水稻显性感光抑制基因Su-E_1(t)的定位及遗传分析

利用粳稻品种Asominori和籼稻品种IR24衍生的重组自交系群体,在南京和海南2种自然环境下对水稻抽穗期QTL进行检测,分别检测到5个和6个影响抽穗期的QTL,其中位于第6染色体的qDTH-6在2种环境下都能被检测到,LOD值分别为6.28和12.93,贡献率分别为12.26%和17.18%。对以Asominori为背景、在qDTH-6处置换了IR24片段的染色体片段置换系CSSL45及背景亲本进行人工短日照处理,发现qDTH-6来自籼稻IR24的等位基因具有显性感光抑制效应。利用抽穗期基因型测验系和9311等一些常规稻与CSSL45杂交分析,进一步证实了qDTH-6的显性感光抑制功能,并初步判断其抑制对象为主效感光基因E_1(Ghd7),本研究将其命名为Su-E_1(t)。同时利用CSSL45×Asominori次级F2群体分别在人工短日照和自然长日照条件下对Su-E_1(t)进行了进一步定位,将其定位在SSR标记RM527附近。本研究对有效地解决水稻籼粳亚种间杂种生育期超亲晚熟的难题具有重要意义。     

水稻分蘖角度的QTL定位和主效基因的遗传分析

利用水稻籼粳亚种间组合Asominori×IR24重组自交系(RIL)群体71个株系和相应的全基因组染色体片段置换系(Chromosomesegmentsubstitutionline,CSSL)群体65个株系,在2种环境下对分蘖角度性状进行了数量性状基因座(QTL)定位和上位性效应的遗传分析。在两种群体中都出现了分蘖角度的超亲分离。在RIL群体中发现了5个主效QTLs和3对上位性双位点互作标记基因座,控制水稻分蘖角度。其中在第9染色体上位于XNpb108~C506RFLP分子标记区间的qTA-9基因座在2种环境中同时出现,其贡献率平均为28·6%,增加分蘖角度的等位基因来自籼稻品种IR24。利用CSSL群体图示基因型分析,证实在第9染色体上含有RFLP标记C609和C506约15cM的染色体区段,存在增加分蘖角度的基因,来源于染色体片段供体亲本IR24,在Asominori的遗传背景中能增加分蘖角度约15°,该基因的位置与RIL群体在第9染色体上定位的QTL相同,证实了qTA-9的存在。F1表型测定及F2代遗传分析表明,来自IR24的等位基因是一个不完全显性基因。除一对上位性位点存在显著的环境互作效应外,未发现其他位点存在与环境的互作效应。不同基因的加性效应和双位点的上位性效应的共同作用可能是造成水稻分蘖角度超亲分离的主要原因。     

水稻产量及其构成因子对大气CO2浓度升高响应的相关QTL初步分析

以粳稻Asominori与籼稻IR24所衍生的染色体片段置换系(CSSL)为材料,于2003年和2004年连续2年在FACE(free air CO2 enrichment,大气CO2浓度增加200μmol/mol)和正常大气CO2浓度(约370μmol/mol)下,分析了控制单株产量、有效分蘖数、每穗实粒数和千粒重的数量性状位点(QTL)。结果表明,2年共检测到36个控制产量性状的QTL,分布在除第5、10和11染色体的各条染色体上。其中,仅有位于第1染色体上靠近XNbp113标记的1个控制千粒重的QTL,在2年的FACE和对照下都被检测到,并且其加性效应均来自IR24,但其贡献率在各个年份和两CO2浓度下却表现不同。另外,36个QTL中,2个QTL(qTGW1-3QE和qFT3-3QE)被检测到具有显著的基因型×环境互作。     

水稻抗褐飞虱种质Swarnalata抽穗期和休眠性相关QTL检测

为有效利用抗褐飞虱水稻Swarnalata,对2013年南京种植的Swarnalata/02428 F2分离群体进行抽穗期和种子休眠性考察,利用172个分子标记构建了Swarnalata/02428 F2的分子遗传连锁图谱,图谱全长为3311.4c M,标记间平均图距为19.22c M。利用Windows QTL Cartographer V2.5软件对该分离群体进行抽穗期和种子休眠性相关QTL检测,共检测到7个抽穗期相关QTL,分别位于第2、3、6、11染色体,其中位于第11染色体的q HD-11-1贡献率最高,为28.85%;检测到3个种子休眠性相关QTL,分别位于第3、6、9染色体,其中位于第9染色体的q Sd-9贡献率最高,为22.11%。分析表明,本研究检测到的抽穗期QTL与种子休眠QTL所在位置不同,说明该群体中种子休眠与抽穗期没有直接关系,它们分别由不同基因控制。本研究不仅为水稻休眠基因的精细定位及克隆奠定基础,也为更有效利用Swarnalata中的抗褐飞虱基因提供基础和一些优良的中间材料。     

