Mapping the introgression of the Brassica carinata C and B genomes into Brassica napus

The Brassica are a genus containing valuable vegetable, fodder and oilseed crops that are cultivated on a large scale on all five continents. The B genome containing Brassica (B. nigra, B. juncea and B. carinata) carry a number of valuable genetic traits including tolerance to abiotic stresses, and resistance to a number of important pathogens of B. napus- which is the species most commonly used to produce canola quality oil. Several attempts have been made to introgress B genome traits from these species into B. napus, but they have not resulted in the stable integration of B genome resistance into B. napus. This thesis describes why B genome introgressions have been unsuccessful. Two interspecific lineages derived from crosses between B. napus (AACC) and B. carinata (BBCC) were developed, and microsatellite markers were used to monitor the inheritance of the C and B genomes through four generations of introgression breeding. The marker data revealed that B genome chromosomes do not undergo recombination with the A or C genomes of B. napus. Instead, B genome chromosomes were maintained as whole non-recombining chromosomes with the occasional loss of terminal chromosomal regions through successive meioses. The exception was a small terminal region of B5/J15 that was introgressed via translocation into B. napus (A/C) during a meiotic event of an F1 hybrid (ABCC). Recombination between the C genomes of B. carinata and B. napus did occur, and were two-fold higher than values observed in intraspecific crosses. This research suggests that transferring B genome traits to the Brassica A or C genomes would be impractical unless the desired trait was a single gene/single locus trait terminally located on a B genome chromosome. Conversely, traits located on the C genome of B. carinata could be reliably introgressed into the B. napus genome.