Molecular characterization of field resistance to Fusarium head blight in two US soft red winter wheat cultivars

In the soft red winter wheat (Triticum aestivum L.) regions of the US, Fusarium head blight (FHB, caused by Fusarium spp.) resistance derived from locally adapted germplasm has been used predominantly. Two soft red winter wheat cultivars, Massey and Ernie, have moderate resistance to FHB. Mapping populations derived from Becker/Massey (B/M) and Ernie/MO 94-317 (E/MO) were evaluated for FHB resistance and other traits in multiple environments. Eight QTL in B/M and five QTL in E/MO were associated with FHB variables including incidence, severity (SEV), index (IND), Fusarium damaged kernels (FDK), deoxynivalenol (DON), and morphological traits flowering time and plant height. Four QTL were common to both populations. Three of them were located at or near known genes: Ppd-D1 on chromosome 2DS, Rht-B1 on 4BS, and Rht-D1 on 4DS. Alleles for dwarf plant height (Rht-B1b and Rht-D1b) and photoperiod insensitivity (Ppd-D1a) had pleiotropic effects in reducing height and increasing FHB susceptibility. The other QTL detected for FHB variables were on 3BL in both populations, 1AS, 1DS, 2BL, and 4DL in B/M, and 5AL (B1) and 6AL in E/MO. The additive effects of FHB variables ranged from 0.4 mg kg^?1 of DON to 6.2 % for greenhouse (GH) SEV in B/M and ranged from 0.3 mg kg^?1 of DON to 8.3 % for GH SEV in E/MO. The 4DS QTL had epistasis with Ppd-D1, Qdon.umc-6AL, and Qht.umc-4BS, and additive × additive × environment interactions with the 4BS QTL for SEV, IND, and FDK in E/MO. Marker-assisted selection might be used to enhance FHB resistance through selection of favorable alleles of significant QTL, taking into account genotypes at Rht-B1b, Rht-D1a and Ppd-D1a.     

Molecular mapping of QTL for Fusarium head blight resistance introgressed into durum wheat

Key message

The major QTL for FHB resistance from hexaploid wheat line PI 277012 was successfully introgressed into durum wheat and minor FHB resistance QTL were detected in local durum wheat cultivars. A combination of these QTL will enhance FHB resistance of durum wheat.

Abstract

Fusarium head blight (FHB), caused by Fusarium graminearum, is a devastating disease of durum wheat. To combat the disease, great efforts have been devoted to introgress FHB resistance from its related tetraploid and hexaploid wheat species into adapted durum cultivars. However, most of the quantitative trait loci (QTL) for FHB resistance existing in the introgression lines are not well characterized or validated. In this study, we aimed to identify and map FHB resistance QTL in a population consisting of 205 recombinant inbred lines from the cross between Joppa (a durum wheat cultivar) and 10Ae564 (a durum wheat introgression line with FHB resistance derived from the hexaploid wheat line PI 277012). One QTL (Qfhb.ndwp-2A) from Joppa and two QTL (Qfhb.ndwp-5A and Qfhb.ndwp-7A) from 10Ae564 were identified through phenotyping of the mapping population for FHB severity and DON content in greenhouse and field and genotyping with 90K wheat Infinium iSelect SNP arrays. Qfhb.ndwp-2A explained 14, 15, and 9% of the phenotypic variation, respectively, for FHB severity in two greenhouse experiments and for mean DON content across the two greenhouse environments. Qfhb.ndwp-5A explained 19, 10, and 7% of phenotypic variation, respectively, for FHB severity in one greenhouse experiment, mean FHB severity across two field experiments, and mean DON content across the two greenhouse experiments. Qfhb.ndwp-7A was only detected for FHB severity in the two greenhouse experiments, explaining 9 and 11% of the phenotypic variation, respectively. This study confirms the existence of minor QTL in North Dakota durum cultivars and the successful transfer of the major QTL from PI 277012 into durum wheat.

