水稻开花期高温胁迫下的花粉育性QTL定位

 以耐热水稻品系996和热敏感品系4628为亲本构建的重组自交系为材料,采用水稻开花期高温胁迫下的花粉育性为指标,对水稻耐热性进行了QTL分析。采用复合区间作图法检测到2个花粉育性耐热性QTL,暂命名为qPF4和qPF6。qPF4位于第4染色体上的RM5687―RM471区间,LOD值为7.54,对高温胁迫下花粉育性的表型解释率为15.1%,来自耐热亲本996的等位基因使高温下花粉可育率提高7.15%。qPF6位于第6染色体上的RM190―RM225标记区间,LOD值为4.43,对高温胁迫下花粉育性的表型解释率为9.31%,能使高温下花粉可育率提高5.25%,加性效应亦来自耐热亲本996的等位基因。定位到的2个耐热QTL为进一步精细定位以及通过分子标记辅助选择培育耐热水稻新品种奠定了基础。     

Improvement of Upland Rice Variety by Pyramiding Drought Tolerance QTL with Two Major Blast Resistance Genes for Sustainable Rice Production

Varalu is an early maturing rice variety widely grown in the rainfed ecosystem preferred for its grain type and cooking quality. However, the yield of Varalu is substantially low since it is being affected by reproductive drought stress along with the blast disease. The genetic improvement of Varalu was done by introgressing a major yield QTL, qDTY_12.1, along with two major blast resistance genes i.e. Pi54 and Pi1 through marker-assisted backcross breeding. Both traits were transferred till BC₂ generation and intercrossing was followed to pyramid the two traits. Stringent foreground selection was carried out using linked markers as well as peak markers (RM28099, RM28130, RM511 and RM28163) for the targeted QTL (qDTY_12.1), RM206 for Pi54 and RM224 for Pi1. Extensive background selection was done using genome-wide SSR markers. Six best lines (MSM-36, MSM-49, MSM-53, MSM-57, MSM-60 and MSM-63) having qDTY_12.1 and two blast resistance genes in homozygous condition with recurrent parent genome of 95.0%-96.5% having minimal linkage drag of about 0.1 to 0.7 Mb were identified. These lines showed yield advantage under drought stress as well as irrigated conditions. MSM-36 showed better performance in the national coordinated trials conducted across India, which indicated that improved lines of Varalu expected to replace Varalu and may have an important role in sustaining rice production. The present study demonstrated the successful marker-assisted pyramiding strategy for introgression of genes/QTLs conferring biotic stress resistance and yield under abiotic stress in rice.     

Introgression of Two Drought QTLs into FUNAABOR-2 Early Generation Backcross Progenies Under Drought Stress at Reproductive Stage

FUNAABOR-2 is a popular Ofada rice variety grown in a large area under rainfed upland condition across western states of Nigeria. We used the combination of phenotypic and marker-assisted selection(MAS) to improve grain yield of FUNAABOR-2 under drought stress(DS) at the reproductive stage via introgression of two drought quantitative trait loci(QTLs), qDTY12.1 and qDTY2.3. Foreground selection was carried out using peak markers RM511 and RM250, associated with qDTY12.1 and qDTY2.3, respectively, followed by recombinant selection with RM28099 and RM1261 distally flanking qDTY12.1. Furthermore, BC1 F2-derived introgressed lines and their parents were evaluated under DS and non-stress(NS) conditions during the 2015–2016 dry season. Overall reduction of grain yield under DS compared to NS was recorded. Introgressed lines with qDTY12.1 and qDTY2.3 combinations showed higher yield potential compared to lines with single or no QTL under DS, indicating significant positive interactions between the two QTLs under the FUNAABOR-2 genetic background. Pyramiding of qDTY12.1 and qDTY2.3 in the FUNAABOR-2 genetic background led to higher grain yield production under DS and NS.     

