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Poster: Biology & Disease Mgmt: Genetics of Resistance


Development of molecular makers for spinach resistance genes to downy mildew disease
C. FENG (1), J. Correll (1) (1) University of Arkansas, U.S.A.

Spinach is an increasingly popular vegetable crop. Downy mildew, caused by Peronospora farinosa f. sp. spinaciae (Pfs), is the most economically important disease of spinach and the main focus of all spinach breeding programs. Resistant cultivars are the most economical way to manage downy mildew, particularly for organic spinach production, which is approaching 50% in the US. Resistance to downy mildew is typically controlled by single dominant genes, and 11 resistant loci have been hypothesized in spinach. Three resistant loci, RPF1, 2 and 3 have been genetically characterized; each provides resistance to more than 10 of the 16 described races of Pfs. A molecular SCAR marker, linked to RPF1, has been shown to be useful in selecting this locus for resistance. Bulked segregant analysis and genotyping by sequencing approaches were employed to develop markers for RPF2 and 3. One out of 900 10-mer random primers examined generated a fragment specific to resistant plants, and the derived SCAR marker co-segregated with the RPF2 locus. For RFP3, a SNP linkage map was constructed with two SNP markers closely linked (1.1 and 4 cM) to the RPF3 locus. The RPF2 and RPF3 markers have been shown to be effective in selecting the respective resistance loci outside of the original mapping populations demonstrating their utility. These markers could be used to pyramid resistant loci to improve the durability of downy mildew resistance in spinach.