     

Pyramiding QTL increases seedling resistance to crown rot (Fusarium pseudograminearum) of wheat (Triticum aestivum)

Crown rot of wheat (Triticum aestivum), predominantly caused by the fungus Fusarium pseudograminearum, has become an increasingly important disease constraint in many winter cereal production regions in Australia. Our group has previously identified a range of quantitative trait loci (QTL) for partial resistance to crown rot in various bread wheat sources. Here, we report on work that has assessed the effectiveness of pyramiding QTL to improve resistance to crown rot. Two doubled haploid populations were analysed—one from a cross between two previously characterised sources of partial seedling resistance (2-49 and W21MMT70; n = 208) and one from a cross between 2-49 and the commercial variety Sunco, a source of adult field resistance (n = 134). Both populations were phenotyped for seedling resistance to crown rot. Microsatellite and DArT markers were used to construct whole genome linkage maps for use in composite interval mapping (CIM) to identify QTL. Three QTL were detected in both trials conducted on the 2-49/W21MMT70 population. These were located on chromosomes 1D (QCr.usq-1D.1), 3B (QCr.usq-3B.1) and 7A. QCr.usq-1D.1 and the previously undetected 7A QTL were inherited from 2-49. QCr.usq-3B.1, inherited from W21MMT70, was the most significant of the QTL, explaining up to 40.5% of the phenotypic variance. Three QTL were identified in multiple trials of the Sunco/2-49 population. These were located on chromosomes 1D (QCr.usq-1D.1), 2B (QCr.usq-2B.2) and 4B (QCr.usq-4B.1). Only QCr.usq-2B.2 was inherited from Sunco. QCr.usq-4B.1 was the most significant of these QTL, explaining up to 19.1% of the phenotypic variance. In the 2-49/W21MMT70 population, several DH lines performed significantly better than either parent, with the best recording an average disease severity rating of only 3.8% of that scored by the susceptible check cultivar Puseas. These lines represent a new level of seedling crown rot resistance in wheat.     

Stacking quantitative trait loci (QTL) for Fusarium head blight resistance from non-adapted sources in an European elite spring wheat background and assessing their effects on deoxynivalenol (DON) content and disease severity

Fusarium head blight (FHB) is a devastating disease in wheat that reduces grain yield, grain quality and contaminates the harvest with deoxynivalenol (DON). As potent resistance sources Sumai 3 and its descendants from China and Frontana from Brazil had been analysed by quantitative trait loci (QTL) mapping. We introgressed and stacked two donor QTL from CM82036 (Sumai 3/Thornbird) located on chromosomes 3B and 5A and one donor QTL from Frontana on chromosome 3A in elite European spring wheat and estimated the effects of the three individual donor QTL and their four combinations on DON, Fusarium exoantigen content, and FHB rating adjusted to heading date. One class with the susceptible QTL alleles served as control. Each of the eight QTL classes was represented by 12–15 F₃-derived lines tested in F₅ generation as bulked progeny possessing the respective marker alleles homozygously. Traits were evaluated in a field experiment across four locations with spray inoculation of Fusarium culmorum. All three individual donor-QTL alleles significantly reduced DON content and FHB severity compared to the marker class with no donor QTL. The only exception was the donor-QTL allele 3A that had a low, but non-significant effect on FHB severity. The highest effect had the stacked donor-QTL alleles 3B and 5A for both traits. They jointly reduced DON content by 78% and FHB rating by 55% compared to the susceptible QTL class. Analysis of Fusarium exoantigen content illustrates that lower disease severity is associated with less mycelium content in the grain. In conclusion, QTL from non-adapted sources could be verified in a genetic background of German elite spring wheat. Within the QTL classes significant (P<0.05) genotypic differences were found among the individual genotypes. An additional phenotypic selection would, therefore, be advantageous after performing a marker-based selection.     

