Brassinosteroid leaf unrolling QTL mapping in durum wheat

Brassinosteroids are a newly reported class of plant growth phytohormones found in plants throughout the plant kingdom. Functioning at very low concentrations, they play an essential role in improving biomass yield and stress tolerance. There are no reports in the literature of the genetic variability of responsiveness of brassinosteroids in wheat; most studies on brassinosteroids have focused on the physiological effects of exogenous addition of brassinosteroids. Our aim was to study the genetic variation in the responsiveness of a doubled haploid durum wheat population to three brassinosteroid concentrations using the leaf unrolling test, which is a simple bioassay to test brassinosteroid activity. An F₁-derived doubled haploid population of 77 individuals from the cross Strongfield/Blackbird was used to construct a genetic map of 427 molecular marker loci. The leaf unrolling test was performed on the parents and doubled haploid genotypes of the population using 0.2, 2 and 20 nM brassinosteroid concentrations. The results indicated significant differences in leaf unrolling between the two parents, doubled haploid genotypes, treatments and genotype-by-treatment combinations. Transgressive segregation beyond Strongfield of leaf unrolling was observed for all concentrations, with the strongest response at 20 nM. Putative quantitative trait loci were revealed in the intervals Xgwm2–Xbarc45 on chromosome 3A and Xwmc643a–Xwmc625a on chromosome 3B. Additional quantitative trait loci were associated with markers Xwmc48a, Xwmc511, Xwmc89a and Xgwmc692 on chromosome 4B, and Xwmc17 on chromosome 7A. This work should enhance the understanding of the relationship between stress tolerance and productivity, and responsiveness to brassinosteroids.     

Identification and mapping of leaf, stem and stripe rust resistance quantitative trait loci and their interactions in durum wheat

Leaf rust (Puccinia triticina Eriks.), stripe rust (Puccinia striiformis f. tritici Eriks.) and stem rust (Puccinia graminis f. sp. tritici) cause major production losses in durum wheat (Triticum turgidum L. var. durum). The objective of this research was to identify and map leaf, stripe and stem rust resistance loci from the French cultivar Sachem and Canadian cultivar Strongfield. A doubled haploid population from Sachem/Strongfield and parents were phenotyped for seedling reaction to leaf rust races BBG/BN and BBG/BP and adult plant response was determined in three field rust nurseries near El Batan, Obregon and Toluca, Mexico. Stripe rust response was recorded in 2009 and 2011 nurseries near Toluca and near Njoro, Kenya in 2010. Response to stem rust was recorded in field nurseries near Njoro, Kenya, in 2010 and 2011. Sachem was resistant to leaf, stripe and stem rust. A major leaf rust quantitative trait locus (QTL) was identified on chromosome 7B at Xgwm146 in Sachem. In the same region on 7B, a stripe rust QTL was identified in Strongfield. Leaf and stripe rust QTL around DArT marker wPt3451 were identified on chromosome 1B. On chromosome 2B, a significant leaf rust QTL was detected conferred by Strongfield, and at the same QTL, a Yr gene derived from Sachem conferred resistance. Significant stem rust resistance QTL were detected on chromosome 4B. Consistent interactions among loci for resistance to each rust type across nurseries were detected, especially for leaf rust QTL on 7B. Sachem and Strongfield offer useful sources of rust resistance genes for durum rust breeding.     

Identification and validation of quantitative trait loci for grain protein concentration in adapted Canadian durum wheat populations

