Continental sweeps and aggressiveness in wheat rust pathogens

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Robert Park & Colin Wellings
Plant Breeding Institute

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Continental sweeps and aggressiveness in wheat rust pathogens

  1. 1. CIMMYT<br />Australian<br />Cereal<br />Rust<br />Control<br />Program<br />Continental sweeps and aggressiveness in wheat rust pathogens<br />International Wheat Stripe Rust SymposiumICARDA, Aleppo, Syria18-20 April 2011<br />Robert Park & Colin Wellings<br />Plant Breeding Institute<br />
  2. 2. Wheat rusts in Australasia<br />-isolated from other cereal growing regions<br />-wheat rust pathogens are clonal<br />-long-term (90+ years) surveys have provided rare insight into rust pathogen population dynamics<br />
  3. 3. Pathogenic variability in wheat rusts in Australia<br />- surveys since 1919 suggest that pathogenic variability arises from:<br /><ul><li>periodic incursions of exotic rust isolates
  4. 4. mutation
  5. 5. somatic hybridisation
  6. 6. mutation is believed to be most common; frequencies of somatic hybridisation and exotic incursions are thought to be low</li></li></ul><li>Pathogenic variability in wheat rusts in Australia- 11 exotic incursions of wheat rust since 1919<br />
  7. 7. Pathogenic variability in wheat rusts in Australia- 11 exotic incursions of wheat rust since 1919<br />On 4 occasions, exotic isolate has displaced existing rust races in less than 10 years, presumably due to greater aggressiveness<br />
  8. 8. 1. Wheat stem rust race 126-frequency of isolation, 1922 through 1945<br />- Stem rust race surveys began in 1919, 6 races (=“old” races) were detected<br />- Exotic stem rust race 126 was first detected in WA in 1925<br />- By 1929 (5 years), it had all but replaced the “old” races<br />
  9. 9. 1. Wheat stem rust race 126-frequency of isolation, 1922 through 1945<br />- Stem rust race surveys began in 1919, 6 races (=“old” races) were detected<br />- Exotic stem rust race 126 was first detected in WA in 1925<br />- By 1929 (5 years), it had all but replaced the “old” races<br />
  10. 10. 1. Wheat stem rust race 126-frequency of isolation, 1922 through 1945<br />- Stem rust race surveys began in 1919, 6 races (=“old” races) were detected<br />- Exotic stem rust race 126 was first detected in WA in 1925<br />By 1929 (5 years), race 126 had all but replaced the “old” races:<br />
  11. 11. Race 126 group <br />Frequency (%)<br />“Old” races <br />1922<br />1924<br />1926<br />1928<br />1930<br />1932<br />1934<br />1936<br />1938<br />1940<br />1942<br />1944<br />Year<br />1. Wheat stem rust race 126-frequency of isolation, 1922 through 1945<br />- Stem rust race surveys began in 1919, 6 races (=“old” races) were detected<br />- Exotic stem rust race 126 was first detected in WA in 1925<br />By 1929 (5 years), race 126 had all but replaced the “old” races:<br />
  12. 12. 2. Wheat stem rust race 21-frequency of isolation, 1951 through 1970<br />- Exotic stem rust race 21 was first detected in 1954<br />- “Hybrid” group arose from spomatic hybridisation between 126 and 21<br />By 1962 (8 years), the race 21 group had all but replaced race 126:<br />
  13. 13. 2. Wheat stem rust race 21-frequency of isolation, 1951 through 1970<br />- Exotic stem rust race 21 was first detected in 1954<br />- “Hybrid” group arose from spomatic hybridisation between 126 and 21<br />By 1962 (8 years), race 21 group had all but replaced race 126:<br />
  14. 14. Frequency (%)<br />1951<br />1952<br />1953<br />1954<br />1955<br />1956<br />1957<br />1958<br />1959<br />1960<br />1961<br />1962<br />1963<br />1964<br />1965<br />1966<br />1967<br />1968<br />Year<br />2. Wheat stem rust race 21-frequency of isolation, 1951 through 1970<br />- Exotic stem rust race 21 was first detected in 1954<br />- “Hybrid” group arose from spomatic hybridisation between 126 and 21<br />By 1962 (8 years), race 21 group had all but replaced race 126:<br />Race 21 group <br />Race 126 group <br />
