Conversion of RAPD markers for a clubroot resistance gene of Brassica rapainto sequence - Tagged sites (STSs)

We previously identified three random amplified polymorphic DNA (RAPD) mark ers linked to a major gene conferring clubroot resistance (CR) in Brassica rapa. The markers were cloned and sequenced. A pair of primers were designe d for specific amplification of each marker. All three CR markers were spec ifically amplified as clear single and dominant bands. Identity of the loci of the amplified markers with the original RAPD markers was demonstrated u sing a segregating FS population. The marker bands can be amplified by at l east two types of PCR machine. Therefore these three markers may be widely used as a reference to CR genes in the genome of B. rapa. Presence of the m arkers in turnips and Chinese cabbage cultivars was examined. Turnips showe d a high degree of DNA polymorphism within cultivars. No relationship betwe en CR and the presence of the marker bands was detected, while Chinese cabb age hybrid cultivars showed a rather low DNA polymorphism. One of the CR ma rkers, RA12-75A was found to be useful for the breeding of CR Chinese cabba ge, because no clubroot-susceptible cultivars of Chinese cabbage harbour th is marker band. Use of these specifically amplified markers in marker-assis ted selection (MAS) of Brassica crops is discussed.