DNA markers linked to a T10 loose smut resistance gene in wheat (Triticum aestivum L.).

Screening for loose smut resistance in wheat is difficult. Selecting lines with DNA markers linked to loose smut resistance would be more reliable and less costly. Molecular markers linked to a race T10 loose smut resistance gene were identified using a F6 single seed descent segregating population. A RAPD marker and a RFLP marker were located on opposite flanks of the resistance gene and were shown to be loosely linked. The RAPD marker was converted to a user friendly polymorphic SCAR marker that represented a single genetically defined locus in hexaploid wheat. Using these two bracketing markers simultaneously, the error rate for T10 resistance selection due to crossing-over was reduced to 4%. These markers can be used for a faster and more reliable selection of T10 resistant plants than previous conventional loose smut ratings.     

Mapping of the loose smut resistance gene Ut6 in wheat (Triticum aestivum L.)

Loose smut of wheat (Triticum aestivum L.) caused by Ustilago tritici (Pers.) Rostr. can cause considerable yield losses in the absence of appropriate management practices. The use of wheat varieties with loose smut resistance is an efficient and effective control technique. However, the development of commercial wheat lines with resistance to loose smut is time- and labour-consuming. DNA markers linked to loose smut resistance gene(s) would assist the development of loose smut resistant genotypes. The genetics of loose smut resistance was studied in an F5‐derived recombinant inbred line (RIL) population of 94 lines from the cross BW278/AC Foremost. The line AC Foremost is resistant and line BW278 is susceptible to U. tritici race T10. Phenotypic assessment revealed that a single gene, designated Ut6, segregated for resistance to race T10 in the RIL population. A modified bulked segregant analysis identified a microsatellite marker linked to Ut6. A linkage map was developed consisting of linked microsatellite loci and the resistance gene. The loose smut resistance gene Ut6 mapped to the long arm of chromosome 5B. Five microsatellite markers mapped within 6.7 cM of Ut6. The microsatellite markers gpw5029 and barc232 flanked Ut6 at distances of 1.3 and 2.8 cM on the distal and proximal sides, respectively. A diverse set of wheat lines was haplotyped for Ut6 using the linked microsatellite markers gpw5029 and barc232. The haplotype analysis suggested that the microsatellite markers associated with Ut6 will be useful for marker-assisted selection of loose smut resistant wheat lines.     

Association of RGA-SSCP markers with resistance to downy mildew and anthracnose in grapevines

Downy mildew (Plasmopara viticola) and anthracnose (Sphaceloma ampelinum) are two major diseases that severely affect most grapevine (Vitis vinifera) cultivars grown commercially in Thailand. Progress of conventional breeding programs of grapevine for improved resistance to these diseases can be speeded up by selection of molecular markers associated with resistance traits. We evaluated the association between 13 resistance gene analog (RGA)-single-strand conformation polymorphism (SSCP) markers with resistance to downy mildew and anthracnose in 71 segregating progenies of seven cross combinations between susceptible cultivars and resistant lines. F(1) hybrids from each cross were assessed for resistance to downy mildew and anthracnose (isolates Nk4-1 and Rc2-1) under laboratory conditions. Association of resistance traits with RGA-SSCP markers was evaluated using simple linear regression analysis. Three RGA-SSCP markers were found to be significantly correlated with anthracnose resistance, whereas significant correlation with downy mildew resistance was observed for only one RGA-SSCP marker. These results demonstrate the usefulness of RGA-SSCP markers. Four candidate markers with significant associations to resistance to these two major diseases of grapevine were identified. However, these putative associations between markers and resistance need to be verified with larger segregating populations before they can be used for marker-assisted selection.     

