Publications by authors named "Deepmala Sehgal"

26 Publications

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Genome-wide association analysis of Mexican bread wheat landraces for resistance to yellow and stem rust.

PLoS One 2021 29;16(1):e0246015. Epub 2021 Jan 29.

International Maize and Wheat Improvement Center (CIMMYT), El Batán, Texcoco, Mexico.

Deploying under-utilized landraces in wheat breeding has been advocated to accelerate genetic gains in current era of genomics assisted breeding. Mexican bread wheat landraces (Creole wheats) represent an important resource for the discovery of novel alleles including disease resistance. A core set of 1,098 Mexican landraces was subjected to multi-location testing for rust diseases in India, Mexico and Kenya. The landrace core set showed a continuous variation for yellow (YR) and stem rust (SR) disease severity. Principal component analysis differentiated Mexican landraces into three groups based on their respective collection sites. Linkage disequilibrium (LD) decay varied from 10 to 32 Mb across chromosomes with an averge of 23Mb across whole genome. Genome-wide association analysis revealed marker-trait associations for YR resistance in India and Mexico as well as for SR resistance in Kenya. In addition, significant additive-additive interaction effects were observed for both YR and SR resistance including genomic regions on chromosomes 1BL and 3BS, which co-locate with pleiotropic genes Yr29/Lr46/Sr58/Pm39/Ltn2 and Sr2/Yr30/Lr27, respectively. Study reports novel genomic associations for YR (chromosomes 1AL, 2BS, and 3BL) and SR (chromosomes 2AL, 4DS, and 5DS). The novel findings in Creole wheat landraces can be efficiently utilized for the wheat genetic improvement.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0246015PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7846011PMC
January 2021

Genome-Wide Association Study of Tan Spot Resistance in a Hexaploid Wheat Collection From Kazakhstan.

Front Genet 2020 11;11:581214. Epub 2021 Jan 11.

Global Wheat Program, International Maize and Wheat Improvement Center (CIMMYT), Texcoco, Mexico.

Tan spot, caused by , is a serious foliar disease of wheat in Kazakhstan with reported yield losses as high as 50% during epidemic years. Here, we report the evaluation of a collection of 191 hexaploid spring and winter wheat lines for tan spot resistance and its underlying genetic architecture using genome-wide association study (GWAS). Our wheat collection comprised candidate varieties from Kazakhstan, Russia, and CIMMYT. It was genotyped using the DArTseq technology and phenotyped for resistance to tan spot at seedling and adult plant stages in Kazakhstan. DArTseq SNPs revealed high genetic diversity (average polymorphic information content = 0.33) in the panel and genome-wide linkage disequilibrium decay at 22 Mb (threshold = 0.1). Principal component analysis revealed a clear separation of Eurasian germplasm from CIMMYT and IWWIP lines. GWAS identified 34 marker-trait associations (MTA) for resistance to tan spot and the amount of phenotypic variation explained by these MTA ranged from 4% to 13.7%. Our results suggest the existence of novel valuable resistant alleles on chromosomes 3BS, and 5DL and 6AL for resistance to Race 1 and Race 5, respectively, in addition to known genes and On chromosome 6AL, a genomic region spanning 3 Mb was identified conferring resistance to both Race 1 and Race 5. Epistatic interaction of associated loci was revealed on chromosomes 1B, 5B, 7B, 5A, and 6A contributing to additional variation of 3.2-11.7%. Twenty-five lines with the best allele combinations of SNPs associated with resistance to both races have been identified as candidates for future variety release and breeding. The results of the present study will be further validated in other independent genetic backgrounds to be able to use markers in breeding.
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http://dx.doi.org/10.3389/fgene.2020.581214DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7831376PMC
January 2021

Haplotype-Based, Genome-Wide Association Study Reveals Stable Genomic Regions for Grain Yield in CIMMYT Spring Bread Wheat.

Front Genet 2020 3;11:589490. Epub 2020 Dec 3.

International Maize and Wheat Improvement Center (CIMMYT), Texcoco, Mexico.

We untangled key regions of the genetic architecture of grain yield (GY) in CIMMYT spring bread wheat by conducting a haplotype-based, genome-wide association study (GWAS), together with an investigation of epistatic interactions using seven large sets of elite yield trials (EYTs) consisting of a total of 6,461 advanced breeding lines. These lines were phenotyped under irrigated and stress environments in seven growing seasons (2011-2018) and genotyped with genotyping-by-sequencing markers. Genome-wide 519 haplotype blocks were constructed, using a linkage disequilibrium-based approach covering 14,036 Mb in the wheat genome. Haplotype-based GWAS identified 7, 4, 10, and 15 stable (significant in three or more EYTs) associations in irrigated (I), mild drought (MD), severe drought (SD), and heat stress (HS) testing environments, respectively. Considering all EYTs and the four testing environments together, 30 stable associations were deciphered with seven hotspots identified on chromosomes 1A, 1B, 2B, 4A, 5B, 6B, and 7B, where multiple haplotype blocks were associated with GY. Epistatic interactions contributed significantly to the genetic architecture of GY, explaining variation of 3.5-21.1%, 3.7-14.7%, 3.5-20.6%, and 4.4- 23.1% in I, MD, SD, and HS environments, respectively. Our results revealed the intricate genetic architecture of GY, controlled by both main and epistatic effects. The importance of these results for practical applications in the CIMMYT breeding program is discussed.
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http://dx.doi.org/10.3389/fgene.2020.589490DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7737720PMC
December 2020

SNP markers for low molecular glutenin subunits (LMW-GSs) at the Glu-A3 and Glu-B3 loci in bread wheat.

PLoS One 2020 12;15(5):e0233056. Epub 2020 May 12.

