Precise mapping Fhb5, a major QTL conditioning resistance to Fusarium infection in bread wheat (Triticum aestivum L.)

Qfhi.nau-5A is a major quantitative trait locus (QTL) against Fusarium graminearum infection in the resistant wheat germplasm Wangshuibai. Genetic analysis using BC(3)F(2) and BC(4)F(2) populations, derived from selfing two near-isogenic lines (NIL) heterozygous at Qfhi.nau-5A that were developed, respectively, with Mianyang 99-323 and PH691 as the recurrent parent, showed that Qfhi.nau-5A inherited like a single dominant gene. This QTL was thus designated as Fhb5. To fine map it, these two backcross populations and a recombinant inbred line (RIL) population derived from Nanda2419?×?Wangshuibai were screened for recombinants occurring between its two flanking markers Xbarc56 and Xbarc100. Nineteen NIL recombinants were identified from the two backcross populations and nine from the RIL population. In the RIL recombinant selection process, selection against Fhb4 present in the RIL population was incorporated. Genotyping these recombinant lines with ten markers mapping to the Xbarc56-Xbarc100 interval revealed four types of Mianyang 99-323-derived NIL recombinants, three types of PH691-derived NIL recombinants, and four types of RIL recombinants. In different field trials, the percentage of infected spikes of these lines displayed a distinct two-peak distribution. The more resistant class had over 55% less infection than the susceptible class. Common to these resistant genotypes, the 0.3-cM interval flanked by Xgwm304 and Xgwm415 or one of these two loci was derived from Wangshuibai, while none of the susceptible recombinants had Wangshuibai chromatin in this interval. This interval harboring Fhb5 was mapped to the pericentromeric C-5AS3-0.75 bin through deletion bin mapping. The precise localization of Fhb5 will facilitate its utilization in marker-assisted wheat breeding programs.     

Fine mapping TaFLW1, a major QTL controlling flag leaf width in bread wheat (Triticum aestivum L.)

Introduction

Flag leaf width (FLW) is directly related to photosynthetic capacity and yield potential in wheat. In a previous study, Qflw.nau-5A controlling FLW was detected on chromosome 5A in the interval possessing Fhb5 for type I Fusarium head blight (FHB) resistance using a recombinant inbred line population derived from Nanda2419 × Wangshuibai.

Materials and methods

Qflw.nau-5A near-isogenic line (NIL) with the background of Mianyang 99-323 and PH691 was developed and evaluated. FLW inheritance was investigated using two F₂ populations developed from crossing the Qflw.nau-5A NILs with their recurrent parents. One hundred ten and 28 recombinants, which included 10 and 5 types of recombinants, were identified from 2816 F₂ plants with Mianyang 99-323 background and 1277 F₂ plants with PH691 background, respectively, and phenotyped in field trials for FLW and type I FHB resistance. Deletion bin mapping was applied to physically map Qflw.nau-5A.

Results and conclusions

The introduction of Wangshuibai Qflw.nau-5A allele reduced the FLW up to 3 mm. In the F₂ populations, Qflw.nau-5A was inherited like a semi-dominant gene, and was therefore designated as TaFLW1. The FLW of the recombinant lines displayed a distinct two-peak distribution. Recombinants with wider leaves commonly have Mianyang 99-323 or PH691 chromatin in the 0.2 cM Xwmc492-Xwmc752 interval that resided in the 5AL12-0.35–0.57 deletion bin, and recombinants with narrow leaves were Wangshuibai genotype in this interval. Phenotypic recombination between FLW and type I FHB resistance was identified, implying TaFLW1 was in close linkage with Fhb5. These results should aid wheat breeders to break the linkage drag through marker-assisted selection and assist in the map-based cloning of TaFLW1.     

