Discovery and introgression of the wild sunflower-derived novel downy mildew resistance gene <Emphasis Type="Italic">Pl</Emphasis><Subscript><Emphasis Type="Italic">19</Emphasis></Subscript> in confection sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.)

Key message

A new downy mildew resistance gene, Pl ₁₉ , was identified from wild Helianthus annuus accession PI 435414, introduced to confection sunflower, and genetically mapped to linkage group 4 of the sunflower genome.

Abstract

Wild Helianthus annuus accession PI 435414 exhibited resistance to downy mildew, which is one of the most destructive diseases to sunflower production globally. Evaluation of the 140 BC₁F_2:3 families derived from the cross of CMS CONFSCLB1 and PI 435414 against Plasmopara halstedii race 734 revealed that a single dominant gene controls downy mildew resistance in the population. Bulked segregant analysis conducted in the BC₁F₂ population with 860 simple sequence repeat (SSR) markers indicated that the resistance derived from wild H. annuus was associated with SSR markers located on linkage group (LG) 4 of the sunflower genome. To map and tag this resistance locus, designated Pl ₁₉ , 140 BC₁F₂ individuals were used to construct a linkage map of the gene region. Two SSR markers, ORS963 and HT298, were linked to Pl ₁₉ within a distance of 4.7 cM. After screening 27 additional single nucleotide polymorphism (SNP) markers previously mapped to this region, two flanking SNP markers, NSA_003564 and NSA_006089, were identified as surrounding the Pl ₁₉ gene at a distance of 0.6 cM from each side. Genetic analysis indicated that Pl ₁₉ is different from Pl ₁₇ , which had previously been mapped to LG4, but is closely linked to Pl ₁₇ . This new gene is highly effective against the most predominant and virulent races of P. halstedii currently identified in North America and is the first downy mildew resistance gene that has been transferred to confection sunflower. The selected resistant germplasm derived from homozygous BC₂F₃ progeny provides a novel gene for use in confection sunflower breeding programs.

     

<Emphasis Type="Italic">Pl</Emphasis><Subscript><Emphasis Type="Italic">Arg</Emphasis></Subscript> from <Emphasis Type="Italic">Helianthus argophyllus</Emphasis> is unlinked to other known downy mildew resistance genes in sunflower

The Pl _Arg locus in the sunflower (Helianthus annuus L.) inbred line Arg1575-2 conferring resistance to at least four tested races (300, 700, 730, 770) of downy mildew (Plasmopara halstedii) was localized by the use of simple sequence repeat (SSR) markers. Bulked segregant analysis (BSA) was conducted on 126 individuals of an F₂ progeny from a cross between a downy mildew susceptible line, CmsHA342, and Arg1575-2. Twelve SSR markers linked to the Pl _Arg locus were identified. All markers were located proximal to Pl _Arg on linkage group LG1 based on the map of Yu et al. (2003) in a window of 9.3 cM. Since Pl _Arg was mapped to a linkage group different from all other Pl genes previously mapped with SSRs, it can be concluded that Pl _Arg provides a new source of resistance against P. halstedii in sunflower.     

Genetic mapping of rust resistance genes in confection sunflower line HA-R6 and oilseed line RHA 397

Few widely effective resistance sources to sunflower rust, incited by Puccinia helianthi Schwein., have been identified in confection sunflower (Helianthus annuus L.). The USDA inbred line HA-R6 is one of the few confection sunflower lines resistant to rust. A previous allelism test indicated that rust resistance genes in HA-R6 and RHA 397, an oilseed-type restorer line, are either allelic or closely linked; however, neither have been characterized nor molecularly mapped. The objectives of this study are (1) to locate the rust resistance genes in HA-R6 and RHA 397 on a molecular map, (2) to develop closely linked molecular markers for rust resistance diagnostics, and (3) to determine the resistance spectrum of two lines when compared with other rust-resistant lines. Two populations of 140 F_2:3 families each from the crosses of HA 89, as susceptible parent, with HA-R6 and RHA 397 were inoculated with race 336 of P. helianthi in the greenhouse. The resistance genes (R-genes) in HA-R6 and RHA 397 were molecularly mapped to the lower end of linkage group 13, which encompasses a large R-gene cluster, and were designated as R _13a and R _13b, respectively. In the initial maps, SSR (simple sequence repeat) and InDel (insertion and deletion) markers revealed 2.8 and 8.2 cM flanking regions for R _13a and R _13b, respectively, linked with a common marker set of four co-segregating markers, ORS191, ORS316, ORS581, and ZVG61, in the distal side and one marker ORS464 in the proximal side. To identify new markers closer to the genes, sunflower RGC (resistance gene candidate) markers linked to the downy mildew R-gene Pl ₈ and located at the same region as R _13a and R _13b were selected to screen the two F₂ populations. The RGC markers RGC15/16 and a newly developed marker SUN14 designed from a BAC contig anchored by RGC251 further narrowed down the region flanking R _13a and R _13b to 1.1 and 0.1 cM, respectively. Both R _13a and R _13b are highly effective against all rust races tested so far. Our newly developed molecular markers will facilitate breeding efforts to pyramid the R ₁₃ genes with other rust R-genes and accelerate the development of rust-resistant sunflower hybrids in both confection and oilseed sunflowers.     

