Arm Of Chromosome 5B Research Articles

The utility of NBS-profiling for characterization of yellow rust resistance in an F6 durum wheat population

Seedling and adult plant (field) resistance to yellow rust in the durum wheat (Triticum turgidum ssp. durum) cross Kunduru-1149 x Cham-1 was characterized using a functionally-targeted DNA marker system, NBS-profiling. Chi-squared analysis indicated a four gene model conferring seedling yellow rust resistance against Puccinia striiformis f. sp. tritici isolate WYR85/22 (virulent on Yr2, Yr6, Yr7 and Yr9). Interval mapping located two QTL for yellow rust resistance on the long arm of chromosome 1B, while Kruskal-Wallis single marker regression identified a number of additional marker loci associated with seedling and/or adult plant, field resistance to yellow rust. These results suggested that much of the yellow rust resistance seen in the field may be due to seedling expressed resistance (R) genes. Characterization of the DNA sequence of three NBS marker loci indicated that all showed significant homology to functionally-characterized R-genes and resistance gene analogues (RGAs), with the greatest homology being NBS-LRR-type R-genes and RGAs from cereal species.

Molecular evolution and structural variations in nuclear encoded chloroplast localized heat shock protein 26 (sHSP26) from genetically diverse wheat species

Heat shock proteins are an important class of molecular chaperones known to impart tolerance under high temperature stress. sHSP26, a member of small heat shock protein subfamily is specifically involved in protecting plant’s photosynthetic machinery. The present study aimed at identifying and characterizing sequence and structural variations in sHSP26 from genetically diverse progenitor and non-progenitor species of wheat. In silico analysis identified three paralogous copies of TaHSP26 to reside on short arm of chromosome 4A while one homeologue each was localized on long arm of chromosome 4B and 4D of cultivated bread wheat. Wild DD-genome donor Aegilops tauschii carried an additional sHSP26 gene (AET4Gv20569400) which was absent in the cultivated DD genome of bread wheat. In vitro amplification of this novel gene in wild accessions of Ae. tauschii and synthetic hexaploid wheat but not in cultivated bread wheat validated this finding. Further, significant length polymorphism could be identified in exon1 from diverse sHSP26 sequences. Multiple sequence alignment of procured sequences revealed numerous sSNPs and nsSNPs. D3A, P125 L, Q242 K were designated as homeolog specific- while A49 G as non-progenitor specific amino acid replacements. A 9-bp indel in TmHSP26-1(GA) translated into a deletion of SPM amino acid segment in chloroplast specific conserved consensus region III. High degree of divergence in nucleotide sequence between cultivated and wild species appeared in the form of higher ω values (Ka/Ks >1) indicating positive selection during the course of evolution. Phylogenetic analysis elucidated ancestral relationships between wheat sHSP26 proteins and orthologous proteins across plant kingdom. Overall, data mining approach may be employed as an effective pre-breeding strategy to identify and mobilize novel stress responsive genes and distinct allelic variants from wider germplasm collections of wheat to enhance climate resilience of present day elite wheat cultivars.

Mapping of Genetic Loci Conferring Resistance to Leaf Rust From Three Globally Resistant Durum Wheat Sources.

