Genome-Wide Association Mapping of Loci for Blackleg Resistance in Canola.

Blackleg (caused by Leptosphaeria maculans (Desm.) Ces. & de Not.) is one of the most destructive fungal diseases of canola in North Dakota commonly found throughout the state. The fungus may attack the plant throughout its life cycle. However, severe damage occurs at early seedling stage that causes the most yield loss. On the basis of disease reaction to four B. napus genotype, this pathogen is classified into four pathogenicity (PG-1, PG-2, PG-3, PG-4) groups (Mengistu et al., 1991). PG-2 strains were the most devastating for canola. Genes resistant to PG-2 strains have been introgressed into commercial canola cultivars. Recently, PG-4 strains have been identified in North Dakota. These strains can attack on the cultivars considered resistant to PG-2. Therefore, we initiated a research program to identify germplasm resistant to PG-4 strains. A total of 184 genetically diversified B. napus accessions were evaluated in two planting times with each of three replications for their reaction to PG-4 strains in the greenhouse. Nine seedlings of each line per replication were inoculated at the cotyledon stage with 10 µl of a spore suspension containing 10⁷ spores ml^-1. Disease reactions to plant were scored on a 0-9 scale where 0 is no reaction (no lesion on cotyledon) and 9 means death of seedling. We have genotyped the 184 B. napus accessions using Ilumina genotyping by sequencing (GBS) platform at the Institute for Genomic Diversity at Cornell University. The genotypic data is being processed to discover SNPs at NDSU. A combined analysis of disease scores along with genotypic data is in progress, which will identify the genomic regions containing the resistant genes. The association mapping information may further be useful for marker assisted selection in canola breeding program or could be used to clone the resistant genes to PG-4 strains.