Quantitative Trait Loci For Grain Length Research Articles

GL5.2, a Quantitative Trait Locus for Rice Grain Shape, Encodes a RING-Type E3 Ubiquitin Ligase.

Grain weight and grain shape are important traits that determine rice grain yield and quality. Mining more quantitative trait loci (QTLs) that control grain weight and shape will help to further improve the molecular regulatory network of rice grain development and provide gene resources for high-yield and high-quality rice varieties. In the present study, a QTL for grain length (GL) and grain width (GW), qGL5.2, was firstly fine-mapped into a 21.4 kb region using two sets of near-isogenic lines (NILs) derived from the indica rice cross Teqing (TQ) and IRBB52. In the NIL populations, the GL and ratio of grain length to grain width (RLW) of the IRBB52 homozygous lines increased by 0.16-0.20% and 0.27-0.39% compared with the TQ homozygous lines, but GW decreased by 0.19-0.75%. Then, by analyzing the grain weight and grain shape of the knock-out mutant, it was determined that the annotation gene Os05g0551000 encoded a RING-type E3 ubiquitin ligase, which was the cause gene of qGL5.2. The results show that GL and RLW increased by 2.44-5.48% and 4.19-10.70%, but GW decreased by 1.69-4.70% compared with the recipient. Based on the parental sequence analysis and haplotype analysis, one InDel variation located at -1489 in the promoter region was likely to be the functional site of qGL5.2. In addition, we also found that the Hap 5 (IRBB52-type) increased significantly in grain length and grain weight compared with other haplotypes, indicating that the Hap 5 can potentially be used in rice breeding to improve grain yield and quality.

Genome-wide QTL mapping for agronomic traits in the winter wheat cultivar Pindong 34 based on 90K SNP array.

Agronomic traits are key components of wheat yield. Exploitation of the major underlying quantitative trait loci (QTLs) can improve the yield potential in wheat breeding. In this study, we constructed a recombinant inbred line (RIL) population from Mingxian 169 (MX169) and Pindong 34 (PD34) to determine the QTLs for grain length (GL), grain width (GW), grain length-to-width ratio (LWR), plant height (PH), spike length (SL), grain number per spike (GNS), and the thousand grain weight (TGW) across four environments using wheat 90K SNP array. A QTL associated with TGW, i.e., QTGWpd.swust-6BS, was identified on chromosome 6B, which explained approximately 14.1%-16.2% of the phenotypic variation. In addition, eight QTLs associated with GL were detected across six chromosomes in four different test environments. These were QGLpd.swust-1BL, QGLpd.swust-2BL, QGLpd.swust-3BL.1, QGLpd.swust-3BL.2, QGLpd.swust-5DL, QGLpd.swust-6AL, QGLpd.swust-6DL.1, and QGLpd.swust-6DL.2. They accounted for 9.0%-21.3% of the phenotypic variation. Two QTLs, namely, QGWpd.swust-3BS and QGWpd.swust-6DL, were detected for GW on chromosomes 3B and 6D, respectively. These QTLs explained 12.8%-14.6% and 10.8%-15.2% of the phenotypic variation, respectively. In addition, two QTLs, i.e., QLWRpd.swust-7AS.1 and QLWRpd.swust-7AS.2, were detected on chromosome 7A for the grain LWR, which explained 10.9%-11.6% and 11.6%-11.2% of the phenotypic variation, respectively. Another QTL, named QGNSpd-swust-6DS, was discovered on chromosome 6D, which determines the GNS and which accounted for 11.4%-13.8% of the phenotypic variation. Furthermore, five QTLs associated with PH were mapped on chromosomes 2D, 3A, 5A, 6B, and 7B. These QTLs were QPHpd.swust-2DL, QPHpd.swust-3AL, QPHpd.swust-5AL, QPHpd.swust-6BL, and QPHpd.swust-7BS, which accounted for 11.3%-19.3% of the phenotypic variation. Lastly, a QTL named QSLpd.swust-3AL, conferring SL, was detected on chromosome 3A and explained 16.1%-17.6% of the phenotypic variation. All of these QTLs were defined within the physical interval of the Chinese spring reference genome. The findings of this study have significant implications for the development of fine genetic maps, for genomic breeding, and for marker-assisted selection to enhance wheat grain yield.

