Downy Mildew Resistance Genes Research Articles

Registration of HA‐DM15 and HA‐DM16 oilseed sunflower germplasms with resistance to sunflower downy mildew

AbstractSunflower (Helianthus L.) production ranked third in global oilseed production in 2021. Downy mildew (DM), caused by the oomycete pathogen Plasmopara halstedii (Farl.) Berl. et de Toni, is a major constraint for worldwide sunflower production, causing significant yield losses in susceptible hybrids. The search for new sources of resistance to DM is the primary objective of all sunflower breeding programs. Germplasms HA‐DM15 (Reg. no. GP‐385, PI 702359) and HA‐DM16 (Reg. no. GP‐386, PI 702360) were developed by introgressing two new DM resistance genes, Pl37 and Pl38, from the wild sunflower species H. annuus and H. praecox into oilseed sunflower, respectively. The BC1F3‐derived HA‐DM15 harboring the Pl37 gene was selected from the cross of HA 89//NMS HA 89/wild H. annuus PI 435417. The germplasm line HA‐DM16 carrying the Pl38 gene is an improved oilseed derivative of Rf PRA‐417 with DM resistance originally derived from the wild H. praecox PRA‐417 from the cross of cytoplasmic male sterile (CMS) HA89*2/wild H. praecox PRA‐417. HA‐DM15/Pl37 and HA‐DM16/Pl38 are immue to the most predominant and virulent DM races idenfied in North America and Europe. Pl37 and Pl38 have been genetically mapped to sunflower chromosomes 4 and 2, respectively, with single nucleotide polymorphism markers linked to the both genes facilitating their transfer to elite sunflower lines by marker‐assisted selection, providing new and diverse sources for sunflower DM‐resistance breeding.

Registration of HA‐R20 and HA‐R21 confection sunflower germplasms resistant to rust and downy mildew

AbstractRust and downy mildew (DM) are detrimental diseases in global sunflower (Helianthus annuus L.) production. Disease often results in yield loss and reduced seed quality. Host resistance to DM and rust is mediated by single dominant genes in sunflower. To better utilize genetic resistance, gene pyramiding is a common practice in crop breeding to extend the durability and longevity of resistance. Two confection sunflower germplasm lines, HA‐R20 (Reg. no. GP‐387, PI 702361) and HA‐R21 (Reg. no. GP‐388, PI 702362), were developed using the pedigree breeding method and DNA marker‐assisted selection and released by the USDA‐ARS Sunflower and Plant Biology Research Unit in collaboration with the North Dakota Agricultural Experiment Station in September 2022. HA‐R20 is an F3‐derived F4 confection restorer selection from the cross of HA‐DM2 and HA‐R8, carrying rust resistance genes R12 and R15 and DM resistance gene PlArg. HA‐R21 is an F3‐derived F4 confection maintainer selection from the cross of HA‐DM3 and HA‐R8, carrying rust resistance genes R13a and R15 and DM resistance gene Pl17. Disease reaction and marker testing for DM and rust confirmed that both germplasms harbor DM and rust R genes in the homozygous condition and are resistant to all DM and rust races identified in North America to date. These multiple disease‐resistant lines will provide the sunflower industry with durable disease‐resistant sources for the continued improvement of the crop.

Validated Molecular Marker for Downy Mildew Disease Resistance Breeding of Sunflower: A Short Review

The oomycete pathogen Plasmopara halstedii responsible for sunflower downy mildew (DM), that is a significant and important disease that greatly affects the economy. As of now, there is no non-race-specific resistance for this disease and breeders are depended on race-specific resistance to control DM disease. On the other hand, using conventional breeding procedure introgression of the DM resistance genes is a long-term task due to the highly virulent and aggressive nature of the P. halstedii pathogen. Molecular markers that can be applied at the seedling stage, offers rapid response for selection with higher precision as well as a lower cost. There are currently 36 downy mildew resistance genes (R genes), designated as Pl (Pl1-Pl36, Plhra, and PlArg, in sunflowers, each with a unique linkage group (LGs). The availability of DM resistance genomic data of sunflower, related to Single Nucleotide Polymorphisms (SNP) based markers with mine allelic diversity maximize the opportunity of utilizing Marker assisted selection (MAS) techniques for downy mildew resistance breeding. This review highlights the available genetic marker and their utilization at MAS techniques for enhancing downy mildew disease resistant breeding program of sunflowers.

