GENETIC-LINKAGE MAP OF A BRASSICA-RAPA RECOMBINANT INBRED POPULATION

Recombinant inbred (RI) populations are useful resources for genetic m apping. An RI population of Brassica rapa was derived from a cross bet ween the biennial cultivar Per and the annual cultivar R500 and used t o construct a linkage map oi 144 restriction fragment length polymorph ism (RFLP) loci detected by 102 probes including 22 cloned genes from B. napus and Arabidopsis thaliana, and three qualitative trait loci co ntrolling seed color, leaf pubescence, and resistance to white rust ca used by Albugo candida race 2. The marker loci were assembled into 10 major linkage groups covering 890 cM, with an average marker interval of 6.0 cM. A high proportion (35.3%) of the probes detected duplicated segregating marker loci, but only a few showed conserved duplicated l inkages. Significant (P <.05) deviation from the expected Mendelian se gregation ratio was observed for 19.4% of the mark er loci. Six cluste rs of such marker loci each favoring the alleles from one of the two p arents provided evidence for linkage to alleles with some selective ad vantage. The RI map was found to be mostly congruous to an F-2 map der ived from the same F-1 plant. This RI population can be used for build ing a reference map of B. rapa and for studying the genetic control of important traits.