Grain protein concentration (GPC) is one of the most important factors influencing pasta-making quality. Durum wheat (Triticum turgidum L. var durum) cultivars with high GPC produce pasta with increased tolerance to overcooking and greater cooked firmness. However, the large environmental effect on expression of GPC and the negative correlation with grain yield have slowed genetic improvement of this important trait. Understanding the genetics and identification of molecular markers associated with high GPC would aid durum wheat breeders in trait selection at earlier generations. The objectives of this study were to identify and validate molecular markers associated with quantitative trait loci (QTL) for elevated GPC in durum wheat. A genetic map was constructed using SSR and DArT^® markers in an F₁-derived doubled haploid (DH) population derived from the cross DT695 × Strongfield. The GPC data were collected from replicated trials grown in six Canadian environments from 2002 to 2005. QTL associated with variation for GPC were identified on the group 1, 2, and 7 chromosomes and on 5B and 6B, but only QGpc.usw-B3 on 2B and QGpc.usw-A3 on 7A were expressed consistently in four and six environments, respectively. Positive alleles for GPC at these loci were contributed by the high-GPC parent Strongfield. The QGpc.usw-A3 QTL was validated in a second DH population, and depending on environment, selection for the Strongfield allele at barc108 resulted in +0.4% to +1.0% increase in GPC, with little effect on yield in most environments. Given the consistent expression pattern in multiple populations and environments, barc108 could be useful for marker-assisted selection for high GPC.     

Identification of QTL and association of a phytoene synthase gene with endosperm colour in durum wheat

The yellow colour of durum wheat (Triticum turgidum L. var durum) semolina is due in part to the presence of carotenoid pigments found in the endosperm and is an important end-use quality trait. We hypothesized that variation in the genes coding for phytoene synthase (Psy), a critical enzyme in carotenoid biosynthesis, may partially explain the phenotypic variation in endosperm colour observed among durum cultivars. Using rice sequence information, primers were designed to PCR clone and sequence the Psy genes from Kofa (high colour) and W9262-260D3 (medium colour) durum cultivars. Sequencing confirmed the presence of four Psy genes in each parent, corresponding to a two member gene family designated as Psy1-1, Psy1-2 and Psy2-1 and Psy2-2. A genetic map was constructed using 155 F1-derived doubled haploid lines from the cross W9262-260D3/Kofa with 194 simple sequence repeat and DArT markers. Using Psy1-1 and Psy2-1 allele-specific markers and chromosome mapping, the Psy1 and Psy2 genes were located to the group 7 and 5 chromosomes, respectively. Four quantitative trait loci (QTL) underlying phenotypic variation in endosperm colour were identified on chromosomes 2A, 4B, 6B, and 7B. The Psy1-1 locus co-segregated with the 7B QTL, demonstrating an association of this gene with phenotypic variation for endosperm colour. This work is the first report of mapping Psy genes and supports the role of Psy1-1 in elevated levels of endosperm colour in durum wheat. This gene is a target for the further development of a molecular marker to enhance selection for endosperm colour in durum wheat breeding programs.     

QTL mapping of flag leaf-related traits in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Key message

QTL controlling flag leaf length, flag leaf width, flag leaf area and flag leaf angle were mapped in wheat.

Abstract

This study aimed to advance our understanding of the genetic mechanisms underlying morphological traits of the flag leaves of wheat (Triticum aestivum L.). A recombinant inbred line (RIL) population derived from ND3331 and the Tibetan semi-wild wheat Zang1817 was used to identify quantitative trait loci (QTLs) controlling flag leaf length (FLL), flag leaf width (FLW), flag leaf area (FLA), and flag leaf angle (FLANG). Using an available simple sequence repeat genetic linkage map, 23 putative QTLs for FLL, FLW, FLA, and FLANG were detected on chromosomes 1B, 2B, 3A, 3D, 4B, 5A, 6B, 7B, and 7D. Individual QTL explained 4.3–68.52% of the phenotypic variance in different environments. Four QTLs for FLL, two for FLW, four for FLA, and five for FLANG were detected in at least two environments. Positive alleles of 17 QTLs for flag leaf-related traits originated from ND3331 and 6 originated from Zang1817. QTLs with pleiotropic effects or multiple linked QTL were also identified on chromosomes 1B, 4B, and 5A; these are potential target regions for fine-mapping and marker-assisted selection in wheat breeding programs.