Global Wheat Program, International Maize and Wheat Improvement Center (CIMMYT), Texcoco, Mexico.

The content and composition of seed storage proteins is largely responsible for wheat end-use quality. They mainly consist of polymeric glutenins and monomeric gliadins. According to their electrophoretic mobility, gliadins and glutenins are subdivided into several fractions. Glutenins are classified as high molecular weight or low molecular weight glutenin subunits (HMW-GSs and LMW-GSs, respectively). LMW-GSs are encoded by multigene families located at the orthologous Glu-3 loci. We designed a set of 16 single-nucleotide polymorphism (SNP) markers that are able to detect SDS-PAGE alleles at the Glu-A3 and Glu-B3 loci. The SNP markers captured the diversity of alleles in 88 international reference lines and 27 Mexican cultivars, when compared to SDS-PAGE and STS markers, however, showed a slightly larger percent of multiple alleles, mainly for Glu-B3. SNP markers were then used to determine the Glu-1 and Glu-3 allele composition in 54 CIMMYT historical lines and demonstrated to be useful tool for breeding programs to improve wheat end product properties.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0233056PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7217469PMC
July 2020

Molecular Markers Associated with Agro-Physiological Traits under Terminal Drought Conditions in Bread Wheat.

Int J Mol Sci 2020 Apr 30;21(9). Epub 2020 Apr 30.

International Maize and Wheat Improvement Centre (CIMMYT) km, 45, Carretera Mex-Veracruz, El-Batan, Texcoco CP 56237, Mexico.

Terminal drought stress poses a big challenge to sustain wheat grain production in rain-fed environments. This study aimed to utilize the genetically diverse pre-breeding lines for identification of genomic regions associated with agro-physiological traits at terminal stage drought stress in wheat. A total of 339 pre-breeding lines panel derived from three-way crosses of 'exotics × elite × elite' lines were evaluated in field conditions at Obregon, Mexico for two years under well irrigated as well as drought stress environments. Drought stress was imposed at flowering by skipping the irrigations at pre and post anthesis stage. Results revealed that drought significantly reduced grain yield (Y), spike length (SL), number of grains spikes (NGS) and thousand kernel weight (TKW), while kernel abortion (KA) was increased. Population structure analysis in this panel uncovered three sub-populations. Genome wide linkage disequilibrium (LD) decay was observed at 2.5 centimorgan (cM). The haplotypes-based genome wide association study (GWAS) identified significant associations of Y, SL, and TKW on three chromosomes; 4A (HB10.7), 2D (HB6.10) and 3B (HB8.12), respectively. Likewise, associations on chromosomes 6B (HB17.1) and 3A (HB7.11) were found for NGS while on chromosome 3A (HB7.12) for KA. The genomic analysis information generated in the study can be efficiently utilized to improve Y and/or related parameters under terminal stage drought stress through marker-assisted breeding.
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http://dx.doi.org/10.3390/ijms21093156DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7247584PMC
April 2020

Incorporating Genome-Wide Association Mapping Results Into Genomic Prediction Models for Grain Yield and Yield Stability in CIMMYT Spring Bread Wheat.

Front Plant Sci 2020 4;11:197. Epub 2020 Mar 4.

Global Wheat Program, International Maize and Wheat Improvement Center, Texcoco, Mexico.

Untangling the genetic architecture of grain yield (GY) and yield stability is an important determining factor to optimize genomics-assisted selection strategies in wheat. We conducted in-depth investigation on the above using a large set of advanced bread wheat lines (4,302), which were genotyped with genotyping-by-sequencing markers and phenotyped under contrasting (irrigated and stress) environments. Haplotypes-based genome-wide-association study (GWAS) identified 58 associations with GY and 15 with superiority index (measure of stability). Sixteen associations with GY were "environment-specific" with two on chromosomes 3B and 6B with the large effects and 8 associations were consistent across environments and trials. For , 8 associations were from chromosomes 4B and 7B, indicating 'hot spot' regions for stability. Epistatic interactions contributed to an additional 5-9% variation on average. We further explored whether integrating consistent and robust associations identified in GWAS as fixed effects in prediction models improves prediction accuracy. For GY, the model accounting for the haplotype-based GWAS loci as fixed effects led to up to 9-10% increase in prediction accuracy, whereas for this approach did not provide any advantage. This is the first report of integrating genetic architecture of GY and yield stability into prediction models in wheat.
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http://dx.doi.org/10.3389/fpls.2020.00197DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7064468PMC
March 2020

GWAS to Identify Genetic Loci for Resistance to Yellow Rust in Wheat Pre-Breeding Lines Derived From Diverse Exotic Crosses.

Front Plant Sci 2019 30;10:1390. Epub 2019 Oct 30.

Department of Bioscience, Centro Internacional de Mejoramiento de Maíz y Trigo, Texcoco, Mexico.