QTL Analysis for Grain Iron and Zinc Concentrations in Two O. nivara Derived Backcross Populations

Identification of quantitative trait loci (QTLs) for grain mineral elements can assist in faster and more precise development of micronutrient dense rice varieties through marker-assisted breeding. In the present study, QTLs were mapped for Fe and Zn concentrations in two BC₂F₃ mapping populations derived from the crosses of O. sativa cv Swarna with two different accessions of O. nivara. In all, 10 and 8 QTLs were identified for grain Fe and Zn concentrations in population 1, and 7 and 5 QTLs were identified in population 2, respectively. Eighty percent of the QTLs detected in both populations were derived from O. nivara. Five QTLs for Fe and three QTLs for Zn explained more than 15% phenotypic variance either in interval or composite interval mapping. The locations of O. nivara derived QTLs such as qFe2.1, qFe3.1, qFe8.2 and qZn12.1 were consistently identified in both the populations. Epistatic interaction was observed only between RM106 and RM6 on chromosome 2 and between RM22 and RM7 on chromosome 3 for Fe concentration in population 1. Sixteen candidate genes for metal homeostasis were found to co-locate with 10 QTLs for Fe and Zn concentrations in both the populations. Most of the Fe and Zn QTLs were found to co-locate with QTLs for grain yield and grain quality traits. Some of the major effect QTLs identified can be used to improve rice grain Fe and Zn concentrations.     

Genetic Analysis and QTL Mapping of Large Flag Leaf Angle Trait in Japonica Rice

Genetic segregation analysis for flag leaf angle was conducted using six generations of P1,P2,F1,B1,B2 and F2 derived from a cross of 863B(a maintainer line of japonica rice) and A7444(a germplasm with large flag leaf angle).Genotypes and phenotypes of flag leaf angle were investigated in 863B(P1),A7444(P2) and 141 plants in BC1F1(863B/A7444$$$$863B) population.An SSR genetic linkage map was constructed and QTLs for flag leaf angle were detected.The genetic map containing 79 information loci was constructed,which covers a total distance of 441.6 cM,averaging 5.6 cM between two neighboring loci.Results showed that the trait was controlled by two major genes plus polygene and the major genes were more important.Fifteen markers showed highly significant correlations with flag leaf angle based on single marker regression analysis.Two QTLs(qFLA2 and qFLA8) for flag leaf angle were detected by both composite interval method in software WinQTLCart 2.5 and composite interval method based on mixed linear model in QTL Network 2.0.The qFLA2 explained 10.50% and 13.28% of phenotypic variation,respectively,and was located at the interval of RM300 and RM145 on the short arm of chromosome 2.The qFLA8 explained 9.59% and 7.64% of phenotypic variation,respectively,and was located at the interval flanking RM6215 and RM8265 on the long arm of chromosome 8.The positive alleles at the two QTLs were both contributed from A7444.     

Identification and validation of QTLs for cold tolerance at the booting stage and other agronomic traits in a rice cross of a Japanese tolerant variety,Hananomai, and a NERICA parent,WAB56-104

In Africa, cold temperatures occur in the highlands of East and Southern Africa and in some areas of the Sahel region of West Africa leading to substantial rice yield losses. Cold tolerance (CT) at booting stage on basis of spikelet fertility after cold water irrigation was evaluated using F₂ population derived from a cross between temperate japonica, Hananomai, and tropical japonica, WAB56-104. Two Quantitative trait loci (QTLs) for CT were detected on chromosome 8 and 10 with enhanced effects on the trait coming from Hananomai and WAB56-104 allele, respectively. The QTLs explained 30% and 33% of phenotypic variation in spikelet fertility, respectively. CT was negatively correlated with panicle number (r = ?0.35, p < 0.01) and positively correlated with panicle weight (r = 0.61, p < 0.001). Selected BC₁F₄ and BC₁F₅ genotypes having homozygous alleles for both CT QTLs exhibited higher spikelet fertility under cold stress. The identified QTLs will be useful in the development of cold-tolerant varieties for production in high altitude areas through marker-assisted selection.     

