| Cytoplasmic mutaion induced by chemical mutagens
Toshiro KINOSHITA Plant Breeding Institute, Faculty of Agriculture, Hokkaido University, Sapporo, 060, Japan. It is known that cytoplasmic gene or genes have an important role in the inheritance of some characters such as male sterility, disease registance and chlorophyll aberration. In this paper, the author wish to report the induction of the cytoplasmic mutation related to the male sterility in sugar beets. These informations may be wrothwhile for the breeding of hybrid wheat by the use of cytoplasmic male sterility. Three kinds of chemical mutagens, acriflavine, streptomycin and ethidium bromide were applied to seeds by the following procedures. Seeds of the maintainer strains having N cytoplasm dipped in different concentrations of aqueous solutions of acriflavine and streptomycin for 24 hours at 30C in a dark room. The ethidium bromide treatment at 2000 ppm was carried out in a dark room kept at 5C for 40 hours. After the treatments, seeds were washed in running water for 30 minutes. Photohermal induction was applied for the acceleration of the generations. Male sterile plants (S.S.b or C.S.) occurred in M1 generation which were raised from seeds treated with the chemical mutagens. The progenies of male sterile plants were examined under open pollination to detect the possibility of tramsmission to the next generation. All S.S.b plants from the check strains did not transmit the male sterility to the next generation, while six S.S.b or C.S. plants in M1 transmitted the male sterility to M2 lines. By using complete sterile plants segregated from M2 lines, test crossings were tried with type 0 plants which have the genotype, N rf1rf1rf2rf.2 In the cross combinations between C.S. plants in M2 and type 0 plants, most of the progenies produced 100% of C.S. plants (Table 1). Therefore it is assumed that the genotype of C.S. plant from mutant lines if S rf2rf2rf2rf2 as well as that of the CMS strain of spontaneous origins. Cytoplasmic inheritance was confirmed by the reciprocal crossings between the male fertile plants which were segregated from M2 lines and the type 0 plants with N cytoplasm. The segregation of male sterile type differed prominently between reciprocal crossings indicating maternal inheritance of the male sterility. Then the evidence remains consistent with that the cytoplasmic mutation from N to S cytoplasm was induced by chemicals. Though the cyloplasmic alternation or changes on male sterility in sorghum (ERICHSEN & Ross 1963, MALINOVSKY et al. 1973) and pearl millet (BURTON & HANNA 1976) are reported, the proof of cytoplasmic inheritance has remained insufficiently without confirmation. However, it was evident in this experiment that the chemical mutagens induced the cytoplasmic mutation on male sterility as well as gamma rays (Kinoshita and Takahashi 1969). It is known that acridine dyes are potent inducers of the petite mutation in mitochondria genome of yeast and that streptomycin acts as a highly effective mutagen for chloroplast genes in Chlamydomonas (SAGER 1972). In the present experiment, the mutagens were effective for induction of the mutation for the cytoplasmic gene in higher plants. |