Molecular markers linked to stem rot resistance in rice

Stem rot (Sclerotium oryzae) is an important disease constraint in Californian rice production. Measurement of resistance is laborious, and the low heritability of the trait limits the effectiveness of selection in breeding programs. Molecular markers linked to the trait would therefore provide a superior selection screen to assist in transferring resistance into improved cultivars. The genetics of resistance to stem rot was studied in the germplasm line 87-Y-550 (PI566666), which inherited its resistance from the wild species Oryza rufipogon. Four crosses of 87-Y-550 with susceptible lines were made and recombinant inbred lines of only the most-resistant and most-susceptible progeny within each cross were advanced for late-generation testing. Approximately 900 AFLP (amplified fragment length polymorphism) primer combinations were applied to resistant and susceptible bulks within each cross. One AFLP marker showed significant association with stem rot resistance and accounted for approximately 45.0% of the phenotypic variation in 59 progenies. This marker was mapped on rice chromosome 2 between the RFLP markers RZ166 and RG139 by using F₂-reference population information. The accuracy of AFLP marker mapping was validated by size and sequence comparison of AFLP bands from 87-Y-550 and the reference population. With the strategy of selective genotyping combined with a parental survey, two microsatellite markers, RM232 and RM251, on chromosome 3 were also found associated with stem rot resistance and accounted for 41.1% and 37.9% of the phenotypic variation, respectively. The multiple linear regression model included TAA/GTA167 on chromosome 2 and RM232 on chromosome 3 and cumulatively explained 49.3% of total variation. The molecular markers linked to stem rot resistance should facilitate selection for this recalcitrant trait in rice breeding programs by eliminating the need for early generation screening. Received: 27 March 2000 / Accepted: 4 June 2000     

Marker Assisted Selection of Fusarium Head Blight Resistance Genes in Two Doubled­ Haploid Populations of Wheat

Fusarium head blight, caused primarily by Fusarium graminearum, is the most important wheat disease in Canada causing both grain yield and quality losses. Selection for resistance to Fusarium head blight in breeding programs has been difficult because of the complex inheritance of resistance and the environmental effect on disease development and expression. The present study was conducted to examine microsatellite markers associated with resistance to Fusarium head blight and evaluate the effectiveness of these microsatellite markers in selecting for resistance to Fusarium head blight in two doubled-haploid populations segregating for Sumai 3-derived resistance genes. Both doubled-haploid populations were evaluated for resistance to Fusarium head blight by inoculation with F. graminearum in the greenhouse. Eight microsatellite markers from chromosomes 3BS, 6B and 5AL were applied to both doubled-haploid populations. The most significant microsatellite markers were found on the short arm of chromosome 3B, explaining 12% and 36% of phenotypic variation for resistance in the DH181/AC Foremost and AC Foremost/93FHB 21 doubled-haploid populations, respectively. Another important microsatellite marker, gwm644 on 6B, explained 21 % of the phenotypic variation for resistance to Fusarium head blight in the DH181/AC Foremost doubled-haploid population. There was a general lack of marker polymorphism on 5AL for the parents used in this study. Microsatellite markers on chromosome 3BS in addition to microsatellite markers on 6B have the potential for accelerating the development of wheat cultivars with improved Fusarium head blight resistance through the use of marker-assisted selection.     

Development of markers linked to Diuraphisnoxia resistance in wheat using a novel PCR-RFLP approach

Through random amplified polymorphic DNA (RAPD) analysis we identified a putative marker linked to the Dn5 resistance gene. This marker was converted to a more reliable sequence-characterised-amplified regions (SCAR) marker. The initial SCAR marker amplified the correct amplification product but failed to discern between the susceptible and resistant individuals. Hence, it was utilised to sequence the internal fragment. All nested primers designed from the internal sequences were also unable to produce any polymorphism between the susceptible and resistant cultivars. Restriction digests were then performed on these fragments, and the restriction enzyme EcoRI was able to discern between the susceptible and resistant F₂ individuals of the Dn5 population. This granted one marker amplified with the internal SCAR primer set OPF14₁₀₈₃ the ability to differentiate between parental individuals carrying the Dn5 genes. This marker was tested in a segregating F₂ population carrying the Dn5 resistance gene and proved able to differentiate between the segregating individuals. This marker may prove useful in marker assisted selection (MAS), although performing restriction digests may hamper the throughput of a high number of samples. Received: 4 August 1999 / Accepted: 27 August 1999     

Assay development and marker validation for marker assisted selection of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">niveum</Emphasis> race 1 in watermelon