Positional cloning of a candidate gene for resistance to the sunflower downy mildew, Plasmopara halstedii race 300

The resistance of sunflower to Plasmopara halstedii is conferred by major resistance genes denoted Pl. Previous genetic studies indicated that the majority of these genes are clustered on linkage groups 8 and 13. The Pl6 locus is one of the main clusters to have been identified, and confers resistance to several P. halstedii races. In this study, a map-based cloning strategy was implemented using a large segregating F2 population to establish a fine physical map of this cluster. A marker derived from a bacterial artificial chromosome (BAC) clone was found to be very tightly linked to the gene conferring resistance to race 300, and the corresponding BAC clone was sequenced and annotated. It contains several putative genes including three toll-interleukin receptor-nucleotide binding site-leucine rich repeats (TIR-NBS-LRR) genes. However, only one TIR-NBS-LRR appeared to be expressed, and thus constitutes a candidate gene for resistance to P. halstedii race 300.     

Genetic mapping of microsatellite markers around the arcelin bruchid resistance locus in common bean

The deployment in common beans (Phaseolus vulgaris L.) of arcelin-based bruchid resistance could help reduce post-harvest storage losses to the Mexican bean weevil [(Zabrotes subfasciatus (Boheman)]. Arcelin is a member of the arcelin-phytohemagglutinin-α-amylase inhibitor (APA) family of seed proteins, which has been extensively studied but not widely used in bean breeding programs. The purpose of this study was to evaluate microsatellite markers for genetic analysis of arcelin-based bruchid resistance and to determine the orientation of markers and the rate of recombination around the APA locus. A total of 10 previously developed microsatellites and 22 newly developed markers based on a sequenced BAC from the APA locus were screened for polymorphism and of these 15 were mapped with an F₂ population of 157 individuals resulting from a susceptible × resistant cross of SEQ1006 × RAZ106 that segregated for both the arcelin 1 allele and resistance to the bruchid, Z. subfasciatus. Microsatellites derived from APA gene sequences were linked within 0.8 cM of each other and were placed relative to the rest of the b04 linkage group. In a comparison of genetic to physical distance on the BAC sequence, recombination was found to be moderate with a ratio of 125 kb/cM, but repressed within the APA locus itself. Several markers were predicted to be very effective for genetic studies or marker-assisted selection, based on their significant associations with bruchid resistance and on low adult insect emergence and positions flanking the arcelin and phytohemagglutinin genes.     

Inheritance and molecular mapping of a downy mildew resistance gene, Pl 13 in cultivated sunflower (Helianthus annuus L.)