Identification of <i>Rpv3</i> and <i>Rpv12</i> loci in the progenies of the ‘Talisman’ grape cultivar

Currently, when implementing breeding programs to produce pathogen-resistant grape genotypes, the DNA marker assessment method is used both directly in breeding-oriented selection and in evaluation of the initial gene pool. The ‘Talisman’ grape cultivar, with its fine consumer characteristics, resistance to diseases and frost, and a functionally female type of flower, is promising for breeding.We performed a DNA marker assessment of the ‘Talisman’ genotype and cultivars as well as new hybrids of grapes developed with the participation of cv. ‘Talisman’ for the presence of the Rpv3 and Rpv12 downy mildew resistance loci. It is known that the presence of these two genes in the same grape genotype has an additive effect. According to the pedigree of cv. ‘Talisman’ (Frumoasa Albe × Vostorg), the presence of these genes can be assumed in the studied sample. The study was based on PCR with an analysis of the results on an automatic genetic analyzer. DNA was isolated from young shoots of the analyzed plants by the CTAB method. We used closely linked microsatellite markers recommended for DNA identification of the allelic status of the Rpv3 (UDV305, UDV737) and Rpv12 (UDV343, UDV360) genes. The simultaneous presence of Rpv3 and Rpv12 was detected only in the cv. ‘Talisman’ genotype. When analyzing the progeny genotypes of cv. ‘Talisman’, the presence of the Rpv3 downy mildew resistance gene was found in the grape hybrids “Agat Dubovskiy”, “Pestry”, and Rpv12 gene in the ‘Viktor’ and ‘Preobrazheniye’ genotypes. DNA-marker analysis confirmed the prospects of the cv. ‘Talisman’ genotype for breeding of table cultivars as a donor of the downy mildew resistance genes Rpv3 and Rpv12.

Skim resequencing finely maps the downy mildew resistance loci RPF2 and RPF3 in spinach cultivars whale and Lazio.

Commercial production of spinach (Spinacia oleracea L.) is centered in California and Arizona in the US, where downy mildew caused by Peronospora effusa is the most destructive disease. Nineteen typical races of P. effusa have been reported to infect spinach, with 16 identified after 1990. The regular appearance of new pathogen races breaks the resistance gene introgressed in spinach. We attempted to map and delineate the RPF2 locus at a finer resolution, identify linked single nucleotide polymorphism (SNP) markers, and report candidate downy mildew resistance (R) genes. Progeny populations segregating for RPF2 locus derived from resistant differential cultivar Lazio were infected using race 5 of P. effusa and were used to study for genetic transmission and mapping analysis in this study. Association analysis performed with low coverage whole genome resequencing-generated SNP markers mapped the RPF2 locus between 0.47 to 1.46Mb of chromosome 3 with peak SNP (Chr3_1, 221, 009) showing a LOD value of 61.6 in the GLM model in TASSEL, which was within 1.08 Kb from Spo12821, a gene that encodes CC-NBS-LRR plant disease resistance protein. In addition, a combined analysis of progeny panels of Lazio and Whale segregating for RPF2 and RPF3 loci delineated the resistance section in chromosome 3 between 1.18-1.23 and 1.75-1.76Mb. This study provides valuable information on the RPF2 resistance region in the spinach cultivar Lazio compared to RPF3 loci in the cultivar Whale. The RPF2 and RPF3 specific SNP markers, plus the resistant genes reported here, could add value to breeding efforts to develop downy mildew resistant cultivars in the future.

Introgression and targeting of the Pl37 and Pl38 genes for downy mildew resistance from wild Helianthus annuus and H. praecox into cultivated sunflower (Helianthus annuus L.)

