1990 Fiscal Year Final Research Report Summary
Genetic Study on Reproductive Isolating Mechanisms Differentiating Cultivated Rice Varieties
| Project/Area Number |
63480029
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Breeding science
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| Research Institution | National Institute of Genetics |
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Principal Investigator |
MORISHIMA Hiroko Nat. Inst. Genet., Dept. of Integrated Genet. Professor, 総合遺伝研究系, 教授 (70000247)
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| Co-Investigator(Kenkyū-buntansha) |
YONEZAWA Katsuei Kyoto Sagyo University, Dept. of Engineering, Professor, 工学部, 教授 (90026542)
SATO Yo-Ichiro Nat. Inst. Genet., Dept. of Integrated Genet. Research Associate, 総合遺伝研究系, 助手 (20145113)
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| Project Period (FY) |
1988 – 1990
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| Keywords | rice / evolution / reproductive isolation / indica-japonica / Monte Carlo simulation / gene analysis / distorted segregation |
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| Research Abstract |
Varieties of cultivated rice Oryza sativa are differentiated into indica and japonica at subspecies level. Between these two subspecies, F_i hibrid sterility and many other reproductive isolating barriers have been developed. Our primary concerns are genetic basis and evolutionaly significance of reproductive isolating mechanisms in rice. In the present study, we took up F_1 weakness as a case of sporophytic basis, and segregation distortion as a case of gametophytic basis.
Further, theoretical study was carried out to examine whether or not reproductive isolation brings about sub-populational differentiation as indica and japonica.
(1) F_1 weakness gene
A set of complementary gene (Hwc-1 and Hwc-2) is known to cause F_1 weakness in certain varietal crosses. Allelic frequency of Hwc-2 showed distinct geographical variation. Distribution pattern of this gene, together with other evidence, led us to consider that tropical insular clutivars, in addition to those of Chinese origin, have playe
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d a role in the establishment of Japanese rice.
(2) Segregation distortion
Extensive survey of F_2 populations revealed frequent occurrence of segregation distortion in indicajaponica crosses. Our isozymic study showed that genes responsible for segregation distortion are linked with some isozyme locus suggesting their wide distribution in the whole genome, and that presence or absence and degree of this phenomenon greatly differ according to cross combinations.
(3) Environmental effect on gamete genotype
Factors conditioning segregation distortion are multiple. In the present study, conditioning factors of F_2 segregation through environments to which F_1 hybrids are subjected were tested. It was found that indicajaponica F_1 hybrids treated by ozons and {low temperature + drought} produced different F_2 segregation ratios in gl gene and some isozyme loci from those derived from non-treated F_1 hybrids when grown under the same condition.
(4) Computer simulation
Whether or not reproductive isolation brings about differentiation into two groups defined by a particular association of alleles at multiple loci was examined by Monte Carlo simulation. The result showed that reproductive isolation does not cause non-random association of alleles, nor preserve such association. This suggests that reproductive isolation in rice is the result of differentiation, rather than the cause of differentation. Less
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