Identification and validation of stable quantitative trait loci for yield component traits in wheat

Grain weight and grain number are important yield component traits in wheat and identification of underlying genetic loci is helpful for improving yield. Here, we identified eight stable quantitative trait loci (QTL) for yield component traits, including five loci for thousand grain weight (TGW) and three for grain number per spike (GNS) in a recombinant inbred line population derived from cross Yangxiaomai/Zhongyou 9507 across four environments. Since grain size is a major determinant of grain weight, we also mapped QTL for grain length (GL) and grain width (GW). QTGW.caas-2D, QTGW.caas-3B, QTGW.caas-5A and QTGW.caas-7A.2 for TGW co-located with those for grain size. QTGW.caas-2D also had a consistent genetic position with QGNS.caas-2D, suggesting that the pleiotropic locus is a modulator of trade-off effect between TGW and GNS. Sequencing and linkage mapping showed that TaGL3-5A and WAPO-A1 were candidate genes of QTGW.caas-5A and QTGW.caas-7A.2, respectively. We developed Kompetitive allele specific PCR (KASP) markers linked with the stable QTL for yield component traits and validated their genetic effects in a diverse panel of wheat cultivars from the Huang-Huai River Valley region. KASP-based genotyping analysis further revealed that the superior alleles of all stable QTL for TGW but not GNS were subject to positive selection, indicating that yield improvement in the region largely depends on increased TGW. Comparative analyses with previous studies showed that most of the QTL could be detected in different genetic backgrounds, and QTGW.caas-7A.1 is likely a new QTL. These findings provide not only valuable genetic information for yield improvement but also useful tools for marker-assisted selection.

Identifying QTLs for Grain Size in a Colossal Grain Rice (Oryza sativa L.) Line, and Analysis of Additive Effects of QTLs.

Grain size is an important component of quality and harvest traits in the field of rice breeding. Although numerous quantitative trait loci (QTLs) of grain size in rice have been reported, the molecular mechanisms of these QTLs remain poorly understood, and further research on QTL observation and candidate gene identification is warranted. In our research, we developed a suite of F2 intercross populations from a cross of 9311 and CG. These primary populations were used to map QTLs conferring grain size, evaluated across three environments, and then subjected to bulked-segregant analysis-seq (BSA-seq). In total, 4, 11, 12 and 14 QTLs for grain length (GL), grain width (GW), 1000-grain weight (TGW), and length/width ratio (LWR), respectively, were detected on the basis of a single-environment analysis. In particular, over 200 splicing-related sites were identified by whole-genome sequencing, including one splicing-site mutation with G>A at the beginning of intron 4 on Os03g0841800 (qGL3.3), producing a smaller open reading frame, without the third and fourth exons. A previous study revealed that the loss-of-function allele caused by this splicing site can negatively regulate rice grain length. Furthermore, qTGW2.1 and qGW2.3 were new QTLs for grain width. We used the near-isogenic lines (NILs) of these GW QTLs to study their genetic effects on individuals and pyramiding, and found that they have additive effects on GW. In summary, these discoveries provide a valuable genetic resource, which will facilitate further study of the genetic polymorphism of new rice varieties in rice breeding.