Two new downy mildew resistance genes, Pl37 and Pl38, were introgressed from wild sunflower species into cultivated sunflower and mapped to sunflower chromosomes 4 and 2, respectively Downy mildew (DM), caused by the oomycete pathogen Plasmopara halstedii (Farl.) Berl. & de Toni, is known as the most prevalent disease occurring in global sunflower production areas, especially in North America and Europe. In this study, we report the introgression and molecular mapping of two new DM resistance genes from wild sunflower species, Helianthus annuus and H. praecox, into cultivated sunflower. Two mapping populations were developed from the crosses of HA 89/H. annuus PI 435417 (Pop1) and CMS HA 89/H. praecox PRA-417 (Pop2). The phenotypic evaluation of DM resistance/susceptibility was conducted in the BC1F2-derived BC1F3 populations using P. halstedii race 734. The BC1F2 segregating Pop1 was genotyped using an Optimal GBS AgriSeq™ Panel consisting of 768 mapped SNP markers, while the BC1F2 segregating Pop2 was genotyped using a genotyping-by-sequencing approach. Linkage analysis and subsequent saturation mapping placed the DM resistance gene, designated Pl37, derived from H. annuus PI 435417 in a 1.6cM genetic interval on sunflower chromosome 4. Pl37 co-segregated with SNP markers SPB0003 and C4_5738736. Similarly, linkage analysis and subsequent saturation mapping placed the DM resistance gene, designated Pl38, derived from H. praecox PRA-417 in a 0.8cM genetic interval on sunflower chromosome 2. Pl38 co-segregated with seven SNP markers. Multi-pathotype tests revealed that lines with Pl37 or Pl38 are immune to the most prevalent and virulent P. halstedii races tested. Two germplasm lines, HA-DM15 with Pl37 and HA-DM16 with Pl38, were developed for use in sunflower DM-resistance breeding.

Genetic Insight into Disease Resistance Gene Clusters by Using Sequencing-Based Fine Mapping in Sunflower (Helianthus annuus L.).

Rust and downy mildew (DM) are two important sunflower diseases that lead to significant yield losses globally. The use of resistant hybrids to control rust and DM in sunflower has a long history. The rust resistance genes, R13a and R16, were previously mapped to a 3.4 Mb region at the lower end of sunflower chromosome 13, while the DM resistance gene, Pl33, was previously mapped to a 4.2 Mb region located at the upper end of chromosome 4. High-resolution fine mapping was conducted using whole genome sequencing of HA-R6 (R13a) and TX16R (R16 and Pl33) and large segregated populations. R13a and R16 were fine mapped to a 0.48 cM region in chromosome 13 corresponding to a 790 kb physical interval on the XRQr1.0 genome assembly. Four disease defense-related genes with nucleotide-binding leucine-rich repeat (NLR) motifs were found in this region from XRQr1.0 gene annotation as candidate genes for R13a and R16. Pl33 was fine mapped to a 0.04 cM region in chromosome 4 corresponding to a 63 kb physical interval. One NLR gene, HanXRQChr04g0095641, was predicted as the candidate gene for Pl33. The diagnostic SNP markers developed for each gene in the current study will facilitate marker-assisted selections of resistance genes in sunflower breeding programs.

Marker assisted selection (MAS) for downy mildew resistance in grapevines using Rpv3.1 associated markers

Powdery mildew and downy mildew are primary fungal diseases that cause significant damage in viticulture. Therefore, breeding powdery and/or downy mildew resistance is one of the priority subjects in grapevine breeding programs. This study aims to conduct early-selection by marker assisted selection (MAS) method among 869 genotypes obtained through crossbreeding ‘Alphonse Lavallee’ × ‘Regent’ cultivars using the markers (GF18-06 and GF18-08) associated with downy mildew resistance gene region Rpv3.1 to develop new grapevine cultivars resistant to downy mildew caused by Plasmopara viticola. A total of 869 hybrid plants which were obtained after crossing ‘Alphonse Lavallee’ × ‘Regent’ in a 3-year breeding program were used in the study. The hybrid plants were scored for the resistance level based on their sporulation intensity after artificial inoculation of P. viticola. DNA samples of the hybrid plants were amplified with GF18-06 and GF18-08 markers in Polymerase Chain Reaction (PCR) for MAS. The alleles which were associated to Rpv3.1 resistance locus and the results of resistance scoring were compared, and the applicability of the markers in MAS was verified. It was determined that the GF18-08/410 bp marker can be used successfully for MAS. Gf 18-06 marker 385 bp, 390 bp and 407 bp gave false positive results in our population, respectively 8.86%, 9.02% and 37.94%. Therefore, this may limit its use for MAS.

Characterization and mapping of a downy mildew resistance gene, Pl36, in sunflower (Helianthus annuus L.).

The online version contains supplementary material available at 10.1007/s11032-022-01280-1.