利用粳稻染色体片段置换系群体检测水稻抗亚铁毒胁迫有关性状QTL

潜育性水稻田广泛分布于中国、斯里兰卡、印度、印度尼西亚、塞拉里昂、利比亚、尼日利亚、哥伦比亚和菲律宾等国,其中我国南方稻区就有近700万公顷低产潜育性水稻田。该类水稻田还原性强,矿质营养失调,尤以Fe^2 过量积累,对水稻生长发育产生不良的逆境胁迫作用。培育抗亚铁毒的水稻品种是简便、经济有效地提高稻谷产量的重要途径之一。该文利用由粳稻品种Asominori与籼稻品种IR24杂交衍生的Asominori染色体片段置换系(Chromosome Segment Substitution Lines,CSSLs)群体为材料,检测与抗亚铁毒胁迫有关性状QTL。共检测到与抗亚铁毒胁迫有关性状QTL14个,各QTL的LOD值为2．72～6．63。其中检测到与抗亚铁毒胁迫直接有关的性状叶片棕色斑点指数QTL3个,分别位于第3、9、11染色体C515～XNpb279、R2638～C1263和G1465～C950之间,对应的贡献率分别为16．45％、11．16％和28．02％;与其他已发表的定位结果比较发现,位于第三染色体C515～XNpb279间控制叶片棕色斑点指数的QTL与水稻功能图谱上控制叶绿素含量的QTL的位置一致;表明在亚铁毒胁迫条件下,水稻在其叶片表面出现棕色斑点,叶片衰老,产生一些叶绿素降解物或衍生物,以提高叶片细胞对亚铁等重金属毒害的耐受力。另外,在第11染色体G1465～C950之间检测到了控制叶片棕色斑点指数、茎干重和根干重QTL1个,为主效QTL。在第6染色体XNpb386～XNpb342之间检测到控制茎干重、株高、根长和根干重QTL1个,是否与水稻抗亚铁毒有关需要进一步研究。本研究旨在通过定位与抗亚铁毒有关的QTL,借助与之紧密连锁的分子标记有效地聚合这些QTL,培育出抗亚铁毒性强的水稻新种质材料。     

基于CSSL的水稻穗颈长度QTL的代换作图

水稻穗颈长度是影响杂交水稻制种产量提高的重要农艺性状之一。文章利用94个以籼稻品种9311为遗传背景、粳稻品种日本晴为染色体片段供体的覆盖全基因组的染色体片段置换系(Chromosome segment substi-tution lines, CSSL)为材料, 调查和分析CSSL群体及双亲的穗颈长度。结果表明: 在17个置换系中检测到8个控制水稻穗颈长度的数量性状位点(Quantitative trait loci, QTL), 分别位于第2、3、7、8、9和第11染色体; 利用代换作图法, 定位了其中的7个穗颈长度QTL; 其加性效应值介于0.10~3.20之间, 其中qPE-9和qPE-11的加性效应值较大, 平均效应值分别为3.15和2.95, 表现为主效基因特征; qPE-2-2、qPE-3-1、qPE-3-2、qPE-7和qPE-8等5个QTL被定位在小于10.0 cM的区段内。利用CSSL可以有效地鉴定水稻穗颈长度QTL, 这些QTL为分子标记辅助选育穗颈长度适中的水稻品系及其进一步的精细定位奠定了基础。     

基于染色体片段置换系的野生稻粒宽QTL qGW8的精细定位与遗传分析

利用以栽培稻9311为受体、普通野生稻为供体的染色体单片段置换系CSSL182,检测到一个与粒宽相关的QTL。CSSL182与受体亲本9311粒型性状差异显著,且只在8号染色体有一个野生稻导入片段。构建CSSL182/9311的F2次级分离群体,将粒宽QTL初定位在8号染色体的标记RM447和RM264之间,贡献率达22.49,将该QTL命名为qGW8。随后进一步设计区间内多态性分子标记引物,检测F2群体的2000株分离个体以及F2：3群体交换单株,结合后代表型验证,最终将qGW8精细定位到8号染色体10kb区间内。该区间内含有3个候选基因,基因测序发现这3个基因在双亲之间均含有丰富的变异。对双亲籽粒颖壳细胞电镜扫描观察发现,CSSL182的颖壳细胞宽度比9311减少16.7%。这一结果表明qGW8中来自野生稻的等位基因通过改变颖壳细胞形状影响粒型。     

