Kutcher: Determination of pathogenic variability of Leptosphaeria maculans in western Canada and resistance in Canadian Brassica napus cultivars
Date: March 2009
Term: 3 years
Status: Completed
Researcher(s): Dr. H.R. Kutcher, Agriculture and Agri-Food Canada, Melfort, SK., S. R. Rimmer, Agriculture and Agri-Food Canada, Saskatoon, SK
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: ACPC, AAFC Matching Investment Initiative
Project Summary
Blackleg continues to be found throughout the canola growing area and new strains of Leptosphaeria maculans have been observed in western Canada. This study provides significant knowledge of avirulence allele variation of the pathogen population of L. maculans in western Canada and therefore some of the information needed to develop effective, durable blackleg resistance management strategies.
Blackleg disease of canola, caused by the fungal pathogen Leptosphaeria maculans is the most damaging disease of this crop in Canada and worldwide. The disease was a serious impediment to canola production throughout western Canada in the 1980s. Since the introduction of cultivars with improved resistance to blackleg, the threat to the canola industry has been reduced, but not eliminated.
Blackleg continues to be found throughout the canola growing area and new strains or changes in the pathogenic variability of L. maculans have been observed in western Canada. These new strains, coupled with more intensive production of canola increases the risk that the current genetic resistance in canola may be overcome by the pathogen. The specific resistance (R) genes in Canadian canola cultivars and the corresponding avirulence (AvrLm) genes carried in isolates of L. maculans collected from western Canada are unknown. Therefore understanding the genetic control of the host-pathogen interaction between L. maculans and B. napus is necessary to develop integrated management strategies and durable resistance to the disease.
The objectives of this project are to characterize L. maculans isolates from the Canadian prairies against differential genotypes of Brassica spp. to identify avirulence genes (Avr- genes) carried by each isolate, and to characterize a selection of canola cultivars for R- genes using a differential set of L. maculans isolates carrying known Avr-genes. This research was conducted in collaboration with scientists at the Institut National de la Recherche Agronomique (INRA), France.
New strains of L. maculans in western Canada are believed to have resulted from the use of specific resistance genes in Brassica spp., many of which have only recently been identified. For this study, an analysis was conducted under controlled conditions for 103 isolates of Leptosphaeria spp. collected between 1997 and 2005 in western Canada. A limited number of races were detected among the 96 isolates of L. maculans identified and characterized.
In the second part of the study, a selection of open-pollinated, non-herbicide-tolerant Brassica napus, B. rapa and B. juncea varieties or lines were evaluated for the presence of 10 specific resistance genes to L. maculans. Most importantly, specific resistance genes were not detected in many currently grown Canadian varieties, most of which are herbicide tolerant hybrids. These varieties generally have a high resistance rating in the field evaluation, which suggests that resistance to L. maculans in these varieties may depend on quantitative resistance rather than specific gene resistance.
Although this research was based on a rather limited number of isolates collected from unidentified varieties of B. napus, a more precise study is currently being undertaken to obtain isolates from a variety of B. napus known to have no specific R-genes to be sown at various locations to obtain an unbiased and extensive characterization of the western Canadian L. maculans population.
Overall, the results of this study provide the first analysis of the Avr-gene frequency among isolates from the population of L. maculans present in western Canada. It also provides significant knowledge of avirulence gene variation of the pathogen population of L. maculans in western Canada and therefore provides some of the information needed to develop effective, durable blackleg resistance management strategies.
Scientific Publications
Kutcher, H.R., Balesdent, M.H., Rouxel, T., Chevre, A.M., Delourme, R., Rimmer, S.R. and Brun, H. 2008. Variation in frequency of avirulence genes in Leptosphaeria maculans in western Canada. Proceedings of the Soils & Crops Workshop 2008 [CD- ROM], University of Saskatchewan, Saskatoon, SK. February 28 - 29.
Kutcher, H.R., Rimmer, S.R., Balesdent, M.H., Rouxel, T. and Brun, H. 2008. Detection of specific resistance genes against Leptosphaeria maculans in Brassica napus. Can. J. Plant Pathol. 30:386.
Kutcher, H.R., Yu, F., Brun, H. 2009. Using knowledge of genetic interactions between Brassica napus and Leptosphaeria maculans to manage specific resistance of blackleg of oilseed rape. Can. J. Plant Pathol. 31:502.
Kutcher, H.R., Balesdent, M.H., Rimmer, S.R., Rouxel, T., Chèvre, A.M., Delourme, R. and Brun, H. 2009. Identifying races of Leptosphaeria maculans, cause of blackleg disease of canola in western Canada. Proceedings of FarmTech 2009, Edmonton, AB. January 28-30.
Kutcher, H.R., and Yu, F. 2009. Blackleg revisited – races and resistance. Proceedings of the Manitoba Agronomists Conference. December 14-16. Published on-line at http://umanitoba.ca/afs/agronomists_conf/proceedings.html
Kutcher, H.R., Balesdent, M.H., Rimmer, Rouxel, T., S.R., Delourme, R., Chèvre, A.M., and Brun, H. 2010. Frequency of avirulence genes among isolates of Leptosphaeria maculans in western Canada. Can. J. Plant Pathol. 32 (1): 77-85.
Kutcher, H.R., Yu, F., and Brun, H. 2010. Using knowledge of genetic interactions between Brassica napus and Leptosphaeria maculans to manage specific resistance of blackleg of oilseed rape. Can. J. Plant Pathol. 32 (1): 29-34.