Short Arm Of Chromosome 5D Research Articles

Dissection of two quantitative trait loci with pleiotropic effects on plant height and spike length linked in coupling phase on the short arm of chromosome 2D of common wheat (Triticum aestivum L.).

Two QTL with pleiotropic effects on plant height and spike length linked in coupling phase on chromosome 2DS were dissected, and diagnostic marker for each QTL was developed. Plant height (PHT) is a crucial trait related to plant architecture and yield potential, and dissection of its underlying genetic basis would help to improve the efficiency of designed breeding in wheat. Here, two quantitative trait loci (QTL) linked in coupling phase on the short arm of chromosome 2D with pleiotropic effects on PHT and spike length, QPht/Sl.cau-2D.1 and QPht/Sl.cau-2D.2, were separated and characterized. QPht/Sl.cau-2D.1 is a novel QTL located between SNP makers BS00022234_51 and BobWhite_rep_c63957_1472. QPht/Sl.cau-2D.2 is mapped between two SSR markers, SSR-2062 and Xgwm484, which are located on the same genomic interval as Rht8. Moreover, the diagnostic marker tightly linked with each QTL was developed for the haplotype analysis using diverse panels of wheat accessions. The frequency of the height-reduced allele of QPht/Sl.cau-2D.1 is much lower than that of QPht/Sl.cau-2D.2, suggesting that this novel QTL may be an attractive target for genetic improvement. Consistent with a previous study of Rht8, a significant difference in cell length was observed between the NILs of QPht/Sl.cau-2D.2. By contrast, there was no difference in cell length between NILs of QPht/Sl.cau-2D.1, indicating that the underlying molecular mechanism for these two QTL may be different. Collectively, these data provide a new example of QTL dissection, and the developed diagnostic markers will be useful in marker-assisted pyramiding of QPht/Sl.cau-2D.1 and/or QPht/Sl.cau-2D.2 with the other genes in wheat breeding.

Genetic mapping of Stb19, a new resistance gene to Zymoseptoria tritici in wheat.

A new and dominant R gene Stb19 is identified from a soft wheat cultivar 'Lorikeet' and was mapped on the distal region of chromosome 1DS. Two tightly linked KASP markers were also discovered and validated for molecular-assisted breeding programs. A new R gene, designated as Stb19, provides resistance to Zymoseptoria tritici in wheat. This new dominant gene resides on the short arm of chromosome 1D, exhibiting complete resistance to three Z. tritici isolates, WAI332, WAI251, and WAI161, at the seedling stage. A genetic linkage map, based on an F2:3 population of 'Lorikeet' and 'Summit,' found the Stb19 gene at a 9.3cM region on 1DS, closely linked with two Kompetitive Allele-Specific PCR markers, snp_4909967 and snp_1218021. Further, the two markers were tested and validated in another F2:3 population and 266 different wheat accessions, which gave over 95% accuracy of resistance/susceptibility prediction. Combined with the physical location of the identified SNPs and the previous evidence of gene order on chromosome 1DS (centromere-Sr45-Sr33-Lr21-telomere), Stb19 is proposed to be located between Sr33 and Lr21. Thus, the newly discovered Stb19 along with the KASP markers represents an increase in genetic resources available for wheat breeding resistance to Z. tritici.

Genetic mapping of a novel recessive allele for non-glaucousness in wild diploid wheat Aegilops tauschii: implications for the evolution of common wheat.

Cuticular wax on the aerial surface of plants has a protective function against many environmental stresses. The bluish-whitish appearance of wheat leaves and stems is called glaucousness. Most modern cultivars of polyploid wheat species exhibit the glaucous phenotype, while in a wild wheat progenitor, Ae. tauschii, both glaucous and non-glaucous accessions exist. Iw2, a wax inhibitor locus on the short arm of chromosome 2D, is the main contributor to this phenotypic variation in Ae. tauschii, and the glaucous/non-glaucous phenotype of Ae. tauschii is usually inherited by synthetic hexaploid wheat. However, a few synthetic lines show the glaucous phenotype although the parental Ae. tauschii accessions are non-glaucous. Molecular marker genotypes indicate that the exceptional non-glaucous Ae. tauschii accessions share the same genotype in the Iw2 chromosomal region as glaucous accessions, suggesting that these accessions have a different causal locus for their phenotype. This locus was assigned to the long arm of chromosome 3D using an F2 mapping population and designated W4, a novel glaucous locus in Ae. tauschii. The dominant W4 allele confers glaucousness, consistent with phenotypic observation of Ae. tauschii accessions and the derived synthetic lines. These results implied that glaucous accessions of Ae. tauschii with the W2W2iw2iw2W4W4 genotype could have been the D-genome donor of common wheat.