Genetic resistance in the host plant is the most economical and environmentally friendly strategy for controlling wheat leaf rust, caused by Puccinia triticina Eriks. The durum wheat lines Gaza (Middle East), Arnacoris (France) and Saragolla (Italy) express high levels of resistance to the Mexican races of P. triticina. Three recombinant inbred line (RIL) populations, derived from crosses of each of these resistance sources to the susceptible line ATRED #2, were evaluated for leaf rust reactions at CIMMYT’s leaf rust nurseries in Mexico. Genetic analyses of host reactions suggested oligogenic control of resistance in all populations. The F8 RILs from each cross were genotyped using the Illumina iSelect 90K array, and high-density genetic maps were constructed for each population. Using composite interval mapping, a total of seven quantitative trait loci (QTL) that provide resistance to leaf rust were identified. Two QTL designated as QLr.usw-6BS and QLr.usw-6BL were identified on chromosome 6B in Gaza, which explained up to 78.5% and 21.3% of the observed leaf rust severity variance, respectively. A major QTL designated as QLr.usw-7BL was detected on the long arm of chromosome 7B in Arnacoris, which accounted for up to 65.9% of the disease severity variance. Arnacoris also carried a minor QTL on chromosome 1BL, designated as QLr.usw-1BL.1 that explained up to 17.7% of the phenotypic variance. Three QTL conferred leaf rust resistance in Saragolla, namely QLr.usw-2BS, QLr.usw-3B, and QLr.usw-1BL.2, which accounted for up to 42.3, 9.4, and 7.1% of the phenotypic variance, respectively. Markers flanking each QTL were physically mapped against the durum wheat reference sequence and candidate genes involved in disease resistance were identified within the QTL intervals. The QTL identified in this study and their closely linked markers are useful resources for gene pyramiding and breeding for durable leaf rust resistance in durum wheat.

The Use of Pentaploid Crosses for the Introgression of Amblyopyrum muticum and D-Genome Chromosome Segments Into Durum Wheat.

The wild relatives of wheat provide an important source of genetic variation for wheat improvement. Much of the work in the past aimed at transferring genetic variation from wild relatives into wheat has relied on the exploitation of the ph1b mutant, located on the long arm of chromosome 5B. This mutation allows homologous recombination to occur between chromosomes from related but different genomes, e.g. between the chromosomes of wheat and related chromosomes from a wild relative resulting in the generation of interspecific recombinant chromosomes. However, the ph1b mutant also enables recombination to occur between the homologous genomes of wheat, e.g. A/B, A/D, B/D, resulting in the generation of wheat intergenomic recombinant chromosomes. In this work we report on the presence of wheat intergenomic recombinants in the genomic background of hexaploid wheat/Amblyopyrum muticum introgression lines. The transfer of genomic rearrangements involving the D-genome through pentaploid crosses provides a strategy by which the D-genome of wheat can be introgressed into durum wheat. Hence, a pentaploid crossing strategy was used to transfer D-genome segments, introgressed with either the A- and/or the B-genome, into the tetraploid background of two durum wheat genotypes Karim and Om Rabi 5 in either the presence or absence of different Am. muticum (2n = 2x = 14, TT) introgressions. Introgressions were monitored in backcross generations to the durum wheat parents via multi-color genomic in situ hybridization (mc-GISH). Tetraploid lines carrying homozygous D-genome introgressions, as well as simultaneous homozygous D- and T-genome introgressions, were developed. Introgression lines were characterized via Kompetitive Allele-Specific PCR (KASP) markers and multi-color fluorescence in situ hybridization (FISH). Results showed that new wheat sub-genomic translocations were generated at each generation in progeny that carried any Am. muticum chromosome introgression irrespective of the linkage group that the segment was derived from. The highest frequencies of homologous recombination were observed between the A- and the D-genomes. Results indicated that the genotype Karim had a higher tolerance to genomic rearrangements and T-genome introgressions compared to Om Rabi 5. This indicates the importance of the selection of the parental genotype when attempting to transfer/develop introgressions into durum wheat from pentaploid crosses.

Identification of a new source of stripe rust resistance Yr82 in wheat.

Stripe rust resistance gene, Yr82, was mapped in chromosome 3BL using SNP markers. Yr82 interacted with Yr29 to produce lower stripe rust responses at the adult plant stage. Landrace Aus27969 produced low infection types against Australian Puccinia striiformis f. sp. tritici (Pst) pathotypes. A recombinant inbred line (RIL) F7 population from the Aus27969/Avocet S cross was developed. Monogenic segregation for seedling stripe rust response was observed among the RIL population, and the resistance locus was named Yr82. Bulk segregant analysis performed using the iSelect wheat 90K Infinium SNP array located Yr82 in the long arm of chromosome 3B. The RIL population was screened against stripe rust under field conditions and was genotyped with targeted genotyping-by-sequencing assay. QTL analysis detected the involvement of chromosomes 1B and 3B in controlling stripe rust resistance carried by Aus27969. Incorporation of Yr82 and marker SNPLr46G22 into the linkage map showed that the QTL in 1B and 3B represented Yr29 and Yr82, respectively. Kompetitive allele-specific PCR (KASP) markers sun KASP_300 and KASP_8775 flanked Yr82 distally and proximally, respectively, each at 2cM distance. These Yr82-linked markers were polymorphic among 84% of Australian cultivars and can be used for marker-assisted selection of Yr82.

