Rapid identification of QTLs underlying resistance to <Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> in pepper (<Emphasis Type="Italic">Capsicum frutescens</Emphasis>)

Key message

Next-generation sequencing enabled a fast discovery of QTLs controlling CMV resistant in pepper. The gene CA02g19570 as a possible candidate gene of qCmr2.1 was identified for resistance to CMV in pepper.

Abstract

Cucumber mosaic virus (CMV) is one of the most important viruses infecting pepper, but the genetic basis of CMV resistance in pepper is elusive. In this study, we identified a candidate gene for CMV resistance QTL, qCmr2.1 through SLAF-seq. Segregation analysis in F₂, BC₁ and F_2:3 populations derived from a cross between two inbred lines ‘PBC688’ (CMV-resistant) and ‘G29’ (CMV-susceptible) suggested quantitative inheritance of resistance to CMV in pepper. Genome-wide comparison of SNP profiles between the CMV-resistant and CMV-susceptible bulks constructed from an F₂ population identified two QTLs, designated as qCmr2.1 on chromosome 2 and qCmr11.1 on chromosome 11 for resistance to CMV in PBC688, which were confirmed by InDel marker-based classical QTL mapping in the F₂ population. As a major QTL, joint SLAF-seq and traditional QTL analysis delimited qCmr2.1 to a 330 kb genomic region. Two pepper genes, CA02g19570 and CA02g19600, were identified in this region, which are homologous with the genes LOC104113703, LOC104248995, LOC102603934 and LOC101248357, which were predicted to encode N-like protein associated with TMV-resistant in Solanum crops. Quantitative RT-PCR revealed higher expression levels of CA02g19570 in CMV resistance genotypes. The CA02g19600 did not exhibit obvious regularity in expression patterns. Higher relative expression levels of CA02g19570 in PBC688 and F₁ were compared with those in G29 during days after inoculation. These results provide support for CA02g19570 as a possible candidate gene of qCmr2.1 for resistance to CMV in pepper.

     

Map-based cloning and functional analysis of the chromogen gene <Emphasis Type="Italic">C</Emphasis> in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

The chromogen gene C is critical for anthocyanin regulation in rice, and apiculus color is an important agronomic trait in selective breeding and variety purification. Mapbased cloning and in-depth functional analysis of the C gene will be useful for understanding the molecular mechanism of anthocyanin biosynthesis and for rice breeding. Japonica landrace Lijiangxintuanheigu (LTH) has red apiculi and purple stigmas. Genetic analysis showed that red apiculus and purple stigma in LTH co-segregated indicating control by a single dominant gene, or by two completely linked genes. Using 1,851 recessive individuals from two F₂ populations, the target gene OsC was delimited to a 70.8 kb interval on chromosome 6 that contains the rice homologue of the maize anthocyanin regulatory gene C1. When the entire OsC gene and its full-length cDNA cloned from LTH were transformed into japonica cultivar Kitaake with colorless apiculi and stigmas all positive transformants had red apiculi but non-colored stigmas, validating that OsC alone was responsible for the apiculus color and represented the functional C gene. OsC was constitutively expressed in all tissues examined, with strongest expression in leaf blades. These results set a foundation to clarify the regulatory mechanisms of OsC in the anthocyanin biosynthetic pathway.     

Fine mapping of a quantitative trait locus <Emphasis Type="Italic">qHD3-1</Emphasis>, controlling the heading date,to a 29.5-kb DNA fragment in rice

In our previous studies, a single segment substitution line (SSSL) W23-03-8-9-1 with substituted interval of PSM301-PSM306-PSM305-PSM304-RM3894-RM3372-RM569-RM231-RM545 on chromosome 3 has been found to comprise a gene for extremely early heading date. To map this gene, the SSSL W23-03-8-9-1 was crossed with the recipient Huajingxian (HJX74) to develop an F2 segregating population. The distribution of early and late heading plants in this population fitted a segregation ratio of 3: 1, indicating that early heading was controlled by a dominant gene. Using a random sample of 520 individuals from the F2 segregation population, the qHD3-1 locus was mapped between two SSR markers, RM3894 and RM3372, with genetic distances of 1.2 and 1.1 cM, respectively. For fine mapping of qHD3-1, a large F_{2: 3} segregating population was developed, with 6000 individuals from the F₂ plants heterozygous in the RM3894 and RM3372 regions. The analysis of recombinants in the qHD3-1 region put the gene locus into an interval of 29.5 kb flanked by the left marker 3HD8 and the right marker 3HD9. Sequence analysis of this fragment predicted eight open reading frames. One of them, ORF8, with its molecular function predicted to encode ribonuclease III activity and RNA binding, is considered the most interesting candidate gene.     