Structural consequences of the interaction of puroindolines with gluten proteins

The effect of puroindolines (PINs) on structural characteristics of wheat proteins was investigated in Triticum turgidum ssp. durum (cv. Svevo) and Triticum aestivum (cv. Alpowa) and in their respective derivatives in which PIN genes were expressed (Soft Svevo) or the distal end of the short arm of chromosome 5D was deleted and PINs were not expressed (Hard Alpowa). The presence of PINs decreased the amount of cold-SDS extractable proteins and the accessibility of protein thiols to specific reagents, but resulted in facilitated solvation of gluten proteins, as detected by tryptophan fluorescence measurements carried out on minimally mixed flour/water mixtures. We propose that PINs and gluten proteins are interacting in the grain or flour prior to mixing. Hydrophobic interactions between PINs and some of the gluten proteins modify the pattern of interactions among gluten proteins, thus providing an additional mechanistic rationale for the effects of PINs on kernel hardness.

Genetic mapping reveals a dominant awn-inhibiting gene related to differentiation of the variety anathera in the wild diploid wheat Aegilops tauschii.

Aegilops tauschii, a wild wheat relative, is the D-genome donor of common wheat. Subspecies and varieties of Ae. tauschii are traditionally classified based on differences in their inflorescence architecture. However, the genetic information for their diversification has been quite limited in the wild wheat relatives. The variety anathera has no awn on the lemma, but the genetic basis for this diagnostic character is unknown. Wide variations in awn length traits at the top and middle spikes were found in the Ae. tauschii core collection, and the awn length at the middle spike was significantly smaller in the eastward-dispersed sublineage than in those in other sublineages. To clarify loci controlling the awnless phenotype of var. anathera, we measured awn length of an intervariety F2 mapping population, and found that the F2 individuals could be divided into two groups mainly based on the awn length at the middle of spike, namely short and long awn groups, significantly fitting a 3:1 segregation ratio, which indicated that a single locus controls the awnless phenotype. The awnless locus, Anathera (Antr), was assigned to the distal region of the short arm of chromosome 5D. Quantitative trait locus analysis using the awn length data of each F2 individual showed that only one major locus was at the same chromosomal position as Antr. These results suggest that a single dominant allele determines the awnless diagnostic character in the variety anathera. The Antr dominant allele is a novel gene inhibiting awn elongation in wheat and its relatives.

Aegilops tauschii Accessions with Geographically Diverse Origin Show Differences in Chromosome Organization and Polymorphism of Molecular Markers Linked to Leaf Rust and Powdery Mildew Resistance Genes.

Aegilops tauschii (2n = 2x = 14) is a diploid wild species which is reported as a donor of the D-genome of cultivated bread wheat. The main goal of this study was to examine the differences and similarities in chromosomes organization among accessions of Ae. tauschii with geographically diversed origin, which is believed as a potential source of genes, especially determining resistance to fungal diseases (i.e., leaf rust and powdery mildew) for breeding of cereals. We established and compared the fluorescence in situ hybridization patterns of 21 accessions of Ae. tauschii using various repetitive sequences mainly from the BAC library of wheat cultivar Chinese Spring. Results obtained for Ae. tauschii chromosomes revealed many similarities between analyzed accessions, however, some hybridization patterns were specific for accessions, which become from cognate regions of the World. The most noticeable differences were observed for accessions from China which were characterized by presence of distinct signals of pTa-535 in the interstitial region of chromosome 3D, less intensity of pTa-86 signals in chromosome 2D, as well as lack of additional signals of pTa-86 in chromosomes 1D, 5D, or 6D. Ae. tauschii of Chinese origin appeared homogeneous and separate from landraces that originated in western Asia. Ae. tauschii chromosomes showed similar hybridization patterns to wheat D-genome chromosomes, but some differences were also observed among both species. What is more, we identified reciprocal translocation between short arm of chromosome 1D and long arm of chromosome 7D in accession with Iranian origin. High polymorphism between analyzed accessions and extensive allelic variation were revealed using molecular markers associated with resistance genes. Majority of the markers localized in chromosomes 1D and 2D showed the diversity of banding patterns between accessions. Obtained results imply, that there is a moderate or high level of polymorphism in the genome of Ae. tauschii determined by a geographical origin, which we proved by cytogenetic and molecular markers analysis. Therefore, selected accessions might constitute an accessible source of variation for improvement of Triticeae species like wheat and triticale.