Anther extrusion and plant height are associated with Type I resistance to Fusarium head blight in bread wheat line ‘Shanghai-3/Catbird’

Fusarium head blight (FHB) is a destructive wheat disease of global importance. Resistance breeding depends heavily on the Fhb1 gene. The CIMMYT line Shanghai-3/Catbird (SHA3/CBRD) is a promising source without this gene. A recombinant inbred line (RIL) population from the cross of SHA3/CBRD with the German spring wheat cv. Naxos was evaluated for FHB resistance and related traits in field trials using spray and spawn inoculation in Norway and point inoculation in China. After spray and spawn inoculation, FHB severities were negatively correlated with both anther extrusion (AE) and plant height (PH). The QTL analysis showed that the Rht-B1b dwarfing allele co-localized with a QTL for low AE and increased susceptibility after spawn and spray inoculation. In general, SHA3/CBRD contributed most of the favorable alleles for resistance to severity after spray and spawn inoculation, while Naxos contributed more favorable alleles for reduction in FDK and DON content and resistance to severity after point inoculation. SHA3/CBRD contributed a major resistance QTL close to the centromere on 2DLc affecting FHB severity and DON after all inoculation methods. This QTL was also associated with AE and PH, with high AE and tall alleles contributed by SHA3/CBRD. Several QTL for AE and PH were detected, and low AE or reduced PH was always associated with increased susceptibility after spawn and spray inoculation. Most of the other minor FHB resistance QTL from SHA3/CBRD were associated with AE or PH, while the QTL from Naxos were mostly not. After point inoculation, no other QTL for FHB traits was associated with AE or PH, except the 2DLc QTL which was common across all inoculation methods. Marker-assisted selection based on the 2DLc QTL from SHA3/CBRD combined with phenotypic selection for AE is recommended for resistance breeding based on this valuable source of resistance.     

<Emphasis Type="Italic">Rht24</Emphasis> reduces height in the winter wheat population ‘Solitär × Bussard’ without adverse effects on Fusarium head blight infection

Key message

The dwarfing gene Rht24 on chromosome 6A acts in the wheat population ‘Solitär × Bussard’, considerably reducing plant height without increasing Fusarium head blight severity and delaying heading stage.

Abstract

The introduction of the Reduced height (Rht)-B1 and Rht-D1 semi-dwarfing genes led to remarkable increases in wheat yields during the Green Revolution. However, their utilization also brings about some unwanted characteristics, including the increased susceptibility to Fusarium head blight. Thus, Rht loci that hold the potential to reduce plant height in wheat without concomitantly increasing Fusarium head blight (FHB) susceptibility are urgently required. The biparental population ‘Solitär × Bussard’ fixed for the Rht-1 wild-type alleles, but segregating for the recently described gibberellic acid (GA)-sensitive Rht24 gene, was analyzed to identify quantitative trait loci (QTL) for FHB severity, plant height, and heading date and to evaluate the effect of the Rht24 locus on these traits. The most prominent QTL was Rht24 on chromosome 6A explaining 51% of genotypic variation for plant height and exerting an additive effect of ? 4.80 cm. For FHB severity three QTL were detected, whereas five and six QTL were found for plant height and heading date, respectively. No FHB resistance QTL was co-localized with QTL for plant height. Unlike the Rht-1 semi-dwarfing alleles, Rht24b did not significantly affect FHB severity. This demonstrates that the choice of semi-dwarfing genes used in plant breeding programs is of utmost consideration where resistance to FHB is an important breeding target.

     

Quantitative trait loci controlling aluminum tolerance in soybean: candidate gene and single nucleotide polymorphism marker discovery

