In hybrid rice breeding programs, genetic diverity between maintainers and restore, enhances heterosis. The objective was to measure the level of diversity between the two groups of rice (Oryza sativa L.) breeding lines or cultvars which were screened as potential maintainers or restnrers by test-cross to WA (wild abrtive)-cytoplasm. Allele frequencies at 15 isozyme loci were compared between 51 potential maintainers and 56 potential restorers. Differences between the two types were found at eight isozyme Iocl on chromosomes 4, 6, 7, 8,11, and 12. The majority of the potential maintaines exhibited japonica type alleles, whereas most of the potential restorers exhibited indica type alleles. This pattern is consdered to be due to retained associations between Rf (restorer)/rf (maintainer) genes and genetic markers on chromosomes other than those carrying Rflrf genes. The diversity as well as differentiation of indica and japonica type alleles between maintainers and restorers should contribute to enhanced heterosis in hybrid rice.

以杂交水稻协优63为对照，对亩产800kg以上的超高产杂交水稻组合协优9308抽穗前、后的物质生产特性及剑叶光合作用与穗部物质积累的关系进行研究。结果表明：（i）与协优63相比，协优9308抽穗前、后的物质生产能力无论生物量还是日干物质生产量，均极显著高于协优63，尤以抽穗后更为明显。（ii）协优9308剑叶的光合碳同化能力（叶源量）极显著高于协优63，且能够切合籽粒灌浆需求，在单株水平上其净同化产物基本满足籽粒灌浆的需求，而协优63抽穗后20d左右剑叶光合功能快速衰退，单株净同化产物不能满足籽粒灌浆的需求。结果证明，灌浆后期仍能保持高效光合功能、并且能够切合籽粒灌浆需求是实现水稻超高产的关键环节。

In rice breeding, genes for seed dormanoy as well as the markers for each of them are required of an incorporation of an adequate seed domancy into japonica cultivrs To screen genetic Ioci for seed dormancy in rice (Orvza saliva L.), two kinds of populations were tested: (i)an Fz population of a hybrid Milyang 23 I Todorokiwase. and (fi) Fl populations from a three-way cross, in which an indica donor of strong dormancy, IR 36, was crossed with non-dormant japonica cultivars, Nekken 2 and Miyukimochi, in the form of IR 36/ Nekken 2// Miyukimochi. The seeds predated on the F2 plants from the single cross and those on FI plants from the three-way cross were tested at three times: immediately after maturation, after 60 d storage at 4C, and after breaking dormancy (7 d at 50C). Of 24 marker Ioci assayed, at least fore loci linked to seed dormancy were detected. The strong seed dormancy of Milyang 23 was linked with three isozyme genes: Pgi-I1 on chrompsome 3, Amp-32 on chromosome 6, and Est92 on chrmosome 7, while the strong seed dormancy of IR 36 was linked with C+ (apiculus color) on chromosome 6, Est-92 on Chromosome 7, and Acp-21 an chromosome 12. The high level of seed dorloci. Differential responses of inch Iocl to a dormacy-breaking treatment were detected. An allele from IR 36 at a locus on chromosome 6 seemed to be responsible for strong seed dormany after maturation and to be easliy broken during storage. This allele may be incorporated into japonica ries by means of marker C for apiculus color.

Backcross inbred lines (BILs) derived from a cross of Nipponbare (japonica) / Kasalath (indica) // Nipponbare were used to identify quantitative trait loci (QTLs) controlling physico-chemical properties of rice grains such as amylose content (AC), alkali spreading score (ASS) and gel consistency (GC) by composite interval mapping over a period of two years. A total of 4 QTLs for AC were detected; qAC-5 and qAC-6 showed significant effects (hereafter referred to as “significant”) in both years, and qAC-6 explained more than 80 % of the phenotypic variance and was located in the wx region on the short arm of chromosome 6. The other 2 QTLs for AC with small additive effects were detected and were significant only in one year. Three QTLs for ASS were identified; qASS-6a and qASS-6b were significant in both years, and qASS-6a corresponded to a major gene located in the alk region on chromosome 6, while qASS-3 on chromosome 3 was significant only in one year. Five QTLs for GC were detected and all were significant only in one year. The lock of detection of major gene(s) for GC may be due to the fact that none of the parents were differentiated in terms of GC. These results showed that AC and ASS were mainly controlled by known gene loci, i.e., wx and alk, respectively, with modification by minor genes.

Female gamete abortion in Indica-Japonica crosses of rice was earlier identified to be due to an allelic interaction at the S-5 locus on chromosome 6. Recently. in other crosses of rice, similar afielic interactions were found at loci designated as S-7 and S-8, located on chromosomes 7 and 6 respectively. All of them are independent of each other. At the S-5 locus, Indica and Japonica rice have S-5i and S-Y alleles respectively and Javanieas, such as Ketan Nangka, have a neutral allele S-5". The S-5i/S-5j genotype is senti-sterile due to partial abortion of female gametes carrying S-U, hul both the S 5"/S-5i and S-5"/S-5J genotypes are fertile. The S-5" allele is thus a "wide-compatibility gene" (WCG), and parents homozygous for this allele are called wide-com patible varieties (WCV), Such parents when crossed with Indica or Japonica varieties do not show F1 hybrid sterility. Wide compatible parents have been used to overcome sterility barriers in crosses between Indica and Japonica rice, However, a Javanica variety, Ketan Nangka (WCV), showed typical hybrid sterility when crossed to the Indian varieties N22 and Jaya. Further. Dular+ another WCV from India, showed typical hybrid sterility when crossed to an I RRI line, IR2061-628 1-6-4-3(IR2061-628). By genetic analyses using isozyme markers, a new locus causing hybrid stetihty in crosses between Ketan Nangka and the Indicas was located near isozyme loci Est-I and Mal-I on chromosome 4, and w as designated as S-9. An other new locus for hybrid sterility in the crosses between Du]ar and the IR2061 628 was identified and was found lin ked to four isozyme loci, Sdh-l, Pox-g, Aep-1 and Acp-2. on chromosome 12 It was designated as S-15. On the basis of allelic interac tlons causing female-gamete abortion, two alleles were found at S-9, S-9kn in Ketan Nangka and S-9iin N22 and Jaya. In the heterozygote, S-9kn/S-9i, which was semisterile, female gametes carrying S-9kn" were aborted. The hybrid of Dular and IR2061-628, with a genetic constitution of S-15Du/S-I5i, was semi-sterile and the female gametes carrying S-I 5Du were aborted. A Japonica tester variety, Akihikari, and an Indica variety, IR36, were found to have neutral alleles, S-9n and S-15n, at these loci, in addition to S-7" and at S-7. The accumulation of three neutral alleles into a breeding line should help solve the hybrid sterility problem in wide crosses office.