Chromosome regions associated with the activity of lipoxygenase in the genome D of Triticum aestivum L. under water deficit

Quantitative trait loci (QTLs) associated with the phenotypic expression of the activity of different forms of lipoxygenase (LOX) under water deficit were detected in the chromosomes of the D-genome using intogression lines of common wheat Triticum aestivum L. Chinese Spring (Synthetic 6x). QTL associated with the activity of seed soluble LOX was identified on the short arm of chromosome 4D. The activity of membranebound form of enzyme in the seedlings was mapped to the short arm, while that of a soluble form was on the long arm of chromosome 5D. Two regions responsible for the activity of soluble LOX in the leaves were found on the short arm of chromosome 2D. Three QTLs associated with the activities of chloroplast LOXs were found on the same chromosome: the activity of the soluble form was linked to Xgwm261 and Xgwm539 markers, and the membrane form to Xgdm93 marker. QTLs for the activities of both soluble and membrane-bound LOX in the leaves were identified in the centromeric region of chromosome 7D. The activities of two membrane enzymes in the leaves were linked to Xgdm130 marker on the short arm of this chromosome. Loci associated with the activity of different LOX forms colocalized with QTLs for the shoot mass, gas exchange parameters, chlorophyll fluorescence, content of photosynthetic pigments, and grain productivity of wheat. A correlation between these parameters and the LOX activity was detected and it was shown that various forms of the enzyme were differentially involved in the adaptation of wheat plants to water deficit. The current paper discusses their presumed physiological role.

Characterization of a common wheat (Triticum aestivum L.) high-tillering dwarf mutant.

A novel high-tillering dwarf mutant in common wheat Wangshuibai was characterized and mapped to facilitate breeding for plant height and tiller and the future cloning of the causal gene. Tiller number and plant height are two major agronomic traits in cereal crops affecting plant architecture and grain yield. NAUH167, a mutant of common wheat landrace Wangshuibai induced by ethylmethyl sulfide (EMS) treatment, exhibits higher tiller number and reduced plant height. Microscope observation showed that the dwarf phenotype was attributed to the decrease in the number of cells and their length. The same as the wild type, the mutant was sensitive to exogenous gibberellins. Genetic analysis showed that the high-tillering number and dwarf phenotype were related and controlled by a partial recessive gene. Using a RIL2:6 population derived from the cross NAUH167/Sumai3, a molecular marker-based genetic map was constructed. The map consisted of 283 loci, spanning a total length of 1007.98cM with an average markers interval of 3.56cM. By composite interval mapping, a stable major QTL designated QHt.nau-2D controlling both traits, was mapped to the short arm of chromosome 2D flanked by markers Xcfd11 and Xgpw361. To further map the QHt.nau-2D loci, another population consisted of 180 F2 progeny from a cross 2011I-78/NAUH167 was constructed. Finally, QHt.nau-2D was located within a genetic region of 0.8cM between markers QHT239 and QHT187 covering a predicted physical distance of 6.77Mb. This research laid the foundation for map-based cloning of QHt.nau-2D and would facilitate the characterization of plant height and tiller number in wheat.

Characterization of morphology and resistance to Blumeria graminis of winter triticale monosomic addition lines with chromosome 2D of Aegilops tauschii.

