ISOLATION AND CHARACTERIZATION OF RAPD-BASED MARKERS LINKED TO THE BEET CYST-NEMATODE RESISTANCE LOCUST HS1(PAT-1) ON CHROMOSOME-1 OF B-PATELLARIS

A beet cyst nematode (BCN)-resistant telosomic addition of B. patellar is chromosome 1 in B. vulgaris was used to isolate 6 RAPD markers link ed to the BCN resistance locus Hs1(pat-1). Southern analysis showed th at the analyzed RAPD products contain either low-, middle- or high-rep etitive DNA. The relative positions of the random amplified polymorphi c DNA (RAPD) markers and of the restriction fragment length polymorphi sm (RFLP) loci corresponding to the low-repetitive RAPD products were determined by deletion mapping using a panel of seven nematode-resista nt B. patellaris chromosome-1 fragment additions. One RAPD marker, OPB 11(800), was found to be present in two copies on the long arm telosom e of B. patellaris chromosome 1. These copies are closely linked to th e BCN resistance gene and flank the gene on both sides. On the basis o f the nucleotide sequence of OPB11(800), sequence-tagged site (STS) pr imers were developed that amplify specific fragments derived from the two OPB11(800) loci. These STS markers can be used in the map-based cl oning 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 middl e-repetitive OPX2(1100) marker were mapped in the same interval of the deletion mapping panel as the resistance gene locus and thereby belon g to the nearest markers as yet found for the BCN gene in B. patellari s.