Aluminum (Al) toxicity is an important abiotic stress that affects soybean production in acidic soils throughout the world. Development of Al-tolerant cultivars is an efficient and environmentally friendly solution to the problem. A previous report identified quantitative trait loci (QTL) for Al tolerance inherited from PI 416937, using restriction fragment length polymorphism markers, in a population of Young × PI 416937. The population was genotyped with 162 simple sequence repeats to enhance the power of QTL detection and enable the selection of candidate genes for functional marker development. Two QTL that explained 54 % of the phenotypic variation in root extension under Al stress conditions (HIAL) were refined on chromosomes (chr) Gm08 and Gm16. Three QTL located on chr Gm08, Gm16 and Gm19 explained 59 % of the phenotypic variation in root extension as a percent of control (PC). Two major QTL, designated qAL_HIAL_08 and qAL_PC_08, controlling HIAL and PC, respectively, were mapped to the same genomic region on chr Gm08 and inherited their favorable allele from PI 416937. These QTL explained 45 and 41 % of phenotypic variation in HIAL and PC, respectively. Six homologues for citrate synthase (CS) genes were found in the soybean genome sequence at chr Gm02, Gm08, Gm14, Gm15, and Gm18. Sixteen single nucleotide polymorphisms (SNPs) were identified in the CS homologue on chr Gm08. A SimpleProbe assay of Glyma08g42400-SNP was developed for the major QTL on chr Gm08. The SNPs identified from this region could be used for marker-assisted selection of Al tolerance.     

Using near-isogenic barley lines to validate deoxynivalenol (DON) QTL previously identified through association analysis

Fusarium head blight (FHB) and its associated mycotoxin, deoxynivalenol (DON), are the major biotic factors limiting cereal production in many parts of the world. A recent association mapping (AM) study of US six-row spring barley identified several modest effect quantitative trait loci (QTL) for DON and FHB. To date, few studies have attempted to verify the results of association analyses, particularly for complex traits such as DON and FHB resistance in barley. While AM methods use measures to control for the effects of population structure and multiple testing, false positive associations may still occur. A previous AM study used elite breeding germplasm to identify QTL for FHB and DON. To verify the results of that study, we evaluated the effects of the nine DON QTL using near-isogenic lines (NILs). We created families of contrasting homozygous haplotypes from lines in the original AM populations that were heterozygous for the DON QTL. Seventeen NIL families were evaluated for FHB and DON in three field experiments. Significant differences between contrasting NIL haplotypes were detected for three QTL across environments and/or genetic backgrounds, thereby confirming QTL from the original AM study. Several explanations for those QTL that were not confirmed are discussed, including the effect of genetic background and incomplete sampling of relevant haplotypes.     

Genotyping-by-sequencing to remap QTL for type II Fusarium head blight and leaf rust resistance in a wheat–tall wheatgrass introgression recombinant inbred population

Fusarium graminearum Schwabe (Fusarium head blight, FHB) and Puccinia triticina Eriks (leaf rust) are two major fungal pathogens posing a continuous threat to the wheat crop; consequently, identifying resistance genes from various sources is always of importance to wheat breeders. We identified tightly linked single nucleotide polymorphism (SNP) markers for the FHB resistance quantitative trait locus (QTL) Qfhs.pur-7EL and the leaf rust resistance locus Lr19 using genotyping-by-sequencing (GBS) in a wheat–tall wheatgrass introgression-derived recombinant inbred line (RIL) population. One thousand and seven hundred high-confidence SNPs were used to conduct the linkage and QTL analysis. Qfhs.pur-7EL was mapped to a 2.9 cM region containing four markers within a 43.6 cM segment of wheatgrass chromosome 7el₂ that was translocated onto wheat chromosome 7DL. Lr19 from 7el₁ was mapped to a 1.21 cM region containing two markers in the same area, in repulsion. Five lines were identified with the resistance-associated SNP alleles for Qfhs.pur-7EL and Lr19 in coupling. Two SNP markers in the Qfhs.pur-7EL region were converted into PCR-based KASP markers. Investigation of the genetic characteristics of the parental lines of this RIL population indicated that they are translocation lines in two different wheat cultivar genetic backgrounds instead of 7E–7D substitution lines in Thatcher wheat background, as previously reported in the literature.     