Fusarium wilt, Fusarium oxysporum f. sp. niveum (FON), of watermelon (Citrullus lanatus) is a fungal pathogen that causes significant yield losses in the US watermelon industry. FON damages watermelon through invasion of the root system and remains a difficult pathogen to manage due to its long-lasting survival spores which persist in the soil. Chemical control options for this pathogen are lacking, making development of genetic resistance the best option. There are four known races of FON (0, 1, 2, and 3) which are distinguished based on their pathogenicity of differential cultivars. Most modern cultivar releases have FON race 1 (FON-1) resistance, which has been mapped on the end of chromosome 1. Application of marker assisted selection (MAS) would improve the efficiency of FON-1 resistance breeding. In order to identify markers for selection in the FON-1 region, the QTL-seq method was utilized on an F₂ population segregating for FON-1 resistance. Single nucleotide polymorphism (SNP) markers in the region were developed into Kompetitive allele-specific PCR (KASP?) assays and tested for trait association on the segregating F_2:3 population. Marker validation was done using an F₂ population from a cross between FON-1 susceptible “New Hampshire Midget” and FON-1-resistant “Calhoun Gray.” Further validation on a panel of susceptible and resistant cultivars and Plant Introductions identified SNP marker UGA1_502161 as a useful marker for selection of FON-1 resistance from Calhoun Gray.     

Genetic linkage maps of two apricot cultivars ( Prunus armeniaca L.), and mapping of PPV (sharka) resistance

Genetic linkage maps for two apricot cultivars have been constructed using AFLP, RAPD, RFLP and SSR markers in 81 F1 individuals from the cross 'Goldrich' x 'Valenciano'. This family segregated for resistance to 'plum pox virus' (PPV), the most-important virus affecting Prunus species. Of the 160 RAPD arbitrary primers screened a total of 44 were selected. Sixty one polymorphic RAPD markers were scored on the mapping population: 30 heterozygous in 'Goldrich', 19 heterozygous in 'Valenciano', segregating 1:1, and 12 markers heterozygous in both parents, segregating 3:1. A total of 33 and 19 RAPD markers were mapped on the 'Goldrich' and 'Valenciano' maps respectively. Forteen primer combinations were used for AFLPs and all of them detected polymorphism. Ninety five markers segregating 1:1 were identified, of which 62 were heterozygous in the female parent 'Goldrich' and 33 in the male parent 'Valenciano'. Forty five markers were present in both parents and segregated 3:1. A total of 82 and 48 AFLP markers were mapped on the 'Goldrich' and 'Valenciano' maps. Twelve RFLPs probes were screened in the population, resulting in five loci segregating in the family, one locus heterozygous for 'Valenciano' and four heterozygous for both, segregating 1:2:1. Of the 45 SSRs screened 17 segregated in the mapping family, resulting in seven loci heterozygous for the maternal parent and ten heterozygous for both, segregating 1:2:1 or 1:1:1:1. A total of 16 and 13 co-dominant markers were mapped in the female and male parent maps respectively. A total of 132 markers were placed into eight linkage groups on the 'Goldrich' map, defining 511 cM of the total map-length. The average distance between adjacent markers was 3.9 cM. A total of 80 markers were placed into seven linkage groups on the 'Valenciano' map, defining 467.2 cM of the total map-distance, with an average interval of 5.8 cM between adjacent markers. Thirty six marker loci heterozygous in both parents revealed straightforward homologies between five linkage groups in both maps. The sharka resistance trait mapped on linkage group 2. The region containing sharka resistance is flanked by two co-dominant markers that will be used for targeted SSR development employing a recently constructed complete apricot BAC library. SSRs tightly linked to sharka resistance will facilitate MAS in breeding for resistance in apricot.     