Identification and mapping of <Emphasis Type="Italic">MLIW30</Emphasis>, a novel powdery mildew resistance gene derived from wild emmer wheat

Powdery mildew, caused by Blumeria graminis f.sp. tritici (Bgt), is a destructive foliar disease of common wheat in areas with cool or maritime climates. Wild emmer wheat, Triticum turgidum ssp. dicoccoides, the progenitor of both domesticated tetraploid durum wheat and hexaploid bread wheat, harbors abundant genetic diversity related to resistance to powdery mildew that can be utilized for wheat improvement. An F₂ segregating population was obtained from a cross between resistant bread wheat line 2L6 and susceptible cultivar Liaochun 10, after which genetic analysis of F₂ and F₂-derived F₃ families was performed by inoculating plants with isolate Bgt E09. The results of this experiment demonstrated that powdery mildew resistance in 2L6, which was derived from wild emmer wheat accession IW30, was controlled by a single dominant gene, temporarily designated MLIW30. Nineteen SSR markers and two STS markers linked with MLIW30 were acquired by applying bulked segregant analysis. Finally, MLIW30 was located to the long arm of chromosome 4A and found to be flanked by simple sequence repeat markers XB1g2000.2 and XB1g2020.2 at 0.1 cM. Because no powdery mildew resistance gene in or derived from wild emmer wheat has been reported in wheat chromosome 4A, MLIW30 might be a novel Pm gene.     

Fine Mapping of <Emphasis Type="Italic">qHD4-1</Emphasis>, a QTL Controlling the Heading Date,to a 20.7-kb DNA Fragment in Rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

A library consisting of 1,123 single-segment substitution lines (SSSLs) in the same genetic background of an elite rice variety Huajingxian74 (HJX74) was evaluated for heading date. From this library, the SSSL W05-1-11-5-16-2-5 with the substituted interval of PSM103—RM348-OSR15-PSM382-RM131-RM127—RM280 was found having a gene, which stably performed extreme late heading date which performed stable and late heading in the different environments of Shandong, Guangdong, and Hainan. To map the gene governing heading date, the SSSL W05-1-11-5-16-2-5 was crossed with the recipient HJX74 to develop an F₂ segregating population. The distribution of late and early heading plants in this population fitted a segregation ratio of 3:1, indicating the late heading was controlled by a dominant gene. The gene locus for heading date was tentatively designated as qHD4-1. Using a random sample of 460 individuals from the F₂ segregation population, the qHD4-1 locus was mapped between two SSR markers RM3335 and RM17572, with genetic distances of 0.1 and 0.2 cM, respectively. For fine mapping of qHD4-1, a large F_2:3 segregating population of 3,000 individuals were developed from F₂ plants heterozygous in the RM3335-RM17572 region. Recombinants analyses further mapped qHD4-1 to an interval of 20.7-kb-bounded WB05 and the WB06. Sequence analysis of this 20.7-kb region revealed that it contains three open reading frames (ORFs), encoding wall-associated receptor kinase-like 5, putative F-box domain containing protein, and putative arogenate/prephenate dehydratase. Of them, ORF1, predicting to encode serine/threonine kinase, is considered the most likely as the candidate gene. The genetic and physical map of the qHD4-1 locus will be very useful in molecular cloning of the qHD4-1gene.     

Fine mapping of QTL <Emphasis Type="Italic">qCTB10</Emphasis>-<Emphasis Type="Italic">2</Emphasis> that confers cold tolerance at the booting stage in rice

Key message

The QTL qCTB10 - 2 controlling cold tolerance at the booting stage in rice was delimited to a 132.5 kb region containing 17 candidate genes and 4 genes were cold-inducible.