Novel SNPs in the bovine ADIPOQ and PPARGC1A genes are associated with carcass traits in Hanwoo (Korean cattle)

Adiponectin (ADIPOQ) modulates several biological processes including energy homeostasis, glucose and lipid metabolism. The bovine ADIPOQ gene was located near the QTL affecting marbling, ribeye muscle area and fat thickness on BTA1. The gene encoding peroxisome proliferator-activated receptor-γ coactivator-1α (PPARGC1A) was located within the QTL region of the traits on BTA6. Moreover, its protein product has various biological functions such as cellular energy homeostasis, including adaptive thermogenesis, adipogenesis and gluconeogenesis. Therefore, the ADIPOQ and PPARGC1A genes are a positional and functional candidate gene for carcass traits in beef cattle. The objectives of this study were to identify polymorphisms in the bovine ADIPOQ and PPARGC1A genes, to evaluate their associations with carcass traits in Hanwoo (Korean cattle) population. We identified nine SNPs in the ADIPOQ gene. Two SNPs (DQ156119: g.1436T > C and DQ156119: g.1454A > G) in the promoter region were recognized as new SNPs identified in Hanwoo. Association analysis indicated that the g.1454A > G SNP genotype was significantly associated with effects on LMA (P = 0.004) and BF (P = 0.021). The ADIPOQ haplotype was also found to have significant effect on the LMA. In the PPARGC1A gene, we identified 11 SNPs in the two unexplored regions (intron 3 and 5). Among them, seven SNPs were located in intron 3 and four SNPs were located in intron 5. Of these 11 putative novel SNPs, two SNPs (AY839822: g.292C > T and AY839823: g.1064C > T) with minor allele frequency (MAF) > 0.20 were examined for associations with carcass traits. The association analysis revealed that both SNPs in PPARGC1A gene were significantly associated with LMA (P < 0.05). These findings suggest that the SNPs of bovine ADIPOQ and PPARGC1A genes may be a useful molecular marker for selection of carcass traits in Hanwoo.     

Mapping of durable stripe rust resistance in a durum wheat cultivar Wollaroi

Wollaroi, an Australian durum wheat cultivar, produced a low stripe rust response and the alternative parent Bansi was highly susceptible. The Wollaroi/Bansi recombinant inbred line (RIL) population was phenotyped across three consecutive crop seasons. A genetic map of the Wollaroi/Bansi RIL population comprising 799 markers (diversity arrays technology and simple sequence repeat markers) was used to determine the genomic location of stripe rust resistance genes carried by the cultivar Wollaroi. Composite interval mapping detected three consistent quantitative trait loci (QTL) in chromosomes 2A, 3B and 5B. These QTL were named QYr.sun-2A, QYr.sun-3B and QYr.sun-5B. Another QTL, QYr.sun-1B, was detected only in the 2009 crop season. QTL in chromosomes 1B, 2A, 3B and 5B explained on average 6, 9.3, 26.7 and 8.7 %, respectively, of the variation in stripe rust response. All QTL were contributed by Wollaroi. RILs carrying these QTL singly produced intermediate stripe rust severities ranging from 46.2 to 55.7 %, whereas RILs with all four QTL produced the lowest disease severity (34.3 %). The consistently low stripe rust response of Wollaroi for 20 years demonstrated the durability of the resistance loci involved. The QTL combination detected in this study is being transferred to common wheat.     

Multiple loci associated with canine hip dysplasia (CHD) in German shepherd dogs

Canine hip dysplasia (CHD) is the most common hereditary skeletal disorder in dogs. To identify common alleles associated with CHD, we developed 37 informative single nucleotide polymorphisms (SNPs) within 13 quantitative trait loci (QTL) previously identified for German shepherd dogs. These SNPs were genotyped in 95 German shepherd dogs affected by CHD and 95 breed, sex, and birth year-matched controls. A total of ten SNPs significant at a nominal P value of 0.05 were validated in 843 German shepherd dogs including 277 unaffected dogs and 566 CHD-affected dogs. Cases and controls were sampled from the whole German shepherd dog population in Germany in such a way that mean coancestry coefficients were below 0.1 % within cases and controls as well as among cases and controls. We identified nine SNPs significantly associated with CHD within five QTL on dog chromosomes (CFA) 3, 9, 26, 33, and 34. Genotype effects of these nine SNPs explained between 22 and 34 % of the phenotypic variance of hip dysplasia in German shepherd dogs. The strongest associated SNPs were located on CFA33 and 34 within the candidate genes PNCP, TRIO, and SLC6A3. Thus, the present study validated positional candidate genes within five QTL for CHD.     