QTL Analysis of Rice Grain Size Using Segregating Populations Derived from the Large Grain Line

Grain size affects the yield and quality of rice. The large grain line (LGL), showing a large grain size and japonica-like genome, was selected in the breeding field. The 94 F2 plants derived from a cross between LGL and Hanareum (a high-yielding tongil-type variety) were used for the quantitative trait loci (QTL) analysis of grain length (GL), grain width (GW), and grain thickness (GT). A linkage map of the F2 population, covering 1312 cM for all 12 chromosomes, was constructed using 123 Fluidigm SNP markers. A total of nine QTLs for the three traits were detected on chromosomes two, three, four, six, and seven. Two QTLs for GL on chromosomes two and six explained 17.3% and 16.2% of the phenotypic variation, respectively. Two QTLs were identified for GW on chromosomes two and three, and explained 24.3% and 23.5% of the phenotypic variation, respectively. The five QTLs for GT detected on chromosomes two, three, five, six and seven, explained 13.2%, 14.5%, 16.6%, 10.9%, and 10.2% of the phenotypic variation, respectively. A novel QTL for GT, qGT2, was validated on the same region of chromosome two in the selected F3 population. The QTLs identified in this study, and LGL, could be applied to the development of large-grain rice varieties.

Utilization of a Wheat50K SNP Microarray-Derived High-Density Genetic Map for QTL Mapping of Plant Height and Grain Traits in Wheat.

Plant height is significantly correlated with grain traits, which is a component of wheat yield. The purpose of this study is to investigate the main quantitative trait loci (QTLs) that control plant height and grain-related traits in multiple environments. In this study, we constructed a high-density genetic linkage map using the Wheat50K SNP Array to map QTLs for these traits in 198 recombinant inbred lines (RILs). The two ends of the chromosome were identified as recombination-rich areas in all chromosomes except chromosome 1B. Both the genetic map and the physical map showed a significant correlation, with a correlation coefficient between 0.63 and 0.99. However, there was almost no recombination between 1RS and 1BS. In terms of plant height, 1RS contributed to the reduction of plant height by 3.43 cm. In terms of grain length, 1RS contributed to the elongation of grain by 0.11 mm. A total of 43 QTLs were identified, including eight QTLs for plant height (PH), 11 QTLs for thousand grain weight (TGW), 15 QTLs for grain length (GL), and nine QTLs for grain width (GW), which explained 1.36–33.08% of the phenotypic variation. Seven were environment-stable QTLs, including two loci (Qph.nwafu-4B and Qph.nwafu-4D) that determined plant height. The explanation rates of phenotypic variation were 7.39–12.26% and 20.11–27.08%, respectively. One QTL, Qtgw.nwafu-4B, which influenced TGW, showed an explanation rate of 3.43–6.85% for phenotypic variation. Two co-segregating KASP markers were developed, and the physical locations corresponding to KASP_AX-109316968 and KASP_AX-109519968 were 25.888344 MB and 25.847691 MB, respectively. Qph.nwafu-4B, controlling plant height, and Qtgw.nwafu-4B, controlling TGW, had an obvious linkage relationship, with a distance of 7–8 cM. Breeding is based on molecular markers that control plant height and thousand-grain weight by selecting strains with low plant height and large grain weight. Another QTL, Qgw.nwafu-4D, which determined grain width, had an explanation rate of 3.43–6.85%. Three loci that affected grain length were Qgl.nwafu-5A, Qgl.nwafu-5D.2, and Qgl.nwafu-6B, illustrating the explanation rates of phenotypic variation as 6.72–9.59%, 5.62–7.75%, and 6.68–10.73%, respectively. Two QTL clusters were identified on chromosomes 4B and 4D.

Validation of the QTL for grain length linked to the Rht-B1 locus in two genetic backgrounds of bread wheat (Triticum aestivum L.)