Fine Mapping of C（Chromogen for Anthocyanin） Gene in Rice

Seven residual heterozygous lines (RHLs) displaying different genotypic compositions in the genomic region covering probable locations of C (Chromogen for anthocyanin) gene on the short arm of rice chromosome 6 were selected from the progenies of the indica cross Zhenshan 97B/Milyang 46. Seeds were harvested from each of the seven plants, and the resultant F_2:3 populations were used for fine mapping of C gene. It was shown in the populations that the apiculus coloration matched to basal leaf sheath coloration in each plant. By relating the coloration performances of the populations with the genotypic compositions of the RHLs, the C locus was located between rice SSR markers RM314 and RM253. By using a total of 1279 F_2:3 individuals from two populations showing coloration segregation, the C locus was then located between RM111 and RM253, with genetic distances of 0.7 cM to RM111 and 0.4 cM to RM253. Twenty-two recombinants found in the two populations were assayed with seven more markers located between RM111 and RM253, including six SSR markers and one marker for the C gene candidate, OsC1. The C locus was delimited to a 59.3-kb region in which OsC1 was located.     

Identification of QTLs and Validation of qCd-2 Associated with Grain Cadmium Concentrations in Rice

Cadmium(Cd) is one of heavy metals harmful to human health. As rice is the main staple food in Asia and Cd is easily contaminated in rice, the molecular regulation of Cd accumulation should be explored. In this study, a recombinant inbred population derived from Xiang 743/Katy was grown in Cd-polluted fields and used to map the quantitative trait loci(QTLs) for Cd accumulation in rice grains. We identified seven QTLs distributed on chromosomes 2, 3, 6, 7, 8 and 10. These QTLs displayed phenotypic variances of 58.50% and 40.59% in 2014 and 2015, respectively. Two QTLs, qCd-2 and qCd-7, were identified in both the two years. qCd-2 was detected on the interval of RM250–RM207 on chromosome 2, with an LOD of 2.51 and a phenotypic contribution of 13.75% in 2014, and an LOD of 3.35 and a phenotypic contribution of 14.16% in 2015. qCd-7 co-localized with the cloned qCdT7 on chromosome 7 and may represent the correct candidate. The other five QTLs were detected only in one year. To further confirm the effects of qCd-2, a residual heterozygous line designated as RHL945, with a heterozygous interval of RM263–RM207 on chromosome 2, was selected from the recombinant inbred population and used to develop an F2 population consisting of 155 individual plants. By incorporating further simple sequence repeat markers into the segmental linkage map of the target region, qCd-2 was delimited in the interval of RM5404–RM3774, with an LOD value of 4.38 and a phenotypic contribution of 15.52%. These results reflected the genetic regulation of grain Cd in rice and paved the way for the future cloning of qCd-2.     

Evaluation and Bulked Segregant Analysis of Major Yield QTL qtl12.1 Introgressed into Indigenous Elite Line for Low Water Availability under Water Stress

Near isogenic lines carrying large-effect QTL (qtl12.1), which has a consistent influence on grain yield under upland drought stress conditions in a wide range of environments, were evaluated under water stress in the fields. The line which gave higher yield under drought was crossed with a local elite line, PMK3, and forwarded to F2:3 generation. Significant variation was found among the F2:3 lines for agronomic traits under water stress in the fields. Low to high broad sense heritability (H) for investigated traits was also found. Water stress indicators such as leaf rolling and leaf drying were negatively correlated with plant height, biomass and grain yield under stress. Bulked segregant analysis (BSA) was performed with the markers in the vicinity of qtl12.1, and RM27933 was found to be segregated perfectly well in individual components of drought resistant and drought susceptible bulks which were bulked based on yield under water stress among F2:3 lines. Hence, this simple and breeder friendly marker, RM27933, may be useful as a potentially valuable candidate marker for the transfer of the QTL qtl12.1 in the regional breeding program. Bioinformatic analysis of the DNA sequence of the qtl12.1 region was also done to identify and analyze positional candidate genes associated with this QTL and to ascertain the putative molecular basis of qtl12.1.     