Genetic mapping of QTL for resistance to Fusarium head blight spread (type 2 resistance) in a Triticum dicoccoides × Triticum durum backcross-derived population

Improvement of resistance to Fusarium head blight (FHB) is a continuous challenge for durum wheat breeders, particularly due to the limited genetic variation within this crop species. We accordingly generated a backcross-derived mapping population using the type 2 FHB resistant Triticum dicoccoides line Mt. Gerizim #36 as donor and the modern Austrian T. durum cultivar Helidur as recipient; 103 BC₁F_6:7 lines were phenotyped for type 2 FHB resistance using single-spikelet inoculations and genotyped with 421 DNA markers (SSR and AFLP). QTL mapping revealed two highly significant QTL, mapping to chromosomes 3A and 6B, respectively. For both QTL the T. dicoccoides allele improved type 2 FHB resistance. Recombinant lines with both favorable alleles fixed conferred high resistance to FHB similar to that observed in the T. dicoccoides parent. The results appear directly applicable for durum wheat resistance breeding.     

Characterization of Yr54 and other genes associated with adult plant resistance to yellow rust and leaf rust in common wheat Quaiu 3

Leaf rust (LR) and yellow rust (YR), caused by Puccinia triticina and Puccinia striiformis f. sp. tritici, respectively, are important diseases of wheat. Quaiu 3, a common wheat line developed at the International Maize and Wheat Improvement Center (CIMMYT), is immune to YR in Mexico despite seedling susceptibility to predominant races. Quaiu 3 also shows immunity to LR in field trials and is known to possess the race-specific gene Lr42. A mapping population of 182 recombinant inbred lines (RILs) was developed by crossing Quaiu 3 with susceptible Avocet-YrA and phenotyped with LR and YR in field trials for 2 years in Mexico. Quantitative trait loci (QTL) associated with YR and LR resistance in the RILs were identified using Diversity Arrays Technology and simple sequence repeat markers. A large-effect QTL on the long arm of chromosome 2D explained 49–54 % of the phenotypic variation in Quaiu 3 and was designated as Yr54. Two additional loci on 1BL and 3BS explained 8–17 % of the phenotypic variation for YR and coincided with previously characterized adult plant resistance (APR) genes Lr46/Yr29 and Sr2/Yr30, respectively. QTL on 1DS and 1BL corresponding to Lr42 and Lr46/Yr29, respectively, contributed 60–71 % of the variation for LR resistance. A locus on 3D associated with APR to both diseases explained up to 7 % of the phenotypic variance. Additional Avocet-YrA-derived minor QTL were also detected for YR on chromosomes 1A, 3D, 4A, and 6A. Yr54 is a newly characterized APR gene which can be combined with other genes by using closely linked molecular markers.     

Identification of the quantitative trait loci (QTL) underlying water soluble protein content in soybean

Water soluble protein content (SPC) plays an important role in the functional efficacy of protein in food products. Therefore, for the identification of quantitative trait loci (QTL) associated with SPC, 212 F_2:9 lines of the recombinant inbred line (RIL) population derived from the cross of ZDD09454 × Yudou12 were grown along with the parents, in six different environments (location × year) to determine inheritance and map solubility-related genes. A linkage map comprising of 301 SSR markers covering 3,576.81 cM was constructed in the RIL population. Seed SPC was quantified with a macro-Kjeldahl procedure in samples collected over multiple years from three locations (Nantong in 2007 and 2008, Zhengzhou in 2007 and 2008, and Xinxiang in 2008 and 2009). SPC demonstrated transgressive segregation, indicating a complementary genetic structure between the parents. Eleven putative QTL were associated with SPC explaining 4.5–18.2 % of the observed phenotypic variation across the 6 year/location environments. Among these, two QTL (qsp8-4, qsp8-5) near GMENOD2B and Sat_215 showed an association with SPC in multiple environments, suggesting that they were key QTL related to protein solubility. The QTL × environment interaction demonstrated the complex genetic mechanism of SPC. These SPC-associated QTL and linked markers in soybean will provide important information that can be utilized by breeders to improve the functional quality of soybean varieties.     