Grain size is an important agronomic trait that influences the yield and end-use quality of bread wheat (Triticum aestivum L.). We conducted quantitative trait loci (QTL) analysis using recombinant inbred lines derived from a cross of a semi-dwarf modern variety with large grains (Zenkoujikomugi: Zen) and a landrace with small grains (Chinese Spring: CS). Grain size was evaluated as grain length (GL), grain width (GW), grain thickness (GT), and thousand-grain weight (TGW) under two environmental conditions. A major QTL (QGl.obu-4B) associated with GL was detected in both environments near the Rht-B1 locus for the semi-dwarf trait on chromosome 4B, despite Zen and CS having the same Rht-B1a allele. No QTL for GW was found in the QGl.obu-4B region, and QTLs for GT and TGW was detected in only one environment. To validate the effect of QGl.obu-4B, we developed two backcrossed populations in the CS and Zen genetic backgrounds. The Zen-derived allele conferred larger GL, GW, and GT, resulting in greater TGW (13.7% increase compared to the CS-derived allele) in the CS background. In contrast, the QGl.obu-4B effect was smaller in the Zen background, and the Zen-derived allele increased TGW by only 7.0%. The QTL was located within the 168-Mbp region tightly linked to the Rht-B1 locus. Further characterization and fine-mapping of QGl.obu-4B will facilitate the use of this allele by marker-assisted selection in wheat breeding programs.

A High-Density Genetic Linkage Map of SLAFs and QTL Analysis of Grain Size and Weight in Barley (Hordeum vulgare L.).

Grain size is an important agronomic trait determines yield in barley, and a high-density genetic map is helpful to accurately detect quantitative trait loci (QTLs) related to grain traits. Using specific-locus amplified fragment sequencing (SLAF-seq) technology, a high-density genetic map was constructed with a population of 134 recombinant inbred lines (RILs) deriving from a cross between Golden Promise (GP) and H602, which contained 12,635 SLAFs with 26,693 SNPs, and spanned 896.74 cM with an average interval of 0.07 cM on seven chromosomes. Based on the map, a total of 16 QTLs for grain length (GL), grain width and thousand-grain weight were detected on 1H, 2H, 4H, 5H, and 6H. Among them, a major QTL locus qGL1, accounting for the max phenotypic variance of 16.7% was located on 1H, which is a new unreported QTL affecting GL. In addition, the other two QTLs, qGL5 and qTGW5, accounting for the max phenotypic variances of 20.7 and 21.1%, respectively, were identified in the same region, and sequencing results showed they are identical to HvDep1 gene. These results indicate that it is a feasible approach to construct a high-quality genetic map for QTL mapping by using SLAF markers, and the detected major QTLs qGL1, qGL5, and qTGW5 are useful for marker-assisted selection (MAS) of grain size in barley breeding.

Mapping and genetic validation of a grain size QTL qGS7.1 in rice (Oryza sativa L.)

Grain size is a major determinant of grain weight, which is one of the components of rice yield. The objective o this study was to identify novel, and important quantitative trait loci (QTLs) for grain size and weight in rice. QTLs were mapped using a BC4F4 population including 192 backcross inbred lines (BILs) derived from a backcross between Xiaolijing (XLJ) and recombinant inbred lines (RILs). The mapping population was planted in both Lingshui (Hainan, 2015) and Fuyang (Zhejiang, 2016), with the short- and long-day conditions, respectively. A total of 10 QTLs for grain length, four for grain width, four for the ratio of grain length to width, and 11 for grain weight were detected in at least one environment and were distributed across 11 chromosomes. The phenotypic variance explained ranged from 6.76–25.68%, 14.30–34.03%, 5.28–26.50%, and 3.01–22.87% for grain length, grain width, the ratio of grain length to width, and thousand grain weight, respectively. Using the sequential residual heterozygotes (SeqRHs) method, qGS7.1, a QTL for grain size and weight, was mapped in a 3.2-Mb interval on chromosome 7. No QTLs about grain size and weight were reported in previous studies in this region, providing a good candidate for functional analysis and breeding utilization.