Molecular markers linked with bruchid resistance in Vigna radiata var. Sublobata and their validation

Bruchid, Callosobruchus chinensis (L.) is an important pest of Vigna radiata during storage. RFLP and PCR based markers identified, linked with bruchid resistance gene in wild accession of greengram (V. radiata var. Sublobata) either collected from Madagaskar or Australia. Whether these markers will be useful for marker assisted introgression of bruchid resistance gene from the Indian accession into the existing cultivars are not known. Here, we employed two STS based markers which were found earlier, to be linked with bruchid resistance gene in Australian accession ACC41. Only one primer pair, STSbr1 showed polymorphism among Indian Sublobata accession (Sub2) and other twelve green gram cultivars. Analysis of 113 segregating lines (F₆) of a cross between a popular cultivar of West Bengal, B1 and Sub2 showed a cent percent co-segregation of resistant locus with the polymorphic fragment. STSbr1 behave as a dominant marker among Indian genotypes although it has been shown earlier a co-dominant banding pattern between ACC41 and other Australian Susceptible cultivars. Other STS marker, STSbr2, does not produce any polymorphic fragment among Sub2 and 18 greengram genotypes. STSbr1 employed in screening of 50 green gram accessions and found high efficiency in screening of bruchid resistant genotypes also. So STSbr1 will be useful for marker assisted selection and germplasm screening for development of bruchid resistant greengram.     

Identification of RFLP markers linked to the H1 gene conferring resistance to the potato cyst nematode Globodera rostochiensis.

The H1 gene from Solanum tuberosum ssp. andigena confers high levels of resistance to the potato cyst nematode Globodera rostochiensis and is used extensively in potato breeding. Using a dihaploid segregating population, a search was conducted for linkage between this gene and markers on the potato/tomato RFLP map. A total of 60 RFLP markers covering the entire genome were screened on bulk resistant and susceptible segregants. Linkage was indicated for eight markers on chromosome 5. Individual plant analysis placed the closest marker, CD78, at a maximum map distance of 2.7 cM from H1. A molecular marker for the H1 should be useful both as a correlative screening tool for incorporation of resistance into new cultivars and as starting point for map-based cloning of this important gene.     

A gene controlling sex in grapevines placed on a molecular marker-based genetic map.

Genetic maps of Vitis (2n = 38) have been constructed from an interspecific hybrid population of 58 seedlings of the cross 'Horizon' ('Seyval' x 'Schuyler') x Illinois 547-1 (V. cinerea B9 x V. rupestris B38). The maps were initially constructed based on 277 RAPD (random amplified polymorphic DNA) markers using a double-pseudotestcross strategy. Subsequently, 25 microsatellites, 4 CAPS (cleaved amplified polymorphic sequence), and 12 AFLP (amplified fragment length polymorphism) markers were added to the maps. Another 120 markers, mostly those segregating 3:1, were also assigned but not positioned on the linkage groups in the two maps. The 'Horizon' map consisted of 153 markers covering 1199 cM, with an average map distance of 7.6 cM between markers. The Illinois 547-1 map had 179 markers covering 1470 cM, with an average map distance of 8.1 cM. There were 20 linkage groups in each map, one more than the basic number of chromosomes in grapes. Ten linkage groups in each map were identified as homologous using 16 microsatellite and 2 CAPS markers polymorphic in both parents. A single locus controlling sex in grapes mapped close to a microsatellite marker. These maps provide enough coverage of the genome for QTL (quantitative trait loci) analysis and as a starting point for positional gene cloning in grapes.     

Allele-specific CAPS markers based on point mutations in resistance alleles at the pvr1 locus encoding eIF4E in Capsicum

Marker-assisted selection has been widely implemented in crop breeding and can be especially useful in cases where the traits of interest show recessive or polygenic inheritance and/or are difficult or impossible to select directly. Most indirect selection is based on DNA polymorphism linked to the target trait, resulting in error when the polymorphism recombines away from the mutation responsible for the trait and/or when the linkage between the mutation and the polymorphism is not conserved in all relevant genetic backgrounds. In this paper, we report the generation and use of molecular markers that define loci for selection using cleaved amplified polymorphic sequences (CAPS). These CAPS markers are based on nucleotide polymorphisms in the resistance gene that are perfectly correlated with disease resistance, the trait of interest. As a consequence, the possibility that the marker will not be linked to the trait in all backgrounds or that the marker will recombine away from the trait is eliminated. We have generated CAPS markers for three recessive viral resistance alleles used widely in pepper breeding, pvr1, pvr1 ¹, and pvr1 ². These markers are based on single nucleotide polymorphisms (SNPs) within the coding region of the pvr1 locus encoding an eIF4E homolog on chromosome 3. These three markers define a system of indirect selection for potyvirus resistance in Capsicum based on genomic sequence. We demonstrate the utility of this marker system using commercially significant germplasm representing two Capsicum species. Application of these markers to Capsicum improvement is discussed.     