Marker-assisted development and evaluation of near-isogenic lines for scab resistance QTLs of wheat

Fusarium head blight or scab resistance in wheat is a complex quantitative trait affected greatly by environments. Therefore, the quantitative trait loci (QTL) for scab resistance found in mapping projects require validation to be effectively utilized in breeding programs. In this study, by employing both forward and background selections with the help of molecular markers, near-isogenic lines (NILs) for scab resistance QTLs Qfh.nau-2B, Qfhs.nau-3B, Qfhi.nau-4B and Qfhi.nau-5A, three of which originating in scab resistance germplasm Wangshuibai, were developed with the elite line Miangyang 99-323 as the recurrent parent. During the process of backcross, selection was based solely on marker genotypes of the target regions, and on recipient genome recovery rate in BC₂F₁ and BC₃F₁. All the identified BC₃F₁ plants with the target QTL regions have more than 94% recipient genome composition (RGC), and out of four to five of them a plant with over 97% RGC were obtained in each backcross combination. Compared with Mianyang 99-323, the Qfhs.nau-3B NIL showed much better resistance to disease spread within spikes, the Qfhi.nau-4B and Qfhi.nau-5A NILs showed much better resistance to initial infection, and the Qfh.nau-2B NIL showed improvement in both types of resistance. These results were consistent with findings in the previous QTL mapping studies. Morphologically and agronomically these NILs were similar to Mianyang 99-323 except that Qfhi.nau-4B NIL was taller and had a longer spike, and Qfhi.nau-5A NIL had narrower leaves. These results demonstrated the feasibility of marker-assisted utilization of scab resistance QTLs.     

Mapping QTL associated with resistance to Fusarium head blight in the Nanda2419 × Wangshuibai population. II: Type I resistance

Fusarium head blight (FHB) is a serious disease in wheat and barley affecting both yield and quality. To identify genes for resistance to infection, the RIL population derived from ‘Nanda2419’ × ‘Wangshuibai’ and the parents were evaluated for percentage of infected spikes (PIS) in four different environments. Using a 2,960 cM marker framework map constructed for this population, ten chromosome regions were detected for their association with type I resistance through interval mapping with Mapmaker/QTL, among which QTLs mapped in the intervals of Xwmc349~Xgwm149 on chromosome 4B, of Xwmc96~Xgwm304 on chromosome 5A and of Xgwm408~Xbarc140 on chromosome 5B were revealed in at least three environments and have Wangshuibai as the source of resistance alleles. Qfhi.nau-4B and Qfhi.nau-5A had larger effects and explained up to 17.5 and 27.0% of the phenotypic variance, respectively. To detect epistasis QTLs, two-locus interactions were examined by whole genome scan. Interactions of five locus pairs were found to have significant effects on type I resistance with the LOD score ranging 3.8–6.5 and four of them conferred resistance in parental phase. The one with the most significant effect was Xcfd42~Xgwm469 (6D)/Xwmc390-2~Xbd04 (2A) pair. No QTL × E interaction was detected for PIS. It was found that flowering time did not have significant effects on PIS in this population. Our studies indicated that Wangshuibai is useful for breeding for both type I and type II scab resistance and the markers associated with the QTLs could be used in marker-assisted selection and isolation of scab-resistance QTLs. F. Lin and S.L. Xue equally contributed to this article     

Efficacy of pyramiding elite alleles for dynamic development of plant height in common wheat

Plant height is an important botanical feature closely related to yield. Two populations consisting of 118 and 262 accessions respectively were used to identify elite alleles for plant height and to validate their allelic effects. Plant height was measured from the early booting to the flowering stages. Simple sequence repeat markers for candidate quantitative trait locus (QTL) regions with large effects identified in a doubled haploid (DH) population (Hanxuan 10 × Lumai 14) were selected for further verification by association analysis. Nine loci significantly (P < 0.001) associated with plant height were detected 13 times in the population with 118 accessions. Three loci (Xgwm11-1B, Xwmc349-4B and Xcfd23-4D) were identified in three, two and two periods of plant height growth, respectively. Markers Xbarc168-2D, Xgwm249-2D, Xwmc349-4B, Xcfd23-4D and Xgwm410-5A located at or near additive QTL regions in the DH population proved to coincide with known Rht loci. The results showed a consistency between linkage analysis and association mapping, and also confirmed the value of fine mapping of QTL through combined linkage and association analyses. For final plant height, the alleles Xgwm11-1B ₂₀₈ , Xwmc349-4B ₁₀₃ and Xcfd23-4D ₂₀₂ exhibited negative effects, i.e. reducing plant height; Xwmc349-4B ₁₀₁ and Xcfd23-4D ₂₀₅ showed significant positive effects. A second larger population (262 accessions) was used to validate the effects of these large-effect alleles and the efficacy of pyramiding in eight environments (year × site × water regime combinations). Strong correlations between final plant height and numbers of large-effect alleles indicated that the alleles contributed additively to plant height. The additive effects showed that pyramiding elite alleles for target traits has significant potential for wheat breeding.     