Abstract

Low temperature at the booting stage is a major abiotic stress-limiting rice production. Although some QTL for cold tolerance in rice have been reported, fine mapping of those QTL effective at the booting stage is few. Here, the near-isogenic line ZL31-2, selected from a BC₇F₂ population derived from a cross between cold-tolerant variety Kunmingxiaobaigu (KMXBG) and the cold-sensitive variety Towada, was used to map a QTL on chromosome 10 for cold tolerance at the booting stage. Using BC₇F₃ and BC₇F₄ populations, we firstly confirmed qCTB10-2 and gained confidence that it could be fine mapped. QTL qCTB10-2 explained 13.9 and 15.9% of the phenotypic variances in those two generations, respectively. Using homozygous recombinants screened from larger BC₇F₄ and BC₇F₅ populations, qCTB10-2 was delimited to a 132.5 kb region between markers RM25121 and MM0568. 17 putative predicted genes were located in the region and only 5 were predicted to encode expressed proteins. Expression patterns of these five genes demonstrated that, except for constant expression of LOC_Os10g11820, LOC_Os10g11730, LOC_Os10g11770, and LOC_Os10g11810 were highly induced by cold stress in ZL31-2 compared to Towada, while LOC_Os10g11750 showed little difference. Our results provide a basis for identifying the genes underlying qCTB10-2 and indicate that markers linked to the qCTB10-2 locus can be used to improve the cold tolerance of rice at the booting stage by marker-assisted selection.

     

<Emphasis Type="Italic">Pm61</Emphasis>: a recessive gene for resistance to powdery mildew in wheat landrace Xuxusanyuehuang identified by comparative genomics analysis

Key message

A single recessive powdery mildew resistance gene Pm61 from wheat landrace Xuxusanyuehuang was mapped within a 0.46-cM genetic interval spanning a 1.3-Mb interval of the genomic region of chromosome arm 4AL.

Abstract

Epidemics of powdery mildew incited by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt) have caused significant yield reductions in many wheat (Triticum aestivum)-producing regions. Identification of powdery mildew resistance genes is required for sustainable improvement of wheat for disease resistance. Chinese wheat landrace Xuxusanyuehuang was resistant to several Bgt isolates at the seedling stage. Genetic analysis based on the inoculation of Bgt isolate E09 on the F₁, F₂, and F_2:3 populations produced by crossing Xuxusanyuehuang to susceptible cultivar Mingxian 169 revealed that the resistance of Xuxusanyuehuang was controlled by a single recessive gene. Bulked segregant analysis and simple sequence repeat (SSR) mapping placed the gene on chromosome bin 4AL-4-0.80-1.00. Comparative genomics analysis was performed to detect the collinear genomic regions of Brachypodium distachyon, rice, sorghum, Aegilops tauschii, T. urartu, and T. turgidum ssp. dicoccoides. Based on the use of 454 contig sequences and the International Wheat Genome Sequence Consortium survey sequence of Chinese Spring wheat, four EST-SSR and seven SSR markers were linked to the gene. An F₅ recombinant inbred line population derived from Xuxusanyuehuang?×?Mingxian 169 cross was used to develop the genetic linkage map. The gene was localized in a 0.46-cM genetic interval between Xgwm160 and Xicsx79 corresponding to 1.3-Mb interval of the genomic region in wheat genome. This is a new locus for powdery mildew resistance on chromosome arm 4AL and is designated Pm61.

     

Remapping of the stripe rust resistance gene <Emphasis Type="Italic">Yr10</Emphasis> in common wheat

Key message

Yr10 is an important gene to control wheat stripe rust, and the search for Yr10 needs to be continued.