水稻产量及其构成因子对空气CO2浓度增高响应的QTL分析

自由空气CO2浓度增加设施（Free air carbon dioxide enrichment．FACE）使得实际地模拟未来植物生长所处的CO2浓度增加环境变为可能。FACE下．作物生长和产量发生不同程度的加速和提高,而分析作物产量因子对CO2浓度增加响应的遗传基础将有利于对CO2环境变化做出敏感响应的遗传特性的认识,有利于适合未来空气CO2浓度增加环境的高产品种的培育。以粳稻品种Asominori与籼稻品种IR24的杂交组合所衍生的染色体片段置换系（CSSLs）为材料进行田间试验,分别在FACE（约570umol CO2／mol）和正常大气（约370umol CO2／mol）下对籽粒产量及其构成因子等数量性状位点（QTL）进行了分析。结果表明,在FACE下,Asominori和IR24的有效穗数、穗粒数和单株籽粒产量均显著高于对照下的,并且FACE下,65个置换系的变幅范围均大于对照下的;在第1．2,4,6．7,9和12染色体上检测到LOD值在2．5—5．7范围内的控制上述产量性状的20个QTL．其中有3个可以同时在FACE和正常大气下检测到．其余的则只是在某一种CO2环境下检测到。此外,还检测到2个QTL（qFT12 and qGP4）存在着与环境的加性互作效应。可以推论．空气中CO2浓度的增加诱导了部分对CO2浓度敏感的QTL表达,控制水稻产量性状的QTL与CO2增加的环境发生了互作效应。预计利用分子标记辅助育种途径可以培育出适用于未来CO2浓度增加环境下的高产水稻品种。     

基于染色体片段置换系的野生稻粒宽QTL-qGW8.1的精细定位

利用以栽培稻9311为受体、普通野生稻为供体的染色体单片段置换系CSSL182,检测到一个与粒宽相关的QTL。CSSL182与受体亲本9311粒型性状差异显著,且只在8号染色体有一个野生稻导入片段。构建CSSL182/9311的F_2次级分离群体,将粒宽QTL初定位在8号染色体的标记RM447和RM264之间,贡献率达22.49%,将该QTL命名为qGW8.1。随后进一步设计区间内多态性分子标记引物,检测F_2群体的2000株分离个体以及F_(2∶3)群体交换单株,结合后代表型验证,最终将qGW8.1精细定位到8号染色体10 kb区间内。该区间内含有3个候选基因,基因测序发现这3个基因在双亲之间均含有丰富的变异。对双亲子粒颖壳细胞电镜扫描观察发现,CSSL182的颖壳细胞宽度比9311减少16.7%。这一结果表明qGW8.1中来自野生稻的等位基因通过改变颖壳细胞形状影响粒型。     

水稻米粒延伸性的遗传剖析

以籼稻ZYQ8与粳稻JX17为亲本的DH群体作为研究材料,考察DH群体及双亲的米粒延伸率相关性状,并使用该群体的分子连锁图谱进行QTL分析.共检测到14个与稻米延伸性有关的QTL,包括2个粒长QTL、7个饭粒长QTL和5个米粒延伸率QTL,分别位于第1、2、3、5、6、7、10、11和12染色体.所有QTL的LOD值介于2.26～9.25,分别解释性状变异的5.31%～17.21%.在第3染色体上的G249～G164、第6染色体上的G30～RZ516和第10染色体上的G1082～GA223区间同时检测到控制饭粒长和米粒延伸率的QTL.米粒延伸性受多基因控制,Wx基因与位于第6染色体上的qCRE-6的G30～RZ516区间相近,对米饭的延伸性具重要影响.     