Lines resistant to downy mildew in the sunflower genetic collection at VIR

Background. Downy mildew (DM) caused by the fungus Plasmopara halstedii (Farl) Berl. & De Toni) is one of the most harmful diseases of sunflower (Helianthus annuus L.). Due to the pathogen’s attacks, annual seed harvest losses range between 30% and 70%. Lines resistant to new races of the pathogen should be obtained for the development of commercial sunflower hybrids.Materials and methods. Downy mildew resistance of 323 lines and 10 cultivars from the sunflower collection was assessed in the field at the Kuban Experiment Station of VIR in 2017–2018. Line VIR 845, susceptible during all years of observations, was used as a control. Resistance genes were identified by means of the molecular analysis using diagnostic markers of the Plarg, Pl6 and Pl8 genes that confer resistance to many known P. halstedii races.Results. The founder varieties of VIR’s lines were susceptible to a varying extent. Thirty-nine lines were resistant in 2016 and 2018; among those, 36 lines were susceptible in 2017. Presumably, a more virulent P. halstedii race became widespread in 2017, compared to the races that prevailed in 2016 and 2018, so the genes that determined resistance in 2016 and 2018 turned out to be ineffective. Lines ТА 716-18, VIR 768, and VIR 800, having originated from interspecific hybrids, exhibited absence of pathogenic damage during 3 years of the trials. Molecular markers of the Plarg, Pl6 and Pl8 genes were detected in most lines that demonstrated resistance in 2016 and 2018. There were no markers in lines VIR 768 and VIR 800, whereas in ТА 716-18 the markers of Plarg and Pl8 were present.Conclusion. As a result of the long-term studies, a trait-specific genetic collection was established for sunflower. It comprises genotyped lines with various effective DM resistance genes. Lines ТА 716-18, VIR 768 and VIR 800 appeared highly resistant to the pathogen and probably possess new resistance genes/alleles introgressed from wild species.

Marker-Assisted Pyramiding of Downy Mildew-Resistant Gene Ppa3 and Black Rot-Resistant Gene Xca1bo in Popular Early Cauliflower Variety Pusa Meghna

Cauliflower is an important extensively grown cool season vegetable in India. Black rot and downy mildew are major devastating diseases reducing yield and quality of the crop. To tackle these through host plant resistance, a marker-assisted backcross breeding method was followed to pyramid a black rot-resistant gene (Xca1bo) and a downy mildew-resistant gene (Ppa3) from donors BR-161 and BR-2, respectively, into the background of Pusa Meghna cauliflower cultivar. Marker-assisted backcross breeding was followed up to BC2 generation using SCAR marker ScOPO-04833 and SSR marker BoGMS0624 for black rot and downy mildew resistance genes in foreground selection, respectively. In background selection, at each stage of backcrossing, 47 parental polymorphic SSR markers were used. The graphical genotyping of the five two-gene (Xca1boXca1boPpa3Ppa3) homozygous BC2F2 plants showed an average recovery of 85.44% of the Pusa Meghna genome with highest genome recovery of 91.7%. The genome contribution of donor parents (BR-161 and BR-2) was 8.26 with 6.34% of residual heterozygousity. The backcross derived pyramided lines BC2F2:3-7-16 and BC2F2:3-7-33 showed high resistance to both the diseases and exhibited higher yield and vitamin C content as compared with recipient parent Pusa Meghna. It is, therefore, evident from this study that resistant genes can be introgressed successfully into a Pusa Meghna cultivar without any yield penalty, benefitting farmers with reduced input cost and consumers with chemical residue free produce. Besides, the pyramided lines carrying dominant resistant genes can be exploited in a hybridization programme to develop hybrid(s) in cauliflower.

Marker-assisted breeding of onion (<i>A. cepa L.</i>) maintainer line resistant to Downy mildew

Relevance. F1 hybrids breeding programs of onion are based on the use of nuclear cytoplasmic male sterility (NCMS). Breeding and seed production based on NCMS suggest a development of a female sterile maternal line, a maintainer line and a paternal component. The development of an isogenic pair of sterile line – maintainer line is one of the most labor-, time-consuming and intellectually-intensive stages of a breeding program, the implementation of which becomes more complicated with an increase in the number of traits / genes for which selection is carried out.Methods and results. This paper presents a genetic scheme for the development of a Downy mildewresistant (pathogen P. destructor) maintainer line of onion using marker-assisted selection (MAS). F2 populations were obtained from the cross of the female maintainer inbred line, Bn1- (13) (genotype – cytN msms pdpd) and male inbred line resistant to Downy mildew, No. 136 (genotype – cytT MsMs PdPd). DNA marker DMR1 were used for Downy mildew resistance gene Pd, jnurf13 – for maintainer gene ms and marker system 5`cob: orfA501 – for N, S and T cytoplasms. It was shown that the MAS application allow to develop a stable Downy mildew resistant maintainer line cytN msms PdPd in two generations.