The inheritance of resistance to sunflower downy mildew (SDM) derived from HA-R5 conferring resistance to nine races of the pathogen has been determined and the new source has been designated as Pl ₁₃ . The F₂ individuals and F₃ families of the cross HA-R5 (resistant) × HA 821 (susceptible) were screened against the four predominant SDM races 300, 700, 730, and 770 in separate tests which indicated dominant control by a single locus or a cluster of tightly linked genes. Bulked segregant analysis (BSA) was carried out on 116 F₂ individuals with 500 SSR primer pairs that resulted in the identification of 10 SSR markers of linkage groups 1 (9 markers) and 10 (1 marker) of the genetic map (Tang et al. in Theor Appl Genet 105:1124–1136, 2002) that distinguished the bulks. Of these, the SSR marker ORS 1008 of linkage group 10 was tightly linked (0.9 cM) to the Pl ₁₃ gene. Genotyping the F₂ population and linkage analysis with 20 polymorphic primer pairs located on linkage group 10 failed to show linkage of the markers with downy mildew resistance and the ORS 1008 marker. Nevertheless, validation of polymorphic SSR markers of linkage group 1 along with six RFLP-based STS markers of linkage group 12 of the RFLP map of Jan et al. (Theor Appl Genet 96:15–22, 1998) corresponding to linkage group 1 of the SSR map, mapped seven SSR markers (ORS 965-1, ORS 965-2, ORS 959, ORS 371, ORS 716, and ORS 605) including ORS 1008 and one STS marker (STS10D6) to linkage group 1 covering a genetic distance of 65.0 cM. The Pl ₁₃ gene, as a different source with its location on linkage group 1, was flanked by ORS 1008 on one side at a distance of 0.9 cM and ORS 965-1 on another side at a distance of 5.8 cM. These closely linked markers to the Pl ₁₃ gene provide a valuable basis for marker-assisted selection in sunflower breeding programs.     

Fine genetic and physical mapping of the CRb gene conferring resistance to clubroot disease in Brassica rapa

The use of clubroot resistance (CR) genes is an effective and economical approach for controlling Plasmodiophora brassicae, the causal agent of clubroot disease in Chinese cabbage (Brassica rapa) and other Brassica crops. In a previous study, we identified and mapped the CRb locus on chromosome A03 of B. rapa in the doubled-haploid (DH) line ‘CR Shinki DH line’ of Chinese cabbage. In this study, CRb, a dominant gene conferring resistance to pathotype 4 of P. brassicae, was finely mapped in combination with bulked segregant analysis and bioinformatics analysis (BIA). Using 1,486 highly susceptible individuals and 2,896 individuals from two separate F₂ populations of ‘702-5’ (B. rapa ssp. chinensis) ×  ‘CR Shinki DH line,’ the CRb locus was narrowed to a region of approximately 0.14 cM between two flanking markers, TCR79 and TCR108. The sequences of seven newly developed markers linked to CRb were landed on bacterial artificial chromosome (BAC) of the reference B. rapa ‘Chiifu-401-42’ by BIA, and a physical map consisting of three BAC clones was constructed. The CRb locus was defined as an interval of approximately 83.5 kb on a BAC clone (KBrB085J21). The target interval contained one Toll-interleukin-1 receptor/nucleotide-binding site/leucine-rich repeat (TIR–NBS–LRR) gene, one NBS–LRR gene, and several putative regulatory genes in the B. rapa genome. The CRb gene was tightly linked to two other CR genes, CRa and CRb ^Kato . These results provide useful information for isolation of the CRb gene and tightly linked molecular markers for breeding CR in B. rapa.     

Genetic mapping of a major gene in triticale conferring resistance to bacterial leaf streak

Key message

A major gene conferring resistance to bacterial leaf streak was mapped to chromosome 5R in triticale.

Abstract

Bacterial leaf streak (BLS), caused by Xanthomonas translucens pv. undulosa (Xtu), is an important disease of wheat and triticale around the world. Although resistance to BLS is limited in wheat, several triticale accessions have high levels of resistance. To characterize the genetic basis of this resistance, we developed triticale mapping populations using a resistant accession (Siskiyou) and two susceptible accessions (UC38 and Villax St. Jose). Bulked segregant analysis in an F₂ population derived from the cross of Siskiyou × UC38 led to the identification of a simple sequence repeat (SSR) marker (XSCM138) on chromosome 5R that co-segregated with the resistance gene. The cross of Siskiyou × Villax St. Jose was advanced into an F_2:5 recombinant inbred line population and evaluated for BLS reaction. Genetic linkage maps on this population were assembled with markers generated using genotyping-by-sequencing as well as several SSR markers previously identified on 5R. Quantitative trait locus (QTL) mapping revealed a single major QTL on chromosome 5R, underlined by the same SSR marker as in the Siskiyou × UC38 population. The F₁ hybrids of the two crosses were highly resistant to BLS, indicating that resistance is largely dominant. This work will facilitate introgression of this rye-derived BLS resistance gene into the wheat genome by molecular marker-mediated chromosome engineering.