Quantitative trait loci (QTL) analysis for rice grain width and fine mapping of an identified QTL allele gw-5 in a recombination hotspot region on chromosome 5

Rice grain width and shape play a crucial role in determining grain quality and yield. The genetic basis of rice grain width was dissected into six additive quantitative trait loci (QTL) and 11 pairs of epistatic QTL using an F(7) recombinant inbred line (RIL) population derived from a single cross between Asominori (japonica) and IR24 (indica). QTL by environment interactions were evaluated in four environments. Chromosome segment substitution lines (CSSLs) harboring the six additive effect QTL were used to evaluate gene action across eight environments. A major, stable QTL, qGW-5, consistently decreased rice grain width in both the Asominori/IR24 RIL and CSSL populations with the genetic background Asominori. By investigating the distorted segregation of phenotypic values of rice grain width and genotypes of molecular markers in BC(4)F(2) and BC(4)F(3) populations, qGW-5 was dissected into a single recessive gene, gw-5, which controlled both grain width and length-width ratio. gw-5 was narrowed down to a 49.7-kb genomic region with high recombination frequencies on chromosome 5 using 6781 BC(4)F(2) individuals and 10 newly developed simple sequence repeat markers. Our results provide a basis for map-based cloning of the gw-5 gene and for marker-aided gene/QTL pyramiding in rice quality breeding.     

A Chromosome Segment Substitution Library of Weedy Rice for Genetic Dissection of Complex Agronomic and Domestication Traits

Chromosome segment substitution lines (CSSLs) are a powerful alternative for locating quantitative trait loci (QTL), analyzing gene interactions, and providing starting materials for map-based cloning projects. We report the development and characterization of a CSSL library of a U.S. weedy rice accession ‘PSRR-1’ with genome-wide coverage in an adapted rice cultivar ‘Bengal’ background. The majority of the CSSLs carried a single defined weedy rice segment with an average introgression segment of 2.8 % of the donor genome. QTL mapping results for several agronomic and domestication traits from the CSSL population were compared with those obtained from two recombinant inbred line (RIL) populations involving the same weedy rice accession. There was congruence of major effect QTLs between both types of populations, but new and additional QTLs were detected in the CSSL population. Although, three major effect QTLs for plant height were detected on chromosomes 1, 4, and 8 in the CSSL population, the latter two escaped detection in both RIL populations. Since this was observed for many traits, epistasis may play a major role for the phenotypic variation observed in weedy rice. High levels of shattering and seed dormancy in weedy rice might result from an accumulation of many small effect QTLs. Several CSSLs with desirable agronomic traits (e.g. longer panicles, longer grains, and higher seed weight) identified in this study could be useful for rice breeding. Since weedy rice is a reservoir of genes for many weedy and agronomic attributes, the CSSL library will serve as a valuable resource to discover latent genetic diversity for improving crop productivity and understanding the plant domestication process through cloning and characterization of the underlying genes.     

Identification of a stable quantitative trait locus for percentage grains with white chalkiness in rice (Oryza sativa)

High chalkiness is a major problem in many rice-producing areas of the world, especially in hybrid rice (Oryza sativa L.) in China. We previously showed a major quantitative trait locus for the percentage of grains with white chalkiness (QTLqPGWC-8) in the interval G1149-R727 on chromosome 8 using a chromosome segment substitution line (CSSL). Here, we selected the line-CSSL50 harboring the QTLqPGWC-8 allele from the CSSLs derived from a cross between Asominori (as a recurrent parent) and IR24 (as a donor parent), which had higher percentage chalkiness, markedly different from that of Asominori. There were also significant differences in starch granules, appearance of amylose content (AAC) and milling qualities between Asominori and CSSL50, but not in grain size or thousand grain weight (TGW). The BC(4) F(2) and BC(4) F(3) populations from a cross between CSSL50 and Asominori were used for fine mapping of qPGWC-8. We narrowed down the location of this QTL to a 142 kb region between Indel markers 8G-7 and 8G-9. QTLqPGWC-8 accounted for 50.9% of the difference in PGWC between the parents. The markers tightly linked to qPGWC-8 should facilitate cloning of the gene underlying this QTL and will be of value for marker-assisted selection in breeding rice varieties with better grain quality.     