Genetic analysis of downy mildew resistance and identification of molecular markers linked to resistance gene Ppa207 on chromosome 2 in cauliflower

Downy mildew is one of the most damaging fungal diseases of cauliflower. The present study was undertaken to identify molecular markers linked to the downy mildew resistance gene using 84 recombinant inbred lines (RILs) from a cross of Pusa Sharad (susceptible [S] to downy mildew) and DMR-2-0-7 (resistant [R] to downy mildew). The resistant and susceptible lines in the 84 RILs segregated in 1:1 (R:S) ratio, indicating that resistance for downy mildew disease is monogenic and the gene was named as Ppa207. During polymorphism survey between the parents using 105 simple sequence repeat (SSR) markers, 43 were polymorphic (27.55%). Bulked segregant analysis revealed that two of these markers that showed polymorphism, namely BoGMS0486 and BoGMS0900, could distinguish resistant and susceptible bulks and segregated in 1:1 (R:S) ratio. The recombination frequencies between BoGMS0486 and BoGMS0900, BoGMS0486 and Ppa207 and BoGMS0900 and Ppa207 were 4.8, 3.6 and 1.2%, respectively. The resistant gene Ppa207 was mapped in 4.8 cM linkage interval on linkage group 2 (C02) of cauliflower, flanked by the markers BoGMS0486 and BoGMS0900 at 3.6 and 1.2 cM, respectively, from Ppa207. Markers BoGMS0486 and BoGMS0900 were located 2.9 and 23.2 Mb positions, respectively, on chromosome 2 and the 4.8 cM marker interval corresponds to a physical distance of 20.3 Mb. The identified SSR markers linked to the new resistance gene Ppa207 will be very useful in marker assisted selection in cauliflower for developing varieties and/or hybrids resistant to downy mildew.

QTL Mapping linked to downy mildew resistance genes in maize (Zea mays)

Abstract. Ashan MD, Miftahudin, Reflinur, Pabendon MB, Santoso SB, Salim A. 2020. QTL Mapping linked to downy mildew resistance genes in maize (Zea mays). Biodiversitas 21: 3735-3743. Downy Mildew (DM) caused by Peronosclerospora spp. is one of the most destructive diseases and problems in yield losses of maize production worldwide. Identification of molecular marker-linked to the DM resistance genes is considered as an important step in the improvement of the DM resistance nature in maize breeding program. The objective of the study was to identify molecular markers linked to the DM resistance genes in maize. A total of 198 F3 maize lines generated from a cross between R10-4430 and Kandora was used in microsatellite genetic map construction and the corresponding F3: 4 families were used in phenotypic evaluation to identify quantitative trait loci (QTLs) responsible for DM resistance-related trait. The entire genetic linkage map constructed with 28 SSR markers resulted in 460.3 cM with an average distance between markers of 26.85 cM. Seven main-effect QTLs controlling the DM resistance genes were identified in the entire genome map of F3 population with the phenotypic variation explained (PVE) values ranged from 43.35 to 53.71%. Among detected QTLs, three QTLs, qDM-Pp1a, qDM-Pp1b1, and qDM-Pp1b2 were detected on chromosome 1, one QTL, qDM-Pp5 was on chromosome 5, two QTLs, qDM-Pp6b1 and qDM-Pp6b2 were on chromosome 6 and one QTL, qDM-Pp10 was on chromosome 10. The effect of detected QTLs responsible for DM resistance trait ranged from 43.35 to 53.71% and those will be potential to be further used as molecular aided selection in maize breeding for DM resistance.