Key messageAllocation of the chromosome 2D ofAe. tauschiiin triticale background resulted in changes of its organization, what is related to varied expression of genes determining agronomically important traits.Monosomic alien addition lines (MAALs) are crucial for transfer of genes from wild relatives into cultivated varieties. This kind of genetic stocks is used for physical mapping of specific chromosomes and analyzing alien genes expression. The main aim of our study is to improve hexaploid triticale by transferring D-genome chromatin from Aegilops tauschii × Secale cereale (2n = 4x = 28, DDRR). In this paper, we demonstrate the molecular cytogenetics analysis and SSR markers screening combined with phenotype analysis and evaluation of powdery mildew infection of triticale monosomic addition lines carrying chromosome 2D of Ae. tauschii. We confirmed the inheritance of chromosome 2D from the BC2F4 to the BC2F6 generation of triticale hybrids. Moreover, we unveiled a high variable region on the short arm of chromosome 2D, where chromosome rearrangements were mapped. These events had direct influence on plant height of hybrids what might be connected with changes at Rht8 loci. We obtained 20 semi-dwarf plants of BC2F6 generation carrying 2D chromosome with the powdery mildew resistance, without changes in spike morphology, which can be used in the triticale breeding programs.

Inheritance and Molecular Mapping of an All-Stage Stripe Rust Resistance Gene Derived from the Chinese Common Wheat Landrace "Yilongtuomai".

Yellow or stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a devastating foliar disease that affects common wheat (Triticum aestivum L.) around the world. In China, common wheat landraces are potential sources of disease and abiotic stress resistance genes for wheat improvement. Yilongtuomai (YL), a wheat landrace from Yilong County, Sichuan Province, shows high levels of resistance against most Chinese Pst races. In this study, the resistance of YL to stripe rust disease was examined in detail. Parent strains, YL and Taichung 29, a variety susceptible to Pst race CYR32, and their F1, F2, and F2:3 offspring, were inoculated with CYR32 during the seedling stage in the field or adult-plant stage in the greenhouse. Results indicated that resistance to CYR32 in YL is conferred by a single dominant gene, designated YrYL The segregating F2 population (352 plants), was analyzed in terms of its resistance locus using simple sequence repeats (SSRs), resistance gene analog polymorphisms (RGAPs), and sequence-related amplified polymorphism (SRAP). A linkage group of 6 SSRs, 2 RGAPs, and 1 SRAP was constructed for the YrYL gene. Using the identified SSRs associated with physical mapping of RGAP using Chinese Spring nullisomic-tetrasomic stocks, the YrYL gene was localized to the short arm of chromosome 7D. The gene was flanked by 1 SSR marker, Xbarc92, and 1 RGAP marker, CLRRfor/Ptokin4, at genetic distances of 5.35 and 9.86 cM, respectively. The YrYL gene was compared to other stripe rust resistance genes reported on chromosome 7D by evaluating its reaction patterns to CYR32 and its pedigree relationship. Our results suggest that the YrYL gene is a new stripe rust resistance gene.

BioNano genome mapping of individual chromosomes supports physical mapping and sequence assembly in complex plant genomes.

SummaryThe assembly of a reference genome sequence of bread wheat is challenging due to its specific features such as the genome size of 17 Gbp, polyploid nature and prevalence of repetitive sequences. BAC‐by‐BAC sequencing based on chromosomal physical maps, adopted by the International Wheat Genome Sequencing Consortium as the key strategy, reduces problems caused by the genome complexity and polyploidy, but the repeat content still hampers the sequence assembly. Availability of a high‐resolution genomic map to guide sequence scaffolding and validate physical map and sequence assemblies would be highly beneficial to obtaining an accurate and complete genome sequence. Here, we chose the short arm of chromosome 7D (7DS) as a model to demonstrate for the first time that it is possible to couple chromosome flow sorting with genome mapping in nanochannel arrays and create a de novo genome map of a wheat chromosome. We constructed a high‐resolution chromosome map composed of 371 contigs with an N50 of 1.3 Mb. Long DNA molecules achieved by our approach facilitated chromosome‐scale analysis of repetitive sequences and revealed a ~800‐kb array of tandem repeats intractable to current DNA sequencing technologies. Anchoring 7DS sequence assemblies obtained by clone‐by‐clone sequencing to the 7DS genome map provided a valuable tool to improve the BAC‐contig physical map and validate sequence assembly on a chromosome‐arm scale. Our results indicate that creating genome maps for the whole wheat genome in a chromosome‐by‐chromosome manner is feasible and that they will be an affordable tool to support the production of improved pseudomolecules.