Mapping a Resistance Gene to Puccinia graminis f. sp. tritici in the Bread Wheat Cultivar 'Matlabas'.

Puccinia graminis f. sp. tritici race TTKSF+ was collected from the South African wheat cultivar 'Matlabas' in 2010. F2 and F3 populations derived from a Matlabas × Line 37-07 cross segregated for a single resistance gene to race TTKSF that is avirulent to Matlabas. In screening genomic DNA bulks of susceptible or resistant F2 plants with simple sequence repeat (SSR) markers, three chromosome arm 2BS markers and one multilocus marker amplified alleles present only in the resistant bulks and Matlabas. Additional 2B-specific SSR markers, incorporating markers spanning regions containing Sr9h, SrWLR, Sr28, and Sr47, were screened in the parental lines and mapped in the F2 population. Linkage and QTL mapping showed that the gene is located between Xbarc160 in the centromeric region and Xgwm47 on the long arm of chromosome 2B. When 2B-specific SNP markers were mapped, the area of interest was delimited to a 15.3 cM region on chromosome arm 2BL, with XIWA543-HRM and Xgwm47 as flanking loci. Matlabas, Webster, and related Sr9h lines all produced a similar, low infection type to race TTKSF, but were susceptible to race TTKSF+. Phenotypic data and allelic studies suggested that stem rust resistance in Matlabas was derived from an Sr9h source.

Selective recombination close to the semi-dwarfing locus through bulk-population in the hybrid between Triticum aestivum and Triticum polonicum

The Rht-B1 locus on the short arm of chromosome 4B has multiple alleles that give phenotypic expressions ranging from semi-dwarfism to extreme dwarfism. Allelic variation at Rht-B1 locus was also found in semi-dwarf Triticum polonicum L. cv. IC12196. The semi-dwarf allele from IC12196 could be an alternative source of reduced height gene. The experimental lines derived from the cross between Triticum aestivum L. cv. Novosibirskaya 67 (N67) and IC12196 were analyzed concerning the introgression of semi-dwarf allele from IC12196. The aim of the present study was to assess the selection for the semi-dwarfism and recombination around the locus of semi-dwarf gene using microsatellite markers on the short arm of chromosome 4B. The Rht-IC12196 allele was allelic to Rht-B1b allele, and microsatellite markers indicated that the Rht-IC12196 allele was linked with the markers, Xbarc1045 and Xgwm113 on the short arm of chromosome 4B. Out of 112 hexaploid introgression lines, 29 lines were semi-dwarf. The Xgwm113 and Xhbg226 markers flanking the Rht-B1 locus were replaced by N67 allele in the majority of introgression lines. Although it did not intend, the region around the Rht-B1 locus was highly selectable, but on short arms of chromosome 4B, Rht-IC12196 gene near the locus Xgwm113 explained a large part of the phenotypic variation originated from N67-allele and non-parental allele in tall accessions. The Rht-B1a allele was favorable in the consequence of bulk population breeding and the frequency of Rht-B1a allele was 73% in the hexaploid introgression lines.
 J. Bangladesh Agril. Univ. 17(2): 148–152, June 2019

Characterization of Pm63, a powdery mildew resistance gene in Iranian landrace PI 628024.