Mapping of QTLs for Germination Characteristics under Non-stress and Drought Stress in Rice

Identification of genetic factors controlling traits associated with seed germination under drought stress conditions, leads to identification and development of drought tolerant varieties. Present study by using a population of F2：, derived from a cross between a drought tolerant variety, Gharib （indica） and a drought sensitive variety, Sepidroud （indica）, is to identify and compare QTLs associated with germination traits under drought stress and non-stress conditions. Through QTL analysis, using composite interval mapping, regarding traits such as germination rate （GR）, germination percentage （GP）, radicle length （RL）, plumule length （PL）, coleorhiza length （COL） and coleoptile length （CL）, totally 13 QTLs were detected under pole drought stress （-8 MPa poly ethylene glycol 6000） and 9 QTLs under non-stress conditions. Of the QTLs identified under non-stress conditions, QTLs associated with COL （qCOL-5） and GR （qGR-1） explained 21.28% and 19.73% of the total phenotypic variations, respectively Under drought stress conditions, QTLs associated with COL （qCOL-3） and PL （qPL-5） explained 18.34% and 18.22% of the total phenotypic variations, respectively. A few drought-tolerance-related QTLs identified in previous studies are near the QTLs detected in this study, and several QTLs in this study are novel alleles. The major QTLs like qGR-1, qGP-4, qRL-12 and qCL-4 identified in both conditions for traits GR, GP, RL and CL, respectively, should be considered as the important and stable trait-controlling QTLs in rice seed germination. Those major or minor QTLs could be used to significantly improve drought tolerance by marker-assisted selection in rice.     

基因水稻培矮64S回交后代白叶枯病抗性与育性研究

对筛选到的转[WTBX][STBX]Xa21[WTBZ][STBZ]基因培矮64S后代纯合株系抗性与育性的研究表明,在第5代杂种中,该外源基因仍能稳定遗传表达;以其作父本、培矮64S为母本所配制的F1植株, Xa21基因PCR检测均呈阳性,且绝大多数表现抗白叶枯病,说明该外源基因能够通过常规杂交方式转移利用。这些杂交组合F2群体中抗病与感病株出现3∶1分离,表明转Xa21基因在杂交后代的传递属单基因显性遗传。长日高温下,（培矮64S/转Xa21基因培矮64S）F1雄性完全可育,F2群体可育与不育株出现27∶1分离。     

Transgressive variants for red pericarp grain with high yield potential derived from Oryza rufipogon × Oryza sativa: Field evaluation, screening for blast disease, QTL validation and background marker analysis for agronomic traits

Five transgressive variants (advanced breeding lines from BC₂F₅ and BC₂F₆ generation) were derived from a cross between the wild relative, O. rufipogon Griff. and O. sativa L. subsp. indica cv. MR219, a popular high yielding Malaysian rice cultivar. The aim of the study was to evaluate the pericarp colour of the grains along with yield potential and to validate quantitative trait loci (QTLs) for agronomic traits. The variants were screened against blast disease. Background marker analysis was also done for the promising variants. The field trials were carried out at a single location (due to containment purposes) over two seasons using randomized complete block design (RCBD) with three replications. A trait-based marker analysis was used to identify QTLs for validation in BC₂F₅ generation. Analysis of variance (ANOVA) showed that the seasonal factors influenced different agronomic traits. Variant G33 produced significantly (p < 0.05) higher yield (5.20 t/ha) than the control, MR219 (4.53 t/ha). Eighteen QTLs for different agronomic traits were identified in BC₂F₂ population in a previous study. Among them 14 QTLs were found in BC₂F₅ population of the present study. The yield of variant G33 was influenced by several QTLs viz. qGPL-1, qSPL-1-2, qSPL-8 and qYLD-4, which were introgressed from the donor parent revealed by background marker analysis using BC₂F₇ generation. Percentage (99%) of red pericarp grain of G33 and G34 in BC₂F₅ and BC₂F₆ generations indicated the stability of pericarp colour which was transferred from the wild relative. Variant G33 showed resistance against two pathotype of blast disease (Magnaporthe oryzae). Among the evaluated variants, G33 could be considered for inclusion in the cultivar development program for red rice with high yield potential and resistance to blast disease. This study demonstrated that the alleles from wild relative could improve the yield and yield related traits through allelic interaction, even though the phenotypic traits were inferior to the recurrent parent.     