Abstract

Wheat stripe rust or yellow rust is a devastating fungal disease caused by Puccinia striiformis f. sp. tritici (Pst). Host disease resistance offers a primary source for controlling wheat stripe rust. The stripe rust resistance gene Yr10 confers the race-specific resistance to most tested Pst races in China including CYR29. Early studies proposed that Yr10 was a nucleotide-binding site, leucine-rich repeat gene archived as GenBank accession AF149112 (hereafter designated the Yr10 candidate gene or Yr10 _CG ). In this study, we revealed that 15 Chinese wheat cultivars positive for Yr10 _CG are susceptible to CYR29. We then expressed the Yr10 _CG cDNA in the common wheat ‘Bobwhite’. The Yr10 _CG -cDNA positive transgenic plants were also susceptible to CYR29. Thus, it is highly unlikely that Yr10 _CG corresponds to the Yr10 resistance gene. Using the Yr10 donor ‘Moro’ and the Pst-susceptible wheat ‘Huixianhong’, we generated two F₃ populations that displayed a single Mendelian segregation on the Yr10 gene, and used them to remap the Yr10 gene. Six markers were placed in the Yr10 region, with the Yr10 _CG gene now mapping about 1.2-cM proximal to the Yr10 locus and the Xsdauw79 marker is completely linked to the Yr10 locus. Apparently, the Yr10 gene has not yet been identified. Fine mapping and positional cloning of Yr10 is important for gene pyramiding for stripe rust resistance in wheat.

     

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.

     

Locating QTLs controlling overwintering seedling rate in perennial glutinous rice 89-1 (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

A new cold tolerant germplasm resource named glutinous rice 89-1 (Gr89-1, Oryza sativa L.) can overwinter using axillary buds, with these buds being ratooned the following year. The overwintering seedling rate (OSR) is an important factor for evaluating cold tolerance. Many quantitative trait loci (QTLs) controlling cold tolerance at different growth stages in rice have been identified, with some of these QTLs being successfully cloned. However, no QTLs conferring to the OSR trait have been located in the perennial O. sativa L. To identify QTLs associated with OSR and to evaluate cold tolerance. 286 F₁₂ recombinant inbred lines (RILs) derived from a cross between the cold tolerant variety Gr89-1 and cold sensitive variety Shuhui527 (SH527) were used. A total of 198 polymorphic simple sequence repeat (SSR) markers that were distributed uniformly on 12 chromosomes were used to construct the linkage map. The gene ontology (GO) annotation of the major QTL was performed through the rice genome annotation project system. Three main-effect QTLs (qOSR2, qOSR3, and qOSR8) were detected and mapped on chromosomes 2, 3, and 8, respectively. These QTLs were located in the interval of RM14208 (35,160,202 base pairs (bp))–RM208 (35,520,147 bp), RM218 (8,375,236 bp)–RM232 (9,755,778 bp), and RM5891 (24,626,930 bp)–RM23608 (25,355,519 bp), and explained 19.6%, 9.3%, and 11.8% of the phenotypic variations, respectively. The qOSR2 QTL displayed the largest effect, with a logarithm of odds score (LOD) of 5.5. A total of 47 candidate genes on the qOSR2 locus were associated with 219 GO terms. Among these candidate genes, 11 were related to cell membrane, 7 were associated with cold stress, and 3 were involved in response to stress and biotic stimulus. OsPIP1;3 was the only one candidate gene related to stress, biotic stimulus, cold stress, and encoding a cell membrane protein. After QTL mapping, a total of three main-effect QTLs—qOSR2, qOSR3, and qOSR8—were detected on chromosomes 2, 3, and 8, respectively. Among these, qOSR2 explained the highest phenotypic variance. All the QTLs elite traits come from the cold resistance parent Gr89-1. OsPIP1;3 might be a candidate gene of qOSR2.     

Change of Mendelian ratios and meiotic recombination parameters in F<Subscript>1</Subscript> hybrid tomatoes under the influence of γ-irradiation

The effect of γ-irradiation treatment of seeds of intra- and interspecific F₁ hybrid tomatoes on distortion of Mendelian monohybrid segregation, crossover variability, and recombination frequency of unlinked marker genes of chromosomes 2 and 6 was studied. It was found that more significant distortion effect on the segregation of marker loci of studied chromosomes was detected for seed treatment with 130 Gy. The significant direct relationship between Mendelian segregation for m-2 gene and a rf _m-2c vaue for 60 Gy and for aw and m-2 genes and rf _{aw c} , _{aw m-2} values for 60 and 130 Gy treatment in combination Mo500 × var. cerasiforme was revealed. The latter corresponds to the effect of “quasirepulsion.”     

