Development of coupling-repulsion-phase SCAR markers diagnostic for the sugar beet Rr1 allele conferring resistance to rhizomania

In sugar beet genotypes with the 'Holly' type of resistance to rhizomania, a disease due to infection of the beet necrotic yellow vein virus (BNYVV), the major gene rr1 is responsible for resistance. Twelve RAPD markers linked to rr1 were selected by BSA and mapped on linkage group IV using a segregating population previously analysed by the same group. Markers F61050 and N9600 were tightly linked, respectively in coupling and repulsion, to the Rr1 allele (recombination values of 1.4 cM for both markers). After sequencing the products amplified by F61050 and N9600, new PCR primers were used to generate the two SCAR markers F6 and N9. The simultaneous use of these markers in a PCR reaction allows the correct fingerprinting of rr1 rr1, Rr1 rr1 and Rr1 Rr1 sugar beet plants in populations segregating for the 'Holly' resistance. In a group of sugar beet elite lines containing the 'Holly' type of rhizomania resistance, SCAR F6 is always present whereas the SCAR N9 fragment is absent. Thus, in marker-assisted selection with coupling-repulsion-phase markers, SCAR F6 can be used in combination with N9, or together with any other RAPD marker linked in repulsion to the Rr1 allele.