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Managing Blackleg Resistance Breakdown and Trade Barriers through Blackleg Resistance Stewardship in Canola Dilantha Fernando Department of Plant Science University of Manitoba MB Agronomists Conference, Dec 15, 2010 What is Blackleg? Where does it attack & cause symptoms? Major Problems at the Present Time • The pathogen is reappearing and there is more disease in the farmers’ fields • A trade barrier on the export of canola seed to China General Blackleg Management PracEces • Resistant culEvars – very effecEve • Adequate rotaEon of canola with other crop species • IsolaEng canola producEon from previously infected fields by a specified distance • Efficient weed and volunteer control • The use of cerEfied seed and seed treatment Blackleg is not a new problem • It was well managed with good geneEcs (resistance) for almost 3 decades. • However, New Problems with Blackleg!! • The disease is emerging in farmers’ fields even on MR and Rrated cultivars – outbreaks are now more common! • New races (strains) have been found since 2002 • China has introduced restrictions on the import of canola seed • Several growers practicing Tighter Rotations with canola • Minimum or zero tillage can aggravate the problem Is Plant Resistance the Best Strategy? • Use of plant resistance is one of the most aSracEve approaches to suppressing plant disease. – 1. Requires no ac0on by the farmer during the growing season. Therefore, low produc0on costs. – 2. Is not disrup0ve to the environment. i.e Limits pes0cide applica0on. low produc0on costs – 3. Is generally compa0ble with other disease management techniques. – 4. Most oEen singularly sufficient to suppress disease to tolerable levels (But not always a good method to do so!!) . 8 What are the Types of Resistance we have? • Resistance • Two types: 1. Major gene/qualitative/vertical • single gene • gene-for-gene interactions 2. Minor gene/quantitative/horizontal • many genes each with small impact Pathogenicity Gene Host Gene Rlm1 Qualita4ve Resistance Quan4ta4ve Resistance Single gene resistance Major effects Avrlm1 Avrlm1 Avrlm1 QTL1 QTL2 QTL3 QTL4 QTL5 Multiple gene resistance – minor effects Two types of resistance to L. maculans Quantitative resistance (partial resistance) R gene-mediated resistance (complete resistance) susceptible resistant Canadian Blackleg Situation % Incidence of Blackleg stem canker Infected Plants % plants infected with blackeg 50 Manitoba Saskatchewan Alberta 45 40 35 30 25 20 15 10 5 0 2003 2004 2005 2006 2007 2008 2009 2010 Courtesy Clint Jurke and Faye Dokken-Bouchard Blackleg Situation • Outbreaks of blackleg more common • New races of blackleg appearing • Short rotations and zero tillage increase disease risk. • How durable is the blackleg resistance? Do Rotations of crop help? • Crop Rotations • Getting tighter • Increase risk for disease development How should resistance be deployed? • Resistance can fail if it is not applied correctly, as has happened in Australia and France. Lessons from other canola growing countries: Situation in France • In France, the large-scale use of single Rlm1 gene for ten years (1990 to 2000) shifted the population of isolates from Avrlm1 to others (Rouxel et al., 2003) . • Therefore the efficiency of resistance of the commercially successful cultivars harboring Rlm1 decreased consistently between 1995 and 2003 in France. (Rouxel et. al. 2003) Frequency of isolates harboring AvrLm1 or avrLm1 from Cultivars with the major resistance gene Rlm1 Virulent strains Rouxel et. al. 2003 Lessons from other canola growing countries: Situation in Australia • The