Precise mapping of a quantitative trait locus interval for spike length and grain weight in bread wheat (Triticum aestivum L.)

The spike characteristics length, spikelet density and fertile floret number are related yield components and are important in cereal improvement. QSpl.nau-2D is a major quantitative trait locus controlling spike length (SPL) detected in the recombinant inbred line population developed by crossing wheat (Triticum aestivum) cultivars Nanda2419 with Wangshuibai. In this study, to validate its genetic effect and determine its precise location, QSpl.nau-2D’s near-isogenic line (NIL) was developed using Mianyang99-323 as the recurrent parent through marker-assisted selection. Field trials showed that the NIL not only had significantly longer spikes on average than the recurrent parent but also had significantly higher grain weight, but did not differ in spikelet number and kernel number per spike. In the F2 population derived from a cross of the NIL with Mianyang99-323, QSpl.nau-2D functioned like a single gene and conditioned the SPL in a partially dominant manner, and was thus designated as HL1 (for head length). To precisely map HL1, 89 recombinants, consisting of 11 genotypes, were identified in the NIL-derived F2 population of 674 plants by using markers in the Xwmc25–Xgpw4080 interval. Phenotyping these lines showed that the introduction of a 0.9-cM interval flanked by Xcfd53 and DG371 in Nanda2419 resulted in longer spikes and a higher grain weight in the NIL. The availability of markers closely linked to HL1 could facilitate its use in breeding programs.     

Dissection and fine mapping of a major QTL for preharvest sprouting resistance in white wheat Rio Blanco

Preharvest sprouting (PHS) is a major constraint to white wheat production. Previously, we mapped quantitative trait loci (QTL) for PHS resistance in white wheat by using a recombinant inbred line (RIL) population derived from the cross Rio Blanco/NW97S186. One QTL, QPhs.pseru-3A, showed a major effect on PHS resistance, and three simple sequence repeat (SSR) markers were mapped in the QTL region. To determine the flanking markers for the QTL and narrow down the QTL to a smaller chromosome region, we developed a new fine mapping population of 1,874 secondary segregating F₂ plants by selfing an F6 RIL (RIL25) that was heterozygous in the three SSR marker loci. Segregation of PHS resistance in the population fitted monogenic inheritance. An additive effect of the QTL played a major role on PHS resistance, but a dominant effect was also observed. Fifty-six recombinants among the three SSR markers were identified in the population and selfed to produce homozygous recombinants or QTL near-isogenic lines (NIL). PHS evaluation of the recombinants delineated the QTL in the region close to Xbarc57 flanked by Xbarc321 and Xbarc12. To saturate the QTL region, 11 amplified fragment length polymorphism (AFLP) markers were mapped in the QTL region with 7 AFLP co-segregated with Xbarc57 by using the NIL population. Dissection of the QTL as a Mendelian factor and saturation of the QTL region with additional markers created a solid foundation for positional cloning of the major QTL.     