Reciprocal differences in the photoperiod reaction of hybrid populations inSolanum tuberosum

Large reciprocal differences were observed inSolanum tuberosum, when a mixed population of Group Phureja and Gp. Stenotomum was reciprocally crossed with a population of Gp. Tuberosum haploids. In the progeny reciprocal differences were observed for tuber initiation, tuber set, vine senescence, tuber yield, flowering, and male fertility. These differences were large in the F₁ generation, but were less dramatic when the populations were inter-mated to form F₂ generations. It is proposed that most of the reciprocal differences were due to a difference in photoperiod response in the reciprocal populations. Cytoplasmic inheritance or dauermodification are considered the most likely explanations for this difference in photoperiod reaction.     

Genetic analysis and validation of quantitative trait loci associated with reproductive-growth traits and grain yield under drought stress in a doubled haploid line population of rice (Oryza sativa L.)

Drought is a major constraint for rice production and yield stability in rainfed ecosystems, especially when it occurs during the reproductive stage. Combined genetic and physiological analysis of reproductive-growth traits and their effects on yield and yield components under drought stress is important for dissecting the biological bases of drought resistance and for rice yield improvement in water-limited environments. A subset of a doubled haploid (DH) line population of CT9993-5-10-1-M/IR62266-42-6-2 was evaluated for variation in plant water status, phenology, reproductive-growth traits, yield and yield components under reproductive-stage drought stress and irrigated (non-stress) conditions in the field. Since this DH line population was previously used in extensive quantitative trait loci (QTLs) mapping of various drought resistance component traits, we aimed at identifying QTLs for specific reproductive-growth and yield traits and also to validate the consensus QTLs identified earlier in these DH lines using meta-analysis. DH lines showed significant variation for plant water status, reproductive-growth traits, yield and yield components under drought stress. Total dry matter, number of panicles per plant, harvest index, panicle harvest index, panicle fertility, pollen fertility, spikelet fertility and hundred grain weight had significant positive correlations with grain yield under drought stress. A total of 46 QTLs were identified for the various traits under stress and non-stress conditions with phenotypic effect ranging from 9.5 to 35.6% in this study. QTLs for panicle exsertion, peduncle length and pollen fertility, identified for the first time in this study, could be useful in marker-assisted breeding (MAB) for drought resistance in rice. A total of 97 QTLs linked to plant growth, phenology, reproductive-growth traits, yield and its components under non-stress and drought stress, identified in this study as well as from earlier published information, were subjected to meta-analysis. Meta-analysis identified 23 MQTLs linked to plant phenology and production traits under stress conditions. Among them, four MQTLs viz., 1.3 for plant height, 3.1 for days to flowering, 8.1 for days to flowering or delay in flowering and 9.1 for days to flowering are true QTLs. Consensus QTLs for reproductive-growth traits and grain yield under drought stress have been identified on chromosomes 1 and 9 using meta-QTL analysis in these DH lines. These MQTLs associated with reproductive-growth, grain yield and its component traits under drought stress could be useful targets for drought resistance improvement in rice through MAB and/or map-based positional analysis of candidate genes.     