  15. 15. “Hybrid” group <br />Race 21 group <br />Frequency (%)<br />Race 126 group <br />1951<br />1952<br />1953<br />1954<br />1955<br />1956<br />1957<br />1958<br />1959<br />1960<br />1961<br />1962<br />1963<br />1964<br />1965<br />1966<br />1967<br />1968<br />Year<br />2. Wheat stem rust race 21-frequency of isolation, 1951 through 1970<br />- Exotic stem rust race 21 was first detected in 1954<br />- “Hybrid” group arose from somatic hybridisation between 126 and 21<br />By 1962 (8 years), race 21 group had all but replaced race 126:<br />
  16. 16. 3. Wheat leaf rust race 104-frequency of isolation, 1980 through 2000<br />- Exotic leaf rust race 104 was first detected in 1984 in Victoria<br />- Race 76 is another exotic isolate, first detected in 1993<br />By 1991 (7 years), race 104 group had all but replaced existing races:<br />
  17. 17. 3. Wheat leaf rust race 104-frequency of isolation, 1980 through 2000<br />- Exotic leaf rust race 104 was first detected in 1984 in Victoria<br />- Race 76 is another exotic isolate, first detected in 1993<br />By 1991 (7 years), race 104 group had all but replaced existing races:<br />
  18. 18. 1980<br />1981<br />1982<br />1983<br />1984<br />1985<br />1986<br />1987<br />1988<br />1989<br />1990<br />1991<br />1992<br />1993<br />1994<br />1995<br />1996<br />1997<br />1998<br />1999<br />2000<br />3. Wheat leaf rust race 104-frequency of isolation, 1980 through 2000<br />- Exotic leaf rust race 104 was first detected in 1984 in Victoria<br />- Race 76 is another exotic isolate, first detected in 1993<br />By 1991 (7 years), race 104 group had all but replaced existing races:<br />Race 104 group <br />Frequency (%)<br />“Old” races <br />Year<br />
  19. 19. Race 76 group <br />Race 104 group <br />Frequency (%)<br />“Old” races <br />1980<br />1981<br />1982<br />1983<br />1984<br />1985<br />1986<br />1987<br />1988<br />1989<br />1990<br />1991<br />1992<br />1993<br />1994<br />1995<br />1996<br />1997<br />1998<br />1999<br />2000<br />Year<br />3. Wheat leaf rust race 104-frequency of isolation, 1980 through 2000<br />- Exotic leaf rust race 104 was first detected in 1984 in Victoria<br />- Race 76 is another exotic isolate, first detected in 1993<br />By 1991 (7 years), race 104 group had all but replaced existing races:<br />
  20. 20. 4. Wheat stripe rust race 136-frequency of isolation, 2000 through 2009<br />- Exotic stripe rust race 136 was first detected in 2002 in WA<br />
  21. 21. 4. Wheat stripe rust race 136-frequency of isolation, 2000 through 2009<br />- Exotic stripe rust race 136 was first detected in 2002 in WA<br />By 2004 (2 years), race 136 had all but replaced existing races:<br />
  22. 22. Race 134 <br />Frequency (%)<br />“Old” races <br />2000<br />2001<br />2002<br />2003<br />2004<br />2005<br />2006<br />2007<br />2008<br />2009<br />Year<br />4. Wheat stripe rust race 136-frequency of isolation, 2000 through 2009<br />- Exotic stripe rust race 136 was first detected in 2002 in WA<br />By 2004 (2 years), race 136 had all but replaced existing races:<br />
  23. 23. Aggressiveness in wheat rust isolates<br />- Four clear cases in which an introduced rust genotype has increased rapidly in frequency and displaced existing genotypes:<br /><ul><li>Stem rust race 126 [1925]
  24. 24. Stem rust race 21 [1954]
  25. 25. Leaf rust race 104 [1984]
  26. 26. Stripe rust race 134 [2002]</li></ul>- In each case, the “new” race did not have virulence attributes that conferred a fitness advantage (i.e. virulence for resistance genes)<br />- Evidence available strongly supports the hypothesis that each new genotype was more aggressive<br />- Stripe rust race 134 is considered to be the same as one studied by Milus et al. (2006) who showed it produced 2–3 times more urediniospores per day <br />
  27. 27. Aggressiveness in wheat rust isolates<br />- Four clear cases in which an introduced rust genotype has increased rapidly in frequency and displaced existing genotypes:<br /><ul><li>Stem rust race 126 [1925]