Putative Thinopyrum intermedium-derived stripe rust resistance gene Yr50 maps on wheat chromosome arm 4BL

Stripe rust-resistant wheat introgression line CH223 was developed by crossing the resistant partial amphiploid TAI7047 derived from Thinopyrum intermedium with susceptible cultivars. The resistance is effective against all the existing Chinese stripe rust races, including the most widely virulent and predominant pathotypes CYR32 and CYR33. Cytological analyses using GISH detected no chromosomal segments from Th. intermedium. It was presumed that the segment was too small to be detected. Normal bivalent pairing at meiosis in CH223 and its hybrids confirmed its stability. Genetic analysis of the F₁, F₂, F₃ and BC₁ populations from crosses of CH223 with susceptible lines indicated that resistance was controlled by a single dominant gene. The resistance gene was mapped using an F_2:3 population from Taichung 29/CH223. The gene was linked to five co-dominant genomic SSR markers, Xgwm540, Xbarc1096, Xwmc47, Xwmc310 and Xgpw7272, and flanked by Xbarc1096 and Xwmc47 at 8.0 and 7.2 cM, respectively. Using the Chinese Spring nulli-tetrasomic and ditelosomic lines, the polymorphic markers and the resistance gene were assigned to chromosome arm 4BL. As no permanently named stripe rust resistance genes had been assigned to chromosome 4BL, this new resistance gene is designated Yr50. The gene, together with the identified closely linked markers, could be used in marker-assisted selection to combine two or more resistance genes in a single genotype.     

Molecular mapping of powdery mildew resistance gene <Emphasis Type="Italic">PmHNK</Emphasis> in winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) cultivar Zhoumai 22

The Chinese winter wheat cultivar Zhoumai 22 is highly resistant to powdery mildew. The objectives of this study were to map a powdery mildew resistance gene in Zhoumai 22 using molecular markers and investigate its allelism with Pm13. A total of 278 F₂ and 30 BC₁ plants, and 143 F₃ lines derived from the cross between resistant cultivar Zhoumai 22 and susceptible cultivar Chinese Spring were used for resistance gene tagging. The 137 F₂ plants from the cross Zhoumai 22/2761-5 (Pm13) were employed for the allelic test of the resistance genes. Two hundred and ten simple sequence repeat (SSR) markers were used to test the two parents, and resistant and susceptible bulks. Subsequently, seven polymorphic markers were used for genotyping the F₂ and F₃ populations. The results indicated that the powdery mildew resistance in Zhoumai 22 was conferred by a single dominant gene, designated PmHNK tentatively, flanked by seven SSR markers Xgwm299, Xgwm108, Xbarc77, Xbarc84, Xwmc326, Xwmc291 and Xwmc687 on chromosome 3BL. The resistance gene was closely linked to Xwmc291 and Xgwm108, with genetic distances of 3.8 and 10.3 cM, respectively, and located on the chromosome bin 3BL-7-0.63-1.0 in the test with a set of deletion lines. Seedling tests with seven isolates of Blumeria graminis f. sp. tritici (Bgt) and allellic test indicated that PmHNK is different from Pm13, and Pm41 seems also to be different from PmHNK due to its origin from T. dicoccoides and molecular evidence. These results indicate that PmHNK is likely to be a novel powdery mildew resistance gene in wheat.     

Mapping QTL associated with resistance to <Emphasis Type="Italic">Fusarium</Emphasis> head blight in the Nanda2419 × Wangshuibai population. I. Type II resistance

Scab disease caused by Fusarium spp. has been a major concern for both wheat producers and consumers. Deployment of scab-resistant varieties is the major strategy to curb this disease. To identify the scab resistance genes in wheat cv. Wangshuibai, we produced a F_6:7 recombinant inbred line (RIL) population by crossing Wangshuibai with the scab-susceptible cultivar Nanda2419. The RILs were evaluated for scab resistance in the field by single floret inoculation in two replicates in 2002 and one replicate in 2003. The number of diseased spikelets (NDS) and the length of diseased rachides (LDR) were investigated to reflect the Type II resistance. Among 654 simple sequence repeat (SSR) markers surveyed, 326 were found to be polymorphic between the parents. A partial molecular map was constructed with these markers that covered over 2,210 cM of the wheat genome. Six chromosome regions showed association with both NDS and LDR in a one-way anova analysis, even though the variation explained by them varied between the two traits. Eight intervals were detected for their association with Type II resistance through interval mapping, five of which were not identified in single-point analysis. The quantitative trait loci (QTL) with large effects were the ones in the interval of Xgwm533-3–Xgwm533-1 on chromosome 3B and in the interval of Xwmc539–Xbarc024 on chromosome 6B, whose alleles favoring resistance originate from Wangshuibai. In addition, a QTL whose resistance allele originated from Nanda2419 was consistently detected in the interval of Xs1021m–Xgwm47-1 on chromosome 2B. These results suggest that Wangshuibai is the major source for Type II resistance in this population. The markers associated with these QTL would facilitate the use of scab-resistant genes of Wangshuibai in scab resistance breeding programs of wheat.F. Lin and Z.X. Kong have equally contributed to this work.     

