Characterisation of resistance to turnip mosaic virus in oilseed rape (Brassica napus) and genetic mapping of TuRB01

Turnip mosaic virus (TuMV) is the major virus infecting Brassica crops. A d ominant gene, TuRBO1, that confers extreme resistance to some isolates of T uMV on Brassica napus (oilseed rape), has been mapped genetically. The mapp ing employed a set of doubled-haploid lines extracted from a population use d previously to develop a reference RFLP map of the B. napus genome. The po sitioning of TuRBO1 on linkage group N6 of the B. napus A-genome indicated that the gene probably originated from Brassica rapa. Resistance phenotypes were confirmed by indirect plate-trapped antigen ELISA using a monoclonal antibody raised against TuMV. The specificity of TnRBO1 was determined usin g a wide range of TuMV isolates, including representatives of the European and American/Taiwanese pathotyping systems. Some isolates of TuMV that did not normally infect B, napus plants possessing TuRBO1 produced mutant virus es able to overcome the action of the resistance gene. TuRBO1 is the first gene for host resistance to TuMV to be mapped in a Brassica crop. A second locus, TuRBO2, that appeared to control the degree of susceptibility to the TuMV isolate CHN 1 in a quantitative manner, was identified on the C-genom e linkage group N14. The mapping of other complementary genes and the selec tive combining of such genes, using marker-assisted breeding, will make dur able resistance to TuMV a realisable breeding objective.