Impact of synergistic interaction between V. longisporum and L. maculans on canola yield
Term: 5 years, beginning 2024
Status: Ongoing
Researcher(s): Hossein Borhan, AAFC
SaskCanola Investment: $104,506.25
Total Project Cost: $475,860
Funding Partners: WGRF, ACPC
Objective
1. Explore the Leptosphaeria maculans (Lm) and Verticillium longisporum (Vls) compound effect on a susceptible canola cultivar.
2. Determine the severity of VS disease on canola plants pre-inoculated with an incompatible Lm isolate.
3. Discover new sources of resistance to Vls.
4. Develop and test the durability of B. napus introgression lines with multiple resistance genes against blackleg disease.
5. Develop susceptible and resistant control check lines for Vls indoor and outdoor pathology tests.
Project Description
Canola production is threatened by various diseases. Two of such disease are blackleg (BL) and Verticillium stripe (VS). Yield loss due to blackleg is estimated at 17.2% per every unit increase in disease severity. There is no proper estimate of Vls damage to canola production in Canada, but in Europe, yield loss ranges from 10 to 50%. Lm and Vls are common and often co-existing pathogens across the prairies. There is little information on the combined impact of Vls and Lm on canola. This is because plant pathology studies are often conducted with a pure monoculture pathogen isolate. Yet, such monocultures likely never occur in nature, so inter-pathogen synergies are probably much more common than we are aware of. The limited research conducted to date has indicated that Lm and Vls interact synergistically to significantly increase disease severity and reduce canola growth and yield. This could lead to serious implications for VS and BL disease management if the effect size of such interactions is practically significant. Possible consequences could include I) increased yield losses; II) inaccurate evaluation of BL or VS in field trials; III) rapid evolution and dispersion of Lm and Vls isolates and IV) an impact on R gene durability.
Lm has been present in Canada since 1970s when canola (rapeseed) was promoted for production of edible oil. Severe yield losses due to BL in 70s and 80s was controlled by the introduction of genetically resistant cultivars. To date 22 race-specific R genes against Lm (Rlm/LepR) have been identified. We have mapped the genome location of Rlm1,2,3,4,7,9,11; LepR1,2,3,4,5 &6. All these genes have been introgressed into the BL susceptible B. napus cv Topas. B. napus Topas Rlm/LepR introgression lines have been instrumental as control checks in blackleg field trials, and in determining Lm race structure. Compared to Lm, Vls is a relatively new pathogen of concern for Canadian canola producers. Vls was first reported from a field in Manitoba. However additional field surveys revealed the presence of Vls in Saskatchewan and Alberta, raising concern about its impact on canola growth and yield and its effect on other diseases such as BL. The soil-borne nature of Vls makes it difficult to control the disease once it is established in a field.
Genetic resistance is the best method to control Vls. In a recently completed project funded through canola cluster initiative we screened, the founder B. napus accessions of a Nested-Association Mapping population (NAM) for resistance to Vls. NAM14 with high level of resistance to Vls and several moderately resistant lines were identified. Two quantitative loci were identified controlling resistance to VS in NAM14. We will expand our search for resistance to Vls using a subset of the AAFC-PGRC (Plant Gene Resources of Canada) spring-type B. napus accessions that were identified to contain R and QTL against BL. To enable screening of NAM mapping populations for resistance to VS in the abovementioned completed project funded through canola cluster project, we developed a method for scoring B. napus/Vls interaction phenotypes in indoor hydroponic assays after root-dip inoculation. The method repeatably differentiates between susceptible, moderately resistant, and resistant materials. Using other funding, we also used machine vision and machine learning to build several algorithms for scoring phenotypes from images. Two of the VS research priorities set by the Canola Council of Canada are the cultural controls for effective management of Vls and the interaction and relationship between Lm and Vls. One of the tools required to conduct this research is genetically defined differential lines to be used as control in field and greenhouse studies. Presently, there are no common differential lines to be used as checks in Vls field trials. B. napus check lines for Vls should be resistant to blackleg to avoid complications due to co-infection by both pathogens. Topas-blackleg R gene introgression lines could be a suitable susceptible check for VS. Introgression lines with multiple Rlm and/or LepR genes could provide more durable resistance against Lm and provide a better check for VS. In addition, pyramiding several blackleg R genes in the Topas genotype will be highly useful for testing the durability of multiple R genes against blackleg, providing valuable information for future canola breeding efforts. Gene stacking has been reported to enhance resistance of potato to late blight and wheat against stem rust diseases. There is little published data on the durability of multiple R genes against blackleg disease. A recent study in France using B. napus cv with Rlm3, Rlm7 or Rm3+Rlm7 indicated that these genes were more durable when used individually in a rotation than combined (Rlm3+Rlm7). However additional studies are needed to test the durability of single vs multiple blackleg R genes under Canadian climate conditions and farming practices. Combining blackleg R genes by crossing the desired Topas-Rlm/LepR lines will allow us to test the durability of multiple R genes in a uniform background against the prevalent Lm races in Canada.