Fine Mapping of Rhizomania Resistance using in situ Populations of the Wild Beet Beta vulgaris ssp. maritima

Rhizomania is one of the most important sugar beet (Beta vulgaris) diseases causing losses in sugar yield of up to 80%. Resistance in current cultivars is conferred mainly by the two resistance genes Rz1 and Rz2. Aiming at fine mapping and cloning Rz2, a wild beet in situ population nearby Kalundborg, Denmark, was sampled. Progenies from 200 wild plants were tested for Rhizomania resistance. Based on molecular and phenotypic data, the population was shown to be in Hardy-Weinberg equilibrium without apparent population structure. DNA pools of homozygous resistant and homozygous susceptible plants were sequenced using 2x 100 bp paired-end Illumina HiSeq short reads at 20x coverage and mapped to a reference sequence of the Rz2 donor accession WB42. The location of Rz2 could be narrowed down by cosegregation analysis to a genomic region of about 800 kb. This region is currently explored by association analysis and investigated for candidate genes.