Researchers successfully transferred both clubroot and blackleg resistance into Brassica napus canola breeding lines from a unique black mustard (B. nigra) line.
Canola with genetic resistance remains the most important management strategy for blackleg and clubroot, however virulent pathogen populations have recently been reported that are able to overcome the resistance of canola cultivars for both diseases. In this four-year study, researchers studied black mustard (B. nigra), which is highly resistant to canola diseases, to identify unique and novel sources of clubroot and blackleg resistance genes and transfer those genes into B. napus breeding lines.
The objectives of the project were to determine how many genes control clubroot resistance and the genetic location of each resistance gene in the B. nigra line CR2716 (highly resistant to both clubroot and blackleg), and to discover SNP markets associated with each clubroot resistance gene. Researchers also wanted to develop B. napus breeding lines introgressed with resistance to clubroot and with resistance to blackleg.
In this study, genetic mapping of clubroot resistance in a B. nigra line CR2716 was performed. Testing confirmed that resistance is controlled by a single dominant gene, and this novel clubroot resistance gene is highly resistant to pathotypes 3 and 5X, and potentially other new pathotypes. This novel resistance gene was mapped into a genomic region close to a previously identified clubroot resistance gene Rcr6. Researchers also identified more than 1000 high quality SNP sites in the target region. More than ten markers tightly linked to the resistance gene using KASP assay were developed.
The next part of the project focused on the introgression of resistance to both diseases from the B. nigra resistant line CR2716 into the B. napus canola line DH 16156. The clubroot breeding lines were tested for resistance to pathotypes 3 and 5X, and marker assisted selection was performed on each generation. A single gene was confirmed to control resistance to clubroot. Similar studies were performed for blackleg, with plant resistance identified in all populations. Four phenotypes for resistance to two isolates of L. maculans were found in most of the populations, indicating that blackleg resistance to isolates is likely controlled by different genes. Homozygous lines have been developed for both clubroot and blackleg resistant breeding lines.
Researchers identified and genetically mapped a novel clubroot resistance gene highly resistant to pathotypes 3 and 5X, and other new pathotypes. They then successfully transferred this resistance into the B. napus (BC4) from the B. nigra. For blackleg, BC4 populations with resistance to two highly aggressive isolates collected in the Prairies were developed. The molecular markers and the new B. napus breeding lines will be made available to canola breeders for new cultivar development.