     

Quantitative trait loci mapping of dark-induced senescence in winter wheat (Triticum aestivum)

In order to explore the genetics of dark-induced senescence in winter wheat(Triticum aestivum L.),a quantitative trait loci(QTL)analysis was carried out in a doubled haploid population developed from a cross between the varieties Hanxuan 10(HX)and Lumai 14(LM).The senescence parameters chlorophyll content(Chl a+b,Chl a,and Chl b),original fluorescence(Fo),maximum fluorescence level(Fm),maximum photochemical efficiency(Fv/Fm),and ratio of variable fluorescence to original fluorescence(Fv/Fo)were evaluated in the second leaf of whole three-leaf seedlings subjected to 7 d of darkness.A total of 43 QTLs were identified that were associated with dark-induced senescence using composite interval mapping.These QTLs were mapped to 20 loci distributed on 11 chromosomes:1B,1D,2A,2B,3B,3D,5D,6A,6B,7A,and 7B.The phenotypic variation explained by each QTL ranged from 7.5% to 19.4%.Eleven loci coincided with two or more of the analyzed parameters.In addition,14 loci co-located or were linked with previously reported QTLs regulating flag leaf senescence,tolerance to high light stress,and grain protein content(Gpc),separately.     

Molecular mapping of stomatal‐conductance‐related traits in durum wheat (Triticum turgidum ssp. durum)

The most promising traits identified in wheat to raise yield potential via an increase in biomass accumulation are stomatal conductance and stomatal‐conductance‐related traits, such as carbon isotope discrimination (CID) and photosynthetic rate. The evaluation of the extent of genetic variation and the mapping of chromosomal regions controlling these traits are essential for the development of effective breeding strategies in durum wheat. A population of 161 F2‐derived, F8–F9 recombinant inbred lines obtained from a cross between durum wheat (Triticum turgidum ssp. durum) cultivars Ofanto and Cappelli was phenotyped for heading date, plant height, leaf porosity, CID and chlorophyll concentration (estimated through the SPAD index) for 2007/2008 and 2008/2009 seasons, at Ottava, Sardinia (Italy) under irrigated conditions. The genotype mean heritability for leaf porosity, CID and chlorophyll concentration was moderate in size. Six quantitative trait loci were detected for leaf porosity, four for chlorophyll concentration, but only one for CID, because of the small variation expressed in the population for this trait under these experimental conditions. The quantitative trait loci for leaf porosity located on chromosome 3B appear to be more stable with respect to the others, and different microsatellite markers are positioned within the interval of the quantitative trait loci, or in their vicinity, that represent useful tools in programmes for selection assisted by molecular markers.     

Dissecting a wheat QTL for yield present in a range of environments: from the QTL to candidate genes

Previous studies with 95 bread wheat doubled haploid lines (DHLs) from the cross Chinese Spring (CS)xSQ1 trialled over 24 yearxtreatmentxlocations identified major yield quantitative trait loci (QTLs) in homoeologous locations on 7AL and 7BL, expressed mainly under stressed and non-stressed conditions, respectively. SQ1 and CS contributed alleles increasing yield on 7AL and 7BL, respectively. The yield component most strongly associated with these QTLs was grains per ear. Additional results which focus on the 7AL yield QTL are presented here. Trials monitoring agronomic, morphological, physiological, and anatomical traits revealed that the 7AL yield QTL was not associated with differences in flowering time or plant height, but with significant differences in biomass at maturity and anthesis, biomass per tiller, and biomass during tillering. In some trials, flag leaf chlorophyll content and leaf width at tillering were also associated with the QTL. Thus, it is likely that the yield gene(s) on 7AL affects plant productivity. Near-isogenic lines (NILs) for the 7AL yield QTL with CS or SQ1 alleles in an SQ1 background showed the SQ1 allele to be associated with >20% higher yield per ear, significantly higher flag leaf chlorophyll content, and wider flag leaves. Epidermal cell width and distance between leaf vascular bundles did not differ significantly between NILs, so the yield-associated gene may influence the number of cell files across the leaf through effects on cell division. Interestingly, comparative mapping with rice identified AINTEGUMENTA and G-protein subunit genes affecting lateral cell division at locations homologous to the wheat 7AL yield QTL.     