A new powdery mildew resistance gene conferring a wide spectrum of resistance to Bgt isolates in the USA, Pm63 , was identified in Iranian wheat landrace PI 628024 and mapped to the terminal region of the long arm of chromosome 2B. Powdery mildew is a globally important wheat disease causing severe yield losses, and host resistance is the preferred strategy for managing this disease. The objective of this study was to characterize a powdery mildew resistance gene in Iranian landrace PI 628024, which exhibited a wide spectrum of resistance to representative Blumeria graminis f. sp. tritici (Bgt) isolates collected from different regions of the USA. An F2 population and F2:3 lines derived from the cross PI 628024 × CItr 11349 were used in this study, and genetic analysis indicated that a single dominant gene, designated Pm63, conferred resistance to Bgt isolate OKS(14)-B-3-1. Linkage analysis located Pm63 to an interval of about 13.1Mb on the long arm of chromosome 2B, spanning 710.3-723.4Mb in the Chinese Spring reference sequence. Bin mapping assigned Pm63 to the terminal bin 2BL6-0.89-1.0, 1.1cM proximal to STS marker Xbcd135-2 and 0.6cM distal to SSR marker Xstars419. Allelism tests indicated that Pm63 is a new powdery mildew resistance gene, which differs from other genes in the terminal bin by origin, genomic location, and responses to a set of 16 representative US Bgt isolates. Pm63 can be widely used to enhance powdery mildew resistance in the Great Plains, western, and southeastern regions of the USA.

Genetic architecture of wheat stripe rust resistance revealed by combining QTL mapping using SNP-based genetic maps and bulked segregant analysis.

A major stripe rust resistance QTL was mapped to a 0.4 centimorgan (cM) genetic region on the long arm of chromosome 7B, using combined genome-wide linkage mapping and bulk segregant analysis. The German winter wheat cv. Centrum has displayed high levels of adult plant stripe rust resistance (APR) in field environments for many years. Here, we used the combined genome-wide linkage mapping and pool-extreme genotyping to characterize the APR resistance. One hundred and fifty-one F2:7 recombinant inbred lines derived from a cross between susceptible landrace Mingxian 169 and Centrum were evaluated for stripe rust resistance in multiple environments and genotyped by the wheat 35K single nucleotide polymorphism (SNP) array. Three stable quantitative trait loci (QTL) were identified using QTL analysis across five field environments. To saturate the major QTL, the wheat 660K SNP array was also used to genotype bulked extremes. A major QTL named QYrcen.nwafu-7BL from Centrum was mapped in a 0.4cM genetic interval flanking by AX-94556751 and AX-110366788 across a 2Mb physical genomic region, explaining 19.39-42.81% of the total phenotypic variation. It is likely a previously uncharacterized QTL based on pedigree analysis, reaction response, genotyping data and map comparison. The SNP markers closely linked with QYrcen.nwafu-7BL were converted to KASP markers and validated in a subset of 120 wheat lines. A 211 F2 breeding population from a cross of an elite cultivar Xinong 979 with Centrum were developed for marker-based selection. Three selected lines with desirable agronomic traits and the positive alleles of both KASP markers showed acceptable resistance which should be used as resistance donors in wheat breeding programs. The other QTL QYrcen.nwafu-1AL and QYrcen.nwafu-4AL with additive effects could enhance the level of resistance conferred by QYrcen.nwafu-7BL.

Delimitation of wheat ph1b deletion and development of ph1b-specific DNA markers.

We detected the deletion breakpoints of wheat ph1b mutant and the actual size of the deletion. Also, we developed ph1b deletion-specific markers useful for ph1b-mediated gene introgression and genome studies. The Ph1 (pairing homoeologous) locus has been considered a major genetic system for the diploidized meiotic behavior of the allopolyploid genome in wheat. It functions as a defense system against meiotic homoeologous pairing and recombination in polyploid wheat. A large deletion of the genomic region harboring Ph1 on the long arm of chromosome 5B (5BL) led to the ph1b mutant in hexaploid wheat 'Chinese Spring,' which has been widely used to induce meiotic homoeologous recombination for gene introgression from wild grasses into wheat. However, the breakpoints and physical size of the deletion remain undetermined. In the present study, we first anchored the ph1b deletion on 5BL by the high-throughput wheat 90K SNP assay and then delimited the deletion to a genomic region of 60,014,523bp by chromosome walking. DNA marker and sequence analyses detected the nucleotide positions of the distal and proximal breakpoints (DB and PB) of the ph1b deletion and the deletion junction as well. This will facilitate understanding of the genomic region harboring the Ph1 locus in wheat. In addition, we developed user-friendly DNA markers specific for the ph1b deletion. These new ph1b deletion-specific markers will dramatically improve the efficacy of the ph1b mutant in the meiotic homoeologous recombination-based gene introgression and genome studies in wheat and its relatives.