Genetic mapping and inheritance of Russian wheat aphid resistance gene in accession IG 100695

AbstractThe Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), is an important pest of small‐grain cereals, particularly wheat, worldwide. The most efficient strategy against the RWA is to identify sources of resistance and to introduce them into susceptible wheat genotypes. This study was conducted to determine the mode of inheritance of the RWA resistance found in ICARDA accession IG 100695, to identify wheat microsatellite markers closely linked to the gene and to map the chromosomal location of the gene. Simple sequence repeat (SSR) marker scores were identified in a mapping population of 190 F2 individuals and compared, while phenotypic screening for resistance was performed in F2 : 3 families derived from a cross between ‘Basribey’ (susceptible) and IG 100695 (resistant). Phenotypic segregation of leaf chlorosis and rolling displayed the effect of a single dominant gene, temporarily denoted Dn100695, in IG 100695. Dn100695 was mapped on the short arm of chromosome 7D with four linked SSR markers, Xgwm44, Xcfd14, Xcfd46 and Xbarc126. Dn100695 and linked SSR markers may be useful for improving resistance for RWA in wheat breeding.

Allelic Distribution of Puroindoline Genes Affecting the Grain Hardness in Some Iranian Bread Wheat Cultivars

Grain hardness is an important characteristics influencing end-use quality of bread wheat. Wheat with the hard grain texture has higher protein content and more intensive gluten that leads to production of higher bread quality. However, soft texture wheat has lower protein content and weaker gluten, which are suitable for cake and candy production. Grain hardness is determined by the Pina and Pinb genes that are located on the short arm of chromosome 5D. In this study, 83 bread wheat cultivars were characterized for the allelic distribution of Pina and Pinb genes using allele specific markers. At the Pina locus, Pina-D1a and Pina-D1b alleles were observed in 64% and 36% of varieties, respectively. However, at the Pinb locus, 90% of varieties showed Pinb-D1a and 10% had Pinb-D1b allele . Based on the grain hardness index which was measured with the NIR, varieties whit the value less than 50 were considered as soft while above 50 were considered as hard grain texture. The results of marker-trait association showed that Pina had the significant effect (P= 0.019) on the grain hardness, as cultivars with the Pina-D1a allele were significantly softer (49.85±0.37) that those with the Pina-D1b allele (51.38±0.50). The results of regression analysis showed that for the traits including bread volume, grain hardness and water absorption as dependent variables, Pina was entered to the model. The results of this study can help wheat breeders to effectively select parents for the grain hardness in the MAS breeding programs.

Genome-Wide Mapping of Spike-Related and Agronomic Traits in a Common Wheat Population Derived from a Supernumerary Spikelet Parent and an Elite Parent.

In wheat, exotic genotypes harbor a broad range of spike-related traits, and can be used as a source of new genes for germplasm enhancement in wheat breeding programs. In the present study, a population of 163 recombinant inbred lines was derived from a cross between an elite line (WCB414) and an exotic line (WCB617) with branched spike (supernumerary spikelet; SS) head morphology. The population was evaluated over four to six environments to identify quantitative trait loci (QTL) associated with nine spike-related traits and 10 agronomic traits. A genetic map consisting of 939 diversity arrays technology (DArT) markers was constructed. Composite interval mapping identified a total of 143 QTL located on 17 different wheat chromosomes and included 33 consistent and definitive QTL. The amount of phenotype variation explained (PVE) by individual QTL ranged from 0.61 to 91.8%. One major QTL for glume pubescence was located in a QTL-rich region on the short arm of chromosome 1A, where loci for other traits such as for kernels per spike (KS) and spike length (SL) were also identified. Similarly, a cluster of QTL associated with yield-related, agronomic and spike-related traits contributing up to 40.3% of PVE was found on the short arm of chromosome 2D, in the vicinity of a major QTL for SS-related traits. Consistent and major QTL identified in the present study may be useful in marker-assisted breeding programs to facilitate transfer of desirable alleles into other germplasm. Desirable QTL alleles were also contributed by the exotic line, suggesting the possibility of enriching the breeding germplasm with alleles from SS genotypes.