     

Recombination is suppressed in an alien introgression in peanut harboring Rma, a dominant root-knot nematode resistance gene

Rma, a dominant root-knot nematode resistance gene introduced into tetraploid peanut (Arachis hypogaea) from a synthetic allotetraploid donor (TxAG-6), has been widely deployed in modern cultivars. The genomic location and borders of the alien chromosome segment introgressed from TxAG-6 into NemaTAM (a BC₇-derived introgression line) and other modern cultivars carrying Rma have not been genetically mapped, and resistance gene candidates (RGCs) have not been identified for Rma. Our study focused on densely populating the alien introgression with codominant DNA markers, identifying and mapping the borders of the alien introgression carried by NemaTAM, and identifying RGCs for Rma. Altogether, 2,847 simple sequence repeat (SSR) and 380 single strand conformational polymorphism (SSCP) markers were screened for linkage to Rma-247 of the SSCP markers targeted 202 nucleotide binding site (NBS) leucine-rich repeat (LRR) and other resistance (R) gene homologs (75 were identified by mining a peanut EST database). SSR, NBS-LRR, and Ser/Thr receptor-like protein loci within the alien introgression co-segregated with Rma in an F₄ population (Gregory × Tifguard) and were tightly linked and spanned 3.4 cM in an F₅ population (NemaTAM × GP-NC-WS-14). By comparative mapping in the A-genome progenitor of peanut (A. duranensis), Rma was discovered to have been introduced on an interstitial alien chromosome segment spanning one-third to one-half of chromosome 9A. Numerous codominant DNA markers were identified for finer mapping of Rma, shortening the alien introgression harboring Rma by marker-assisted selection, and introducing novel root-knot nematode R-genes into peanut by targeting syntenic segments on chromosomes 9A and 9B in wild diploid donors.     

Molecular tagging of a novel rust resistance gene R 12 in sunflower (Helianthus annuus L.)

Sunflower production in North America has recently suffered economic losses in yield and seed quality from sunflower rust (Puccinia helianthi Schwein.) because of the increasing incidence and lack of resistance to new rust races. RHA 464, a newly released sunflower male fertility restorer line, is resistant to both of the most predominant and most virulent rust races identified in the Northern Great Plains of the USA. The gene conditioning rust resistance in RHA 464 originated from wild Helianthus annuus L., but has not been molecularly marked or determined to be independent from other rust loci. The objectives of this study are to identify molecular markers linked to the rust resistance gene and to investigate the allelism of this gene with the unmapped rust resistance genes present in HA-R6, HA-R8 and RHA 397. Virulence phenotypes of seedlings for the F₂ population and F_2:3 families suggested that a single dominant gene confers rust resistance in RHA 464, and this gene was designated as R ₁₂ . Bulked segregant analysis identified ten markers polymorphic between resistant and susceptible bulks. In subsequent genetic mapping, the ten markers covered 33.4 cM of genetic distance on linkage group 11 of sunflower. A co-dominant marker CRT275-11 is the closest marker distal to R ₁₂ with a genetic distance of 1.0 cM, while ZVG53, a dominant marker linked in the repulsion phase, is proximal to R ₁₂ with a genetic distance of 9.6 cM. The allelism test demonstrated that R ₁₂ is not allelic to the rust resistance genes in HA-R6, HA-R8 and RHA 397, and it is also not linked to any previously mapped rust resistance genes. Discovery of the R ₁₂ novel rust resistance locus in sunflower and associated markers will potentially support the molecular marker-assisted introgression and pyramiding of R ₁₂ into sunflower breeding lines.     

Molecular analysis of a major locus for resistance to downy mildew in sunflower with specific PCR-based markers

Resistance of sunflower to the obligate parasite Plasmopara halstedii is conferred by specific dominant genes, denoted Pl. The Pl6 locus confers resistance to all races of P. halstedii except one, and must contain at least 11 tightly linked genes each giving resistance to different downy mildew races. Specific primers were designed and used to amplify 13 markers covering a genetic distance of about 3 cM centred on the Pl6 locus. Cloning and sequence analysis of these 13 markers indicate that Pl6 contains conserved genes belonging to the TIR-NBS-LRR class of plant resistance genes. Received: 9 April 2001 / Accepted: 10 August 2001     

Downy mildew (Pl ( 8 ) and Pl ( 14 )) and rust (R ( Adv )) resistance genes reside in close proximity to tandemly duplicated clusters of non-TIR-like NBS-LRR-encoding genes on sunflower chromosomes 1 and 13

