V. Segregation distortion and molecular mapping

41. Identification of genes responsible for segregation distortion in a doubled haploid population of rice by using molecular markers

P. K. SUBUDHI and N. HUANG

Genome Mapping Laboratory, Plant Breeding, Genetics and Biochemistry Division, IRRI, P.O.Box 933, Manila, Philippines

The phenomenon of segregation distortion is common in indica x japonica crosses, which has been explained on genetical basis through abortion of male and/or female gametes (Ikehashi and Araki 1998; Lin et al. 1992). Identification of segregation distortion genes, their neutral alleles and their incorporation in different genetic background with the help of linked markers may help in achieving the desirable recombinants. We report here presence of two segregation distortion gene, one each on chromosome 8 and 11 respectively in a doubled haploid population of rice developed from an indica x japonica cross IR64 x Azucena (Guiderdonie et al. 1992).

While mapping RAPD (Random Amplified Polymorphic DNA) markers in the above population, where a RFLP framework map has already been developed (Huang et al. 1994), we noticed segregation distortion in respect of 23% of mapped markers towards either parent. The distorted loci were distributed over nine chromosomes except chromosome 3, 4 and 5. Half of the skewed markers (24/47) mapped to chromosome 8 and 11 in equal frequency. There were 7 skewed loci on chromosome 7 and 6 on chromosome 1. These RAPD markers showing segregation distortion were also found to be linked to skewed RFLP markers. To examine the pattern of segregation of the markers on the chromosome, x2 values (1:1) were plotted against DNA markers (both RFLP and RAPD) on the respective chromosome (Fig. 1). A single peak was observed indicating one segregation distortion gene is located around the RAPD marker A11B920 on chromosome 8 and another between a RAPD A 15J 1250 and RFLP marker RG167 on chromosome 11. The frequency of marker alleles linked to such genes was dependant on the strength of linkage and thus proportionately deviated from the expected Mendelian segregation pattern. It was not clear whether single or multiple genes control this phenomenon on chromosomes 1 and 7. There was an earlier indication regarding presence of gametophytic genes on chromosome 8 and 11 through segregation study of two isozyme loci Amp-2 (located on chromosome 8) and Pgd-1 (located on chromosome 11) by Lin et al. 1992. These two isozyme loci were also reported to show segregation distortion in F2, backcross, anther culture derived calli and doubled haploid lines in indica x japonica crosses (Guiderdoni et al. 1988; Lin et al. 1992). Further molecular mapping of Pgd-1 locus placed it between RG103 and RG167 (IRRI 1992), where a segregation distortion gene was placed in this study. Therefore it is believed that the segregation distortion genes reported here might be the gametophytic genes.

The study of segregation distortion will have practical implication in breeding effort, since the genes closer to these segregation distortion genes on these chromosome will be inherited in lower frequency thus limiting the recombination of characters in indica x japonica crosses. It will be interesting to know the segregation distortion in number of crosses for concrete conclusion and thus the identification of neutral alleles at these loci for practical use. Future work should also be aimed at better understanding of the specific action of these genes in indica and japonica crosses.

The technical help rendered by Tita Mew and Gerard Magpantay is gratefully acknowledged. PKS was supported with a post doctoral fellowship by the Rockefeller Foundation.

References

Guiderdoni, E., E. Galinato, J. Luistro and G. Vergara, 1992. Anther culture of tropical japonica x indica hybrids of rice (Oryza sativa L.). Euphytica 62: 219-224.

Guiderdoni. E., J. C. Glaszmann and B. Courtois, 1989. Segregation of 12 isozyme genes among doubled haploid lines derived from & japonica x indica cross of rice (Oryza sativa L.). Euphytica 42: 45-53.

Guiderdoni, E., G. Vergara and B. Delos Reyes, 1988. Segregation of eight isozyme genes among microspore derived calli of a japonica x indica cross of rice (Oryza sativa L.). Philipp. J. Crop Sci. 13: 65-68.

Huang, N., S. McCouch, T. Mew, A. Parco and E. Guiderdoni, 1994. Development of an RFLP map from a doubled haploid population in rice. RGN 11: 134-137.

Ikehashi, H. and H. Araki, 1988. Multiple alleles controlling F1 sterility in remote crosses of rice (Oryza sativa L.). Japan. J. Breed. 38: 283-291.

International Rice Research Institute, 1992. Program Report for 1992. IRRI, P.O.Box 933, Manila, Philippines pp. 146.

Lin, S. Y., H. Ikehashi, S. Yanagihara and K. Kawashima, 1992. Segregation distortion via male gametes in hybrids between Indica and Japonica or wide compatibility varieties of rice (Oryza sativa L.). Theor. Appl. Genet. 84: 812-818.