AustralianCerealRustControlProgram

Robert Park & Colin WellingsPlant Breeding Institute

International Wheat Stripe Rust SymposiumICARDA, Aleppo, Syria18-20 April 2011

Continental sweeps and aggressiveness in wheat rust pathogens

CIMMYT

Wheat rusts in Australasia

-isolated from other cereal growing regions

-wheat rust pathogens are clonal

-long-term (90+ years) surveys have provided rare insight into rust pathogen population dynamics

- surveys since 1919 suggest that pathogenic variability arises from:

• periodic incursions of exotic rust isolates• mutation• somatic hybridisation

- mutation is believed to be most common; frequencies of somatic hybridisation and exotic incursions are thought to be low

Pathogenic variability in wheat rusts in Australia

Pathogen Pathotype Year Likely origin

1. Stem rust 126-5,6,7,11 1925 ?

2. Stem rust 21-0 1954 Central Africa?

3. Stem rust 326-1,2,3,5,6 1969 Central Africa

4. Stem rust 194-1,2,3,5,6 1969 Central Africa

5. Stripe rust 104 E137 A- 1979 France

6. Leaf rust 53-1,(6),(7),10,11 1981 ?

7. Leaf rust 104-2,3,(6),(7),11 1984 ?

8. Leaf rust 76-1,3,5,10,12 1996 ?

9. Stripe rust 134 E16 A+ 2002 North America?

10. Leaf rust

11. Leaf rust

10-1,3,9,10,12

76-3,5,9,10 +Lr37

2004

2004

?

?

Pathogenic variability in wheat rusts in Australia- 11 exotic incursions of wheat rust since 1919

Pathogen Pathotype Year Likely origin

1. Stem rust 126-5,6,7,11 1925 ?

2. Stem rust 21-0 1954 Central Africa?

3. Stem rust 326-1,2,3,5,6 1969 Central Africa

4. Stem rust 194-1,2,3,5,6 1969 Central Africa

5. Stripe rust 104 E137 A- 1979 France

6. Leaf rust 53-1,(6),(7),10,11 1981 ?

7. Leaf rust 104-2,3,(6),(7),11 1984 ?

8. Leaf rust 76-1,3,5,10,12 1996 ?

9. Stripe rust 134 E16 A+ 2002 North America?

10. Leaf rust

11. Leaf rust

10-1,3,9,10,12

76-3,5,9,10 +Lr37

2004

2004

?

?

Pathogenic variability in wheat rusts in Australia- 11 exotic incursions of wheat rust since 1919

On 4 occasions, exotic isolate has displaced existing rust races in less than 10 years, presumably due to greater aggressiveness

- Stem rust race surveys began in 1919, 6 races (=“old” races) were detected- Exotic stem rust race 126 was first detected in WA in 1925- By 1929 (5 years), it had all but replaced the “old” races

1. Wheat stem rust race 126-frequency of isolation, 1922 through 1945

- Stem rust race surveys began in 1919, 6 races (=“old” races) were detected- Exotic stem rust race 126 was first detected in WA in 1925- By 1929 (5 years), it had all but replaced the “old” races

1. Wheat stem rust race 126-frequency of isolation, 1922 through 1945

- Stem rust race surveys began in 1919, 6 races (=“old” races) were detected- Exotic stem rust race 126 was first detected in WA in 1925

1. Wheat stem rust race 126-frequency of isolation, 1922 through 1945

By 1929 (5 years), race 126 had all but replaced the “old” races:

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“Old” races

Race 126 group

- Stem rust race surveys began in 1919, 6 races (=“old” races) were detected- Exotic stem rust race 126 was first detected in WA in 1925

1. Wheat stem rust race 126-frequency of isolation, 1922 through 1945

By 1929 (5 years), race 126 had all but replaced the “old” races:

2. Wheat stem rust race 21-frequency of isolation, 1951 through 1970

- Exotic stem rust race 21 was first detected in 1954- “Hybrid” group arose from spomatic hybridisation between 126 and 21

By 1962 (8 years), the race 21 group had all but replaced race 126:

2. Wheat stem rust race 21-frequency of isolation, 1951 through 1970

- Exotic stem rust race 21 was first detected in 1954- “Hybrid” group arose from spomatic hybridisation between 126 and 21

By 1962 (8 years), race 21 group had all but replaced race 126:

2. Wheat stem rust race 21-frequency of isolation, 1951 through 1970

- Exotic stem rust race 21 was first detected in 1954- “Hybrid” group arose from spomatic hybridisation between 126 and 21

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Year

Race 126 group

Race 21 group

By 1962 (8 years), race 21 group had all but replaced race 126:

2. Wheat stem rust race 21-frequency of isolation, 1951 through 1970

- Exotic stem rust race 21 was first detected in 1954- “Hybrid” group arose from somatic hybridisation between 126 and 21

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Race 126 group

Race 21 group

“Hybrid” group

By 1962 (8 years), race 21 group had all but replaced race 126:

3. Wheat leaf rust race 104-frequency of isolation, 1980 through 2000

- Exotic leaf rust race 104 was first detected in 1984 in Victoria- Race 76 is another exotic isolate, first detected in 1993