Linkage Disequilibrium and Genome-Wide Association Mapping in Tetraploid Wheat (Triticum turgidum L.)

Association mapping is a powerful tool for the identification of quantitative trait loci through the exploitation of the differential decay of linkage disequilibrium (LD) between marker loci and genes of interest in natural and domesticated populations. Using a sample of 230 tetraploid wheat lines (Triticum turgidum ssp), which included naked and hulled accessions, we analysed the pattern of LD considering 26 simple sequence repeats and 970 mostly mapped diversity array technology loci. In addition, to validate the potential for association mapping in durum wheat, we evaluated the same genotypes for plant height, heading date, protein content, and thousand-kernel weight. Molecular and phenotypic data were used to: (i) investigate the genetic and phenotypic diversity; (ii) study the dynamics of LD across the durum wheat genome, by investigating the patterns of LD decay; and (iii) test the potential of our panel to identify marker–trait associations through the analysis of four quantitative traits of major agronomic importance. Moreover, we compared and validated the association mapping results with outlier detection analysis based on population divergence. Overall, in tetraploid wheat, the pattern of LD is extremely population dependent and is related to the domestication and breeding history of durum wheat. Comparing our data with several other studies in wheat, we confirm the position of many major genes and quantitative trait loci for the traits considered. Finally, the analysis of the selection signature represents a very useful complement to validate marker–trait associations.     

Factors inducing regeneration response in oat (Avena sativa L.) anther culture

The efficiency of embryogenesis of anther culture was compared using four cultivars of oat (Avena sativa L.): ‘Akt’, ‘Bingo’, ‘Bajka’, and ‘Chwat’. Despite the high resistance of oat to the process of androgenesis, all tested cultivars produced embryo-like structures and only two of them, ‘Akt’ and ‘Chwat’, produced fertile doubled haploid plants. A strong cultivar dependency was observed during induction of androgenesis. Further, cold pretreatment together with high temperature shock enhanced the efficiency of this technique. The highest number of embryo-like structures and haploid plants was obtained from cv. ‘Chwat’ (3.6% and 0.8%, respectively). Embryo-like structure formation also depended on the distance from the base of the flag leaf to the penultimate leaf of the panicle. Most of them were observed on anthers harvested from panicles of which the distance from the base of the flag leaf to the penultimate leaf was less than 4 cm. The presence of the induction medium supplemented with different plant growth regulators was essential for the induction of embryo-like structures but did not increase the production of haploid plants and doubled haploid lines. The highest number of embryo-like structures and plants was obtained on W14 medium with the addition of 2.0 mg/dm³ 2,4-dichlorophenoxyacetic acid and 0.5 mg/dm³ kinetin (2.7%). The low haploid plant regeneration rate (from 0.03 to 0.05%) still limits the practical application of anther culture for the production of doubled haploid lines in oat.

     

Mapping quantitative trait loci controlling common bunt resistance in a doubled haploid population derived from the spring wheat cross RL4452 × AC Domain

Wheat resistance to common bunt is a highly desirable trait for environmentally friendly grain grade protection. Valuable breeding achievements have been made to develop wheat varieties with enhanced resistance to the disease, and mapping of race-specific resistance genes has been reported. However, less is known of the chromosomal regions that control non-race specific resistance to common bunt. In this study, we have characterized a segregating population of 185 doubled haploid spring wheat lines derived from the cross RL4452 × AC Domain. Reactions to a mixture of common bunt races were assessed under field simulated spring-sown conditions in greenhouses in two locations over 2 years. A total 369 polymorphic maker loci including 356 microsatellite loci, five expressed sequences tag (ESTs), and eight genes were used to develop a linkage map. Quantitative trait loci (QTL) analysis using composite interval mapping detected three QTLs associated with common bunt resistance, of which two were located on chromosome 1B and one on chromosome 7A. AC Domain alleles contributed the common bunt resistance at all three QTLs. Usefulness of gene tagging within the identified chromosomal regions for common bunt resistance breeding is discussed.     

