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 B1 individuals, was generated. Six complementary B1 individuals enriched for recurrent genotype and collectively carrying almost all the donor genome were selected. A total of 288 B2 plants derived from the selected B1 individuals were analysed and complementary individuals carrying five or fewer donor segments were identified. Similar selection, carried out on 250 B3 plants from two distinct B1 lineages, identified 74 B3 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 B3 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. Key words : QTL mapping, quantitative genetics, backcross, genetic linkage map, plant breeding, restriction fragment length polymorphism.