Genetic dissection of yield-related traits in a recombinant inbred line population created using a key breeding parent in China’s wheat breeding

Understanding the genetics underlying yield formation of wheat is important for increasing wheat yield potential in breeding programs. Nanda2419 was a widely used cultivar for wheat production and breeding in China. In this study, we evaluated yield components and a few yield-related traits of a recombinant inbred line (RIL) population created by crossing Nanda2419 with the indigenous cultivar Wangshuibai in three to four trials at different geographical locations. Negative and positive correlations were found among some of these evaluated traits. Five traits had over 50 % trial-wide broad sense heritability. Using a framework marker map of the genome constructed with this population, quantitative trait loci (QTL) were identified for all traits, and epistatic loci were identified for seven of them. Our results confirmed some of the previously reported QTLs in wheat and identified several new ones, including QSn.nau-6D for effective tillers, QGn.nau-4B.2 for kernel number, QGw.nau-4D for kernel weight, QPh.nau-4B.2 and QPh.nau-4A for plant height, and QFlw.nau-5A.1 for flag leaf width. In the investigated population, Nanda2419 contributed all QTLs associated with higher kernel weight, higher leaf chlorophyll content, and a major QTL associated with wider flag leaf. Seven chromosome regions were related to more than one trait. Four QTL clusters contributed positively to breeding goal-based trait improvement through the Nanda2419 alleles and were detected in trials set in different ecological regions. The findings of this study are relevant to the molecular improvement of wheat yield and to the goal of screening cultivars for better breeding parents.     

Quantitative trait loci responsible for Fusarium head blight resistance in Chinese landrace Baishanyuehuang

Fusarium head blight (FHB), mainly caused by Fusarium graminearum, is a destructive disease that can significantly reduce grain yield and quality. Deployment of quantitative trait loci (QTLs) for FHB resistance in commercial cultivars has been the most effective approach for minimizing the disease losses. 'Baishanyuehuang' is a highly FHB-resistant landrace from China. Recombinant inbred lines (RILs) developed from a cross of 'Baishanyuehuang' and 'Jagger' were evaluated for FHB resistance in three greenhouse experiments in 2010 and 2011 by single-floret inoculation. Percentage of symptomatic spikelets in an inoculated spike was recorded 18 days post-inoculation. The RIL population was screened with 251 polymorphic simple sequence repeats. Four QTLs were associated with FHB resistance and mapped on three chromosomes. Two QTLs were located on the short arm of chromosome 3B (3BS) with one in distal of 3BS and another near centromere (3BSc), designated as Qfhb.hwwg-3BSc. The QTL in the distal of 3BS is flanked by Xgwm533 and Xgwm493, thus corresponds to Fhb1. This QTL explained up to 15.7 % of phenotypic variation. Qfhb.hwwg-3BSc flanked by Xwmc307 and Xgwwm566 showed a smaller effect than Fhb1 and explained up to 8.5 % of phenotypic variation. The other two QTLs were located on 3A, designated as Qfhb.hwwg-3A, and 5A, designated as Qfhb.hwwg-5A. Qfhb.hwwg-3A was flanked by Xwmc651 and Xbarc356 and explained 4.8-7.5 % phenotypic variation, and Qfhb.hwwg-5A was flanked by markers Xgwm186 and Xbarc141, detected in only one experiment, and explained 4.5 % phenotypic variation for FHB resistance. 'Baishanyuehuang' carried all resistance alleles of the four QTL. Qfhb.hwwg-3BSc and Qfhb.hwwg-3A were new QTLs in 'Baishanyuehuang'. 'Baishanyuehuang' carries a combination of QTLs from different sources and can be a new source of parent to pyramid FHB-resistant QTLs for improving FHB resistance in wheat.     