Conversion of an RFLP marker for the barley stem rust resistance geneRpg1 to a specific PCR-amplifiable polymorphism

TheRpg1 gene in barley has provided satisfactory levels of stem rust resistance for the last 50 years. The appearance of a new race of stem rust that is virulent toRpg1 has resulted in efforts to incorporate new stem rust resistance genes into barley. Marker-assisted selection may provide the only means of combining this useful gene with resistance genes for which no virulent races have been identified. Several RFLP markers have been identified as linked to theRpg1 locus. One of these, ABG704 was converted into a post-amplification restriction polymorphism. To generate a specific PCR-amplifiable polymorphism the sequence of the ABG704 locus from four barley cultivars was determined. Primers were developed that can detect a single-base difference between resistant and susceptible cultivars. The successful conversion of an RFLP marker to an allele-specific PCR-based marker not only demonstrates that this type of conversion is possible for cereals, but also results in an immediately useful marker for application to plant breeding programmes.     

A genetic linkage map of Pacific white shrimp (<Emphasis Type="Italic">Litopenaeus vannamei</Emphasis>): sex-linked microsatellite markers and high recombination rates

Pacific white shrimp (Litopenaeus vannamei) is the leading species farmed in the Western Hemisphere and an economically important aquaculture species in China. In this project, a genetic linkage map was constructed using amplified fragment length polymorphism (AFLP) and microsatellite markers. One hundred and eight select AFLP primer combinations and 30 polymorphic microsatellite markers produced 2071 markers that were polymorphic in either of the parents and segregated in the progeny. Of these segregating markers, 319 were mapped to 45 linkage groups of the female framework map, covering a total of 4134.4 cM; and 267 markers were assigned to 45 linkage groups of the male map, covering a total of 3220.9 cM. High recombination rates were found in both parental maps. A sex-linked microsatellite marker was mapped on the female map with 6.6 cM to sex and a LOD of 17.8, two other microsatellite markers were also linked with both 8.6 cM to sex and LOD score of 14.3 and 16.4. The genetic maps presented here will serve as a basis for the construction of a high-resolution genetic map, quantitative trait loci (QTLs) detection, marker-assisted selection (MAS) and comparative genome mapping.     

Development of RAPD and SCAR markers linked to the Russian wheat aphid resistance gene Dn2 in wheat

 RAPD (random amplified polymorphic DNA) analysis was used to identify molecular markers linked to the Dn2 gene conferring resistance to the Russian wheat aphid (Diuraphis noxia Mordvilko). A set of near-isogenic lines (NILs) was screened with 300 RAPD primers for polymorphisms linked to the Dn2 gene. A total of 2700 RAPD loci were screened for linkage to the resistance locus. Four polymorphic RAPD fragments, two in coupling phase and two in repulsion phase, were identified as putative RAPD markers for the Dn2 gene. Segregation analysis of these markers in an F₂ population segregating for the resistance gene revealed that all four markers were closely linked to the Dn2 locus. Linkage distances ranged from 3.3 cM to 4.4 cM. Southern analysis of the RAPD products using the cloned RAPD markers as probes confirmed the homology of the RAPD amplification products. The coupling-phase marker OPB10_880c and the repulsion-phase marker OPN1_400r were converted to sequence characterized amplified region (SCAR) markers. SCAR analysis of the F₂ population and other resistant and susceptible South African wheat cultivars corroborated the observed linkage of the RAPD markers to the Dn2 resistance locus. These markers will be useful for marker-assisted selection of the Dn2 gene for resistance breeding and gene pyramiding. Received: 1 July 1997 / Accepted: 20 October 1997     

Inheritance of resistance to covered smut in barley and development of a tightly linked SCAR marker