Genetics of pre-harvest sprouting resistance in a cross of Canadian adapted durum wheat genotypes

Severe losses attributable to pre-harvest sprouting (PHS) have been reported in Canada in recent years. The genetics of PHS resistance have been more extensively studied in hexaploid wheat and generally not using combinations of elite agronomic parents. The objective of our research was to understand the genetic nature of PHS resistance in an elite durum cross. A doubled haploid (DH) population and checks were phenotyped in replicated trials for grain yield and PHS traits over 3 years in western Canada. The response of intact spikes to sprouting conditions, sampled over two development time points, was measured in a rain simulation chamber. The DH population was genotyped with simple sequence repeat and Diversity Arrays Technology markers. Genotypes were a significant source of variation for grain yield and PHS resistance traits in each tested environment. Transgressive segregant DH genotypes were identified for grain yield and PHS resistance measurements. Low or no correlation was detected between grain yield and PHS, while correlation between PHS resistance measurements was moderate. The heritability of PHS resistance was moderate and higher than grain yield. Significant quantitative trait loci with small effect were detected on chromosomes 1A, 1B, 5B, 7A and 7B. Both parents contributed to the PHS resistance. Promising DH genotypes with high and stable grain yield as well as PHS resistance were identified, suggesting that grain yield and PHS can be improved simultaneously in elite genetic materials, and that these DH genotypes will be useful parental material for durum breeding programs.     

A genetic map constructed using a doubled haploid population derived from two elite Chinese common wheat varieties

Genetic mapping provides a powerful tool for the analysis of quantitative trait loci (QTLs) at the genomic level.Herein,we report a new genetic linkage map developed from an F1-derived doubled haploid (DH) population of 168 lines,which was generated from the cross between two elite Chinese common wheat (Triticum aestivum L.) varieties,Huapei 3 and Yumai 57.The map contained 305 loci,represented by 283 simple sequence repeat (SSR) and 22 expressed sequence tag (EST)-SSR markers,which covered a total length of 2141.7 cM with an average distance of 7.02 cM between adjacent markers on the map.The chromosomal locations and map positions of 22 new SSR markers were determined,and were found to distribute on 14 linkage groups.Twenty SSR loci showed different chromosomal locations from those reported in other maps.Therefore,this map offers new information on the SSR markers of wheat.This genetic map provides new opportunities to detect and map QTLs controlling agronomically important traits.The unique features of this map are discussed.     

Identification of QTL for flag leaf length in common wheat and their pleiotropic effects

Leaf size is an important factor contributing to the photosynthetic capability of wheat plants. It also significantly affects various agronomic traits. In particular, the flag leaves contribute significantly to grain yield in wheat. A recombinant inbred line (RIL) population developed between varieties with significant differences in flag leaf traits was used to map quantitative trait loci (QTL) of flag leaf length (FLL) and to evaluate its pleiotropic effects on five yield-related traits, including spike length (SL), spikelet number per spike (SPN), kernel number per spike (KN), kernel length (KL), and thousand-kernel weight (TKW). Two additional RIL populations were used to validate the detected QTL and reveal the relationships in different genetic backgrounds. Using the diversity arrays technology (DArT) genetic linkage map, three major QTL for FLL were detected, with single QTL in different environments explaining 8.6–23.3% of the phenotypic variation. All the QTL were detected in at least four environments, and validated in two related populations based on the designed primers. These QTL and the newly developed primers are expected to be valuable for fine mapping and marker-assisted selection in wheat breeding programs.     