Nucleotide binding site-leucine rich repeat (NBS-LRR) proteins are encoded by a ubiquitous gene family in sunflower and frequently harbor disease resistance genes. We investigated NBS-LRR-encoding resistance gene candidates (RGCs) flanking the downy mildew resistance genes Pl ₈ and Pl ₁₄ and the rust resistance gene R _Adv , which map on the NBS-LRR clusters of linkage groups 1 and 13 in sunflower genome. We shotgun sequenced bacterial artificial chromosome (BAC) clones proximal to Pl ₈ , Pl ₁₄ , and R _Adv and identified seven novel non-Toll/interleukin-1 receptor (TIR)-like NBS-LRR RGCs, which clustered with previously identified RGCs of linkage group 13 but were phylogenetically distant from the TIR- and non-TIR-NBS-LRR-encoding superfamilies of sunflower. Six of the seven predicted RGCs have intact open reading frames and reside in genomic segments with abundant transposable elements. The genomic localization and sequence similarity of the novel non-TIR-like predicted RGCs suggests that they originated from tandem duplications. RGCs in the proximity of Pl ₈ and R _Adv were likely introgressed from silverleaf sunflower genome, where the RGC cluster of linkage group 13 is duplicated in two independent chromosomes that have different architecture and level of recombination from the respective common sunflower chromosomes.     

Chromosome location and allele-specific PCR markers for marker-assisted selection of the oat crown rust resistance gene Pc91

Race-specific seedling resistance genes are the primary means of controlling crown rust of oat caused by Puccinia coronata Corda f. sp. avenae Eriks in Canada. Pc91 is a seedling crown rust resistance gene that is highly effective against the current crown rust population in North America. A number of race-specific resistance genes have been mapped and markers that are closely linked to them have been identified. However, the use of these markers in oat breeding has been limited by the economics of marker-assisted selection (MAS). A crucial step in the successful application of MAS in breeding programs is the development of inexpensive and easy-to-use molecular markers. The primary objective of this study was to develop co-dominant KBioscience competitive allele-specific PCR (KASP) markers linked to Pc91 for deployment in high-throughput MAS in oat breeding programs. The allele-specific marker showed consistent diagnostic polymorphism between the selected 16 North American oat breeding lines. The developed co-dominant marker was also validated on three F₂ populations (AC Morgan × Stainless; SW Betania × Stainless; AC Morgan × CDC Morrison) and one recombinant inbred line population (CDC Sol-Fi × HiFi) segregating for Pc91 using KASP genotyping technology. We recommend the simple, low-cost marker as a powerful tool for pyramiding Pc91 with other effective crown rust resistance loci into a single line. The mapping results indicate that crown rust resistance gene Pc91 resides on the translocated oat chromosome 7C-17A.     

Genetic localization of a bruchid resistance gene and its relationship to insecticidal cyclopeptide alkaloids, the vignatic acids, in mungbean (Vigna radiata L. Wilczek)

Bruchid resistance, controlled by a single dominant gene (Br) in a wild mungbean accession (TC1966), has been incorporated into cultivated mungbean (Vigna radiata). The resistance gene simultaneously confers inhibitory activity against the bean bug, Riptortus clavatus Thunberg (Hemiptera: Alydidae). The resultant isogenic line (BC₂₀ generation) was characterized by the presence of a group of novel cyclopeptide alkaloids, called vignatic acids. A linkage map was constructed for Br and the vignatic acid gene (Va) using restriction fragment length polymorphism (RFLP) markers and a segregating BC₂₀F₂ population. By screening resistant and susceptible parental lines with 479 primers, eight randomly amplified polymorphic DNA (RAPD) markers linked to Br were identified and cloned for use as RFLP probes. All eight RAPD-based markers, one mungbean, and four common bean genomic clones were effectively integrated around Br within a 3.7-cM interval. Br was mapped to a 0.7-cM segment between a cluster consisting of six markers and a common bean RFLP marker, Bng110. The six markers are closest to the bruchid resistance gene, approximately 0.2?cM away. The vignatic acid gene, Va, cosegregated with bruchid resistance. However, one individual was identified in the BC₂₀F₂ population that retained vignatic acids in spite of its bruchid susceptibility. Consequently, Va was mapped to a single locus at the same position as the cluster of markers and 0.2?cM away from Br. These results suggest that the vignatic acids are not the principal factors responsible for bruchid resistance in V. radiata but will facilitate the use of map-based cloning strategies to isolate the Br gene.     