Detection and location of Lr11 and other leaf rust resistance genes in the durably resistant wheat cultivar Buck Poncho

Three race-specific genes were identified in a cross between the durably leaf rust resistant wheat cultivar Buck Poncho (BP) and leaf rust susceptible cultivar Purple Straw (P). Two seedling resistance genes, temporarily named LrBP1 and LrBP2, and one adult plant resistance gene named LrBP3 were identified. Multi-pathotype tests on seedlings of BP and Thatcher near-isogenic lines carrying single resistance genes indicated that Lr10 and Lr11 were candidates for LrBP1 and LrBP2, respectively. The identification of LrBP1 as Lr10 was corroborated by markers previously reported to be linked to Lr10. LrBP2 was linked to 12 markers located on the short arm of chromosome 2D, the closest of which was SCAR32/35 at 0.3 cM. Lr11 was previously located in chromosome 2A, but monosomic analysis and telocentric mapping indicated that Lr11 was distally located in chromosome 2DS. The presence of the expected PCR fragment of SCAR32/35 in BP and wheat lines carrying Lr11, and results from an allelism test between a stock carrying LrBP2 with one carrying Lr11, indicated that these two genes are most likely the same. Thirteen markers located in chromosome 6A were loosely linked to LrBP3. Lines carrying the three resistance genes were evaluated for leaf rust response in the field. None of the gene combinations showed infection severities as low as BP, indicating that the three genes only partially explained the observed level of resistance in BP.

Genetic control of lutein esterification in wheat (Triticum aestivum L.) grain

Lutein is a naturally occurring plant carotenoid compound that is also an important micro-nutrient for humans. While the biosynthesis of lutein in bread wheat (Triticum aestivum L.) is well understood, in contrast, there is little information on the mechanism or the genetic control involved in conversion of lutein to lutein esters during storage of wheat grain. The purpose of this research was to investigate the genetic control of lutein ester formation in wheat.Lutein esterification varied between accessions of bread wheat, some related species and even grain tissues. A single locus controlling lutein esterification (designated Lute) was mapped on the short arm of chromosome 7D using a mapping population derived from zero-ester and high-ester parents. A GDSL-like lipase gene was identified in a syntenic region of the rice genome and wheat sequences with similarity to that gene were genetically mapped at the same position as Lute.Since lutein esters seem to be more stable than free lutein, improved understanding of the genetics and biochemistry of lutein esterification could be useful for optimising the retention of lutein during the storage, handling and processing of wheat and other products that contain this important micronutrient.

Fine mapping of <i>Hch1</i>, the causal D-genome gene for hybrid chlorosis in interspecific crosses between tetraploid wheat and <i>Aegilops tauschii</i>

Hybrid chlorosis, one of the reproductive barriers between tetraploid wheat and its D-genome progenitor, Aegilops tauschii, inhibits normal growth of synthetic wheat hexaploids. Hybrid chlorosis appears to be due to an epistatic interaction of two loci from the AB and D wheat genomes. Our previous study assigned the causal D-genome gene for hybrid chlorosis, Hch1, to the short arm of chromosome 7D. Here, we constructed a fine map of 7DS near Hch1 using 280 F2 individuals from a cross of two wheat synthetic lines, one showing normal growth and the other showing hybrid chlorosis. The hybrid chlorosis phenotype was controlled by a single dominant allele of the Hch1 locus in the synthetic hexaploids. Hch1 was closely linked to four new markers within 0.2 cM, and may be localized near or within the two Ae. tauschii scaffolds containing the linked markers on 7DS. Comparative analysis of the Hch1 chromosomal region for Ae. tauschii, barley and Brachypodium showed that a local inversion occurred in the region proximal to Hch1 during the divergence between barley and Ae. tauschii, and that the Hch1 region on wheat 7DS is syntenic to Brachypodium chromosome 1. These observations provide useful information for further studies toward map-based cloning of Hch1.