Yellow rust (YR) or stripe rust, caused by f. sp Eriks (), is a major challenge to resistance breeding in wheat. A genome wide association study (GWAS) was performed using 22,415 single nucleotide polymorphism (SNP) markers and 591 haplotypes to identify genomic regions associated with resistance to YR in a subset panel of 419 pre-breeding lines (PBLs) developed at International Center for Maize and Wheat Improvement (CIMMYT). The 419 PBLs were derived from an initial set of 984 PBLs generated by a three-way crossing scheme (exotic/elite1//elite2) among 25 best elites and 244 exotics (synthetics, landraces) from CIMMYT's germplasm bank. For the study, 419 PBLs were characterized with 22,415 high-quality DArTseq-SNPs and phenotyped for severity of YR disease at five locations in Mexico. A population structure was evident in the panel with three distinct subpopulations, and a genome-wide linkage disequilibrium (LD) decay of 2.5 cM was obtained. Across all five locations, 14 SNPs and 7 haplotype blocks were significantly ( < 0.001) associated with the disease severity explaining 6.0 to 14.1% and 7.9 to 19.9% of variation, respectively. Based on average LD decay of 2.5 cM, identified 14 SNP-trait associations were delimited to seven quantitative trait loci in total. Seven SNPs were part of the two haplotype blocks on chromosome 2A identified in haplotypes-based GWAS. analysis of the identified SNPs showed hits with interesting candidate genes, which are related to pathogenic process or known to regulate induction of genes related to pathogenesis such as those coding for glunolactone oxidase, quinate O-hydroxycinnamoyl transferase, or two-component histidine kinase. The two-component histidine kinase, for example, acts as a sensor in the perception of phytohormones ethylene and cytokinin. Ethylene plays a very important role in regulation of multiple metabolic processes of plants, including induction of defense mechanisms mediated by jasmonate. The SNPs linked to the promising genes identified in the study can be used for marker-assisted selection.
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http://dx.doi.org/10.3389/fpls.2019.01390DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6831551PMC
October 2019

Validation of Candidate Gene-Based Markers and Identification of Novel Loci for Thousand-Grain Weight in Spring Bread Wheat.

Front Plant Sci 2019 26;10:1189. Epub 2019 Sep 26.

Department of Bioscience, CIMMYT, Texcoco, Mexico.

Increased thousand-grain weight (TGW) is an important breeding target for indirectly improving grain yield (GY). Fourteen reported candidate genes known to enhance TGW were evaluated in two independent and existing datasets of wheat at CIMMYT, the Elite Yield Trial (EYT) from 2015 to 2016 (EYT2015-16) and the Wheat Association Mapping Initiative (WAMI) panel, to study their allele effects on TGW and to verify their suitability for marker-assisted selection. Of these, significant associations were detected for only one gene () in the EYT2015-16 and two genes ( and ) in WAMI. The reported favorable alleles of and genes decreased TGW in the datasets. A haplotype-based genome wide association study was implemented to identify the genetic determinants of TGW on a large set of CIMMYT germplasm (4,302 lines comprising five EYTs), which identified 15 haplotype blocks to be significantly associated with TGW. Four of them, identified on chromosomes 4A, 6A, and 7A, were associated with TGW in at least three EYTs. The locus on chromosome 6A (Hap-6A-13) had the largest effect on TGW and additionally GY with increases of up to 2.60 g and 258 kg/ha, respectively. Discovery of novel TGW loci described in our study expands the opportunities for developing diagnostic markers and for multi-gene pyramiding to derive new allele combinations for enhanced TGW and GY in CIMMYT wheat.
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http://dx.doi.org/10.3389/fpls.2019.01189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6775465PMC
September 2019

Population-dependent reproducible deviation from natural bread wheat genome in synthetic hexaploid wheat.

Plant J 2019 11 3;100(4):801-812. Epub 2019 Sep 3.

Agriculture Victoria, AgriBio, Centre for AgriBiosciences, Bundoora, VIC, Australia.

Sequence elimination is one of the main mechanisms that increases the divergence among homoeologous chromosomes after allopolyploidization to enhance the stability of recently established lineages, but it can cause a loss of some economically important genes. Synthetic hexaploid wheat (SHW) is an important source of genetic variation to the natural hexaploid wheat (NHW) genepool that has low genetic diversity. Here, we investigated the change between SHW and NHW genomes by utilizing a large germplasm set of primary synthetics and synthetic derivatives. Reproducible segment elimination (RSE) was declared if a large chromosomal chunk (>5 cM) produced no aligned reads in more than five SHWs. RSE in five genomic regions was the major source of variation between SHW and NHW. One RSE eliminated almost the complete short arm of chromosome 1B, which contains major genes for flour quality, disease resistance and different enzymes. The occurrence of RSE was highly dependent on the choice of diploid and tetraploid parental lines, their ancestral subpopulation and admixture, e.g. SHWs derived from Triticum dicoccon or from one of two Aegilops tauschii subpopulations were almost free of RSE, while highly admixed parents had higher RSE rates. The rate of RSE in synthetic derivatives was almost double that in primary synthetics. Genome-wide association analysis detected four loci with minor effects on the occurrence of RSE, indicating that both parental lines and genetic factors were affecting the occurrence of RSE. Therefore, pre-pre-breeding strategies should be applied before introducing SHW into pre-breeding programs to ensure genomic stability and avoid undesirable gene loss.
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http://dx.doi.org/10.1111/tpj.14480DOI Listing
November 2019

Identification of Novel Quantitative Trait Loci Linked to Crown Rot Resistance in Spring Wheat.

Int J Mol Sci 2018 Sep 8;19(9). Epub 2018 Sep 8.

Global Wheat Program, International Maize and Wheat Improvement Center (CIMMYT), Ankara 06511, Turkey.

Crown rot (CR), caused by various species, is a major disease in many cereal-growing regions worldwide. is one of the most important species, which can cause significant yield losses in wheat. A set of 126 advanced International Maize and Wheat Improvement Center (CIMMYT) spring bread wheat lines were phenotyped against CR for field crown, greenhouse crown and stem, and growth room crown resistance scores. Of these, 107 lines were genotyped using Diversity Array Technology (DArT) markers to identify quantitative trait loci linked to CR resistance by genome-wide association study. Results of the population structure analysis grouped the accessions into three sub-groups. Genome wide linkage disequilibrium was large and declined on average within 20 cM (centi-Morgan) in the panel. General linear model (GLM), mixed linear model (MLM), and naïve models were tested for each CR score and the best model was selected based on quarantine-quarantine plots. Three marker-trait associations (MTAs) were identified linked to CR resistance; two of these on chromosome 3B were associated with field crown scores, each explaining 11.4% of the phenotypic variation and the third MTA on chromosome 2D was associated with greenhouse stem score and explained 11.6% of the phenotypic variation. Together, these newly identified loci provide opportunity for wheat breeders to exploit in enhancing CR resistance via marker-assisted selection or deployment in genomic selection in wheat breeding programs.
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http://dx.doi.org/10.3390/ijms19092666DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6165080PMC
September 2018

Harnessing genetic potential of wheat germplasm banks through impact-oriented-prebreeding for future food and nutritional security.