Genetic control of dormancy in a Triumph/Morex cross in barley

Seed dormancy in barley (Hordeum vulgare L.) is one of the most important parameters affecting malting. Seed dormancy is quantitatively inherited and variously influenced by the environment. The objectives of the present study were to determine the genome location and effects of quantitative trait loci (QTLs) involved in the expression of seed dormancy in a barley cross between two varieties derived from different germplasm pools. Using a doubled-haploid population of 107 lines of the cross between the malting types Triumph (two-row, dormant) and Morex (six-row, non-dormant), seed dormancy phenotypic data sets from five environments and a 147-marker linkage map were developed in order to perform QTL analyses with simple interval mapping and simplified composite interval mapping procedures. Two different types of variables were considered for seed dormancy characterization: (1) level of dormancy induced during seed development, which was indirectly measured as germination percentage at 3 days and 7 days, GP3 and GP7 respectively; (2) rate of dormancy release in the course of a period after seed harvest (after-ripening). Different mechanisms of genetic control were detected for these two types of dormancy-related traits. A major and consistent dormancy QTL near the centromere on chromosome 7(5H) was associated with the establishment of dormancy during seed development and accounted for 52% and 33% of the variability for GP3 and GP7, respectively. Two other QTLs located in the vicinity of the vrs1 locus on chromosome 2(2H) and near the long arm telomere on chromosome 7(5H) explained 9% and 19% of variation, respectively, for the rate of dormancy release during after-ripening. Likewise, seed dormancy was assessed in an F₂ population derived from the cross between two dormant types of distinct germplasm groups, Triumph (European, two-row, malt) and Steptoe (North American, six-row, feed), which showed similar but not identical genetic control for dormancy. Interestingly, there is remarkable dormancy QTL conservation in both regions on chromosome 7(5H) identified in this study and among other barley mapping populations. These widely conserved QTLs show potential as targets for selection of a moderate level of seed dormancy in breeding programs.Communicated by P. Langridge     

Identification of Indica rice chromosome segments for the improvement of Japonica inbreds and hybrids

Exploitation of heterosis has brought significant advance in plant breeding and agricultural production, although its genetic basis is still poorly understood. In this study, a total of 66 chromosome segment substitution (CSS) lines, derived from a cross between japonica rice inbred line Asominori (as the recurrent parent) and indica rice inbred line IR24 (as the donor parent), were used to investigate the genetic basis of heterosis in indica × japonica inter-subspecific rice hybrids. Each CSS line was crossed with the background parent Asominori, and the heterosis of F(1) hybrids was estimated by comparing the F(1) performance with its two parental lines. Field experiments were carried out across six different environments to evaluate yield and yield-related traits in the 66 CSS lines and their 66 corresponding F(1) hybrids. Quantitative trait loci (QTL) analyses were conducted using a likelihood ratio test based on the stepwise regression. Thirty-six QTL were identified with significant effects in CSSL, 21 with significant effects in hybrids and 13 with significant effects in both. On the basis of average dominance degree, of all the 70 QTL affecting yield-related agronomic traits, 28.6% (20) showed an overdominance, 35.7% (25) a partial dominance and 30% (21) an additive effect, indicating that all effects contribute to trait variation in japonica-indica rice hybrids. Effects of these QTL were examined to identify Indica rice chromosome segments of interest for the improvement of japonica inbred lines and hybrids.     

The genetic basic and fine-mapping of a stable quantitative-trait loci for aluminium tolerance in rice

Aluminium (Al) toxicity is a primary cause of low rice productivity in acid soils. We have mapped a number of quantitative-trait loci (QTL) controlling Al tolerance in a recombinant inbred line population derived from a cross between the tolerant japonica cultivar Asominori and the sensitive indica cultivar IR24. Tolerance was assessed on the basis of relative root elongation. QTL were detected on chromosomes 1, 9, and 11, with the percentages of phenotypic variance explained ranging from 13.5 to 17.7%. Alleles from Asominori at all three QTL were associated with increased Al tolerance. qRRE-9 is expressed both in the genetic background of IR24 and in an Asominori/IR24-mixed background. qRRE-9 was reduced to the single recessive Mendelian factor Alt-9. High-resolution genetic and physical maps were constructed for Alt-9 in a BC₃F₂ population of 1,043 individuals. Alt-9 maps between RM24702 and ID47-2 on chromosome 9, and co-segregates with RM5765.     

QTL analysis for rice grain length and fine mapping of an identified QTL with stable and major effects

Grain length in rice plays an important role in determining rice appearance, milling, cooking and eating quality. In this study, the genetic basis of grain length was dissected into six main-effect quantitative trait loci (QTLs) and twelve pairs of epistatic QTLs. The stability of these QTLs was evaluated in four environments using an F₇ recombinant inbred line (RIL) population derived from the cross between a Japonica variety, Asominori, and an Indica variety, IR24. Moreover, chromosome segment substitution lines (CSSLs) harboring each of the six main-effect QTLs were used to evaluate gene action of QTLs across eight environments. A major QTL denoted as qGL-3a, was found to express stably not only in the isogenic background of Asominori but also in the recombinant background of Asominori and IR24 under multiple environments. The IR24 allele at qGL-3a has a positive effect on grain length. Based on the test of advanced backcross progenies, qGL-3a was dissected as a single Mendelian factor, i.e., long rice grain was controlled by a recessive gene gl-3. High-resolution genetic and physical maps were further constructed for fine mapping gl-3 by using 11 simple sequence repeat (SSR) markers designed using sequence information from seven BAC/PAC clones and a BC₄F₂ population consisting of 2,068 individuals. Consequently, the gl-3 gene was narrowed down to a candidate genomic region of 87.5 kb long defined by SSR markers RMw357 and RMw353 on chromosome 3, which provides a basis for map-based cloning of this gene and for marker-aided QTL pyramiding in rice quality breeding.     