Surpass 400 (LepR3 gene resistance) derived cultivars became susceptible to blackleg within 2 years after being released – ‘Boom and Bust’! • Cause - due to large-scale use of single gene resistance (2001 to 2003) – loss $ 5 – 10 million / year • Dominant single gene resistance being easily overcome by pathogen population shifts (Li et al, 2003). Blackleg • Australian experience • Surpass 400 (LepR3) released commercially in 2001 • Epidemic in 2003. Hyola 60 – LepR3 resistance Conventional Resistance Situation in Western Canada in early 2000’s Chen and Fernando, 2006 Can J of Plant Pathology Blackleg symptoms on R-Rated canola cultivar Distribution of New Pathogenicity groups How does one isolate react to different culEvars with known R‐genes? • Visual indica0on of the varia0on observed on the various R genes. This isolate is 05‐08, which is one of the isolates recovered from the canola debris that Coreen Franke collected at the Killam site in 2005. Percentage of isolates carrying avirulence allele AvrLm2 at each site Kutcher et al. 2010 Overcoming Glacier which has Rlm2 (Plum Coulee) Percentage of isolates carrying avirulence allele AvrLm3 at each site Kutcher et al. 2010 Rlm3 not effective in Brandon, Carberry, Plum Coulee Percentage of isolates carrying avirulence allele AvrLm4 at each site Kutcher et al. 2010 Avrlm4 – not so good in the west The success in Breeding for disease resistance - the future? Mean Incidence (% of Total Plants Surveyed) 12% 10% 8% 6% Blackleg 4% 2% 0% 1999 2000 2001 2003 2004 2005 2006 2007 2008 2009 Year Courtesy Faye Dokken‐Bouchard Strategy for stable resistance deployment • Therefore resistance should be deployed as part of a larger strategy to control this disease. • Stewardship of blackleg resistance and agronomic prac0ces designed to control blackleg should be recommended together. Pathogenicity Gene Host Gene Rlm1 Avrlm1 Rlm1 Quan4ta4ve Resistance Avrlm1 Avrlm1 Qualita4ve Resistance QTL1 QTL2 QTL3 QTL4 QTL5 Fitness cost of virulence can be used as indicator of durability of the corresponding R gene • Near isogenic isolates at AvrLm1 or AvrLm4 loci • Host without the corresponding R gene (no selec0on pressure) Avr gene in L .maculans population Deploy Brassica napus R gene L. maculans evolves to virulence Remove Brassica napus R gene Consequence for L. maculans Consequence for Brassica napus AvrLm4 Rlm4 Point mutation No Rlm4 Large fitness cost of virulence Can redeploy Rlm4 Rapid selection for AvrLm4 avrLm4 AvrLm1 Rlm1 Deletion of gene No Rlm1 Rlm2 Rlm3 ? May be able to redeploy Rlm1 Less rapid selection for AvrLm1 avrLm1 AvrLm2 AvrLm3 Smaller fitness cost of virulence No Rlm2 No Rlm3 avrLm2 avrLm3 Time (years) No fitness cost of virulence No selection for AvrLm2, AvrLm3 Cannot redeploy Rlm2, Rlm3 Durability of Brassica napus resistance Fitness cost of virulence at L. maculans locus Fitness cost of virulence & potential durability of R gene resistance Blackleg • Known: • R-rated cultivars can and do break down • Pathogen diversity is high • Virulence genes available to compromise most R genes • Tight rotations recipe for epidemic What factors decide the durability of resistance? • Resistance Durability • Resistance may not be durable if: • pathogen diversity is high • pathogen gene flow is high • pathogen reproductive capacity is high • Canola resistance diversity is low QuanEtaEve resistance • Not race specific • QuanEtaEve resistance is non race specific • QuanEtaEve resistance is durable • Difficult to screen for ‐ at seedling stage • Screening for quanEtaEve resistance currently relies on field assessment at harvest Keeping Resistance to Blackleg Alive! • How should resistance be deployed? Pathogenic Diversity low high high Gene flow low R genes & quant. Use resist. in mulE‐lines quanEtaEve or regional resistance deployment Gene flow high Pyramid R genes low Use R gene McDonald BA. and Linde C. EuphyFca 124 (2): 163‐180, 2002 Pathogenicity Gene Host Gene Rlm1 Avrlm1 Avrlm1 Quan4ta4ve Resistance QTL1 QTL2 QTL3 QTL4 QTL5 Blackleg Resistance Stewardship Options (Falls well within Environmental Stewardship) • Want current resistance genes to last • What are the options? 