A RFLP-BASED LINKAGE MAP OF MUSTARD [BRASSICA-JUNCEA (L) CZERN AND COSS]

A genetic linkage map of Brassica juncea was constructed based on rest riction fragment length polymorphism (RFLP) detected by anonymous cDNA markers from B. napus, using a segregating F-1-derived doubled haploi d (DH) progeny from a cross between a canola-quality mustard line (J90 -4317) and a high-oil-content mustard line (J90-2733). The RFLP probes consisted of 229 cDNA probes from B. napus and a B. napus tandem repe at sequence, RDA2. The map consisted of 343 marker loci arranged in 18 major linkage groups plus five small segments with two to five marker loci, covering a total map distance of 2073 cM. Twenty-four percent o f the markers were dominant in nature. Sixty-two percent of the marker loci were duplicated, and the majority were involved in interlinkage group duplications, illustrating that complex duplications and subsequ ent rearrangements occurred after allopolyploidy. Deviation from the M endelian segregation ratio for a DH population was observed for 27% of the markers. Two-thirds of these markers with a skewed segregation we re clustered in 6 linkage groups and two unassigned segments. The over all average marker interval of the B. juncea map reported here was 6.6 cM, which would provide a marker density satisfactory for efficient u se of the map in breeding applications, such as tagging of important a gronomic traits and marker-assisted selection.