A new leaf rust resistance gene Lr79 mapped in chromosome 3BL from the durum wheat landrace Aus26582.

A new leaf rust resistance gene Lr79 has been mapped in the long arm of chromosome 3B and a linked marker was identified for marker-assisted selection. Aus26582, a durum wheat landrace from the A. E. Watkins Collection, showed seedling resistance against durum-specific and common wheat-specific Puccinia triticina (Pt) pathotypes. Genetic analysis using a recombinant inbred line (RIL) population developed from a cross between Aus26582 and the susceptible parent Bansi with Australian Pt pathotype showed digenic inheritance and the underlying loci were temporarily named LrAW2 and LrAW3. LrAW2 was located in chromosome 6BS and this study focused on characterisation of LrAW3 using RILs lacking LrAW2. LrAW3 was incorporated into the DArTseq map of Aus26582/Bansi and was located in chromosome 3BL. Markers linked with LrAW3 were developed from the chromosome survey sequence contig 3B_10474240 in which closely-linked DArTseq markers 1128708 and 3948563 were located. Although bulk segregant analysis (BSA) with the 90K Infinium array identified 51 SNPs associated with LrAW3, only one SNP-derived KASP marker mapped close to the locus. Deletion bin mapping of LrAW3-linked markers located LrAW3 between bins 3BL11-0.85-0.90 and 3BL7-0.63. Since no other all stage leaf rust resistance gene is located in chromosome 3BL, LrAW3 represented a new locus and was designated Lr79. Marker sun786 mapped 1.8cM distal to Lr79 and Aus26582 was null for this locus. However, the marker can be reliably scored as it also amplifies a monomorphic fragment that serves as an internal control to differentiate the null status of Aus26582 from reaction failure. This marker was validated among a set of durum and common wheat cultivars and was shown to be useful for marker-assisted selection of Lr79 at both ploidy levels.

Genetics of Na+ exclusion and salinity tolerance in Afghani durum wheat landraces

BackgroundSelecting for low concentration of Na+ in the shoot provides one approach for tackling salinity stress that adversely affects crop production. Novel alleles for Na+ exclusion can be identified and then introduced into elite crop cultivars.ResultsWe have identified loci associated with lower Na+ concentration in leaves of durum wheat landraces originating from Afghanistan. Seedlings of two F2 populations derived from crossings between Australian durum wheat (Jandaroi) and two Afghani landraces (AUS-14740 and AUS-14752) were grown hydroponically and evaluated for Na+ and K+ concentration in the third leaf. High heritability was found for both third leaf Na+ concentration and the K+/Na+ ratio in both populations. Further work focussed on line AUS-14740. Bulk segregant analysis using 9 K SNP markers identified two loci significantly associated with third leaf Na+ concentration. Marker regression analysis showed a strong association between all traits studied and a favourable allele originating from AUS-14740 located on the long arm of chromosome 4B.ConclusionsThe candidate gene in the relevant region of chromosome 4B is likely to be the high affinity K+ transporter B1 (HKT1;5-B1). A second locus associated with third leaf Na+ concentration was located on chromosome 3BL, with the favourable allele originating from Jandaroi; however, no candidate gene can be identified.