Inheritance and mapping of powdery mildew resistance gene <Emphasis Type="Italic">Pm43</Emphasis> introgressed from <Emphasis Type="Italic">Thinopyrum</Emphasis><Emphasis Type="Italic">intermedium</Emphasis> into wheat

Powdery mildew resistance from Thinopyrum intermedium was introgressed into common wheat (Triticum aestivum L.). Genetic analysis of the F₁, F₂, F₃ and BC₁ populations from powdery mildew resistant line CH5025 revealed that resistance was controlled by a single dominant allele. The gene responsible for powdery mildew resistance was mapped by the linkage analysis of a segregating F₂ population. The resistance gene was linked to five co-dominant genomic SSR markers (Xcfd233, Xwmc41, Xbarc11, Xgwm539 and Xwmc175) and their most likely order was Xcfd233–Xwmc41–Pm43–Xbarc11–Xgwm539–Xwmc175 at 2.6, 2.3, 4.2, 3.5 and 7.0 cM, respectively. Using the Chinese Spring nullisomic-tetrasomic and ditelosomic lines, the polymorphic markers and the resistance gene were assigned to chromosome 2DL. As no powdery mildew resistance gene was previously assigned to chromosome 2DL, this new resistance gene was designated Pm43. Pm43, together with the identified closely linked markers, could be useful in marker-assisted selection for pyramiding powdery mildew resistance genes. Runli He and Zhijian Chang contributed equally to this work.     

Molecular mapping of stripe rust resistance gene YrCH42 in Chinese wheat cultivar Chuanmai 42 and its allelism with Yr24 and Yr26

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most devastating diseases in common wheat (Triticum aestivum L.) worldwide. The objectives of this study were to map a stripe rust resistance gene in Chinese wheat cultivar Chuanmai 42 using molecular markers and to investigate its allelism with Yr24 and Yr26. A total of 787 F₂ plants and 186 F₃ lines derived from a cross between resistant cultivar Chuanmai 42 and susceptible line Taichung 29 were used for resistance gene tagging. Also 197 F₂ plants from the cross Chuanmai 42×Yr24/3*Avocet S and 726 F₂ plants from Chuanmai 42×Yr26/3*Avocet S were employed for allelic test of the resistance genes. In all, 819 pairs of wheat SSR primers were used to test the two parents, as well as resistant and susceptible bulks. Subsequently, nine polymorphic markers were employed for genotyping the F₂ and F₃ populations. Results indicated that the stripe rust resistance in Chuanmai 42 was conferred by a single dominant gene, temporarily designated YrCH42, located close to the centromere of chromosome 1B and flanked by nine SSR markers Xwmc626, Xgwm273, Xgwm11, Xgwm18, Xbarc137, Xbarc187, Xgwm498, Xbarc240 and Xwmc216. The resistance gene was closely linked to Xgwm498 and Xbarc187 with genetic distances of 1.6 and 2.3 cM, respectively. The seedling tests with 26 PST isolates and allelic tests indicated that YrCH42, Yr24 and Yr26 are likely to be the same gene.G.Q. Li and Z.F. Li contributed equally to the work.     