QTL Analysis of Aluminum Resistance in Rice (Oryza sativa L.)

Aluminum (Al) toxicity is considered as one of the primary causes of low-rice productivity in acid soils. In the present study, quantitative trait loci (QTLs) controlling Al resistance based on relative root elongation (RRE) were dissected using a complete linkage map and a recombinant inbred lines (RILs) derived from a cross of Al-tolerant japonica cultivar Asominori (Oryza sativa L.) and Al-sensitive indica cultivar IR24 (O. sativa L.). A total of three QTLs (qRRE-1, qRRE-9, and qRRE-11) were detected on chromosomes 1, 9, and 11 with LOD score ranging from 2.64 to 3.60 and the phenotypic variance explained from 13.5 to 17.7%. The Asominori alleles were all associated with Al resistance at all the three QTLs. The existence of these QTLs was confirmed using Asominori chromosome segment substitution lines (CSSLs) in IR24 genetic background (IAS). By QTL comparative analysis, the two QTLs (qRRE-1and qRRE-9) on chromosomes 1 and 9 appeared to be consistent among different rice populations while qRRE-11 was newly detected and syntenic with a major Al resistance gene on chromosome 10 of maize. This region may provide an important case for isolating genes responsible for different mechanisms of Al resistance among different cereals. These results also provide the possibilities of enhancing Al resistance in rice breeding program by marker-assisted selection (MAS) and pyramiding QTLs.     

与稻米高垩白率相关的qPGWC-9的生理功能

利用携带qPGWC-9目标区段而其他置换片段上不带有与垩白率相关QTL(quantitative trait locus)的高垩白染色体片段置换系(chromosomal segment substitution line,CSSL)AIS82,以其轮回亲本Asominori(低垩白)为对照,从源库关系角度探讨qPGWC-9的生理功能。结果发现,籽粒灌浆期AIS82与Asominori的剑叶净光合速率没有显著差异,说明光合作用强弱不是AIS82高垩白率产生的直接原因。灌浆前期AIS82的淀粉合成关键酶活性显著高于Asominori,但中后期AIS82酶活下降快,整个灌浆期变化幅度相对较大,推测qPGWC-9主要影响了淀粉合成关键酶活性的动态变化,从而决定了高垩白表型。     

Molecular dissection of a dormancy QTL region near the chromosome 7 (5H) L telomere in barley

Moderate seed dormancy is desirable in barley (Hordeum vulgare L.). It is difficult for breeders to manipulate seed dormancy in practical breeding programs because of complex inheritance and large environmental effects. Quantitative trait locus (QTL) mapping opens a way for breeders to manipulate quantitative trait genes. A seed dormancy QTL, SD2, was mapped previously in an 8-cM interval near the chromosome 7 (5H) L telomere from a cross of 'Steptoe' (dormant)/'Morex' (non-dormant) by the North American Barley Genome Project using an interval mapping method and a relatively low-resolution genetic map. SD2 has a moderate dormancy effect, which makes it a promising candidate gene for moderate seed dormancy in barley cultivar development. The fine mapping of SD2 is required for efficient manipulation of SD2 in breeding and would facilitate the study of dormancy in barley. Ten different Morex isolines were generated, including regenerated Morex, of which nine lines had duplicates. The isolines together with Steptoe and Morex were grown in growth room and field environments for 2 years (2000 and 2001). In the growth room, relatively low growing temperatures (25 degrees C day/15 degrees C night) were employed to promote seed dormancy development. Seed germination percentage, determined at different post-harvest after-ripening periods, was used to measure seed dormancy. Fine mapping using the substitution mapping method based on differences among isolines resolved the SD2 QTL into an 0.8-cM interval between molecular markers MWG851D and MWG851B near the chromosome 7 (5H) L telomere. Relatively low temperatures (< or =25 degrees C) during seed development promoted the expression of the SD2 dormancy QTL. The chromosome region above the MWG851D-MWG851B interval might play a role in reducing barley seed dormancy during after-ripening.