Mapping quantitative traits for grain physical and textural quality in Cambodian Jasmine rice PRD

Grain physical and textural traits are key parameters that are assessed in rice quality improvement programs. In order to dissect the genetic basis of the premium Cambodian quality rice Phka Rumduol (PRD), a population including more than 300 recombinant inbred lines derived from PRD and Thmar Krem was used to map quantitative trait loci (QTLs) for grain length (GL), grain width (GW), degree of chalkiness, grain translucency and texture-associated traits including amylose content (AC), gelatinisation temperature (GT), gel consistency and pasting properties derived from a rapid visco analyser. QTL analysis revealed large-effect QTLs and minor QTLs for these traits of quality, indicating a complex interplay between major and minor genes. The QTL located on chromosome 3 is the major locus for GL, and the one on chromosome 5 plays a major role in determining GW. A novel QTL for GL was identified on the short arm of chromosome 6 and explained about 20% of the phenotypic variation in GL. Grain translucency and chalkiness were largely controlled by QTLs on chromosome 5 and 6. Putative genes for texture-associated traits relate back to the starch biosynthesis pathways. Major QTLs for AC and GT colocalised to the Waxy and starch synthase IIa genes on chromosome 6, respectively. Minor QTLs on chromosomes 3 and 8 were identified for AC, setback, peak viscosity and hot-paste consistency, and on chromosomes 4 and 7 for GT and pasting temperature. This is the first QTL mapping study for the quality of Cambodian rice.

Discovery of QTL Alleles for Grain Shape in the Japan-MAGIC Rice Population Using Haplotype Information.

A majority of traits are determined by multiple quantitative trait loci (QTL) that can have pleiotropic effects. A multi-parent advanced generation inter-cross (MAGIC) population is well suited for genetically analyzing the effects of multiple QTL on traits of interest because it contains a higher number of QTL alleles than a biparental population. We previously produced the JAPAN-MAGIC (JAM) population, derived from eight rice (Oryza sativa L.) cultivars with high yield and biomass in Japan, and developed the method of genome-wide association study (GWAS) using haplotype information on the JAM lines. This method was effective for identifying major genes such as Waxy for eating quality and Sd1 for culm length. Here, we show that haplotype-based GWAS is also effective for the evaluation of multiple QTL with small effects on rice grain shape in the JAM lines. Although both the haplotype- and SNP-based GWAS identified multiple QTL for grain length and width, the sum of the estimated trait values of each allele for the QTL detected by haplotype-based GWAS had higher correlation with observed values than those detected by SNP-based GWAS, indicating high-accuracy QTL detection in the haplotype-based GWAS. Furthermore, the study revealed pleiotropic effects of some QTL regions in regulation of grain shape, suggesting that the haplotype-based GWAS using the JAM lines is an effective means to evaluate the main and side effects of haplotypes at each QTL. Information on the pleiotropic effects of haplotypes on various traits will be useful for designing ideal lines in a breeding program.

QTL-Seq Identified a Major QTL for Grain Length and Weight in Rice Using Near Isogenic F2 Population

Abstract: Mapping and isolation of quantitative trait loci (QTLs) or genes controlling grain size or weight is very important to uncover the molecular mechanisms of seed development and crop breeding. To identify the QTLs controlling grain size and weight, we developed a near isogenic line F2 (NIL-F2) population, which was derived from a residual heterozygous plant in an F7 generation of recombinant inbred line (RIL). With the completion of more than 30y whole genome re-sequencing of the parents, two DNA bulks for large and small grains, a total of 58.94 Gb clean nucleotide data were generated. A total of 455 262 single nucleotide polymorphisms (SNPs) between the parents were identified to perform bulked QTL-seq. A candidate genomic region containing SNPs strongly associated with grain length and weight was identified from 15 to 20 Mb on chromosome 5. We designated the major QTL in the candidate region as qTGW5.3. Then, qTGW5.3 was further validated with PCR-based conventional QTL mapping method through developing simple sequence repeat and Insertion/Deletion markers in the F2 population. Furthermore, recombinants and the progeny tests delimited the candidate region of qTGW5.3 to 1.13 Mb, flanked by HX5009 (15.15 Mb) and HX5003 (16.28 Mb). A set of NILs, selected from the F2 population, was developed to evaluate the genetic effect of qTGW5.3. Significant QTL effects were detected on grain length, grain width and 1000-grain weight of H12-29 allele with 1.14 mm, -0.11 mm and 3.11 g, which explained 99.64%, 95.51% and 97.32% of the phenotypic variations, respectively.