Sci Rep 2018 08 21;8(1):12527. Epub 2018 Aug 21.

ICAR-Indian Agricultural Research Institute, Regional Station, Shimla, 171004, India.

The value of exotic wheat genetic resources for accelerating grain yield gains is largely unproven and unrealized. We used next-generation sequencing, together with multi-environment phenotyping, to study the contribution of exotic genomes to 984 three-way-cross-derived (exotic/elite1//elite2) pre-breeding lines (PBLs). Genomic characterization of these lines with haplotype map-based and SNP marker approaches revealed exotic specific imprints of 16.1 to 25.1%, which compares to theoretical expectation of 25%. A rare and favorable haplotype (GT) with 0.4% frequency in gene bank identified on chromosome 6D minimized grain yield (GY) loss under heat stress without GY penalty under irrigated conditions. More specifically, the 'T' allele of the haplotype GT originated in Aegilops tauschii and was absent in all elite lines used in study. In silico analysis of the SNP showed hits with a candidate gene coding for isoflavone reductase IRL-like protein in Ae. tauschii. Rare haplotypes were also identified on chromosomes 1A, 6A and 2B effective against abiotic/biotic stresses. Results demonstrate positive contributions of exotic germplasm to PBLs derived from crosses of exotics with CIMMYT's best elite lines. This is a major impact-oriented pre-breeding effort at CIMMYT, resulting in large-scale development of PBLs for deployment in breeding programs addressing food security under climate change scenarios.
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http://dx.doi.org/10.1038/s41598-018-30667-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6104032PMC
August 2018

Identification of genomic regions for grain yield and yield stability and their epistatic interactions.

Sci Rep 2017 02 1;7:41578. Epub 2017 Feb 1.

International Maize and Wheat Improvement Center (CIMMYT), Km. 45, Carretera Méx-Veracruz, El Batán, Texcoco, CP 56237, México.

The task of identifying genomic regions conferring yield stability is challenging in any crop and requires large experimental data sets in conjunction with complex analytical approaches. We report findings of a first attempt to identify genomic regions with stable expression and their individual epistatic interactions for grain yield and yield stability in a large elite panel of wheat under multiple environments via a genome wide association mapping (GWAM) approach. Seven hundred and twenty lines were genotyped using genotyping-by-sequencing technology and phenotyped for grain yield and phenological traits. High gene diversity (0.250) and a moderate genetic structure (five groups) in the panel provided an excellent base for GWAM. The mixed linear model and multi-locus mixed model analyses identified key genomic regions on chromosomes 2B, 3A, 4A, 5B, 7A and 7B. Further, significant epistatic interactions were observed among loci with and without main effects that contributed to additional variation of up to 10%. Simple stepwise regression provided the most significant main effect and epistatic markers resulting in up to 20% variation for yield stability and up to 17% gain in yield with the best allelic combination.
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http://dx.doi.org/10.1038/srep41578DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5286416PMC
February 2017

Mining Centuries Old Conserved Turkish Wheat Landraces for Grain Yield and Stripe Rust Resistance Genes.

Front Genet 2016 18;7:201. Epub 2016 Nov 18.

Crop Pathology Department, International Center for Maize and Wheat Improvement Ankara, Turkey.

Wheat landraces in Turkey are an important genetic resource for wheat improvement. An exhaustive 5-year (2009-2014) effort made by the International Winter Wheat Improvement Programme (IWWIP), a cooperative program between the Ministry of Food, Agriculture and Livestock of Turkey, the International Center for Maize and Wheat Improvement (CIMMYT) and the International Center for Agricultural Research in the Dry Areas (ICARDA), led to the collection and documentation of around 2000 landrace populations from 55 provinces throughout Turkey. This study reports the genetic characterization of a subset of bread wheat landraces collected in 2010 from 11 diverse provinces using genotyping-by-sequencing (GBS) technology. The potential of this collection to identify loci determining grain yield and stripe rust resistance via genome-wide association (GWA) analysis was explored. A high genetic diversity (diversity index = 0.260) and a moderate population structure based on highly inherited spike traits was revealed in the panel. The linkage disequilibrium decayed at 10 cM across the whole genome and was slower as compared to other landrace collections. In addition to previously reported QTL, GWA analysis also identified new candidate genomic regions for stripe rust resistance, grain yield, and spike productivity components. New candidate genomic regions reflect the potential of this landrace collection to further increase genetic diversity in elite germplasm.
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http://dx.doi.org/10.3389/fgene.2016.00201DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5114521PMC
November 2016

Identification of Genomic Associations for Adult Plant Resistance in the Background of Popular South Asian Wheat Cultivar, PBW343.

Front Plant Sci 2016 8;7:1674. Epub 2016 Nov 8.

Campo Experimental Valle de México, Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, Universidad Autónoma Chapingo Texcoco, Mexico.