The genetics of nitrogen use in hexaploid wheat: N utilisation, development and yield

A genetic study is presented for traits relating to nitrogen use in wheat. Quantitative trait loci (QTLs) were established for 21 traits relating to growth, yield and leaf nitrogen (N) assimilation during grain fill in hexaploid wheat (Triticum aestivum L.) using a mapping population from the cross Chinese Spring × SQ1. Glutamine synthetase (GS) isozymes and estimated locations of 126 genes were placed on the genetic map. QTLs for flag leaf GS activity, soluble protein, extract colour and fresh weight were found in similar regions implying shared control of leaf metabolism and leaf size. Flag leaf traits were negatively associated with days to anthesis both phenotypically and genetically, demonstrating the complex interactions of metabolism with development. One QTL cluster for GS activity co-localised with a GS2 gene mapped on chromosome 2A, and another with the mapped GSr gene on 4A. QTLs for GS activity were invariably co-localised with those for grain N, with increased activity associated with higher grain N, but with no or negative correlations with grain yield components. Peduncle N was positively correlated, and QTLs co-localised, with grain N and flag leaf N assimilatory traits, suggesting that stem N can be indicative of grain N status in wheat. A major QTL for ear number per plant was identified on chromosome 6B which was negatively co-localised with leaf fresh weight, peduncle N, grain N and grain yield. This locus is involved in processes defining the control of tiller number and consequently assimilate partitioning and deserves further examination. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.     

Genetic map of Triticum turgidum based on a hexaploid wheat population without genetic recombination for D genome

ABSTRACT: BACKGROUND: A synthetic doubled-haploid hexaploid wheat population, SynDH1, derived from the spontaneous chromosome doubling of triploid F1 hybrid plants obtained from the cross of hybrids Triticum turgidum ssp. durum line Langdon (LDN) and ssp. turgidum line AS313, with Aegilops tauschii ssp. tauschii accession AS60, was previously constructed. SynDH1 is a tetraploidization-hexaploid doubled haploid (DH) population because it contains recombinant A and B chromosomes from two different T. turgidum genotypes, while all the D chromosomes from Ae. tauschii are homogenous across the whole population. This paper reports the construction of a genetic map using this population. RESULTS: Of the 606 markers used to assemble the genetic map, 588 (97%) were assigned to linkage groups. These included 513 Diversity Arrays Technology (DArT) markers, 72 simple sequence repeat (SSR), one insertion site-based polymorphism (ISBP), and two high-molecular-weight glutenin subunit (HMW-GS) markers. These markers were assigned to the 14 chromosomes, covering 2048.79 cM, with a mean distance of 3.48 cM between adjacent markers. This map showed good coverage of the A and B genome chromosomes, apart from 3A, 5A, 6A, and 4B. Compared with previously reported maps, most shared markers showed highly consistent orders. This map was successfully used to identify five quantitative trait loci (QTL), including two for spikelet number on chromosomes 7A and 5B, two for spike length on 7A and 3B, and one for 1000-grain weight on 4B. However, differences in crossability QTL between the two T. turgidum parents may explain the segregation distortion regions on chromosomes 1A, 3B, and 6B. CONCLUSIONS: A genetic map of T. turgidum including 588 markers was constructed using a synthetic doubled haploid (SynDH) hexaploid wheat population. Five QTLs for three agronomic traits were identified from this population. However, more markers are needed to increase the density and resolution of this map in the future study.     

QTL for root angle and number in a population developed from bread wheats (Triticum aestivum) with contrasting adaptation to water-limited environments

Root architecture traits in wheat are important in deep soil moisture acquisition and may be used to improve adaptation to water-limited environments. The genetic architecture of two root traits, seminal root angle and seminal root number, were investigated using a doubled haploid population derived from SeriM82 and Hartog. Multiple novel quantitative trait loci (QTL) were identified, each one having a modest effect. For seminal root angle, four QTL (?log₁₀(P) >3) were identified on 2A, 3D, 6A and 6B, and two suggestive QTL (?log₁₀(P) >2) on 5D and 6B. For root number, two QTL were identified on 4A and 6A with four suggestive QTL on 1B, 3A, 3B and 4A. QTL for root angle and root number did not co-locate. Transgressive segregation was found for both traits. Known major height and phenology loci appear to have little effect on root angle and number. Presence or absence of the T1BL.1RS translocation did not significantly influence root angle. Broad sense heritability (h ²) was estimated as 50 % for root angle and 31 % for root number. Root angle QTL were found to be segregating between wheat cultivars adapted to the target production region indicating potential to select for root angle in breeding programs.     