Alternative splicing of OsLG3b controls grain length and yield in japonica rice.

SummaryGrain size, one of the important components determining grain yield in rice, is controlled by the multiple quantitative trait loci (QTLs). Intensive artificial selection for grain size during domestication is evidenced in modern cultivars compared to their wild relatives. Here, we report the molecular cloning and characterization of OsLG3b, a QTL for grain length in tropical japonica rice that encodes MADS‐box transcription factor 1 (OsMADS1). Six SNPs in the OsLG3b region led to alternative splicing, which were associated with grain length in an association analysis of candidate region. Quantitative PCR analysis indicated that OsLG3b expression was higher during the panicle and seed development stages. Analysis of haplotypes and introgression regions revealed that the long‐grain allele of OsLG3b might have arisen after domestication of tropical japonica and spread to subspecies indica or temperate japonica by natural crossing and artificial selection. OsLG3b is therefore a target of human selection for adaptation to tropical regions during domestication and/or improvement of rice. Phylogenetic analysis and pedigree records showed that OsLG3b had been employed by breeders, but the gene still has much breeding potential for increasing grain length in indica. These findings will not only aid efforts to elucidate the molecular basis of grain development and domestication, but also facilitate the genetic improvement of rice yield.

OsLG3 contributing to rice grain length and yield was mined by Ho-LAMap

BackgroundMost agronomic traits in rice are complex and polygenic. The identification of quantitative trait loci (QTL) for grain length is an important objective of rice genetic research and breeding programs.ResultsHerein, we identified 99 QTL for grain length by GWAS based on approximately 10 million single nucleotide polymorphisms from 504 cultivated rice accessions (Oryza sativa L.), 13 of which were validated by four linkage populations and 92 were new loci for grain length. We scanned the Ho (observed heterozygosity per locus) index of coupled-parents of crosses mapping the same QTL, based on linkage and association mapping, and identified two new genes for grain length. We named this approach as Ho-LAMap. A simulation study of six known genes showed that Ho-LAMap could mine genes rapidly across a wide range of experimental variables using deep-sequencing data. We used Ho-LAMap to clone a new gene, OsLG3, as a positive regulator of grain length, which could improve rice yield without influencing grain quality. Sequencing of the promoter region in 283 rice accessions from a wide geographic range identified four haplotypes that seem to be associated with grain length. Further analysis showed that OsLG3 alleles in the indica and japonica evolved independently from distinct ancestors and low nucleotide diversity of OsLG3 in indica indicated artificial selection. Phylogenetic analysis showed that OsLG3 might have much potential value for improvement of grain length in japonica breeding.ConclusionsThe results demonstrated that Ho-LAMap is a potential approach for gene discovery and OsLG3 is a promising gene to be utilized in genomic assisted breeding for rice cultivar improvement.

Advanced backcross QTL analysis reveals complicated genetic control of rice grain shape in a <i>japonica</i> × <i>indica</i> cross

Grain shape is an important trait for improving rice yield. A number of quantitative trait loci (QTLs) for this trait have been identified by using primary F2 mapping populations and recombinant inbred lines, in which QTLs with a small effect are harder to detect than they would be in advanced generations. In this study, we developed two advanced mapping populations (chromosome segment substitution lines [CSSLs] and BC4F2 lines consisting of more than 2000 individuals) in the genetic backgrounds of two improved cultivars: a japonica cultivar (Koshihikari) with short, round grains, and an indica cultivar (IR64) with long, slender grains. We compared the ability of these materials to reveal QTLs for grain shape with that of an F2 population. Only 8 QTLs for grain length or grain width were detected in the F2 population, versus 47 in the CSSL population and 65 in the BC4F2 population. These results strongly suggest that advanced mapping populations can reveal QTLs for agronomic traits under complicated genetic control, and that DNA markers linked with the QTLs are useful for choosing superior allelic combinations to enhance grain shape in the Koshihikari and IR64 genetic backgrounds.