Rusts, a fungal disease as old as its host plant wheat, has caused havoc for over 8000 years. As the rust pathogens can evolve into new virulent races which quickly defeat the resistance that primarily rely on race specificity, adult plant resistance (APR) has often been found to be race non-specific and hence is considered to be a more reliable and durable strategy to combat this malady. Over decades sets of donor lines have been identified at International Maize and Wheat Improvement Center (CIMMYT) representing a wide range of APR sources in wheat. In this study, using nine donors and a common parent "PBW343," a popular Green Revolution variety at CIMMYT, the nested association mapping (NAM) population of 1122 lines was constructed to understand the APR genetics underlying these founder lines. Thirty-four QTL were associated with APR to rusts, and 20 of 34 QTL had pleiotropic effects on SR, YR and LR resistance. Three chromosomal regions, associated with known APR genes (, and ), were also identified, and 13 previously reported QTL regions were validated. Of the 18 QTL first detected in this study, 7 were pleiotropic QTL, distributing on chromosomes 3A, 3B, 6B, 3D, and 6D. The present investigation revealed the genetic relationship of historical APR donor lines, the novel knowledge on APR, as well as the new analytical methodologies to facilitate the applications of NAM design in crop genetics. Results shown in this study will aid the parental selection for hybridization in wheat breeding, and envision the future rust management breeding for addressing potential threat to wheat production and food security.
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http://dx.doi.org/10.3389/fpls.2016.01674DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5099247PMC
November 2016

Unlocking the genetic diversity of Creole wheats.

Sci Rep 2016 03 15;6:23092. Epub 2016 Mar 15.

International Maize and Wheat Improvement Center (CIMMYT), Apdo. Postal 6-641, 06600, Mexico DF, Mexico.

Climate change and slow yield gains pose a major threat to global wheat production. Underutilized genetic resources including landraces and wild relatives are key elements for developing high-yielding and climate-resilient wheat varieties. Landraces introduced into Mexico from Europe, also known as Creole wheats, are adapted to a wide range of climatic regimes and represent a unique genetic resource. Eight thousand four hundred and sixteen wheat landraces representing all dimensions of Mexico were characterized through genotyping-by-sequencing technology. Results revealed sub-groups adapted to specific environments of Mexico. Broadly, accessions from north and south of Mexico showed considerable genetic differentiation. However, a large percentage of landrace accessions were genetically very close, although belonged to different regions most likely due to the recent (nearly five centuries before) introduction of wheat in Mexico. Some of the groups adapted to extreme environments and accumulated high number of rare alleles. Core reference sets were assembled simultaneously using multiple variables, capturing 89% of the rare alleles present in the complete set. Genetic information about Mexican wheat landraces and core reference set can be effectively utilized in next generation wheat varietal improvement.
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http://dx.doi.org/10.1038/srep23092DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4791556PMC
March 2016

Exploring and Mobilizing the Gene Bank Biodiversity for Wheat Improvement.

PLoS One 2015 15;10(7):e0132112. Epub 2015 Jul 15.

International Maize and Wheat Improvement Center (CIMMYT), Km. 45 Carretera México-Veracruz, Colonia El Batán, Texcoco, Edo. de México, CP, 56130, Mexico.

Identifying and mobilizing useful genetic variation from germplasm banks to breeding programs is an important strategy for sustaining crop genetic improvement. The molecular diversity of 1,423 spring bread wheat accessions representing major global production environments was investigated using high quality genotyping-by-sequencing (GBS) loci, and gene-based markers for various adaptive and quality traits. Mean diversity index (DI) estimates revealed synthetic hexaploids to be genetically more diverse (DI= 0.284) than elites (DI = 0.267) and landraces (DI = 0.245). GBS markers discovered thousands of new SNP variations in the landraces which were well known to be adapted to drought (1273 novel GBS SNPs) and heat (4473 novel GBS SNPs) stress environments. This may open new avenues for pre-breeding by enriching the elite germplasm with novel alleles for drought and heat tolerance. Furthermore, new allelic variation for vernalization and glutenin genes was also identified from 47 landraces originating from Iraq, Iran, India, Afghanistan, Pakistan, Uzbekistan and Turkmenistan. The information generated in the study has been utilized to select 200 diverse gene bank accessions to harness their potential in pre-breeding and for allele mining of candidate genes for drought and heat stress tolerance, thus channeling novel variation into breeding pipelines. This research is part of CIMMYT's ongoing 'Seeds of Discovery' project visioning towards the development of high yielding wheat varieties that address future challenges from climate change.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0132112PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4503568PMC
April 2016

Exploring potential of pearl millet germplasm association panel for association mapping of drought tolerance traits.

PLoS One 2015 13;10(5):e0122165. Epub 2015 May 13.

Institute of Biological, Environmental and Biological Sciences (IBERS), Aberystwyth University, Gogerddan, Aberystwyth, Ceredigion, United Kingdom.

A pearl millet inbred germplasm association panel (PMiGAP) comprising 250 inbred lines, representative of cultivated germplasm from Africa and Asia, elite improved open-pollinated cultivars, hybrid parental inbreds and inbred mapping population parents, was recently established. This study presents the first report of genetic diversity in PMiGAP and its exploitation for association mapping of drought tolerance traits. For diversity and genetic structure analysis, PMiGAP was genotyped with 37 SSR and CISP markers representing all seven linkage groups. For association analysis, it was phenotyped for yield and yield components and morpho-physiological traits under both well-watered and drought conditions, and genotyped with SNPs and InDels from seventeen genes underlying a major validated drought tolerance (DT) QTL. The average gene diversity in PMiGAP was 0.54. The STRUCTURE analysis revealed six subpopulations within PMiGAP. Significant associations were obtained for 22 SNPs and 3 InDels from 13 genes under different treatments. Seven SNPs associations from 5 genes were common under irrigated and one of the drought stress treatments. Most significantly, an important SNP in putative acetyl CoA carboxylase gene showed constitutive association with grain yield, grain harvest index and panicle yield under all treatments. An InDel in putative chlorophyll a/b binding protein gene was significantly associated with both stay-green and grain yield traits under drought stress. This can be used as a functional marker for selecting high yielding genotypes with 'stay green' phenotype under drought stress. The present study identified useful marker-trait associations of important agronomics traits under irrigated and drought stress conditions with genes underlying a major validated DT-QTL in pearl millet. Results suggest that PMiGAP is a useful panel for association mapping. Expression patterns of genes also shed light on some physiological mechanisms underlying pearl millet drought tolerance.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0122165PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4430295PMC
April 2016

A high density GBS map of bread wheat and its application for dissecting complex disease resistance traits.