Genetic and physical mapping of blast resistance gene <Emphasis Type="Italic">Pi-42(t)</Emphasis> on the short arm of rice chromosome 12

We have identified, genetically mapped and physically delimited the chromosomal location of a new blast resistance gene from a broad spectrum resistant genotype ‘DHR9’. The segregation analysis of an F₂ progeny of a cross between a susceptible cv. ‘HPU741’ and the resistant genotype ‘DHR9’ suggested that the resistance was conditioned by a single dominant gene. A RAPD marker, OPA8₂₀₀₀, linked to the resistance gene was identified by the linkage analysis of 109 F₂ individuals. By chromosomal landing of the sequence of RAPD marker on the sequence of reference cv. Nipponbare, the gene was mapped onto rice chromosome 12. Further linkage analysis with two polymorphic simple sequence repeat (SSR) markers, RM2529 and RM1337 of chromosome 12, confirmed the chromosomal localization of the resistance gene. Based on linkage analysis of 521 susceptible F₂ plants and comparative haplotype structure analysis of the parental genotypes with SSR and sequence tagged site (STS) markers developed from the Nipponbare PAC/BAC clones of chromosome 12, the resistance gene was delimited within a 2 cM interval defined by STS marker, STS5, on the telomeric side and SSR marker, RRS6 on the centromeric side. By aligning the sequences of linked markers on the sequence of cv. Nipponbare, a ~4.18 Mb cross-over cold region near the centromere of chromosome 12 was delineated as the region of blast resistance gene. In this region, six putatively expressed NBS-LRR genes were identified by surveying the equivalent genomic region of cv. Nipponbare in the TIGR Whole Genome Annotation Database (http://www.tigr.org). NBS-LRR locus, LOC_Os12g18374 situated in BAC clone OJ1115_G02 (Ac. No. AL772419) was short-listed as a potential candidate for the resistance gene identified from DHR9. The new gene was tentatively designated as Pi-42(t). The markers tightly linked to gene will facilitate marker-assisted gene pyramiding and cloning of the resistance gene.     

Molecular analysis of the high stearic acid content in sunflower mutant CAS-14

Increasing the stearic acid content to improve sunflower (Helianthus annuus L.) oil quality is a desirable breeding objective for food-processing applications. CAS-14 is a sunflower mutant line with a high stearic acid content in its seed oil (>35% vs. <6% in currently grown sunflower hybrids), which is controlled by the Es3 gene. However, the expression of the high stearic acid character in CAS-14 is strongly influenced by temperature during seed maturation and it is not uniform along the seed. The objectives of this study were (1) to identify PCR-based molecular markers linked to the Es3 gene from CAS-14, (2) to map this gene on the sunflower genetic map, and (3) to characterize the interaction between CAS-14 and CAS-3, a sunflower high stearic acid (about 26%) mutant line with the Es1 and Es2 genes determining this trait. Two F₂ mapping populations were developed from crosses between CAS-14 and P21, a nuclear male sterile line with the Ms₁₁ gene controlling this character, and between CAS-14 and CAS-3. One hundred and thirty-three individuals from P21×CAS-14, and 164 individuals from CAS-3×CAS-14 were phenotyped in F₂ and F₃ seed generations for fatty acid composition using gas–liquid chromatography, and they were then genotyped with microsatellite [simple sequence repeat (SSR)] and insertion–deletion (INDEL) markers. Bulk segregant analysis in the P21×CAS-14 population identified two markers on LG 8 putatively linked to Es3. A large linkage group was identified using additional markers mapping to LG 8. Es3 mapped to the distal half of LG 8 and was flanked by the SSR markers ORS243 and ORS1161 at genetic distances of 0.5, and 3.9 cM, respectively. The Ms₁₁ gene was also mapped to LG 8 and genetic distance between this gene and Es3 was found to be 7.4 cM. In the CAS-3×CAS-14 population, two QTLs were identified on LG 1 and LG 8, which underlie the Es1 gene from CAS-3 and the Es3 gene from CAS-14, respectively. A significant epistatic interaction between these two QTLs was found. Results from this study provided a basis for determining CAS-14 efficient breeding strategies.     