DNA marker identification of Rpv3 downy mildew resistance gene in seedless grape varieties

Table grapes are a valuable dietary product. Seedless grapes are in high demand among consumers. For this reason, the breeding of seedless varieties is one of the popular trends in modern viticulture, along with the production of environmentally friendly products. Downy mildew (Plasmopara viticola(Berk. & M.A. Curtis) Berl. & De Toni) is one of the most common fungal diseases of the grapevine. Most downy mildew resistant grape accessions belong to North American species likeVitis aestivalisMichx.,V. berlandieriPlanch.,V. cinerea(Engelm. ex A. Gray) Engelm. ex Millard,V. ripariaMichx.,V. rupestris Scheele, etc. The search for donors of resistance genes is an urgent task.Rpv3is one of the most significant resistance genes from a number of North American grape varieties. The aim of this work is to identify the downy mildew resistance geneRpv3in seedless grape varieties by means of DNA-marker analysis. The grape varieties with rudimentary development of seed in berries and with North American species in the pedigree were chosen as the object of the study. The varieties “Dunavski lazur” and “Seyve Villard 12-375” with reference alleles were used as the positive control, whileV. viniferaL. was used as the negative control. UDV305 and UDV737 DNA-markers were used in this study to identify the allelic type of theRpv3gene. The work was performed using the polymerase chain reaction. The reaction products were separated by capillary electrophoresis using the ABI Prism 3130 automatic genetic analyzer. Evaluation of the results was done using the GeneMapper and PeakScanner software. Functional alleles of the downy mildew resistance geneRpv3were revealed in grape varieties “Kishmish zaporozhskiy”, “Lady Patricia”, “Remaily seedless”, “Pamyati Smirnova” and “Shayan”.Rpv3299-279, one of the seven known haplotypes, was identified in all the varieties. The pedigree analysis of the studied varieties indicated that the parental forms – “Seyve Villard” and “Seibel” hybrids – are presumably the donors of the gene. Grape accessions with the identifiedRpv3gene can be used in seedless varieties breeding as donors of resistance to downy mildew.

Marker-Assisted Gene Pyramiding and the Reliability of Using SNP Markers Located in the Recombination Suppressed Regions of Sunflower (Helianthus annuus L.).

Rust caused by the fungus Puccinia helianthi and downy mildew (DM) caused by the obligate pathogen Plasmopara halstedii are two of the most globally important sunflower diseases. Resistance to rust and DM is controlled by race-specific single dominant genes. The present study aimed at pyramiding rust resistance genes combined with a DM resistance gene, using molecular markers. Four rust resistant lines, HA-R3 (carrying the R4 gene), HA-R2 (R5), HA-R8 (R15), and RHA 397 (R13b), were each crossed with a common line, RHA 464, carrying a rust gene R12 and a DM gene PlArg. An additional cross was made between HA-R8 and RHA 397. Co-dominant simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers linked to the target genes were used to discriminate between homozygotes and heterozygotes in F2 populations. Five pyramids with different combinations of rust resistance genes were selected in the homozygous condition through marker-assisted selection, and three of them were combined with a DM resistance gene PlArg: R4/R12/PlArg, R5/R12/PlArg, R13b/R12/PlArg, R15/R12, and R13b/R15. The pyramiding lines with the stacking of two rust and one DM genes were resistant to all known races of North American sunflower rust and all known races of the pathogen causing DM, potentially providing multiple and durable resistance to both rust and DM. A cluster of 12 SNP markers spanning a region of 34.5 Mb on chromosome 1, which co-segregate with PlArg, were tested in four populations. Use of those markers, located in a recombination suppressed region in marker selection, is discussed.

Molecular dissection of resistance gene cluster and candidate gene identification of Pl17 and Pl19 in sunflower by whole-genome resequencing

Sunflower (Helianthus annuus L.) production is challenged by different biotic and abiotic stresses, among which downy mildew (DM) is a severe biotic stress that is detrimental to sunflower yield and quality in many sunflower-growing regions worldwide. Resistance against its infestation in sunflower is commonly regulated by single dominant genes. Pl17 and Pl19 are two broad-spectrum DM resistance genes that have been previously mapped to a gene cluster spanning a 3.2 Mb region at the upper end of sunflower chromosome 4. Using a whole-genome resequencing approach combined with a reference sequence-based chromosome walking strategy and high-density mapping populations, we narrowed down Pl17 to a 15-kb region flanked by SNP markers C4_5711524 and SPB0001. A prospective candidate gene HanXRQChr04g0095641 for Pl17 was identified, encoding a typical TNL resistance gene protein. Pl19 was delimited to a 35-kb region and was approximately 1 Mb away from Pl17, flanked by SNP markers C4_6676629 and C4_6711381. The only gene present within the delineated Pl19 locus in the reference genome, HanXRQChr04g0095951, was predicted to encode an RNA methyltransferase family protein. Six and eight SNP markers diagnostic for Pl17 and Pl19, respectively, were identified upon evaluation of 96 diverse sunflower lines, providing a very useful tool for marker-assisted selection in sunflower breeding programs.