Evaluation of Rice Seedling Tolerance to Constant and Intermittent Low Temperature Stress

M202,IR50 and advanced backcross(BC 4 F 6) lines carrying the cold tolerance QTLs qCTS4 and qCTS12 were evaluated using three low temperature stress assays(constant,intermittent and constant with recovery period).Under constant stress,two BC 4 F 6 lines(MIb 4853-9 and MIb 6885-2) exhibited differences in seedling growth and accumulation of stress-related compounds although both carry the two QTLs in the IR50 background.Differences between these lines were also observed in the constant with recovery period assay,although both of them performed comparably under intermittent stress.MIb 6885-2 performed more similarly to M202 in the constant and constant with recovery period assays,suggesting that this line contains an introgressed region(s) not present in MIb 4853-9.The three assays were also applied to assess variations in cold tolerance in a set of diverse germplasms.Performance metrics and visual ratings were comparable for evaluating tolerance to constant stress.However,differences in response to intermittent stress were more evident from growth and total chlorophyll measurements than from visual ratings.With regard to the constant with recovery period assay,about 15% of the germplasm accessions did not recover.However,some lines which exhibited chilling injuries of comparable severity were able to overcome them.This recovery phenotype may improve rice performance in the field and warrant further investigation.     

Identification of QTLs for Cadmium Tolerance During Seedling Stage and Validation of qCDSL1 in Rice

Cadmium(Cd)is a non-essential toxic metal that is harmful to plants.To investigate the genetic mechanism of Cd tolerance in rice,quantitative trait loci(QTLs)associated with Cd tolerance at the seedling stage were analyzed using a recombinant inbred line(RIL)population derived from a cross between PA64s and 93-11.A total of 36 QTLs associated with shoot length,root length,shoot dry weight,root dry weight and total dry weight were detected in Hangzhou and Lingshui of China.Among them,15 QTLs were identified under the control condition and 15 QTLs were identified under the Cd stress condition,and 6 QTLs for Cd tolerant coefficient were detected on chromosomes 1,3,7 and 9.The qCDSL1.1 and qCDSL1.2 were identified in Hangzhou and Lingshui,respectively,and had overlapping intervals on chromosome 1.To further confirm the effects of qCDSL1.1 and qCDSL1.2,we developed a chromosome segment substitution line(CSSL),CSSLqCDSL1,in 93-11 background harboring qCDSL1.1/qCDSL1.2 from PA64s.Compared to 93-11,CSSLqCDSL1 had increased shoot length under the Cd stress condition.These results pave the way for further isolation of those genes controlling Cd tolerance in rice and marker-assistant selection of rice elite varieties with Cd tolerance.     

New Stably Expressed Loci Responsible for Panicle Angle Trait in Japonica Rice in Four Environments

Panicle angle (PA) of 254 recombinant inbred lines derived from a cross between two japonica varieties Xiushui 79 and C Bao was investigated under four environments,and a genetic linkage map including 111 SSR markers was constructed.Genetic analysis was conducted by mixed major gene plus polygene inheritance models,and quantitative trait loci (QTLs) identification by the QTLNetwork 2.0 and the composite interval mapping approach of WinQTLCart 2.5 software.Results showed that the PA trait was controlled by two major genes plus polygenes,mainly by major genes.Eight QTLs for PA were detected by the QTLNetwork 2.0 software,and each locus explained 0.01% to 39.89% of the phenotypic variation.Twelve QTLs for PA were detected by the WinQTLCart 2.5 software,with each locus explaining 2.83% to 30.60% of the phenotypic variation.Two major QTLs (qPA9.2 and qPA9.5) distributed between RM3700 and RM3600 and between RM5652 and RM410,respectively,and a moderate QTL (qPA9.7) distributed between RM257 and OSR28,were both detected by the two methods in all of the four environments.The negative effect alleles of the three QTLs were from Xiushui 79.In addition,eight pairs of epistatic QTLs with minor effects were also detected.QTL × environment interactions were not significant for additive QTLs and epistatic QTL pairs.     