QTL Mapping for Grain Size Traits Based on Extra-Large Grain Rice Line TD70

Grain size traits, including grain length, grain width and grain thickness, are controlled by quantitative trait loci (QTLs). Many QTLs relating to rice grain size traits had been reported, but their control mechanisms have not yet been elucidated. A recombinant inbred line (RIL) population of 240 lines, deriving from a cross between TD70, an extra-large grain size japonica line with 80 g of 1000-grain weight, and Kasalath, a small grain size indica variety, were constructed and used to map grain size QTLs to a linkage map by using 141 SSR markers in 2010 and 2011. Five QTLs for grain length, six for grain width and seven for grain thickness were detected distributing over chromosomes 2, 3, 5, 7, 9 and 12. Seven QTLs, namely qGL3.1, qGW2, qGW2.2, qGW5.1, qGW5.2, qGT2.3 and qGT3.1, were detected in either of the two years and explained for 56.19%, 4.42%, 29.41%, 10.37%, 7.61%, 21.19% and 17.06% of the observed phenotypic variances on average, respectively. The marker interval RM1347–RM5699 on chromosome 2 was found common for grain length, grain width and grain thickness; qGL3.1 and qGT3.1 were mapped to the same interval RM6080–RM6832 on chromosome 3. All 18 QTL alleles were derived from the large grain parent TD70. Most of the QTLs mapped in the present study were found the same as the genes previously cloned (GW2, GS3 or qGL3, GW5 and GS5), and several were the same as the QTLs (GS7 and qGL-7) previously mapped. Three QTLs, qGL2.2 on chromosome 2, qGW9 and qGT9 on chromosome 9, were first detected. These results laid a foundation for further fine mapping or cloning of these QTLs.

Detection of QTLs for grain length from large grain rice (Oryza sativa L.)

Grain size is one important trait in the agronomics of rice production. Although several quantitative trait loci (QTLs) controlling the length, width, and thickness of rice grains have been genetically identified, and some have been cloned, the molecular mechanisms of grain size regulation are still unclear. To identify the genetic factors affecting rice grain length, we performed QTL analysis using an F2 population and F3 lines derived from a cross between two Oryza sativa L. varieties: the long-grain japonica cultivar ‘Cytoto’ and the indica variety ‘Kasalath’. Three QTLs for grain length were detected, one each on chromosomes 3, 4 and 7. The presence of the Cytoto-type allele at any of the three loci was associated with increased grain length. Analysis of the QTL detected on chromosome 4, designated qGL4b, using F3 progeny confirmed an allelic difference between ‘Cytoto’ and ‘Kasalath’ at qGL4b. The Cytoto allele of qGL4b appears to increase the length and weight of the rice grain.

Analysis of QTL for lowering cadmium concentration in rice grains from 'LAC23'

Quantitative trait loci (QTLs) for low cadmium concentration in brown rice were analyzed in 2008 and 2009 using 126 RIL (F6 and F7 plants) grown in a paddy field with high Cd concentration, which were derived from a cross between a high yielding Japanese rice cultivar ‘Fukuhibiki’ and an African upland rice cultivar ‘LAC23’ with the lowest cadmium concentration in rice grains. Totally two QTLs controlling low cadmium concentration in grains were identified in both 2008 and 2009, i.e., one on chromosome 3 (qLCdG3) and one on chromosome 11 (qLCdG11), which had opposite additive effects. In qLCdG11, ‘LAC23’ alleles had the effect of reducing cadmium concentration, but qLCdG3 had the opposite effect. The explained phenotypic variances of qLCdG11 were 9.4% in 2008 and 12.9% in 2009, and those of qLCdG3 were 13.9% in 2008 and 8.3% in 2009. Cadmium concentrations in brown rice showed positive correlations with grain length and grain weight. QTLs for grain length and grain weight were detected on chromosomes 3 and 11, but their positions differed from those for cadmium concentrations. These results suggest a possibility of successful marker-assisted selection of low cadmium trait derived from ‘LAC23’.

