Genetic linkage map of a Brassica rapa recombinant inbred population

Recombinant inbred (RI) populations are useful resources for genetic mapping. An RI population of Brassica rapa was derived from a cross between the biennial cultivar Per and the annual cultivar R500 and used to construct a linkage map of 144 restriction fragment length polymorphism (RFLP) loci detected by 102 probes including 22 cloned genes from B. napus and Arabidopsis thaliana, and three qualitative trait loci controlling seed color, leaf pubescence, and resistance to white rust caused 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 linkages. Significant (P <.05) deviation from the expected Mendelian segregation ratio was observed for 19.4% of the mark er loci. Six clusters of such marker loci each favoring the alleles from one of the two parents provided evidence for linkage to alleles with some selective advantage. The RI map was found to be mostly congruous to an F-2 map derived from the same F-1 plant. This RI population can be used for building a reference map of B. rapa and for studying the genetic control of important traits.