An anchored linkage map for sugar beet based on AFLP, SNP and RAPD markers and QTL mapping of a new source of resistance to Beet necrotic yellow vein virus

Rhizomania, caused by Beet necrotic yellow vein virus (BNYVV), is an important sugar-beet disease worldwide and can result in severe losses of root yield and sugar content. We have identified a major QTL for BNYVV resistance from a new source in a segregating population of 158 individuals. The QTL explained an estimated 78% of the observed phenotypic variation and the gene conferring the partial resistance is referred to as Rz4. AFLP was used in combination with bulked segregant analysis (BSA) to develop markers linked to the resistance phenotype. AFLP marker analysis was extended to produce a linkage map that was resolved into nine linkage groups. These were anchored to the nine sugar-beet chromosomes using previously published SNP markers. This represents the first anchored sugar-beet linkage map to be published with non-anonymous markers. The final linkage map comprised 233 markers covering 497.2 cM, with an average interval between markers of 2.1 cM. The Rz4 QTL and an Rz1 RAPD marker were mapped to chromosome III, the known location of the previously identified BNYVV resistance genes Rz1, Rz2 and Rz3. The availability to breeders of new resistance sources such as Rz4 increases the potential for breeding durable disease resistance.