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Characterization and marker development for three resistance loci to the spinach downy mildew pathogen
Chunda Feng: University of Arkansas; Burton Bluhm: University of Arkansas; James Correll: Univ of Arkansas
<div>Downy mildew of spinach, caused by the obligate pathogen <i>Peronospora farinosa</i> f. sp. <i>spinaciae</i> (Pfs), is the most economically important disease of spinach. Growing resistant cultivars is the most economical way to manage downy mildew, particularly for organic spinach production, which is approaching 50% in the US. Breeding resistance cultivars is the primary objective of all spinach breeding programs. Resistance to downy mildew is typically controlled by single dominant genes, and 11 resistant loci have been hypothesized in spinach. Three resistant loci, <i>RPF</i>1, <i>RPF</i>2 and <i>RPF</i>3 have been genetically characterized and segregate as a dominant resistance gene; each locus provides resistance to more than 10 of the 16 described races of Pfs. Bulked segregant analysis, examination of resistance gene analog sequences, and genotyping by sequencing approaches were employed to develop markers for the <i>RPF</i>1, <i>RPF</i>2 and <i>RPF</i>3 loci. Thirteen, four and five markers have been developed for these R loci, respectively. One SNP marker was found to be associated with all three loci, indicating that these three resistant loci are linked. The markers could be used to pyramid resistant loci to improve the durability of downy mildew resistance in spinach. The genetic distances among these loci will be estimated, which will affect the strategies for deployment of these resistance loci.</div>

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