Isolation and characterization of RAPD-based markers linked to the beet cyst nematode resistance locus (Hs1 (pat-1)) on chromosome 1 of B. patellaris.

A beet cyst nematode (BCN)-resistant telosomic addition of B. patellaris chromosome 1 in B. vulgaris was used to isolate 6 RAPD markers linked to the BCN resistance locus Hs1 (pat-1). Southern analysis showed that the analyzed RAPD products contain either low-, middle or high-repetitive DNA. The relative positions of the random amplified polymorphic DNA (RAPD) markers and of the restriction fragment length polymorphism (RFLP) loci corresponding to the low-repetitive RAPD products were determined by deletion mapping using a panel of seven nematode-resistant B. patellaris chromosome-1 fragment additions. One RAPD marker, OPB11800, was found to be present in two copies on the long arm telosome of B. patellaris chromosome 1. These copies are closely linked to the BCN resistance gene and flank the gene on both sides. On the basis of the nucleotide sequence of OPB11800, sequence-tagged site (STS) primers were developed that amplify specific fragments derived from the two OPB11800 loci. These STS markers can be used in the map-based cloning of the BCN gene, as they define start and finishing points of a chromosomal walk towards the Hs1 (pat-1) locus. Two copies of the middle-repetitive OPX21100 marker were mapped in the same interval of the deletion mapping panel as the resistance gene locus and thereby belong to the nearest markers as yet found for the BCN gene in B. patellaris.

Construction of a YAC library from a Beta vulgaris fragment addition and isolation of a major satellite DNA cluster linked to the beet cyst nematode resistance locus Hs1 (pat-1.).

A YAC library was constructed from the Beta vulgaris fragment addition AN5-203b. This monosomic fragment addition harbors an approximate 12-Mbp fragment of B.patellaris chromosome 1 accomodating the Hs1 (pat-1) conferring resistance to the beet cyst nematode (Heterodera schachtii). The YAC library consists of 20,000 YAC clones having an average size of 140 kb. Screening with organelle-specific probes showed that 12% of the clones contain chloroplast DNA while only 0.2% of the clones hybridizes with a mitochondrial specific probe. On the basis of a sugar beet haploid genome size of 750 Mbp this library represents 3.3 haploid genome equivalents. The addition fragment present in AN5-203b harbors a major satellite DNA cluster that is tightly linked to the Hs1 (pat-1) locus. The cluster is located on a single 250-kb EcoRI restriction fragment and consists of an estimated 700-800 copies of a 159-bp core sequence, most of which are arranged in tandem. Using this core sequence as a probe, we were able to isolate 1 YAC clone from the library that contains the entire 250-kb satellite DNA cluster.