A mapping population of 96 BC1F9 lines (Backcross Inbred Lines: BILs), derived by a single-seed descent method from a backcross of Nipponbare (japonica) / Kasalath (indica) // Nipponbare, was used to detect quantitative trait loci (QTLs) for leaf bronzing index(LBI), stem dry weight(SDW), tiller number(TN) and root dry weight(RDW) under Fe2+ stress condition in rice. Two parents and 96 BILs were phenotyped for the traits by growing them in Fe2+ toxicity nutrient solution. A total of four QTLs were detected on chromosome 1 and 3, respectively, with LOD of QTLs ranging from 3.17 to 7.03. One QTL controlling LBI,SDW,TN and RDW was located at the region of C955-C885 on chromosome 1, and their contributions to whole variation were 20.5%, 36.9%, 43.9% and 38.8%, respectively. The QTL located at the region of C955-C885 on chromosome 1 may be important to ferrous iron toxicity tolerance in rice. Another QTL for SDWand RDWwas located at the region of C25-C515 on chromosome 3, with respective contributions of 47.9% and 35.0% to whole variation. Further, two QTLs on chromosome 1 were located for RDWat the region of R2329-R210 and for TN at the region of R1928-C178. Comparing with the other mapping results, the QTL located at the region of C955-C885 on chromosome 1 was identical with the results reported previously. There is a linkage between a QTL detected under Fe2+ stress condition for stem and root dry weight and a QTL detected under phosphorus-deficiency condition for dry weight on chromosome 3.

利用由98个家系组成的Nipponbare/Kasalath∥Nipponbare回交重组自交系（Backcross Inbred lines，BILs）作图群体（BC1F9），进行水稻抗褐飞虱数量性状基因座（Quantative Trait Locus, QTL）的检测和遗传效应分析。采用苗期集团鉴定方法，并以死苗率作为抗褐飞虱表型值，分析亲本和98个BILs的抗褐飞虱表现。共检测到3个苗期抗褐飞虱QTL，分别位于2、10和12染色体上。各QTL的LOD值为2101～2133，贡献率为1014%～1616%，可解释群体总表型变异的3910%。这3个数量性状基因座对褐飞虱的抗性均来自抗虫亲本Kasalath。与这些数量性状基因座连锁的分子标记可望应用于聚合多个抗性基因，培育对褐飞虱具有水平抗性水稻新品种的育种实践中。

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.

Allelic interaction causing gamete abortion in wide crosses of cultivated rice was earber identified at locus S-5 on Chromosome 6 and recently at locus S.7 on Chromosome 7 At S-5 1ocus Indica and Japonica does have S-5i and S-5j, respectively, and Javaaicas such Ketan Nangka have a neutral allele 3-5n. The S-5i/S-5j genotype produces semi-sterile panieles due to abortion of female gametes carting S-5j, but both S-5n/S-5i and S-5n/S-5j genotypes do not. The S-5n is called "wide compatibility gene" (WCG), as one of parents possessing this allele does not show hybrid sterility in their F1. The WCG has been used for breeding hybrid varieties between Indica and Japonica rice. The S-5n allele was incorporated from Ketan Nangka to Japonica lines such as Nekken 1 or 2, which do not show semi-sterility in their cross to many Indica type. However, Nekken 2 showed typical hybrid sterility when it was crossed to a Korean Indica line. Yeong Pung. Therefore. a new Iocus was suggested for the semi-sterility in that hybrid. By genetic analyses using isozyme markers, a new locus for the hybrid stenhty between Nekken 2 and the Korean Indicas was located near Cat-I locius on Chromosome 6, and designated as following our recent report on S-7 On the basis of allelic interaction causing fenale gamete abortion, three alleles were found at S-8 follows: a Japonica line Nekken 2 and Yeong Puny possess S-8kn and S-8yp, respectively, and their hybrid genotype of S-8kn/S-8yp shows semi-sterility a portion of female gametes carrying S-8kn was aborted A Japonica tester variety, Akihikari was found to have a neutral allele, S-8n at this locus, and another neutral allele, S-7n at S-7, A possibility to cumulate three neutral alleles in a breeding line is suggested to solve hybrid sterility problem in wide crosses of rice.

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.