RESUMO
Downy mildew, caused by Plasmopara halstedii, is one of the most destructive diseases in cultivated sunflower (Helianthus annuus L.). The dominant resistance locus Pl(ARG) originates from silverleaf sunflower (H. argophyllus Torrey and Gray) and confers resistance to all known races of P. halstedii. We mapped Pl(ARG) on linkage group (LG) 1 of (cms)HA342 × ARG1575-2, a population consisting of 2,145 F(2) individuals. Further, we identified resistance gene candidates (RGCs) that cosegregated with Pl(ARG) as well as closely linked flanking markers. Markers from the target region were mapped with higher resolution in NDBLOS(sel) × KWS04, a population consisting of 2,780 F(2) individuals that does not segregate for Pl(ARG). A large-insert sunflower bacterial artificial chromosome (BAC) library was screened with overgo probes designed for markers RGC52 and RGC151, which cosegregated with Pl(ARG). Two RGC-containing BAC contigs were anchored to the Pl(ARG) region on LG 1.
Assuntos
Loci Gênicos/genética , Helianthus/genética , Helianthus/microbiologia , Imunidade Inata/genética , Peronospora/fisiologia , Mapeamento Físico do Cromossomo/métodos , Doenças das Plantas/imunologia , Sequência de Bases , Segregação de Cromossomos/genética , Cromossomos Artificiais Bacterianos/genética , Cruzamentos Genéticos , Biblioteca Gênica , Genes de Plantas/genética , Ligação Genética , Marcadores Genéticos , Testes Genéticos , Genética Populacional , Haplótipos/genética , Helianthus/imunologia , Mutagênese Insercional/genética , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Plantas Geneticamente Modificadas , Recombinação Genética/genéticaRESUMO
The PlArg 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 PlArg locus were identified. All markers were located proximal to PlArg on linkage group LG1 based on the map of Yu et al. (2003) in a window of 9.3 cM. Since PlArg was mapped to a linkage group different from all other Pl genes previously mapped with SSRs, it can be concluded that PlArg provides a new source of resistance against P. halstedii in sunflower.
Assuntos
Mapeamento Cromossômico , Helianthus/genética , Imunidade Inata/genética , Oomicetos , Doenças das Plantas/microbiologia , Cruzamentos Genéticos , Escore Lod , Repetições Minissatélites/genética , Fenótipo , Doenças das Plantas/genéticaRESUMO
The resistance gene analogue (RGA) pic19 in maize, a candidate for sugarcane mosaic virus (SCMV) resistance gene (R gene) Scmv1, was used to screen a maize BAC library to identify homologous sequences in the maize genome and to investigate their genomic organisation. Fifteen positive BAC clones were identified and could be classified into five physically independent contigs consisting of overlapping clones. Genetic mapping clustered three contigs into the same genomic region as Scmv1 on chromosome 6S. The two remaining contigs mapped to the same region as a QTL for SCMV resistance on chromosome 1. Thus, RGAs mapping to a target region can be successfully used to identify further-linked candidate sequences. The pic19 homologous sequences of these clones revealed a sequence similarity of 94-98% on the nucleotide level. The high sequence similarity reveals potential problems for the use of RGAs as molecular markers. Their application in marker-assisted selection (MAS) and the construction of high-density genetic maps is complicated by the existence of closely linked homologues resulting in 'ghost' marker loci analogous to 'ghost' QTLs. Therefore, implementation of genomic library screening, including genetic mapping of potential homologues, seems necessary for the safe application of RGA markers in MAS and gene isolation.
Assuntos
Zea mays/genética , Sequência de Bases , Cromossomos Artificiais Bacterianos , Clonagem Molecular , Primers do DNA , Ligação Genética , Marcadores Genéticos , Vírus do Mosaico/genética , Vírus do Mosaico/patogenicidade , Locos de Características Quantitativas , Zea mays/virologiaRESUMO
Quantitative trait loci (QTLs) and bulked segregant analyses (BSA) identified the major genes Scmv1 on chromosome 6 and Scmv2 on chromosome 3, conferring resistance against sugarcane mosaic virus (SCMV) in maize. Both chromosome regions were further enriched for SSR and AFLP markers by targeted bulked segregant analysis (tBSA) in order to identify and map only markers closely linked to either Scmv1 or Scmv2. For identification of markers closely linked to the target genes, symptomless individuals of advanced backcross generations BC5 to BC9 were employed. All AFLP markers, identified by tBSA using 400 EcoRI/ MseI primer combinations, mapped within both targeted marker intervals. Fourteen SSR and six AFLP markers mapped to the Scmv1 region. Eleven SSR and 18 AFLP markers were located in the Scmv2 region. Whereas the linear order of SSR markers and the window size for the Scmv2 region fitted well with publicly available genetic maps, map distances and window size differed substantially for the Scmv1 region on chromosome 6. A possible explanation for the observed discrepancies is the presence of two closely linked resistance genes in the Scmv1 region.
