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Canola Resistance Breeding to Fight against Blackleg Caused by Leptosphaeria maculans

Yu Chen: Cargill Inc

<div>Canola Resistance Breeding to Fight against Blackleg Caused by <em>Leptosphaeria maculans</em></p> <p>Y. Chen, P. Covey and R. Fletcher<br /="/">Cargill, GEOS</p> <p>Blackleg [<em>Leptosphaeria maculans</em> (Desmaz.) Ces. & de Not.] is one of the major diseases in canola (<em>Brassica napus</em> L.) worldwide that can cause significant yield loss. Tight rotation imposes extreme selection pressure against cultivar resistance, resulting in shift in <em>L. maculans</em> races. This has lead to breakdown of the resistance and more severe disease epidemics across western Canada. The best risk management is the introgression of major gene (Rlm) and multigenic sources of resistance into canola hybrids, along with integrated risk management to slow down the erosion of resistance and ensure sustainable yield in Cargill’s Victory canola hybrids. The method is to evaluate <em>L. maculans</em> AvrLm allele frequency and identify unique sources of genetic resistance from Cargill gemplasm; fine mapping of the genes using 60K SNP genotyping array to find the gene-specific markers for marker-assisted breeding; In-vitro assessment over near-isogenic lines carrying introgressed genes, followed by outdoor assessment of adult plant resistance; finally judicious deployment of resistant varieties and risk management strategies recommended to the growers. Stacked Rlm genes in combination with QTL haplotypes provide Cargill Victory hybrids with broad and durable resistance to the blackleg. The resistance in Cargill products has been in a leading position since 2010, indicating that this breeding strategy is effective. Monitoring the dynamics of AvrLm allele frequency in the pathogen population is a great tool in determining the usefulness of Rlm genes. Trait-specific markers are proving to be powerful tools in marker-assisted gene introgressions, selection in doubled-haploid (DH) breeding populations and hybrid evaluation.</div>