Haplotype analysis of QTLs attributed to salinity tolerance in wheat (Triticum aestivum)

A diverse collection of wheat germplasm, consisting of 100 bread wheat lines with varying levels of salinity tolerance were evaluated based on incomplete block design (lattice) with two replications in field conditions. Plant material was screened for salinity tolerance under normal and saline field conditions. Subsequently in order to assess the haplotype diversity of QTLs attributed to salinity tolerance in wheat (Triticum aestivum), a collection of 30 extremes tolerant and sensitive genotypes among them were selected for genotyping on the basis of morphological, physiological and phenological traits. Genotyping was done using microsatellite markers which had been detected as the flanking regions of large effect QTLs attributed to salinity tolerance on chromosomes 2A, 4D and 3B. Combined analysis of saline and normal conditions revealed that genotypes showed highly significant responses. Association analysis of SSR markers with traits, showed markers Xcfa2121b, Xgwm10 and Xgwm296 on chromosome 2A and markers Xgwm194 and xgwm624 for chromosome 4D, had significant association with most of measured traits. Haplotype diversity analysis showed markers Xgwm10, Xgwm445, Xbarc353.2, Xgwm312, Xgwm515 and Xwmc296 on chromosome 2A as well as markers Xwmc326 and Xgwm345, Xbarc48.4 on chromosomes 3B and 4D were identified as the best markers attributed to salinity tolerance and they can be informative markers for improvement of salinity tolerance through marker-assisted selection programs.     

Association of microsatellite loci alleles of the group-5 of chromosomes and the frost resistance of winter wheat

Determination of the frost resistance and a microsatellite analysis of the group 5 chromosomes were performed on parental varieties and recombinant inbred lines F ₇ Luzanovka odesskaya/Odesskaya krasnokolosaya. The allelic differences of the Xcfd7-5B, Xwmc415-5B, and Xgwm182-5D microsatellite loci were associated with the level of frost resistance of the lines.     

Genetic mapping of a putative Thinopyrum intermedium-derived stripe rust resistance gene on wheat chromosome 1B

Key message

Stripe rust resistance transferred from Thinopyrum intermedium into common wheat was controlled by a single dominant gene, which mapped to chromosome 1B near Yr26 and was designated YrL693.

Abstract

Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is a highly destructive disease of wheat (Triticum aestivum). Stripe rust resistance was transferred from Thinopyrum intermedium to common wheat, and the resulting introgression line (L693) exhibited all-stage resistance to the widely virulent and predominant Chinese pathotypes CYR32 and CYR33 and to the new virulent pathotype V26. There was no cytological evidence that L693 had alien chromosomal segments from Th. intermedium. Genetic analysis of stripe rust resistance was performed by crossing L693 with the susceptible line L661. F₁, F₂, and F_2:3 populations from reciprocal crosses showed that resistance was controlled by a single dominant gene. A total 479 F_2:3 lines and 781 pairs of genomic simple sequence repeat (SSR) primers were employed to determine the chromosomal location of the resistance gene. The gene was linked to six publicly available and three recently developed wheat genomic SSR markers. The linked markers were localized to wheat chromosome 1B using Chinese Spring nulli-tetrasomic lines, and the resistance gene was localized to chromosome 1B based on SSR and wheat genomic information. A high-density genetic map was also produced. The pedigree, molecular marker data, and resistance response indicated that the stripe rust resistance gene in L693 is a novel gene, which was temporarily designated YrL693. The SSR markers that co-segregate with this gene (Xbarc187-1B, Xbarc187-1B-1, Xgwm18-1B, and Xgwm11-1B) have potential application in marker-assisted breeding of wheat, and YrL693 will be useful for broadening the genetic basis of stripe rust resistance in wheat.     

Molecular markers for tracking variation in lipoxygenase activity in wheat breeding

Lipoxygenase (LOX) activity is an important factor determining the color of flour and end-use products of wheat. In the present study, quantitative trait loci (QTL) for LOX activity in common wheat were mapped using 71 doubled haploid (DH) lines derived from a Zhongyou 9507 × CA9632 cross, and SSR markers. Two QTL, QLpx.caas.1AL and QLpx.caas-4B, were identified on chromosomes 1AL and 4B, closely associated with LOX activity. The SSR loci Xwmc312 and Xgwm251 proved to be diagnostic and explained 13.4–25.2% of the phenotypic variance for the 1AL locus and 14.3–27.0% for the 4B locus across four environments. The SSR markers Xgwm251 and Xwmc312 were validated across 198 Chinese wheat cultivars and advanced lines and showed highly significant (P < 0.01) association with LOX activity. We further established a multiplexed PCR with SSR marker combination Xwmc312/Xgwm251 to test these wheat cultivars and advanced lines. The results suggested that the marker combination Xwmc312/Xgwm251 is efficient and reliable for evaluating LOX activity and can be used in marker-assisted selection (MAS) for targeting flour color attributes to noodle and other wheat-based products.     

