The LmR1 locus, which controls seedling resistance to the blackleg fungus Leptosphaeria maculans in the Brassica napus cultivar Shiralee, was positioned on linkage group N7. Fine genetic mapping in a population of 2500 backcross lines identified three molecular markers that cosegregated with LmR1. Additional linkage mapping in a second population colocalized a seedling resistance gene, ClmR1, from the cultivar Cresor to the same genetic interval on N7 as LmR1. Both genes were located in a region that showed extensive inter-and intragenomic duplications as well as intrachromosomal tandem duplications. The tandem duplications seem to have occurred in the Brassica lineage before the divergence of B. rapa and B. oleracea but after the separation of Brassica and Arabidopsis from a common ancestor. Microsynteny was found between the region on N7 carrying the resistance gene and the end of Arabidopsis chromosome 1, interrupted by a single inversion close to the resistance locus. The collinear region in Arabidopsis was assayed for the presence of possible candidate genes for blackleg resistance. These data provided novel insights into the genomic structure and evolution of plant resistance loci and an evaluation of the candidate gene approach using comparative mapping with a model organism.

Background: Safflower, Carthamus tinctorius, is a thistle that is grown commercially for the production of oil and birdseed and recently, as a host for the production of transgenic pharmaceutical proteins. C. tinctorius can cross with a number of its wild relatives, creating the possibility of gene flow from safflower to weedy species. In this study we looked at the introgression potential between different members of the genus Carthamus, measured the fitness of the parents versus the F1 hybrids, followed the segregation of a specific transgene in the progeny and tried to identify traits important for adaptation to different environments. Results: Safflower hybridized and produced viable offspring with members of the section Carthamus and species with chromosome numbers of n = 10 and n = 22, but not with n = 32. The T-DNA construct of a transgenic C. tinctorius line was passed on to the F1 progeny in a Mendelian fashion, except in one specific cross, where it was deleted at a frequency of approximately 21%. Analyzing fitness and key morphological traits like colored seeds, shattering seed heads and the presence of a pappus, we found no evidence of hybrid vigour or increased weediness in the F1 hybrids of commercial safflower and its wild relatives. Conclusion: Our results suggest that hybridization between commercial safflower and its wild relatives, while feasible in most cases we studied, does not generate progeny with higher propensity for weediness.