Identification of loci associated with embryo yield in microspore culture of <Emphasis Type="Italic">Brassica rapa</Emphasis> by segregation distortion analysis

Key message

We identified three physical positions associated with embryo yield in microspore culture of Brassica rapa by segregation distortion analysis. We also confirmed their genetic effects on the embryo yield.

Abstract

Isolated microspore culture is well utilized for the production of haploid or doubled-haploid plants in Brassica crops. Brassica rapa cv. ‘Ho Mei’ is one of the most excellent cultivars in embryo yield of microspore culture. To identify the loci associated with microspore embryogenesis, segregation analysis of 154 DNA markers anchored to B. rapa chromosomes (A01–A10) was performed using a population of microspore-derived embryos obtained from an F₁ hybrid between ‘CR-Seiga’, a low yield cultivar in microspore-derived embryos, and ‘Ho Mei’. Three regions showing significant segregation distortion with increasing ‘Ho Mei’ alleles were detected on A05, A08 and A09, although these regions showed the expected Mendelian segregation ratio in an F₂ population. The additive effect of alleles in these regions on embryo yield was confirmed in a BC₃F₁ population. One region on A08 containing Br071-5c had a higher effect than the other regions. Polymorphism of nucleotide sequences around the Br071-5c locus was investigated to find the gene possibly responsible for efficient embryogenesis from microspores.

     

Genetic marking of glume color in <Emphasis Type="Italic">Triticum spelta</Emphasis> L. var. <Emphasis Type="Italic">caeruleum</Emphasis> using gliadins

Using gliadins as genetic markers, Triticum spelta L. var. caeruleum accessions were analyzed to identify genetic control of the dark color of glumes. The research material was F₂ and BC₁ plants from crosses between spelt accessions and white-glumed common wheat varieties. The segregation for glume color fitted the monogenic control of the trait. The electrophoretic analysis of gliadins in grains from the hybrid plants has shown that the Gli-Alj* allele in the T. spelta var. caeruleum accessions is linked to the allele for the dark (black) color of glumes at the Rg-A1 locus.     

A novel QTL <Emphasis Type="Italic">qSPP2.2</Emphasis> controlling spikelet per panicle identified from <Emphasis Type="Italic">Oryza longistaminata</Emphasis> (A. Chev. et Roehr.), mapped and transferred to <Emphasis Type="Italic">Oryza sativa</Emphasis> (L.)

Increasing the rice productivity from the current 10 to 12 tons/ha to meet the demand of estimated 8.8 billion people in 2035 is posing a major challenge. Wild relatives of rice contain some novel genes which can help in improving rice yield. Spikelet per panicle (SPP) is a valuable trait for determining yield potential in rice. In this study, a major QTL for increasing SPP has been identified, mapped, and transferred from African wild rice O. longistaminata to O. sativa (L.). The QTL was mapped on the long arm of chromosome 2 in a 167.1 kb region flanked by SSR markers RM13743 and RM13750, which are 1.0 cM apart, and is designated as qSPP2.2. The QTL explained up to 30% of phenotypic variance in different generations/seasons and showed positive additive effect of allele contributed by O. longistaminata. In addition, O. longistaminata allele in qSPP2.2 contributed to increase in grains per panicle, but decrease in the tillers per plant. The 167.1 kb region contains 23 predicted genes. Based on the functional annotation, three genes, LOC_Os02g44860, LOC_Os02g44990, and LOC_Os02g45010, were selected as putative candidates for characterization. Sequence analysis of the three genes revealed functional variations between the parental lines for LOC_Os02g44990 and a variation in 5′UTR for LOC_Os02g45010 which will help further to identify putative candidate gene(s). This is the first yield component QTL to be identified, mapped, and transferred from O. longistaminata.     