BMC Genomics 2015 Mar 19;16:216. Epub 2015 Mar 19.

International Maize and Wheat Improvement Center (CIMMYT), Apdo. Postal 6-641, 06600, Mexico City, DF, Mexico.

Background: Genotyping-by-sequencing (GBS) is a high-throughput genotyping approach that is starting to be used in several crop species, including bread wheat. Anchoring GBS tags on chromosomes is an important step towards utilizing them for wheat genetic improvement. Here we use genetic linkage mapping to construct a consensus map containing 28644 GBS markers.

Results: Three RIL populations, PBW343 × Kingbird, PBW343 × Kenya Swara and PBW343 × Muu, which share a common parent, were used to minimize the impact of potential structural genomic variation on consensus-map quality. The consensus map comprised 3757 unique positions, and the average marker distance was 0.88 cM, obtained by calculating the average distance between two adjacent unique positions. Significant variation of segregation distortion was observed across the three populations. The consensus map was validated by comparing positions of known rust resistance genes, and comparing them to wheat reference genome sequences recently published by the International Wheat Genome Sequencing Consortium, Rye and Ae. tauschii genomes. Three well-characterized rust resistance genes (Sr58/Lr46/Yr29, Sr2/Yr30/Lr27, and Sr57/Lr34/Yr18) and 15 published QTLs for wheat rusts were validated with high resolution. Fifty-two per cent of GBS tags on the consensus map were successfully aligned through BLAST to the right chromosomes on the wheat reference genome sequence.

Conclusion: The consensus map should provide a useful basis for analyzing genome-wide variation of complex traits. The identified genes can then be explored as genetic markers to be used in genomic applications in wheat breeding.
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http://dx.doi.org/10.1186/s12864-015-1424-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4381402PMC
March 2015

Further evidence that a terminal drought tolerance QTL of pearl millet is associated with reduced salt uptake.

Environ Exp Bot 2014 Jun;102(100):48-57

Institute of Biological, Environmental and Rural Sciences (IBERS), Aberystwyth University, Gogerddan, Aberystwyth SY23 3EB, UK.

Earlier, we established that a major drought tolerance QTL on linkage group 2 of pearl millet is also associated with reduced salt uptake and enhanced growth under salt stress. Present study was undertaken to re-assess the performance of drought tolerant (PRLT 2/89-33) and drought sensitive (H 77/833-2) parents along with two QTL-NILs (ICMR 01029 and ICMR 01040), under salinity stress specifically imposed during post-flowering growth stages when plants had developed their ion sinks in full. Time course changes in ionic accumulation and their compartmentalization in different plant parts was studied, specifically to monitor and capture changes conferred by the two alleles at this QTL, at small intervals. Amongst different plant parts, higher accumulation of toxic ion Na was recorded in roots. Further, the Na concentration in roots of the testcross hybrid of the drought-sensitive parent (H 77/833-2) reached its maximum at ECiw 15 dS m within 24 h after salinity imposition, whereas it continued to increase with time in the testcross hybrids of the drought tolerant parent PRLT 2/89-33 as well as those of its QTL-NILs (ICMR 01029 and ICMR 01004) and reached at its maximum at 120 h stage. Comparison of differential distribution of toxic ions in individual leaves revealed that Na ions were not uniformly distributed in the leaves of the drought-tolerant parent and drought-tolerant QTL-NILs; but accumulated preferentially in the older leaves, whereas the hybrid of the drought-sensitive parent showed significantly higher Na concentration in all main stem leaves irrespective of their age. Dynamics of chlorophyll and proline concentration variation studied under salt stress at late flowering stages revealed a greater reduction, almost twice, in both leaf chlorophyll and proline concentrations in younger leaves in the hybrids of the sensitive parent as compared to the tolerant parent and QTL NILs. Imposition of salinity stress even at flowering stage affected the yield performance in pearl millet, wherein higher yield was recorded in drought tolerant parent and the two QTL-NILs compared to drought sensitive parent.
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http://dx.doi.org/10.1016/j.envexpbot.2014.01.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4003388PMC
June 2014

Integration of gene-based markers in a pearl millet genetic map for identification of candidate genes underlying drought tolerance quantitative trait loci.

BMC Plant Biol 2012 Jan 17;12. Epub 2012 Jan 17.

Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Gogerddan, Aberystwyth, Ceredigion, UK.

Background: Identification of genes underlying drought tolerance (DT) quantitative trait loci (QTLs) will facilitate understanding of molecular mechanisms of drought tolerance, and also will accelerate genetic improvement of pearl millet through marker-assisted selection. We report a map based on genes with assigned functional roles in plant adaptation to drought and other abiotic stresses and demonstrate its use in identifying candidate genes underlying a major DT-QTL.

