Conversion of RAPD Markers for a Clubroot Resistance Gene of Brassica rapa into Sequence - Taged Sites (STSs).

Abstract

We previously identiffed three random amplified polymorphic DNA (RAPD) markers linked to a major gene conferring clubroot resistance (CR) in Brassica rapa. The markers were cloned and sequenced. A pair of primers were designed for specific amplification of each marker. All three CR markers were specifically amplified as clear single and dominant bands. Identity of the loci of the amplified markers with the original RAPD markers was demonstrated using a segregating F₂ population. The marker bands can be amplified by at least 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 markers in turnips and Chinese cabbage cultivars was examined. Turnips showed a high degree of DNA polymorphism within cultivars. No relationship between CR and the presence of the marker bands was detected, while Chinese cabbage hybrid cultivars showed a rather low DNA polymorphism. One of the CR markers, RA12-75A was found to be useful for the breeding of CR Chinese cabbage, because no clubroot-susceptible cultivars of Chinese cabbage harbour this marker band. Use of these specifically amplified markers in marker-as-sisted selection (MAS) of Brassica crops is discussed.