  28. 28. Stem rust race 21 [1954]
  29. 29. Leaf rust race 104 [1984]
  30. 30. Stripe rust race 134 [2002]</li></ul>- In each case, the “new” race did not have virulence attributes that conferred a fitness advantage (i.e. virulence for resistance genes)<br />- Evidence available strongly supports the hypothesis that each new genotype was more aggressive<br />- Stripe rust race 134 is considered to be the same as one studied by Milus et al. (2006) who showed it produced 2–3 times more urediniospores per day <br />
  31. 31. Aggressiveness in wheat rust isolates<br />- Four clear cases in which an introduced rust genotype has increased rapidly in frequency and displaced existing genotypes:<br /><ul><li>Stem rust race 126 [1925]
  32. 32. Stem rust race 21 [1954]
  33. 33. Leaf rust race 104 [1984]
  34. 34. Stripe rust race 134 [2002]</li></ul>- In each case, the “new” race did not have virulence attributes that conferred a fitness advantage (i.e. virulence for resistance genes)<br />- Evidence available strongly supports the hypothesis that each new genotype was more aggressive<br />- Stripe rust race 134 is considered to be the same as one studied by Milus et al. (2006) who showed it produced 2–3 times more urediniospores per day <br />
  35. 35. Aggressiveness in wheat rust isolates<br />- Four clear cases in which an introduced rust genotype has increased rapidly in frequency and displaced existing genotypes:<br /><ul><li>Stem rust race 126 [1925]
  36. 36. Stem rust race 21 [1954]
  37. 37. Leaf rust race 104 [1984]
  38. 38. Stripe rust race 134 [2002]</li></ul>- In each case, the “new” race did not have virulence attributes that conferred a fitness advantage (i.e. virulence for resistance genes)<br />- Evidence available strongly supports the hypothesis that each new genotype was more aggressive<br />- Stripe rust race 134 is considered to be the same as that shown by Milus et al. (2009;Phytopathology99, 89–94.) to produce 2–3 times more urediniospores per day <br />
  39. 39. Economic impact of exotic wheat rust isolates<br />- Stem rust race 126:<br /><ul><li>epidemic in 1930 - losses of £380,000
  40. 40. epidemic in 1934 – losses of £470,000
  41. 41. epidemic in 1947 – losses of £7 million</li></ul>- Stem rust race 21:<br /><ul><li>epidemic in 1973 – losses of $200 million
  42. 42. epidemics in triticale in 1983 and 1984</li></ul>- Leaf rust race 104:<br /><ul><li>epidemic in WA in 1991, extensive fungicide usage</li></ul>- Stripe rust race 134:<br /><ul><li>from 2003 onwards, up to $90 million spent on fungicides per year </li></ul>WA 1991 courtesy of Dr R. Loughman<br />
  43. 43. Pathogenic variability in wheat rusts in Australia- 11 exotic incursions of wheat rust since 1919<br />The frequency of exotic incursions is increasing:<br />Number of incursions<br />1919-1935<br />1996-2010<br />1936-1955<br />1956-1975<br />1976-1995<br />Year<br />
  44. 44. Intercontinental tracking of rust pathogens<br />-modelling wind trajectories, Dr Dave Hodson FAO [UN]<br />“Rustmapper”<br />10 day prediction, made November 4th<br />
  45. 45. Concluding remarks<br />“It is remarkable that a change in frequency of pathotypes can occur so rapidly in the absence of a pathogenic advantage (Luig 1985)”. <br /><ul><li> long-term pathogen surveys in Australia have shown four instances of new exotic rust pathogen genotypes with greater aggressivness</li></ul>- all four have had major impacts on cereal production (wheat and triticale)<br /><ul><li> breeders were successful in responding to three of these; despite some setbacks, good progress has also been made in relation to the most recent stripe rust incursion
  46. 46. exotic incursions seem to be occurring more frequently; intercontinental spread of rust pathogens will therefore likely continue to be a challenge in rust control</li></li></ul><li>© University of Sydney<br />

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