Theor Appl Genet (2002) 105:100–105 DOI 10.1007/s00122-001-0859-z Abstract Sugar beet (Beta vulgaris L.) is a biennial spe- cies. Shoot elongation (bolting) starts after a period of low temperature. The dominant allele of locus B causes early bolting without cold treatment. This allele is abun- dant in wild beets whereas cultivated beets carry the re- cessive allele. Fifteen AFLP markers, tightly linked to the bolting locus, have been identified using bulked se- gregant analysis. The F 2 -population consisted of 2,134 individuals derived after selfing a single F 1 -plant (Bb). In a first step, a linkage map was established with 249 markers based on 775 F 2 -individuals with a coverage of 822.3 cM. The loci are dispersed over nine linkage groups corresponding to the haploid chromosome num- ber of Beta species. Seventeen marker loci were placed at a distance less than 3.2 cM around the bolting gene. In a second step, four of those markers most closely linked to B were mapped with the entire F 2 -population. Two of the markers were mapped flanking the B gene at distanc- es of 0.14 and 0.23 cM. The other two markers were mapped at a distance of 0.5 cM from the gene. The tight linkage could be verified by testing 88 unrelated plants from a breeding program. The closely linked markers will enable breeders to select for the non-bolting charac- ter without laborious test crossings. Moreover, these markers are being used for map-based cloning of the bolting gene. Keywords Beta vulgaris · Early bolting · Vernalisation · Bulked segregant analysis · AFLP Introduction Sugar beet (Beta vulgaris ssp. vulgaris L.) belongs to the family Chenopodiaceae. It is a diploid species with 18 chromosomes (x=9) and a nuclear DNA content of 758 Mbp per haploid genome (Arumuganathan and Earle 1991). Sugar beet is a biennial root crop that grows veg- etatively in the first season. It initiates stem elongation (bolting) after exposure to a period of low temperature followed by cultivation under long-day conditions. The B locus controlling early bolting (annuality) was first de- scribed in a commercial sugar beet cultivar by Munerati (1931). Later it was found that the annual habit in related wild beets (B. vulgaris ssp. maritima L.) is controlled by the B allele, which induces bolting under long-day con- ditions without requirement for vernalization (Abe et al. 1997). The penetration of gene B has been found to be influenced by both environmental and genetic factors (Abegg 1936; Owen and Mc Farlane 1958; Sadeghian 1993). Long days are essential for homozygous B plants to initiate bolting; they do not display the annual habit under short-day conditions. A more-complicated behav- ior was recognized in heterozygous B plants. Their bolt- ing behaviour is strongly influenced by environmental factors (Shimamoto et al. 1990; Boudry et al. 1994). Outcrossing of wild beets on seed multiplication plots may introgress the B allele into cultivated biennial beets, resulting in varieties contaminated with early bolting plants. As a consequence, root yield and sugar content are reduced. Moreover, bolters cause severe problems during crop harvesting. Although breeders are aware of this problem and take strong action to minimize pollen introgression from wild annual beets, a test system to de- tect the B allele within commercial seed lots would be beneficial. For this, molecular markers tightly linked to the bolting gene are a prerequisite. The construction of a high-density genetic map for sugar beet (B. vulgaris L.) allows the identification of markers tightly linked to the bolting locus. Several ge- netic maps for sugar beet have been published. The first linkage map was based on RFLP and morphological Communicated by G. Wenzel A. El-Mezawy · F. Dreyer · G. Jacobs · C. Jung ( ✉ ) Institute for Crop Science and Plant Breeding, Christian-Albrechts-University of Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany e-mail: cjung@plantbreeding.uni-kiel.de A. El-Mezawy · F. Dreyer · G. Jacobs · C. Jung High-resolution mapping of the bolting gene B of sugar beet Received: 16 August 2001 / Accepted: 16 October 2001 / Published online: 17 May 2002 © Springer-Verlag 2002