Identification and mapping of a new powdery mildew resistance allele in the Chinese wheat landrace Hongyoumai

Powdery mildew (Pm) caused by Blumeria graminis f. sp. tritici (Bgt) is one of the world’s major wheat diseases and results in large grain yield losses. Discovery and utilization of Pm resistance genes constitute the most common strategy for wheat Pm control. Hongyoumai, a wheat landrace from Henan Province in China, has excellent resistance to infection by Bgt. In order to identify the basis of such Pm resistance, a segregating population was submitted to genetic analysis, which showed that Pm resistance in Hongyoumai was conferred by a single recessive resistance gene. This gene was temporarily named pmHYM. Molecular marker analysis, chromosomal location, resistance spectrum analysis, and an allelism test showed that pmHYM was located on the long arm of chromosome 7B (7BL), most likely representing a new recessive resistance gene allelic with Pm5e and mlXBD. By using 90-kb single-nucleotide polymorphism sequences (SNP) in the BLASTn analysis against the wheat 7BL genome sequence, 12 new simple sequence repeat (SSR) markers linked with pmHYM were developed to map pmHYM co-segregating with the marker Xmp1207 and between markers Xmp925 and Xmp1158, at genetic distances of 2.8 and 2.7 cM, respectively. In addition, physical mapping of the markers linked with pmHYM using Chinese Spring deletion lines indicated a location in the 0.86–1.00 bin of 7BL.

Cytogenetic analysis and mapping of leaf rust resistance in Aegilops speltoides Tausch derived bread wheat line Selection2427 carrying putative gametocidal gene(s).

Leaf rust (Puccinia triticina) is a major biotic stress affecting wheat yields worldwide. Host-plant resistance is the best method for controlling leaf rust. Aegilops speltoides is a good source of resistance against wheat rusts. To date, five Lr genes, Lr28, Lr35, Lr36, Lr47, and Lr51, have been transferred from Ae. speltoides to bread wheat. In Selection2427, a bread wheat introgresed line with Ae. speltoides as the donor parent, a dominant gene for leaf rust resistance was mapped to the long arm of chromosome 3B (LrS2427). None of the Lr genes introgressed from Ae. speltoides have been mapped to chromosome 3B. Since none of the designated seedling leaf rust resistance genes have been located on chromosome 3B, LrS2427 seems to be a novel gene. Selection2427 showed a unique property typical of gametocidal genes, that when crossed to other bread wheat cultivars, the F1 showed partial pollen sterility and poor seed setting, whilst Selection2427 showed reasonable male and female fertility. Accidental co-transfer of gametocidal genes with LrS2427 may have occurred in Selection2427. Though LrS2427 did not show any segregation distortion and assorted independently of putative gametocidal gene(s), its utilization will be difficult due to the selfish behavior of gametocidal genes.

High density mapping and haplotype analysis of the major stem-solidness locus SSt1 in durum and common wheat.

Breeding for solid-stemmed durum (Triticum turgidum L. var durum) and common wheat (Triticum aestivum L.) cultivars is one strategy to minimize yield losses caused by the wheat stem sawfly (Cephus cinctus Norton). Major stem-solidness QTL have been localized to the long arm of chromosome 3B in both wheat species, but it is unclear if these QTL span a common genetic interval. In this study, we have improved the resolution of the QTL on chromosome 3B in a durum (Kofa/W9262-260D3) and common wheat (Lillian/Vesper) mapping population. Coincident QTL (LOD = 94–127, R2 = 78–92%) were localized near the telomere of chromosome 3BL in both mapping populations, which we designate SSt1. We further examined the SSt1 interval by using available consensus maps for durum and common wheat and compared genetic to physical intervals by anchoring markers to the current version of the wild emmer wheat (WEW) reference sequence. These results suggest that the SSt1 interval spans a physical distance of 1.6 Mb in WEW (positions 833.4–835.0 Mb). In addition, minor QTL were identified on chromosomes 2A, 2D, 4A, and 5A that were found to synergistically enhance expression of SSt1 to increase stem-solidness. These results suggest that developing new wheat cultivars with improved stem-solidness is possible by combining SSt1 with favorable alleles at minor loci within both wheat species.

Genetic mapping of resistance to the Ug99 race group of Puccinia graminis f. sp. tritici in a spring wheat landrace CItr 4311.