Association Mapping and Validation of QTLs for Flour Yield in the Soft Winter Wheat Variety Kitahonami

The winter wheat variety Kitahonami shows a superior flour yield in comparison to other Japanese soft wheat varieties. To map the quantitative trait loci (QTL) associated with this trait, association mapping was performed using a panel of lines from Kitahonami’s pedigree, along with leading Japanese varieties and advanced breeding lines. Using a mixed linear model corrected for kernel types and familial relatedness, 62 marker-trait associations for flour yield were identified and classified into 21 QTLs. In eighteen of these, Kitahonami alleles showed positive effects. Pedigree analysis demonstrated that a continuous pyramiding of QTLs had occurred throughout the breeding history of Kitahonami. Linkage analyses using three sets of doubled haploid populations from crosses in which Kitahonami was used as a parent were performed, leading to the validation of five of the eight QTLs tested. Among these, QTLs on chromosomes 3B and 7A showed highly significant and consistent effects across the three populations. This study shows that pedigree-based association mapping using breeding materials can be a useful method for QTL identification at the early stages of breeding programs.     

Identification of novel quantitative trait loci for days to ear emergence and flag leaf glaucousness in a bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) population adapted to southern Australian conditions

In southern Australia, where the climate is predominantly Mediterranean, achieving the correct flowering time in bread wheat minimizes the impact of in-season cyclical and terminal drought. Flag leaf glaucousness has been hypothesized as an important component of drought tolerance but its value and genetic basis in locally adapted germplasm is unknown. From a cross between Kukri and RAC875, a doubled-haploid (DH) population was developed. A genetic linkage map consisting of 456 DArT and SSR markers was used to detect QTL affecting time to ear emergence and Zadoks growth score in seven field experiments. While ear emergence time was similar between the parents, there was significant transgressive segregation in the population. This was the result of segregation for the previously characterized Ppd-D1a and Ppd-B1 photoperiod responsive alleles. QTL of smaller effect were also detected on chromosomes 1A, 4A, 4B, 5A, 5B, 7A and 7B. A novel QTL for flag leaf glaucousness of large, repeatable effect was detected in six field experiments, on chromosome 3A (QW.aww-3A) and accounted for up to 52 percent of genetic variance for this trait. QW.aww-3A was validated under glasshouse conditions in a recombinant inbred line population from the same cross. The genetic basis of time to ear emergence in this population will aid breeders’ understanding of phenological adaptation to the local environment. Novel loci identified for flag leaf glaucousness and the wide phenotypic variation within the DH population offers considerable scope to investigate the impact and value of this trait for bread wheat production in southern Australia.     

Identification and validation of a major cadmium accumulation locus and closely associated SNP markers in North Dakota durum wheat cultivars

Durum wheat has the tendency of accumulating more cadmium (Cd), a biotoxic heavy metal, in seeds than other commonly grown cereals, thus posing a serious food safety/public health concern. This could have serious negative impact on the national pasta industry and the international export market of durum wheat. The phenotyping for selecting low Cd lines is expensive and time consuming. The use of markers could be a more sustainable approach for selecting lines with low Cd levels. Here, a RIL population developed from a cross between Grenora (high Cd) × Haurani (low Cd) and two association mapping panels consisting of advanced breeding lines from the North Dakota durum wheat breeding program were used to identify QTL and associated markers for Cd. A major QTL, with Haurani contributing low Cd uptake allele and explaining 54.3 % phenotypic variation, was detected on chromosome 5BL. Association mapping using 2010 collection validated the results of linkage mapping and identified major QTL on 5BL. The 2009 collection, showed the presence of a major QTL on chromosome 2B. The SNP marker associated with major QTL on 5BL was converted to user friendly KASPar assay. The major QTL and associated KASPar marker were further validated using another RIL population developed from a cross of Strongfield (low Cd) and Alkabo (high Cd). The development of suitable marker assay, associated with major Cd uptake QTL, would help the selection for low Cd accumulating lines, minimizing the costly phenotypic evaluation for this important trait.