Induction of cytoplasmic male sterility through radiations and chemical
mutagens is one approach to developing alternate sources of male sterility for
use in hybrid rice development. Cytoplasmic male sterility in many higher
plants has been claimed to result from mutations in chloroplast (cp) and
mitochrondrial (mt) DNAs. The possibility of inducing cytoplasmic male
sterility was tested by mutagenesis (i) with chemicals having specificity to
organelle DNA and (ii) of self-fertile genotypes with sterile cytoplasm.
Rice seeds were treated with streptomycin sulfate, an antibiotic known to effect chloroplast DNA (Sager 1972), ethidium bromide, and acridine dye that inhibits nucleic acid synthesis, and other chemicals that have some specificity for these two organelles but are little known for their nuclear mutagenic action (Table 1). None of these chemicals showed any visible effects in M\1\ generation. An exception to this, however, was streptomysin sulfate. The effect of streptomycin treatment was pronounced in the form of variegated seedlings that resulted from the treated seeds (Sarma 1982). Nevertheless, no male sterile sectors could be observed in the surviving M\1\ plants or their M\2\ progenies. This approach to induce cytoplasmic male sterility through the use of chemicals such as streptomycin and ethidium bromide did not meet with success.
Table. 1. Different chemicals tried, duration of treatment and the size of
M\1\ and M\2\ populations in each treatment
============================================================================== Name of the Mol. wt. Concentration/ Number M\1 Number M\2\ chemical mutagen duration families plants screened screened ============================================================================== i) Acriffavin 259.74 2x10-3M (24 hr) 348 6781 ii) Actinomycin 1255.50 1x10-6M (24 hr) 273 4847 iii)Chloramphenicol 323.13 2x10-3M (24 hr) 186 3017 iv)Proflavin 516.58 2x10-3M (24 hr) 109 2170 v)Acridine Orange 669.10 2x10-3M (24 hr) 109 3207 vi)Streptomycin sulfate1457.40 1x10-3M (24 hr) 152 3903 vi)Ethidium bromide 394.30 1x103M (24 hr) 215 4608 ==============================================================================
============================================================================= Genotype/plasma type Variety Test-cross reaction for Wa cytoplasm ============================================================================== i) rf rf (N) Madhu; V-20B Maintainer ii) Rf RF (N) IR 36; IR 50 Restorer iii) Rf Rf (S) T(N)1; CB II ----- =============================================================================
References
Edwardson, J.R. 1970. Cytoplasmic male sterility. Bot. Rev. 36(4): 341-420
Sager, R. 1972. Cytoplasmic genes and organelles. Academic Press, New York.
Sarma, N.P. and A. Patnaik. 1982. Streptomycin induced nuclear and chloroplast mutations in rice. Ind. J. Exptl. Biol. 20: 177-178.