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-I
(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-I 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
Fig. 1. Segregation distortion of loci on chromosomes 1, 7, 8 and 11.
The x2 values are
plotted against the DNA markers in the skewed region.
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.
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