Towards developing intervarietal substitution lines in Brassica napus using marker-assisted selection

Sets of substitution lines have advantages over segregating populations for the rigorous analysis of loci influencing quantitative traits. A general strategy for the rapid production of substitution lines was developed. It involved the systematic application of marker-assisted selection over 2-4 generations of backcrossing. The effectiveness of this strategy was demonstrated by the production of intervarietal substitution lines in Brassica napus. A genetic map containing 158 loci, distributed across all 19 B. napus linkage groups and assayed in 200 B-1 individuals, was generated. Six complementary B-1 individuals enriched for recurrent genotype and collectively carrying almost all the donor genome were selected. A total of 288 B-2 plants derived from the selected B-1 individuals were analysed and complementary individuals carrying five or fewer donor segments were identified. Similar selection, carried out on 250 B-3 plants from two distinct B-1 lineages, identified 74 B-3 individuals carrying one or two donor segments. Together, 12 of these isolated segments represented 33% of the mapped genome. Lines homozygous for single substituted segments were derived from selfed progeny of selected B-3 plants. A full set of substitution lines will be used to elucidate the genetic control of quantitative production traits in oilseed rape over several environments.