By 1991 (7 years), race 104 group had all but replaced existing races:

3. Wheat leaf rust race 104-frequency of isolation, 1980 through 2000

- Exotic leaf rust race 104 was first detected in 1984 in Victoria- Race 76 is another exotic isolate, first detected in 1993

By 1991 (7 years), race 104 group had all but replaced existing races:

3. Wheat leaf rust race 104-frequency of isolation, 1980 through 2000

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“Old” races

Race 104 group

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- Exotic leaf rust race 104 was first detected in 1984 in Victoria- Race 76 is another exotic isolate, first detected in 1993

By 1991 (7 years), race 104 group had all but replaced existing races:

3. Wheat leaf rust race 104-frequency of isolation, 1980 through 2000

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Race 104 group

Race 76 group

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Year

- Exotic leaf rust race 104 was first detected in 1984 in Victoria- Race 76 is another exotic isolate, first detected in 1993

By 1991 (7 years), race 104 group had all but replaced existing races:

4. Wheat stripe rust race 136-frequency of isolation, 2000 through 2009

- Exotic stripe rust race 136 was first detected in 2002 in WA

4. Wheat stripe rust race 136-frequency of isolation, 2000 through 2009

- Exotic stripe rust race 136 was first detected in 2002 in WA

By 2004 (2 years), race 136 had all but replaced existing races:

4. Wheat stripe rust race 136-frequency of isolation, 2000 through 2009

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“Old” races

Race 134

Year

- Exotic stripe rust race 136 was first detected in 2002 in WA

By 2004 (2 years), race 136 had all but replaced existing races:

Aggressiveness in wheat rust isolates

- Four clear cases in which an introduced rust genotype has increased rapidly in frequency and displaced existing genotypes:

• Stem rust race 126 [1925]• Stem rust race 21 [1954]• Leaf rust race 104 [1984]• Stripe rust race 134 [2002]

- In each case, the “new” race did not have virulence attributes that conferred a fitness advantage (i.e. virulence for resistance genes)

- Evidence available strongly supports the hypothesis that each new genotype was more aggressive

- 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

Aggressiveness in wheat rust isolates

- Four clear cases in which an introduced rust genotype has increased rapidly in frequency and displaced existing genotypes:

• Stem rust race 126 [1925]• Stem rust race 21 [1954]• Leaf rust race 104 [1984]• Stripe rust race 134 [2002]

- In each case, the “new” race did not have virulence attributes that conferred a fitness advantage (i.e. virulence for resistance genes)

- Evidence available strongly supports the hypothesis that each new genotype was more aggressive

- 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

Aggressiveness in wheat rust isolates

- Four clear cases in which an introduced rust genotype has increased rapidly in frequency and displaced existing genotypes:

• Stem rust race 126 [1925]• Stem rust race 21 [1954]• Leaf rust race 104 [1984]• Stripe rust race 134 [2002]

- In each case, the “new” race did not have virulence attributes that conferred a fitness advantage (i.e. virulence for resistance genes)

- Evidence available strongly supports the hypothesis that each new genotype was more aggressive

- 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

Aggressiveness in wheat rust isolates

- Four clear cases in which an introduced rust genotype has increased rapidly in frequency and displaced existing genotypes:

• Stem rust race 126 [1925]• Stem rust race 21 [1954]• Leaf rust race 104 [1984]• Stripe rust race 134 [2002]

- In each case, the “new” race did not have virulence attributes that conferred a fitness advantage (i.e. virulence for resistance genes)

- Evidence available strongly supports the hypothesis that each new genotype was more aggressive

- Stripe rust race 134 is considered to be the same as that shown by Milus et al. (2009; Phytopathology 99, 89–94.) to produce 2–3 times more urediniospores per day

Economic impact of exotic wheat rust isolates

- Stem rust race 126:• epidemic in 1930 - losses of £380,000• epidemic in 1934 – losses of £470,000• epidemic in 1947 – losses of £7 million

- Stem rust race 21:• epidemic in 1973 – losses of $200 million• epidemics in triticale in 1983 and 1984

- Leaf rust race 104:• epidemic in WA in 1991, extensive fungicide

usage

- Stripe rust race 134:• from 2003 onwards, up to $90 million spent

on fungicides per year

WA 1991 courtesy of Dr R. Loughman

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1919-1935 1936-1955 1956-1975 1976-1995 1996-2010

The frequency of exotic incursions is increasing:

Pathogenic variability in wheat rusts in Australia- 11 exotic incursions of wheat rust since 1919

“Rustmapper”10 day prediction, made November 4th

Intercontinental tracking of rust pathogens

-modelling wind trajectories, Dr Dave Hodson FAO [UN]

Concluding remarks

“It is remarkable that a change in frequency of pathotypes can occur so rapidly in the absence of a pathogenic advantage (Luig 1985)”.

- long-term pathogen surveys in Australia have shown four instances of new exotic rust pathogen genotypes with greater aggressivness

- all four have had major impacts on cereal production (wheat and triticale)

- 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

- exotic incursions seem to be occurring more frequently; intercontinental spread of rust pathogens will therefore likely continue to be a challenge in rust control

© University of Sydney