Introgression of Resistance Against <i>Leptosphaeria maculans</i> From <i>Brassica juncea</i> Into <i>Brassica napus</i>

ABSTRACT Blackleg disease is caused by the fungal plant pathogen Leptosphaeria maculans . When susceptible cultivars are grown, blackleg infection can result in yield loss of more than 50% under severe pathogen pressure. Host resistance is an effective management strategy, but the breakdown of resistance has been reported in France, Australia and Canada. Introgression of blackleg‐specific resistance genes from Brassica juncea into Brassica napus was performed by crossing and backcrossing. An advanced (BC 5 F 2 ) backcross segregating population as well as the resistant parent ( B. juncea UM3073) and susceptible control ( B. napus ‘Westar’) were inoculated with L. maculans isolate PG4‐1‐M ( AvrLm2 , AvrLm5‐9 , AvrLm6 , AvrLm10 and AvrLm11 ). Screening of the resistant B. juncea × B. napus progeny (UMBJ16) by phenotyping for Rlm3 , Rlm5 and Rlm6 revealed that the UMBJ16 genotypes do not contain any of these genes. Genotyping showed that resistant UMBJ16 genotypes do not contain Rlm2 , Rlm4 , Rlm6 , Rlm7 , Rlm9 , LepR3 or rjlm2 . These results suggest that this recently developed germplasm may contain resistance against the blackleg pathogen that has not been previously characterised. This resistance source will be useful in canola and rapeseed breeding programmes for managing blackleg disease.