High-throughput genotyping-by-sequencing facilitates molecular tagging of a novel rust resistance gene, <Emphasis Type="Italic">R</Emphasis><Subscript><Emphasis Type="Italic">15</Emphasis></Subscript>, in sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.)

Key message

A novel rust resistance gene, R ₁₅ , derived from the cultivated sunflower HA-R8 was assigned to linkage group 8 of the sunflower genome using a genotyping-by-sequencing approach. SNP markers closely linked to R ₁₅ were identified, facilitating marker-assisted selection of resistance genes.

Abstract

The rust virulence gene is co-evolving with the resistance gene in sunflower, leading to the emergence of new physiologic pathotypes. This presents a continuous threat to the sunflower crop necessitating the development of resistant sunflower hybrids providing a more efficient, durable, and environmentally friendly host plant resistance. The inbred line HA-R8 carries a gene conferring resistance to all known races of the rust pathogen in North America and can be used as a broad-spectrum resistance resource. Based on phenotypic assessments of 140 F₂ individuals derived from a cross of HA 89 with HA-R8, rust resistance in the population was found to be conferred by a single dominant gene (R ₁₅ ) originating from HA-R8. Genotypic analysis with the currently available SSR markers failed to find any association between rust resistance and any markers. Therefore, we used genotyping-by-sequencing (GBS) analysis to achieve better genomic coverage. The GBS data showed that R ₁₅ was located at the top end of linkage group (LG) 8. Saturation with 71 previously mapped SNP markers selected within this region further showed that it was located in a resistance gene cluster on LG8, and mapped to a 1.0-cM region between three co-segregating SNP makers SFW01920, SFW00128, and SFW05824 as well as the NSA_008457 SNP marker. These closely linked markers will facilitate marker-assisted selection and breeding in sunflower.

     

Chromosomal location of genomic SSR markers associated with yellow rust resistance in Turkish bread wheat (Triticum aestivum L.)

We have previously reported Xgwm382 as a diagnostic marker for disease resistance against yellow rust in Izgi2001 × ES14 F₂ population. Among the same earlier tested 230 primers, one SSR marker (Xgwm311) also amplified a fragment which is present in the resistant parent and in the resistant bulks, but absent in the susceptible parent and in the susceptible bulks. To understand the chromosome group location of these diagnostic markers, Xgwm382 and Xgwm311, in the same population, we selected 16 SSR markers mapped only in one genome of chromosome group 2 around 1–21 cM distance to these diagnostic markers based on the SSR consensus map of wheat. Out of 16 SSRs, Xwmc658 identified resistant F₂ individuals as a diagnostic marker for yellow rust disease and provided the location of Xgwm382 and Xgwm311 on chromosome 2AL in our plant material.     

Genetic Mapping of the Tph1 Gene Controlling Beta-tocopherol Accumulation in Sunflower Seeds

Tocopherols are a family of fat soluble antioxidants of great value for both nutritional and technological properties of seed oils. The four naturally occurring tocopherols (alpha-, beta-, gamma- and delta-tocopherol) widely differ for their relative in vivo (vitamin E) and in vitro antioxidant properties. Sunflower (Helianthus annuus L.) seeds mainly contain alpha-tocopherol (95% of the total tocopherols), which has a great vitamin E value but a low in vitro activity. Conversely, beta-tocopherol shows more balanced in vitro and in vivo antioxidant properties, which is desired for specific uses of the oil. The sunflower line T589 is characterised by an increased beta-tocopherol content in the seeds ( >30%), which is determined by the single gene Tph1. The objectives of this study were to map the Tph1 gene by molecular markers (SSRs) and to develop a linkage map of the Tph1-encompassing region. High performance liquid chromatography (HPLC) was used to phenotype 103 F₂ and 67 F₃ progeny from the mapping population CAS-12 × T589, which segregates for Tph1. Bulk segregant analysis identified two SSR markers on linkage group (LG) 1 linked to Tph1. A large linkage group was constructed by genotyping additional SSRs and INDEL markers. Tph1 mapped to the upper end of LG 1 and cosegregated with the SSR markers ORS1093, ORS222, and ORS598. The availability of tightly linked PCR-based markers and the location of the Tph1 gene on the sunflower genetic map will be useful for marker-assisted selection in sunflower and provides a basis for the physical mapping and positional cloning of this gene.