Mapping of QTL for Fusarium head blight resistance and morphological and developmental traits in three backcross populations derived from Triticum dicoccum?×?Triticum durum

Breeding for resistance to Fusarium head blight (FHB) in durum wheat continues to be hindered by the lack of effective resistance sources. Only limited information is available on resistance QTL for FHB in tetraploid wheat. In this study, resistance to FHB of a Triticum dicoccum line in the background of three Austrian T. durum cultivars was genetically characterized. Three populations of BC₁F₄-derived RILs were developed from crosses between the resistant donor line T. dicoccum-161 and the Austrian T. durum recipient varieties DS-131621, Floradur and Helidur. About 130 BC₁F₄-derived lines per population were evaluated for FHB response using artificial spray inoculation in four field experiments during two seasons. Lines were genetically fingerprinted using SSR and AFLP markers. Genomic regions on chromosomes 3B, 4B, 6A, 6B and 7B were significantly associated with FHB severity. FHB resistance QTL on 6B and 7B were identified in two populations and a resistance QTL on 4B appeared in three populations. The alleles that enhanced FHB resistance were derived from the T. dicoccum parent, except for the QTL on chromosome 3B. All QTL except the QTL on 6A mapped to genomic regions where QTL for FHB have previously been reported in hexaploid wheat. QTL on 3B and 6B coincided with Fhb1 and Fhb2, respectively. This implies that tetraploid and hexaploid wheat share common genomic regions associated with FHB resistance. QTL for FHB resistance on 4B co-located with a major QTL for plant height and mapped at the position of the Rht-B1 gene, while QTL on 7B overlapped with QTL for flowering time.     

Comparison of phenotypic and marker-based selection for <Emphasis Type="Italic">Fusarium</Emphasis> head blight resistance and DON content in spring wheat

Fusarium head blight (FHB) is one of the most economically important wheat diseases, resulting in losses in grain yield and quality as well as contamination with deoxynivalenol (DON). Cultivar Sumai 3 from China and its descendants as well as var. Frontana from Brazil have been identified as potent sources of resistance and subsequently mapped by molecular markers. The aim of the present study was to compare phenotypic and marker-based selection in spring wheat. In a double cross, we combined two donor-quantitative trat loci (QTL) alleles from CM82036 (Sumai 3/Thornbird) located on chromosomes 3B and 5A and one donor-QTL allele from var. Frontana on chromosome 3A with two high-yielding German spring wheat varieties. This initial population was selected phenotypically by a two- (CP1) and three-step procedure (CP1⁺) and by independent marker-based analysis using one to three flanking markers per QTL (CM). To estimate selection gain, the two phenotypically selected variants and the marker-selected variant as well as an unselected variant (C0) were inoculated with FHB in the field at four locations in 2004. Between 26 and 135 progeny were tested from each variant. FHB severity and DON content were significantly reduced by all selection variants. The highest total selection gain was obtained by the three-step phenotypic selection for both traits, although marker-based selection for the two donor-QTL alleles from CM82036 proved to be more powerful on an annual basis. The large range of variation for FHB resistance and, to a lesser extent, DON content within the marker-based variant, however, shows that an additional phenotypic selection will enhance selection gain.     

Quantitative trait loci for resistance to fusarium head blight in a Chinese wheat landrace Haiyanzhong