Inheritance of resistance to covered smut in the barley line Q21861 was studied using a doubled-haploid population produced by crossing Q21861 with the line SM89010. Based on 3 years of screening in the field and two seasons in the greenhouse, segregation for resistance/susceptibility fits a one-gene ratio, indicating a single major gene for resistance in Q21861. Of 440 random 10-mer primers tested using bulked segregant analysis, one primer (OPJ10) resulted in a reproducible polymorphic band. RAPD marker OPJ10₄₅₀ co-segregated in repulsion with the covered smut resistance. This marker was converted to a sequence-characterized amplified region (SCAR) marker linked in coupling (5.5 cM) with the covered smut resistant gene in Q21861. The SCAR marker was amplified in the line TR640 which is also resistant to covered smut, but not in the other resistant lines. The SCAR marker will be useful for marker-assisted selection for covered smut in barley breeding programs. Received: 9 January 2001 / Accepted: 31 May 2001     

Microsatellite markers flanking a stem solidness gene on chromosome 3BL in durum wheat

Sawfly (Cephus cinctus Norton) is a major insect pest of wheat (Triticum spp.). The development of durum wheat (Triticum turgidum L. var durum) with stem solidness for resistance to sawfly is a strategy to minimize loss from this insect. This study was undertaken to identify a DNA marker linked to stem solidness and sawfly cutting in durum wheat for use in marker-assisted selection. A set of 151 doubled haploid lines developed from the cross of Kyle*2/Biodur sel. (solid stemmed) and Kofa (hollow stemmed) were evaluated for stem solidness and sawfly cutting. Microsatelite primers that generated polymorphisms between the parental genotypes were tested on the whole population, and primers that followed a 1:1 ratio of parental bands were used in linkage analysis with least squares mean stem solidness scores. Three microsatellite markers, Xgwm247, Xgwm181 and Xgwm114 located on chromosome 3BL, were shown to be associated with the stem solidness locus and with sawfly cutting. The Xgwm114 marker was located on one side of the stem solidness locus with Xgwm247 and Xgwm181 on the opposing side. Recombinant inbred line populations G9580B-FE1C/AC Navigator and Golden Ball/DT379//STD65 segregating for the stem solidness trait confirmed the association between the markers and the stem solidness gene. The Golden Ball/DT379//STD65 population was also tested with the Xwmc632 microsatellite marker, which showed a polymorphism associated with stem solidness. The results also indicated the stem solidness trait was controlled by a single locus in both doubled haploid and recombinant inbred line populations. The markers should be useful in breeding programs for the identification and selection of stem solidness.     

Identification of AFLP fragments linked to seed coat colour in Brassica juncea and conversion to a SCAR marker for rapid selection

A Brassica juncea mapping population was generated and scored for seed coat colour. A combination of bulked segregant analysis and AFLP methodology was employed to identify markers linked to seed coat colour in B. juncea. AFLP analysis using 16 primer combinations revealed seven AFLP markers polymorphic between the parents and the bulks. Individual plants from the segregating population were analysed, and three AFLP markers were identified as being tightly linked to the seed coat colour trait and specific for brown-seeded individuals. Since AFLP markers are not adapted for large-scale application in plant breeding, our objective was to develop a fast, cheap and reliable PCR-based assay. Towards this goal, we employed PCR-walking technology to isolate sequences adjacent to the linked AFLP marker. Based on the sequence information of the cloned flanking sequence of marker AFLP8, primers were designed. Amplification using the locus-specific primers generated bands at 0.5 kb and 1.2 kb with the yellow-seeded parent and a 1.1-kb band with the brown-seeded parent. Thus, the dominant AFLP marker (AFLP8) was converted into a simple codominant SCAR (Sequence Characterized Amplified Region) marker and designated as SCM08. Scoring of this marker in a segregating population easily distinguished yellow- and brown-seeded B. juncea and also differentiated between homozygous (BB) and heterozygous (Bb) brown-seeded individuals. Thus, this marker will be useful for the development of yellow seed B. juncea cultivars and facilitate the map-based cloning of genes responsible for seed coat colour trait. Received: 2 October 1999 / Accepted: 11 November 1999     

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.