A gene for Ug99 resistance from wheat landrace CItr 4311 was detected on the long arm of chromosome 2B. Wheat landrace CItr 4311 has seedling resistance to stem rust caused by Puccinia graminis f. sp. tritici race TTKSK and field resistance to the Ug99 race group. Parents, F1 seedlings, 121 doubled haploid (DH) lines, and 124 recombinant inbred lines (RILs) developed from a cross between CItr 4311 and the susceptible line LMPG-6 were evaluated for seedling resistance to race TTKSK. Goodness-of-fit tests indicated that a single dominant gene in CItr 4311 conditioned the TTKSK resistance. The 90K wheat iSelect SNP platform was used to genotype parents and the DH population. The seedling resistance locus was mapped to the chromosome arm 2BL. Parents and the DH population were evaluated for field resistance in Kenya. One major QTL for the field resistance was consistently detected in the same region on 2BL as the seedling resistance. Using KASP assays, five linked SNP markers were used to verify the result in the 124 RIL, 35 wheat accessions, 46 DH lines from the LMPG-6/PI 165194 cross and F1 seedlings, and susceptible bulks derived from crosses between six resistant landraces with LMPG-6. Race specificity, mapping results, and haplotype similarity with lines with Sr9h (Gabo 56, Timstein, and PI 670015), support the hypothesis that the Sr gene in CItr 4311 and the landraces is Sr9h. The KASP assays developed in this study will be useful for pyramiding the TTKSK resistance from CItr 4311 with other Sr genes effective against Ug99.

Change in salt tolerance of bread wheat as a result of the introgression of the genetic material of Aegilops speltoides and Triticum timopheevii

In order to increase the bread wheat (Triticum aestivum L.) tolerance to different biotic and abiotic stress factors, the development of new genotypes using the introgressions of the genomic fragments from other cereals is widely used. One of the most significant abiotic environmental factors that impede the expansion of the wheat cultivation territory is soil salinity. Salt-sensitive wheat varieties have poor yield and impaired grain quality when exposed to salinity. The aim of the present study was the establishment of a degree of influence of the alien genetic material on the salinity tolerance of bread wheat T. aestivum seedlings. The method of laboratory screening of the seedling salinity tolerance was used for the analysis of introgression lines carrying single fragments from Aegilops speltoides and T. timopheevii in bread wheat chromosomes 2A, 5B, and 6B.The initial parental forms of the spring bread wheat (Saratovskaya 29, Novosibirskaya 29, and Rodina-1) with moderate salt tolerance were used as the control. As a result of the estimation, it was established that the presence of the T5BS ⋅ 5BL-5SL translocation in the genome of Novosibirskaya 29 and Rodina-1 increased salt tolerance. On the contrary, another translocation from Ae. speltoides (T6BS • 6BL-6SL) is associated with a reduction in the tolerance. Different T. timopheevii genome fragments also differently affected the salt tolerance; introgression in chromosome 2A increased, while in 5B considerably decreased the wheat tolerance to the salinization. The observed differences between the initial wheat genotypes and introgression lines derived from them are discussed taking into account the localization of alien introgressions in the studied lines and the localization of the known genes (controlling the salt tolerance) in wheat chromosomes. It is assumed that a previously undescribed gene, which influences wheat seedlings salt tolerance, is located distal to the Xgwm0604 marker on the long arm of chromosome 5B.

QTLs for uniform grain dimensions and germination selected during wheat domestication are co-located on chromosome 4B.