Results: Seventy five single nucleotide polymorphism (SNP) and conserved intron spanning primer (CISP) markers were developed from available expressed sequence tags (ESTs) using four genotypes, H 77/833-2, PRLT 2/89-33, ICMR 01029 and ICMR 01004, representing parents of two mapping populations. A total of 228 SNPs were obtained from 30.5 kb sequenced region resulting in a SNP frequency of 1/134 bp. The positions of major pearl millet linkage group (LG) 2 DT-QTLs (reported from crosses H 77/833-2 × PRLT 2/89-33 and 841B × 863B) were added to the present consensus function map which identified 18 genes, coding for PSI reaction center subunit III, PHYC, actin, alanine glyoxylate aminotransferase, uridylate kinase, acyl-CoA oxidase, dipeptidyl peptidase IV, MADS-box, serine/threonine protein kinase, ubiquitin conjugating enzyme, zinc finger C- × 8-C × 5-C × 3-H type, Hd3, acetyl CoA carboxylase, chlorophyll a/b binding protein, photolyase, protein phosphatase1 regulatory subunit SDS22 and two hypothetical proteins, co-mapping in this DT-QTL interval. Many of these candidate genes were found to have significant association with QTLs of grain yield, flowering time and leaf rolling under drought stress conditions.

Conclusions: We have exploited available pearl millet EST sequences to generate a mapped resource of seventy five new gene-based markers for pearl millet and demonstrated its use in identifying candidate genes underlying a major DT-QTL in this species. The reported gene-based markers represent an important resource for identification of candidate genes for other mapped abiotic stress QTLs in pearl millet. They also provide a resource for initiating association studies using candidate genes and also for comparing the structure and function of distantly related plant genomes such as other Poaceae members.
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http://dx.doi.org/10.1186/1471-2229-12-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3287966PMC
January 2012

Using genetic mapping and genomics approaches in understanding and improving drought tolerance in pearl millet.

J Exp Bot 2011 Jan 5;62(2):397-408. Epub 2010 Sep 5.

Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Gogerddan, Aberystwyth, Ceredigion SY23 3EB, UK.

Drought at the reproductive stage is a major constraint to pearl millet [Pennisetum glaucum (L.) R. Br.] productivity. Quantitative trait locus (QTL) mapping provides a means to dissect complex traits, such as drought tolerance, into their components, each of which is controlled by QTLs. Molecular marker-supported genotypic information at the identified QTLs then enables quick and accurate accumulation of desirable alleles in plant breeding programmes. Recent genetic mapping research in pearl millet has mapped several QTLs for grain yield and its components under terminal drought stress conditions. Most importantly, a major QTL associated with grain yield and for the drought tolerance of grain yield in drought stress environments has been identified on linkage group 2 (LG 2) which accounts for up to 32% of the phenotypic variation of grain yield in mapping population testcrosses. The effect of this QTL has been validated in two independent marker-assisted backcrossing programmes, where 30% improvement in grain yield general combining ability (GCA) expected of this QTL under terminal drought stress conditions was recovered in the QTL introgression lines. To transfer effectively favourable alleles of this QTL into pearl millet varieties that otherwise are high yielding and adapted to specific agricultural zones, efforts are currently underway to develop closely spaced gene-based markers within this drought tolerance (DT)-QTL. In this review, an overview is provided of information on the genetic maps developed in pearl millet for mapping drought tolerance traits and their applications in identifying and characterizing DT-QTLs. Marker-assisted transfer of desirable QTL alleles to elite parent backgrounds, and results from introgression line validation in multiple terminal drought stress environments are discussed. Current efforts undertaken towards delimiting the interval of a major DT-QTL mapping to LG 2, and towards identifying candidate genes and physiologies underlying this QTL are presented. Highly specialized genetic stocks [QTL-near-isogenic lines (NILs), a high-resolution cross, and a germplasm population] and genomic resources (gene sequences, gene-based markers, and comparative genomics information) specifically developed for these purposes are discussed.
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http://dx.doi.org/10.1093/jxb/erq265DOI Listing
January 2011

Nuclear DNA assay in solving issues related to ancestry of the domesticated diploid safflower (Carthamus tinctorius L.) and the polyploid (Carthamus) taxa, and phylogenetic and genomic relationships in the genus Carthamus L. (Asteraceae).

Mol Phylogenet Evol 2009 Dec 12;53(3):631-44. Epub 2009 Jul 12.

Laboratory of Cellular and Molecular Cytogenetics, Department of Botany, University of Delhi, Delhi 110007, India.

The multipronged nuclear DNA assay by random amplified polymorphic DNA (RAPD) fingerprinting, ribosomal DNA repeat unit length polymorphism, internal transcribed sequence (ITS) RFLP, and comparative sequence analysis of ITS and external transcribed sequence (ETS) regions of the 29 accessions belonging to 18 Carthamus taxa including five unverified species was undertaken to obtain new information on (1) interrelationships among botanical varieties of cultivated safflower, C. tinctorius, and phylogenetic relationships (2) among the safflower and its close relatives and (3) that of Carthamus species and subspecies. The root tip cells of the 12 accessions contained 24 chromosomes followed by 64, 44 and 20 chromosomes in 9, 6 and 2 accessions, respectively. Barring C. lanatus, the accessions within each taxon had the same zygotic number. The present results strongly support the view that the wild C. palaestinus (2n=24) and the cultivated C. tinctorius (2n=24) are closely related. With few exceptions, all DNA based dendrograms support three lineages within the genus. One lineage is constituted by C. arborescens (2n=24) alone. The present data indicates that because of unique composition of its nuclear genome vis-à-vis other Carthamus taxa, C. arborescens should be placed in a separate subgenus. The two remaining lineages, constituted by the taxa with 2n=24, and the taxa with 2n=20, 2n=44 and 2n=64, respectively should be given the rank of two taxonomic sections in the other subgenus. The present study also demonstrates that none of the present taxa with 2n=24 have contributed to the origin of polyploid taxa. Carthamus boisserii (2n=20) and C. glaucus ssp. anatolicus (2n=20) are more likely to be one of the diploid progenitor of C. lanatus ssp. creticus (2n=64), C. lanatus (2n=44), C. lanatus ssp. lanatus (2n=44) and C. lanatus ssp. montanus (2n=44), and C. lanatus ssp. turkestanicus (2n=64), respectively. Within Lanatus species complex, constituted by C. lanatus, C. lanatus ssp. lanatus, C. lanatus ssp. montanus, C. lanatus ssp. turkestanicus and C. lanatus ssp. creticus, high proportion of autapomorphic characters and low number of synapomorphies in the ITS and ETS sequences suggest a relatively recent diversification of the taxa within the species complex. Carthamus lanatus ssp. creticus (2n=64) and C. lanatus ssp. turkestanicus (2n=64) within the complex deserve species rank. This analysis provided evolutionary relatedness of the five unverified taxa with the known Carthamus taxa.
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http://dx.doi.org/10.1016/j.ympev.2009.07.012DOI Listing
December 2009