Differentially Expressed Proteins Associated with Fusarium Head Blight Resistance in Wheat

Background

Fusarium head blight (FHB), mainly caused by Fusarium graminearum, substantially reduces wheat grain yield and quality worldwide. Proteins play important roles in defense against the fungal infection. This study characterized differentially expressed proteins between near-isogenic lines (NILs) contrasting in alleles of Fhb1, a major FHB resistance gene in wheat, to identify proteins underlining FHB resistance of Fhb1.

Methods

The two-dimensional protein profiles were compared between the Fusarium-inoculated spikes of the two NILs collected 72 h after inoculation. The protein profiles of mock- and Fusarium-inoculated Fhb1⁺NIL were also compared to identify pathogen-responsive proteins.

Results

Eight proteins were either induced or upregulated in inoculated Fhb1⁺NIL when compared with mock-inoculated Fhb1⁺NIL; nine proteins were either induced or upregulated in the Fusarium-inoculated Fhb1⁺NIL when compared with Fusarium-inoculated Fhb1⁻NIL. Proteins that were differentially expressed in the Fhb1⁺NIL, not in the Fhb1⁻NIL, after Fusarium inoculation included wheat proteins for defending fungal penetration, photosynthesis, energy metabolism, and detoxification.

Conclusions

Coordinated expression of the identified proteins resulted in FHB resistance in Fhb1⁺NIL. The results provide insight into the pathway of Fhb1-mediated FHB resistance.     

Identification and genetic mapping of <Emphasis Type="Italic">pm42</Emphasis>, a new recessive wheat powdery mildew resistance gene derived from wild emmer (<Emphasis Type="Italic">Triticum turgidum var. dicoccoides</Emphasis>)

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most important wheat diseases worldwide in areas with cool or maritime climates. Wild emmer (Triticum turgidum var. dicoccoides) is an important potential donor of disease resistances and other traits for common wheat improvement. A powdery mildew resistance gene was transferred from wild emmer accession G-303-1M to susceptible common wheat by crossing and backcrossing, resulting in inbred line P63 (Yanda1817/G-303-1 M//3*Jing411, BC₂F₆). Genetic analysis of an F₂ population and the F_2:3 families developed from a cross of P63 and a susceptible common wheat line Xuezao showed that the powdery mildew resistance in P63 was controlled by a single recessive gene. Molecular markers and bulked segregant analysis were used to characterize and map the powdery mildew resistance gene. Nine genomic SSR markers (Xbarc7, Xbarc55, Xgwm148, Xgwm257, Xwmc35, Xwmc154, Xwmc257, Xwmc382, Xwmc477), five AFLP-derived SCAR markers (XcauG3, XcauG6, XcauG10, XcauG20, XcauG22), three EST–STS markers (BQ160080, BQ160588, BF146221) and one RFLP-derived STS marker (Xcau516) were linked to the resistance gene, designated pm42, in P63. pm42 was physically mapped on chromosome 2BS bin 0.75–0.84 using Chinese Spring nullisomic-tetrasomic, ditelosomic and deletion lines, and was estimated to be more than 30 cM proximal to Xcau516, a RFLP-derived STS marker that co-segregated with the wild emmer-derived Pm26 which should be physically located in 2BS distal bin 0.84–1.00. pm42 was highly effective against 18 of 21 differential Chinese isolates of B. graminis f. sp. tritici. The closely linked molecular markers will enable the rapid transfer of pm42 to wheat breeding populations thus adding to their genetic diversity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. W. Hua, Z. Liu, and J. Zhu contributed equally to this work.