Objective
- Evaluate B. napus genotypes in field trials to identify resistance against L. maculans.
- Screen B. napus genotypes for novel R genes using CRISPR/Cas9-modified L. maculans isolates.
- Analyze genetic variation, population structure, and kinship coefficients of B. napus genotypes.
- Conduct GWAS to identify resistance loci and SNPs against L. maculans.
- Identify major resistance genes/loci and quantitative trait loci through fine mapping and GWAS and developing SNP markers tightly linked to blackleg resistance loci for marker-assisted breeding.
Project Decsription
Blackleg resistance in canola is governed by both qualitative (R gene) and quantitative (Adult plant resistance) resistance. Although several R genes have been identified so far, resistance conferred by R genes breaks down with the overuse of the same R genes. Therefore, it is important to identify novel R genes to address this issue. In addition, it has been reported that the minor R genes enhance the durability of the resistance in canola and the longevity of R gene resistance breakdown. This research aimed to address this critical issue by leveraging Genome-Wide Association Studies (GWAS) to identify R-gene resistance in B. napus genotypes.
Approximately 235 B. napus genotypes were evaluated in field trials, with many genotypes exhibiting strong to moderate resistance to L. maculans. All lines were screened under controlled greenhouse conditions, confirming the presence of adult plant resistance traits. These genotypes were first screened at the cotyledon stage by droplet inoculation with an L. maculans isolate developed in the lab. This isolate, umavr7, is virulent on all the R genes identified in B. napus, so all the lines showing resistance to umavr7 can be identified as the lines having potential novel R genes. This is useful to discover novel resistance to blackleg in unique B. napus lines. Disease ratings were conducted at 12-14 days post-inoculation. Plants were grown to maturity and rated for adult plant resistance. Results suggest the potential of these genotypes for breeding programs to enhance blackleg resistance.
To identify novel R genes in canola, 10 lines of canola from two seed companies were obtained. Four lines were identified as having potential novel R genes. To develop mapping populations to identify and map the novel R gene, each identified line was crossed with the susceptible parent, and the resulting progeny were analyzed further. This confirmed that the resistance in each mapping population was associated with a single recessive gene. The results from these experiments have laid the foundation for both companies to work on the lines for resistance and to include them in their breeding programs.
Genome-wide association analysis was conducted using the FarmCPU model to identify single-nucleotide polymorphisms (SNPs) significantly associated with blackleg resistance. SNPs exceeding the significance threshold were mapped to the reference genome to determine their physical positions. The results demonstrate robust phenotypic and genotypic data quality, appropriate control of population structure, and the successful identification of significant genomic regions contributing to blackleg resistance in canola.
