than methylating agents : In comparison of the highest frequency of chlorophyll mutants and variants in the two agronomic characters, NEUA ranked first, followed by EMS, EI, NMUA and NMUT in turn. The orders of the effectiveness and efficiency of mutagens were NEUA>NMUA >EI>NMUT>EMS and NEUA>EI>EMS>NMUA>NMUT, respectively. These results suggest that NEUA is one of the best mutagens in practical plant breeding. The frequency of variants in each of two agronomic characters was quite exactly proportional to that of chlorophyll mutations throughout all the agents applied.