1. Long rotations 2. Rotating resistance genes 3. Resistance genes with minor genes Acknowledgements • • • • Randy Kutcher, Agriculture & Agri‐Food Canada, Melfort, SK Clint Jurke, Canola Council of Canada Khaled Al‐Taweel, University of Manitoba Yu Chen, University of Manitoba (Cargill Inc., SK) • Natural and Science and Engineering Research Council of Canada • Agriculture Research Development Ini0a0ve, MB • Canola Council of Canada – CARP Program • Seed Industry Carman Blackleg Nursery Thank you 41 Identification of 16 races among 87 isolates of L. maculans from western Canada collected between 1997-2005 – R. Kutcher et.al Race designation1 Number of isolates of each race Frequency (%) Number of avirulence alleles Av1-2-3-4-5-(6)-7-(8)-9-10(LepR3)2 1 1.2 8 Av1-2-4-5-(6)-7-(8)-9-10(LepR3) 1 1.2 7 Av1-2-3-6-(8)-9-10-(LepR3) 1 1.2 6 Av1-2-4-6-7-(8)-10-(LepR3) 1 1.2 6 Av1-4-5-6-7-(8)-10-(LepR3) 1 1.2 6 Av2-3-6-(8)-9-10-LepR3 7 8.1 6 Av2-4-6-7-(8)-10-LepR3 13 14.9 6 Av1-2-6-7-(8)-10-(LepR3) 1 1.2 5 Av1-2-6-(8)-9-10-(LepR3) 20 23.0 5 Av1-4-6-7-(8)-10-(LepR3) 1 1.2 5 Av2-4-6-7-(8)-10 1 1.2 5 Av2-6-7-(8)-10-LepR3 3 3.5 5 Av2-6-(8)-9-10-LepR3 19 21.8 5 Av4-6-7-(8)-10-LepR3 1 1.2 5 13 14.9 4 3 3.5 4 Av1-2-6-(8)-10-(LepR3) Av2-6-(8)-10-LepR3 Air‐borne ascospores R gene resistance Phoma leaf spots Infec0on QTL resistance Damage Severe canker (harvest) QTL resistance Early canker Major gene mediated resistance • Race specific, high risk of overcoming resistance • EffecEve only if corresponding Avr allele is predominant in pathogen populaEon • InformaEon on pathogen races is essenEal • Many factors (e.g. host culEvar, pathogen fitness cost, temperature) affect race composiEon of populaEons Temperature affects R gene resistance Resistant 15°C 25°C Susceptible Darmor DarmorMX (Rlm6) Huang et al., 2006, New Phytologist, 170, 129-141 Monitoring pathogen populaEon R gene is effective only if corresponding Avr allele is predominant in pathogen population, so it is needed to monitor pathogen population • Collec0on of isolates from leaf spots or stem cankers • Collec0on of ascospores from air samplers • Determina0on of pathogen race structure using pathogenicity test or specific PCR primers Detect Avr allele by inoculaEon (Pathogenicity Test) Air sampling to determine alleles b Spore sampler surrounded by diseased OSR stem debris Van de Wouw et al., 2010 Advantages Samples larger populaEon Quicker, cheaper Less laborious than cotyledon assays Temperature affects quantitative resistance Mean internal stem canker severity 100 80 Darmor Eurol 60 40 20 0 15°C 25°C Darmor (with quantitative resistance) Eurol (without quantitative resistance) Huang et al., 2009, Plant Pathology Growth in stem (internal) Resistant Darmor Susceptible Eurol Huang et al., 2009, Plant Pathology Management of Blackleg of Canola Cultural control: Crop rotation for at least 3 years. Tillage – conventional tillage helps reduce inoculum Weeds and volunteer canola removed. Pathogen-free seed. Genetic resistance: Resistant cultivars — the most important and sustainable means of blackleg control in Canada for the past three decades.