Mapping of quantitative trait loci for basmati quality traits in rice (Oryza sativa L.)

Traditional basmati rice varieties are very low yielding due to their poor harvest index, tendency to lodging and increasing susceptibility to foliar diseases; hence there is a need to develop new varieties combining the grain quality attributes of basmati with high yield potential to fill the demand gap. Genetic control of basmati grain and cooking quality traits is quite complex, but breeding work can be greatly facilitated by use of molecular markers tightly linked to these traits. A set of 209 recombinant inbred lines (RILs) developed from a cross between basmati quality variety Pusa 1121 and a contrasting quality breeding line Pusa 1342, were used to map the quantitative trait loci (QTLs) for seven important quality traits namely grain length (GL), grain breadth (GB), grain length to breadth ratio (LBR), cooked kernel elongation ratio (ELR), amylose content (AC), alkali spreading value (ASV) and aroma. A framework molecular linkage map was constructed using 110 polymorphic simple sequence repeat (SSR) markers distributed over the 12 rice chromosomes. A number of QTLs, including three for GL, two for GB, two for LBR, three for aroma and one each for ELR, AC and ASV were mapped on seven different chromosomes. While location of majority of these QTLs was consistent with the previous reports, one QTL for GL on chromosomes 1, and one QTL each for ELR and aroma on chromosomes 11 and 3, respectively, are being reported here for the first time. Contrary to the earlier reports of monogenic recessive inheritance, the aroma in Pusa 1121 is controlled by at least three genes located on chromosomes 3, 4 and 8, and similar to the reported association of badh2 gene with aroma QTL on chromosome 8, we identified location of badh1 gene in the aroma QTL interval on chromosome 4. A discontinuous 5 + 3 bp deletion in the seventh exon of badh2 gene, though present in all the RILs with high aroma, was not sufficient to impart this trait to the rice grains as many of the RILs possessing this deletion showed only mild or no aroma expression.

Identification of QTLs for rice grain size and shape of Iranian cultivars using SSR markers

Grain size is a main component of rice appearance quality. In this study, we performed the SSR mapping of quantitative trait loci (QTLs) controlling grain size (grain length and breadth) and shape (length/breadth ratio) using an F2 population of a cross between two Iranian cultivars, Domsephid and Gerdeh, comprising of 192 individuals. A linkage map with 88 markers was constructed, which covered 1367.9 cM of the rice genome with an average distance of 18 cM between markers. Interval mapping procedure was used to identify the QTLs controlling three grain traits, and QTLs detected were further confirmed using composite interval mapping. A total of 11 intervals carrying 18 QTLs for three traits were identifed, that included five QTLs for grain length, seven QTLs for grain breadth, and six QTLs for grain shape. A major QTL for grain length was detected on chromosome 3, that explained 19.3% of the phenotypic variation. Two major QTLs for grain breadth were mapped on chromosomes 3 and 8, which explained 34.1% and 20% of the phenotypic variation, respectively. Another two major QTLs were identified for grain shape on chromosomes 3 and 8, which accounted for 27.1% and 20.5% of the phenotypic variance, respectively. The two QTLs that were mapped for grain shape coincided with the major QTLs detected for grain length and grain breadth. Intrestingly, gs2 QTL specific to grain shape was detected on chromosome 2 that explained 15% of the phenotypic variation.