Fusarium head blight (FHB) of wheat causes not only significant reduction in grain yield and end-use quality, but also the contamination of the grain with mycotoxins that are detrimental to human and animal health after consumption of infected grain. Growing resistant varieties is an effective approach to minimize the FHB damage. The Chinese wheat landrace Haiyanzhong (HYZ) shows a high level of resistance to FHB. To identify quantitative trait loci (QTL) that contribute to FHB resistance in HYZ, 136 recombinant inbred lines (RIL) were developed from a cross of HYZ and Wheaton, a hard spring wheat cultivar from the USA. The RIL and their parents were evaluated for percentage of scabbed spikelets (PSS) in both greenhouse and field environments. Five QTL were detected for FHB resistance in HYZ with one major QTL on 7DL. The 7DL QTL peaked at SSR marker Xwmc121, which is flanked by the SSR markers Xcfd46 and Xwmc702. This QTL explained 20.4?C22.6% of the phenotypic variance in individual greenhouse experiments and 15.9% in a field experiment. Four other minor QTL on 6BS (two QTL), 5AS and 1AS each explained less than 10% of the phenotypic variance in individual experiments. HYZ carried the favorable alleles associated with FHB resistance at the QTL on 7DL, 6BS and 5AS, and the unfavorable allele at the QTL on 1AS. The major QTL on 7D can be used to improve the FHB resistance in wheat breeding programs and add diversity to the FHB resistance gene pool.     

High density SNP mapping and QTL analysis for fruit quality characteristics in peach (Prunus persica L.)

Single nucleotide polymorphisms (SNPs) were used to construct an integrated SNP linkage map of peach (Prunus persica (L.) Batsch). A set of 1,536 SNPs were evaluated with the GoldenGate® Genotyping assay in two mapping populations, Pop-DF, and Pop-DG. After genotyping and filtering, a final set of 1,400 high quality SNPs in Pop-DF and 962 in Pop-DG with full map coverage were selected and used to construct two linkage maps with JoinMap®4.0. The Pop-DF map covered 422 cM of the peach genome and included 1,037 SNP markers, and Pop-DG map covered 369 cM and included 738 SNPs. A consensus map was constructed with 588 SNP markers placed in eight linkage groups (n?=?8 for peach), with map coverage of 454 cM and an average distance of 0.81 cM/marker site. Placements of SNPs on the “peach v1.0” physical map were compared to placement on the linkage maps and several differences were observed. Using the SNP linkage map of Pop-DG and phenotypic data collected for three harvest seasons, a QTL analysis for fruit quality traits and chilling injury symptoms was carried out with the mapped SNPs. Significant QTL effects were detected for mealiness (M) and flesh bleeding (FBL) QTLs on linkage group 4 and flesh browning (FBr) on linkage group 5. This study represents one of the first examples of QTL detection for quality traits and chilling injury symptoms using a high-density SNP map in a single peach F1 family.     

Construction of an integrative linkage map and QTL mapping of grain yield-related traits using three related wheat RIL populations

Key message

A novel high-density consensus wheat genetic map was obtained based on three related RIL populations, and the important chromosomal regions affecting yield and related traits were specified.

Abstract

A prerequisite for mapping quantitative trait locus (QTL) is to build a genetic linkage map. In this study, three recombinant inbred line populations (represented by WL, WY, and WJ) sharing one common parental line were used for map construction and subsequently for QTL detection of yield-related traits. PCR-based and diversity arrays technology markers were screened in the three populations. The integrated genetic map contains 1,127 marker loci, which span 2,976.75 cM for the whole genome, 985.93 cM for the A genome, 922.16 cM for the B genome, and 1,068.65 cM for the D genome. Phenotypic values were evaluated in four environments for populations WY and WJ, but three environments for population WL. Individual and combined phenotypic values across environments were used for QTL detection. A total of 165 putative additive QTL were identified, 22 of which showed significant additive-by-environment interaction effects. A total of 65 QTL (51.5 %) were stable across environments, and 23 of these (35.4 %) were common stable QTL that were identified in at least two populations. Notably, QTkw-5B.1, QTkw-6A.2, and QTkw-7B.1 were common major stable QTL in at least two populations, exhibiting 11.28–16.06, 5.64–18.69, and 6.76–21.16 % of the phenotypic variance, respectively. Genetic relationships between kernel dimensions and kernel weight and between yield components and yield were evaluated. Moreover, QTL or regions that commonly interact across genetic backgrounds were discussed by comparing the results of the present study with those of previous similar studies. The present study provides useful information for marker-assisted selection in breeding wheat varieties with high yield.