Reducing production of fumonisin mycotoxins in <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> by RNA interference

The fungus Fusarium verticillioides is a maize pathogen that can produce fumonisin mycotoxins in ears under certain environmental conditions. Because fumonisins pose health risks to humans and livestock, control strategies with minimal risk to the environment are needed to reduce fumonisin contamination. Host-induced gene silencing is a promising technique in which double-stranded RNA expressed in the plant host is absorbed by an invading fungus and down-regulates genes critical for pathogenicity or mycotoxin production in the fungus. A key preliminary step of this technique is identification of DNA segments within the targeted fungal gene that can effectively silence the gene. Here, we used segments of the fumonisin biosynthetic gene FUM1 to generate double-stranded RNA in F. verticillioides. Several of the resulting transformants exhibited reduced FUM1 gene expression and fumonisin production (24- to 3675-fold reduction in fumonisin FB₁). Similar reductions in fumonisin production resulted from double-stranded RNA constructs with segments of FUM8, another fumonisin biosynthetic gene (3.5- to 2240-fold reduction in fumonisin FB₁). FUM1 or FUM8 silencing constructs were transformed into three isolates of F. verticillioides. Whole genome sequence analysis of seven transformants revealed that reductions in fumonisin production were not due to mutation of the fumonisin biosynthetic gene cluster and revealed a complex pattern of plasmid integration. These results suggest the cloned FUM1 or FUM8 gene segments could be expressed in maize for host-induced gene silencing of fumonisin production.     

A naturally occurring insertion in the <Emphasis Type="Italic">RsFLC2</Emphasis> gene associated with late-bolting trait in radish (<Emphasis Type="Italic">Raphanus sativus</Emphasis> L.)

Premature flowering reduces the yield and quality of the harvested fleshy taproot in radish. However, there has been little molecular marker research on the radish late-bolting trait. In this study, F₂ and F_2:3 populations derived from a cross of “Ninengo” (late-bolting) and “Maer” (early-bolting) were analyzed to map late-bolting genes. Five hundred insertion and deletion (InDel) markers were designed according to the whole-genome resequencing data of the two parents. A genetic map was constructed based on the F₂ population, and a late-bolting gene was detected in a 1.1-cM region between the markers InDel520 and InDel535 on chromosome R02 that explained the highest (76.4%) phenotypic variance. RsFLC2 was identified as a candidate gene in this region. Notably, “Ninengo” contains a 1627-bp insertion near the 5′ end of the first intron of RsFLC2. Allelic variation analyses in the F₂ population further validated that RsFLC2was associated with the late-bolting trait in radish. The expression pattern of RsFLC2 was significantly different between “Ninengo” and “Maer” during vernalization. Vernalization suppressed RsFLC2 expression, and the 1627-bp insertion in the first intron weakened gene repression in “Ninengo” plants, resulting in late-bolting. This study lays a foundation for uncovering the molecular mechanism of late-bolting and marker-assisted selection for breeding late-bolting varieties of radish.     

Genetic mapping of a barley leaf rust resistance gene <Emphasis Type="Italic">Rph26</Emphasis> introgressed from <Emphasis Type="Italic">Hordeum bulbosum</Emphasis>

Key message

The quantitative barley leaf rust resistance gene, Rph26, was fine mapped within a H. bulbosum introgression on barley chromosome 1HL. This provides the tools for pyramiding with other resistance genes.

Abstract

A novel quantitative resistance gene, Rph26, effective against barley leaf rust (Puccinia hordei) was introgressed from Hordeum bulbosum into the barley (Hordeum vulgare) cultivar ‘Emir’. The effect of Rph26 was to reduce the observed symptoms of leaf rust infection (uredinium number and infection type). In addition, this resistance also increased the fungal latency period and reduced the fungal biomass within infected leaves. The resulting introgression line 200A12, containing Rph26, was backcrossed to its barley parental cultivar ‘Emir’ to create an F₂ population focused on detecting interspecific recombination within the introgressed segment. A total of 1368 individuals from this F₂ population were genotyped with flanking markers at either end of the 1HL introgression, resulting in the identification of 19 genotypes, which had undergone interspecific recombination within the original introgression. F₃ seeds that were homozygous for the introgressions of reduced size were selected from each F₂ recombinant and were used for subsequent genotyping and phenotyping. Rph26 was genetically mapped to the proximal end of the introgressed segment located at the distal end of chromosome 1HL. Molecular markers closely linked to Rph26 were identified and will enable this disease resistance gene to be combined with other sources of quantitative resistance to maximize the effectiveness and durability of leaf rust resistance in barley breeding. Heterozygous genotypes containing a single copy of Rph26 had an intermediate phenotype when compared with the homozygous resistant and susceptible genotypes, indicating an incompletely dominant inheritance.