A major locus on the long arm of wheat chromosome 4B controls within-spikelet variation in both grain size and seed dormancy, the latter an important survival mechanism likely eliminated from wild wheat during domestication. Seed dormancy can increase the probability of survival of at least some progeny under unstable environmental conditions. In wild emmer wheat, only one of the two grains in a spikelet germinates during the first rainy season following maturation; and this within-plant variation in seed dormancy is associated with both grain dimension differences and position within the spikelet. Here, in addition to characterizing these associations, we elucidate the genetic mechanism controlling differential grain dimensions and dormancy within wild tetraploid wheat spikelets using phenotypic data from a wild emmer×durum wheat population and a high-density genetic map. We show that in wild emmer, the lower grain within the spikelet is about 30% smaller and more dormant than the larger, upper grain that germinates usually within 3days. We identify a major locus on the long arm of chromosome 4B that explains>40% of the observed variation in grain dimensions and seed dormancy within spikelets. This locus, designated QGD-4BL, is validated using an independent set of wild emmer×durum wheat genetic stocks. The domesticated variant of this novel locus on chromosome 4B, likely fixed during the process of wheat domestication, favors spikelets with seeds of uniform size and synchronous germination. The identification of locus QGD-4BL enhances our knowledge of the genetic basis of the domestication syndrome of one of our most important crops.

Genetic Mapping of Major‐Effect Seed Dormancy Quantitative Trait Loci on Chromosome 2B using Recombinant Substitution Lines in Tetraploid Wheat

ABSTRACTDurum wheat (Triticum turgidum L.) cultivars can benefit from having some level of seed dormancy to help reduce seed damage and lower grain quality caused by preharvest sprouting (PHS) occurring during wet harvesting conditions. Previously, a single chromosome substitution line carrying chromosome 2B of wild emmer [Triticum turgidum L. subsp. dicoccoides (Körn. ex Asch. & Graebn.) Thell.] in the durum cultivar Langdon background was found to have higher levels of seed dormancy and PHS tolerance. In this study, a population of recombinant substitution lines was developed and used to construct a single nucleotide polymorphism (SNP)‐based high‐density genetic linkage map. Seed germination tests were used to evaluate seed dormancy levels. Multiple interval mapping analysis revealed four quantitative trait loci (QTL) regions affecting seed dormancy. Two regions containing major‐effect QTL contributed by wild emmer were consistently expressed in four environments and explained 5.89 to 11.14% of the phenotypic variation. One QTL region was located near the centromere and the other on the long arm of chromosome 2B in Bayes credible intervals of 4 and 7 cM, respectively. Recombinant inbred lines (RILs) carrying both QTL had an average of 35% reduced rate of germination measured by weighted germination index compared with RILs carrying neither QTL. The two QTL regions identified in this study should be useful for improving PHS tolerance in wheat. Efforts to transfer the two QTL into elite durum cultivars are in progress to examine the effects of genetic background and environment on QTL expression and to evaluate the performance of other agronomic traits in the presence of the QTL.

Fine mapping of a large-effect QTL conferring Fusarium crown rot resistance on the long arm of chromosome 3B in hexaploid wheat.

BackgroundFusarium crown rot (FCR) is a major cereal disease in semi-arid areas worldwide. Of the various QTL reported, the one on chromosome arm 3BL (Qcrs.cpi-3B) has the largest effect that can be consistently detected in different genetic backgrounds. Nine sets of near isogenic lines (NILs) for this locus were made available in a previous study. To identify markers that could be reliably used in tagging the Qcrs.cpi-3B locus, a NIL-derived population consisting of 774 F10 lines were generated and exploited to assess markers selected from the existing linkage map and generated from sequences of the 3B pseudomolecule.ResultsThis is the first report on fine mapping a QTL conferring FCR resistance in wheat. By three rounds of linkage mapping using the NILs and the NIL-derived population, the Qcrs.cpi-3B locus was mapped to an interval of 0.7 cM covering a physical distance of about 1.5 Mb. Seven markers co-segregating with the locus were developed. This interval contains a total of 63 gene-coding sequences based on the 3B pseudomolecule, and six of them were known to encode disease resistance proteins. Several of the genes in this interval were among those responsive to FCR infection detected in an earlier study.ConclusionsThe accurate localization of the Qcrs.cpi-3B locus and the development of the markers co-segregating with it should facilitate the incorporation of this large-effect QTL conferring FCR resistance into breeding programs as well as the cloning of the gene(s) underlying the QTL.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2105-0) contains supplementary material, which is available to authorized users.