32. Induction of cytoplasmic male sterility in rice

N.P. Sarma
Central Rice Research Institute, Cuttack, 753006 India


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

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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
==============================================================================

In the cytoplasmic genic male sterility system, the expression of male sterility is the result of interaction of sterile cytoplasm(s) with recessive nuclear genes for non-restoration (rf rf). Kripanov (cf. Edwardson 1970) pointed out that all species capable of donating sterile cytoplasms are also the sources of corresponding restorer genes. In other words, the varieties with sterile cytoplasms are self-fertile due to the presence of dominant genes for fertility restoration. The prospects of induction of cytoplasmic male sterility using self-fertile genotypes with sterile cytoplasms as experimental test material was examined. The following three genotypes with probable plasma types in parentheses were used:


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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            -----
=============================================================================

The seeds of three varieties, viz. Madhu, IR 50 and T(N)1 were treated with EMS, sodium azide and ethidium bromide. A fairly large number of male sterile plants were isolated in the M\2\ generation of treated populations of these varieties. The male sterile plants may result due to genetic changes which alter the N cytoplasm or recessive mutations in nuclear genes that result in male sterility. The male steriles induced in IR 36 and IR 50 can be explained on the basis of simple recessive nuclear gene mutations. The genetic analysis of induced male steriles from T(N)1 and Madhu would be of interest to determine whether it is posible to induce cytoplasmic male sterility by the use of specific genotypes as test material. Repeated pollination of male steriles with pollen from mother variety is now being attempted to establish the nature of induced sterility.



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.