Registration of Oilseed Sunflower Germplasms HA‐BSR6, HA‐BSR7, and HA‐BSR8 Highly Resistant to Sclerotinia Basal Stalk Rot and Downy Mildew

Sclerotinia basal stalk rot (BSR) and downy mildew (DM) are agronomically important diseases of sunflower (Helianthus annuus L.) worldwide. Three sunflower germplasm lines, HA‐BSR6 (Reg. no. GP‐353, PI 685019), HA‐BSR7 (Reg. no. GP‐354, PI 685020), and HA‐BSR8 (Reg. no. GP‐355, PI 685021), were developed with dual resistance to both BSR and DM. Their resistance to BSR was transferred from the wild annual sunflower H. praecox subsp. runyonii Engelmann & A. Gray (Heiser) (PI 468853), and DM resistance was introgressed from inbred line HA 458 possessing the Pl17 gene. The germplasms were tested for BSR resistance in inoculated field trials in multiple locations over 4 yr. All three germplasm lines showed significantly higher BSR resistance (p < 0.05) than the recurrent parent and the checks across environments, with a 4‐yr mean disease incidence (DI) ranging from 1.2 to 4.8%, while ‘Cargill 270’ (susceptible hybrid check) and HA 89 (recurrent parent) had DI of 36.1 and 31.0%, respectively, and HA 441 (resistant inbred check) and ‘Croplan 305’ (resistant hybrid check) had DI of 19.5 and 11.6%, respectively. Whole genome scan using genotyping‐by‐sequencing revealed the presence of H. praecox subsp. runyonii chromosome segments in HA‐BSR6, HA‐BSR7, and HA‐BSR8, which are potentially associated with BSR resistance. Phenotypic evaluation identified DM resistance in all three germplasm lines, with flanking DNA markers confirming the presence of the Pl17 gene in the lines. These germplasm lines can be used in sunflower breeding programs for pyramiding both BSR and DM resistance genes.

Identification of downy mildew resistance genes Rpv10 and Rpv3 by DNA-marker analysis in a Russian grapevine germplasm collection

Identification of downy mildew resistance genes <i>Rpv10</i> and <i>Rpv3</i> by DNA-marker analysis in a Russian grapevine germplasm collection

Diversification of the downy mildew resistance gene pool by introgression of a new gene, Pl35, from wild Helianthus argophyllus into oilseed and confection sunflowers (Helianthus annuus L.).

We have mapped a new downy mildew resistance gene, Pl35, derived from wild Helianthus argophyllus to sunflower linkage group 1. New germplasms incorporating the Pl35 gene were developed for both oilseed and confection sunflower Sunflower downy mildew (DM), caused by the oomycete pathogen Plasmopara halstedii, is an economically important and widespread sunflower disease worldwide. Non-race-specific resistance is not available in sunflower, and breeding for DM resistance relies on race-specific resistance to control this disease. The discovery of the novel DM resistance genes is a long-term task due to the highly virulent and aggressive nature of the P. halstedii pathogen, which reduces the effectiveness of resistance genes. The objectives of this study were to: (1) transfer DM resistance from a wild sunflower species Helianthus argophyllus (PI 494576) into cultivated sunflowers; (2) map the resistance gene; and (3) develop diagnostic single-nucleotide polymorphism (SNP) markers for efficient targeting of the gene in breeding programs. The H. argophyllus accession PI 494576 previously identified with resistance to the most virulent P. halstedii race 777 was crossed with oilseed and confection sunflower in 2012. Molecular mapping using the BC2F2 and BC2F3 populations derived from the cross CONFSCLB1/PI 494576 located a new resistance gene Pl35 on linkage group 1 of the sunflower genome. The new gene Pl35 was successfully transferred from PI 494576 into cultivated sunflowers. SNP markers flanking Pl35 were surveyed in a validation panel of 548 diversified sunflower lines collected globally. Eleven SNP markers were found to be diagnostic for Pl35 SNP alleles, with four co-segregating with Pl35. The developed oilseed and confection germplasms with diagnostic SNP markers for Pl35 will be very useful resources for breeding of DM resistance in sunflower.