Phylogenetic analysis of Carthamus species based on the nucleotide sequence of the nuclear SACPD gene and chloroplast trnL-trnF IGS region.

Genome 2008 Sep;51(9):721-7

Division of Evolutionary Genetics, Kihara Institute for Biological Research, Yokohama City University, Yokohama 244-0813, Japan.

To clarify the phylogenetic relationships of Carthamus species, we performed sequence analysis of the nuclear stearoyl acyl carrier protein desaturase (SACPD) gene and the chloroplast intergenic spacer region between leucine and phenylalanine tRNA genes (trnL-trnF IGS) in 13 taxa of Carthamus. The previous division of the genus into 4 taxonomic sections and allocation of particular genomes to various taxa on the basis of morphological, cytogenetic, and biosystematic analyses is not supported by the present study. Our results provide evidence of the occurrence of 5 nuclear genomes (A, B, C, X, and Y) and 3 cytoplasm types (A, B, and C) in the genus Carthamus. The cultivated safflower, C. tinctorius (2n = 24), has the B genome and type B cytoplasm. Both of these are not present in the polyploid taxa. This contradicts the earlier view that one of the genomes involved in the origin of the polyploid taxa of Carthamus is the B genome. Comparison with an outgroup species (Cirsium japonicum) indicated that C. arborescens is the most primitive species in the genus. Carthamus palaestinus is genetically closest to the cultivated safflower.
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http://dx.doi.org/10.1139/G08-059DOI Listing
September 2008

Chloroplast DNA diversity reveals the contribution of two wild species to the origin and evolution of diploid safflower (Carthamus tinctorius L.).

Genome 2008 Aug;51(8):638-43

Laboratory of Cellular and Molecular Cytogenetics, Department of Botany, University of Delhi, Delhi, India.

The identity of the wild progenitor of one of the most important oil crop species, Carthamus tinctorius (2n = 2x = 24), commonly known as safflower, has been the subject of numerous studies at morphological, biochemical, cytogenetic, and biosystematic levels, but no definitive conclusions have been made. The nuclear, mitochondrial, and chloroplast genomes of the two botanical varieties of C. tinctorius, C. tinctorius var. tinctorius and C. tinctorius var. inermis, and two wild species, C. palaestinus and C. oxyacantha, were assayed at the nucleotide sequence level and by DNA markers. The nuclear and mitochondrial DNA assays were not helpful in conclusively identifying the diploid ancestor of C. tinctorius. The chloroplast DNA diversity, on the other hand, unambiguously provided new and novel evidence that C. palaestinus and C. oxyacantha contributed their plastomes to the evolution of C. tinctorius var. inermis and C. tinctorius var. tinctorius, respectively. This study, therefore, affirms a startling revelation of a rare event of two wild species contributing to the origin and evolution of safflower, a major world oilseed crop about whose genetics very little is known.
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http://dx.doi.org/10.1139/G08-049DOI Listing
August 2008

Assaying polymorphism at DNA level for genetic diversity diagnostics of the safflower (Carthamus tinctorius L.) world germplasm resources.

Genetica 2009 Apr 23;135(3):457-70. Epub 2008 Jul 23.

Kihara Institute for Biological Research, Yokohama City University, Maioka-cho 641-12, Totsuka-ku, Yokohama, 244, Japan.

Carthamus tinctorius (2n = 2x = 24), commonly known as safflower, is widely cultivated in agricultural production systems of Asia, Europe, Australia, and the Americas as a source of high quality vegetable and industrial oil. Twenty-two RAPD primers, 18 SSR primers, and 10 AFLP primer combinations were used to assess: (1) the genetic diversity of 85 accessions (originating from 24 countries) representing global germplasm variability of safflower and (2) the interrelationships among safflower 'centers of similarity' or 'regional gene pools' proposed earlier. The RAPD and SSR primers and AFLP primer combinations revealed 57.6, 68.0, and 71.2% polymorphism, respectively, among 111, 72, and 330 genetic loci amplified from the accessions. The sum of effective number of alleles (66.44), resolving power (59.16), and marker index (51.3) explicitly revealed the relative superiority of AFLP as a marker system in uncovering variation in safflower. Overall, AFLP markers could recognize 'centers of similarity' or 'regional gene pools'. Analysis of molecular variance and Shannon's information index provided corroborating evidences for the present and previous studies that concluded fragmentation of safflower gene pool into many gene pools. Divergent directional selection is likely to have played an important role in shaping the diversity. From the practical applications standpoint, the diversity of Iran-Afghanistan gene pool is very high, equivalent to the total diversity of the species. The Far East gene pool is the least diverse. The present comprehensive input, first of its own kind in safflower, will assist marker based improvement programmes in the crop.
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http://dx.doi.org/10.1007/s10709-008-9292-4DOI Listing
April 2009