Genetic mapping of resistance to Diuraphis noxia (Kurdjumov) biotype 2 in wheat (Triticum aestivum L.) accession CI2401

AbstractThe RWA, Diuraphis noxia (Kurdjumov), is a devastating insect pest of wheat (Triticumaestivum L.) and barley (Hordeumvulgare) in the United States and in many parts of the world. The use of D. noxia-resistant cultivars is an economically useful approach for protecting cereals from this aphid. However, there are few genes conferring resistance to the most predominant US biotype (Biotype RWA2). Wheat line CI2401, originating from Tajikistan, has been identified to be resistant to RWA2. An F2-derived F3 (F2:3) segregating population developed from a cross between CI2401 and Glupro (a high quality susceptible wheat cultivar) was used to genetically map the resistance in CI2401. Seedlings from F2 individuals and F3 families were infested with RWA2 aphids. Seedling reactions were scored as resistant or susceptible based on the degrees of leaf rolling and chlorosis. The observed segregation ratios in the F2 and F3 generations indicate the presence of a major dominant gene controlling resistance to RWA2. The gene, named Dn2401, was genetically mapped to the short arm of chromosome 7D. Xbarc214 mapped 1.1 cM and Xgwm473 mapped 1.8 cM distal and proximal, respectively, to the gene. Association studies using more than 12,000 SNPs and SilicoDArTs confirmed the presence of a major signal associated with resistance on chromosome 7DS. In addition, a minor signal was detected in chromosome 1D. The markers developed in this study will be useful for marker-assisted-breeding for resistance to RWA2.

The cuticular wax inhibitor locus Iw2 in wild diploid wheat Aegilops tauschii: phenotypic survey, genetic analysis, and implications for the evolution of common wheat.

BackgroundCuticular wax production on plant surfaces confers a glaucous appearance and plays important roles in plant stress tolerance. Most common wheat cultivars, which are hexaploid, and most tetraploid wheat cultivars are glaucous; in contrast, a wild wheat progenitor, Aegilops tauschii, can be glaucous or non-glaucous. A dominant non-glaucous allele, Iw2, resides on the short arm of chromosome 2D, which was inherited from Ae. tauschii through polyploidization. Iw2 is one of the major causal genes related to variation in glaucousness among hexaploid wheat. Detailed genetic and phylogeographic knowledge of the Iw2 locus in Ae. tauschii may provide important information and lead to a better understanding of the evolution of common wheat.ResultsGlaucous Ae. tauschii accessions were collected from a broad area ranging from Armenia to the southwestern coastal part of the Caspian Sea. Linkage analyses with five mapping populations showed that the glaucous versus non-glaucous difference was mainly controlled by the Iw2 locus in Ae. tauschii. Comparative genomic analysis of barley and Ae. tauschii was then used to develop molecular markers tightly linked with Ae. tauschii Iw2. Chromosomal synteny around the orthologous Iw2 regions indicated that some chromosomal rearrangement had occurred during the genetic divergence leading to Ae. tauschii, barley, and Brachypodium. Genetic associations between specific Iw2-linked markers and respective glaucous phenotypes in Ae. tauschii indicated that at least two non-glaucous accessions might carry other glaucousness-determining loci outside of the Iw2 locus.ConclusionAllelic differences at the Iw2 locus were the main contributors to the phenotypic difference between the glaucous and non-glaucous accessions of Ae. tauschii. Our results supported the previous assumption that the D-genome donor of common wheat could have been any Ae. tauschii variant that carried the recessive iw2 allele.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0246-y) contains supplementary material, which is available to authorized users.

Genetic analysis of artificial Triticinae amphidiploid Aurotica based on the glaucousness trait

Changes in plant genomes of hybrid origin which become apparent on different levels of phenotypic manifestation of genetic and epigenetic changes are an important object of cytogenetics and molecular genetics. The changes in expression of the glaucousness trait in the artificial Triticinae amphidiploid Aurotica (AABBTT) were investigated; haplotypes of plants with the appearance of glaucous and non-glaucous genes were determined by hybridization experiments. It was supported that the changes in expression can be explained by (epi)mutations abolishing the efficiency of dominant alleles of orthologous series of glaucous inhibitor gene Iw. Analysis of F2 population with SSR markers specific to 2B and 2D wheat chromosomes and 2T chromosome of Aegilops mutica manifested associated inheritance of the Wms 102 and Wms 702 loci, which mapped to the short arm of chromosome 2D. The Wms702 marker was linked to the Iw2(T) gene and can now be used to detect that gene.