Cytoplasmic evaluations during substitution backcrossing inSolanum

Summary Sterility-resistant cytoplasmic factors ofSolanum tuberosum spp.andigena (Juz. & Buk.) Hawkes and ofSolanum phureja (Juz. & Buk.) were combined with chromosomal genes ofS. tuberosum ssp.tuberosum. Eleven morphological characters of reciprocal F₁ and BC₁ progenies were monitored to evaluate rate of progression towards characteristics occurring in the recurrent ssp.tuberosum parent. Female and male fertilities of F₁ and BC₁ populations were also evaluated. Cytoplasmic factors did not influence morphological parameters consistently, except those relating directly to fertility. Differences between reciprocal progeny depended more upon the genes of individual parents used in crosses than on cytoplasm source. No consistent reciprocal differences occurred in tuber characters and those differences which arose seem to reflect a maternal rather than a cytoplasmic influence. F₁ and BC₁ progenies containing the sterility-resistant cytoplasmic factors of ssp.andigena or ofS. phureja had higher fertility than their respective reciprocal progenies with cytoplasm of ssp.tuberosum. Pennsylvania Agricultural Experiment Station Journal Series No 6212.     

The QTL Analysis of RuBisCO in Flag Leaves and Non-Structural Carbohydrates in Leaf Sheaths of Rice Using Chromosome Segment Substitution Lines and Backcross Progeny F2 Populations

Abstract

In rice (Oryza sativa L.), the maintenance of high photosynthetic rate of flag leaves and the carbon remobilization from leaf sheaths after heading is a critical physiological component affecting the yield. To clarify the genetic basis of RuBisCO content of the flag leaf, a major determinant of photosynthetic rate, and non-structural carbohydrate (NSC) concentration in the third leaf sheath at heading, we carried out quantitative trait loci (QTL) analysis with 39 Koshihikari/Kasalath chromosome segment substitution lines (CSSLs) and backcross progeny F₂ population derived from target CSSL holding the QTL/Koshihikari in the field. QTLs for RuBisCO content and NSC concentration at heading were detected between R2447-C1286 and R2447-R716 on chromosome 10, respectively, by comparing Koshihikari with four CSSLs for chromosome 10 (SL-229, -230, -231 and -232). The progeny QTL for RuBisCO content and for NSC concentration at heading qRCH-10 and qNSCLSH-10-1, respectively, were detected at similar marker intervals between RM8201 and RM5708. In addition, QTLs for RuBisCO content at 14 d after heading, qRCAH-10-1 and qRCAH-10-2, were detected in regions different from that of qRCH-10. No QTL for NSC concentration at 14 d after heading was detected between RM8201 and R716, the region analyzed in this study. The QTLs qRCH-10 and qRCAH-10-1 for RuBisCO content would have additive effects. These QTLs for RuBisCO content and NSC concentration newly found using CSSLs and their backcross progeny F₂ population should be useful for better understanding the genetic basis of source and temporary-sink functions in rice and for genetic improvement of Koshihikari in terms of their functions.     

Molecular Mapping of Sterility QTLs qSS-3, qSS-6a and qSS-7 as Single Mendelian Factors via NIL strategy

Hybrid sterility between Oryza glaberrima and O. sativa seriously hampers the introgression of favorable genes from each other. In order to further understand this issue, identification and isolation of hybrid sterility QTLs as single Mendelian factors are an effective strategy. A genetic map was constructed using a BC₁F₁ population derived from a cross between an O. sativa japonica cultivar and an O. glaberrima accession. Four main-effect QTLs for pollen sterility were detected in the BC₁F₁. Five BC₈F₁ advanced backcross populations were developed via successive backcrosses based on phenotype and molecular selections. The BC₈F₁ populations showed bimodal distribution for pollen fertility and could be classified into semi-sterile and fertile types, fitting single Mendilian factor inheritance ratios. Three QTLs detected in the BC₁F₁ corresponding to qSS-3, qSS-6a and qSS-7 were mapped on chromosomes 6, 3 and 7, respectively, as single Mendilian factors.