Blackleg Resistance Durability

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Blackleg Resistance Durability

• Steve Marcroft Marcroft Grains Pathology,
  Horsham
• Phil Salisbury, Barb Howlett University of
  Melbourne
• Trent Potter - SARDI

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How does blackleg overcome resistance

• Unlike asexual rusts, blackleg is sexually
  reproducing
• In contrast, all cereal rust spores are identical
  so cereal resistance genes will be effective
  against all rust spores until a mutation occurs
  or new introduction of a new strain (pathotype)
  from overseas.

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Blackleg disease cycle
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How does blackleg overcome resistance cont.

• Blackleg spores are all genetically different.
• When you grow a new resistant canola variety
  there are already blackleg spores that can attack
  your variety.
• When you grow the same variety year after year
  you select blackleg spores that can attack and
  therefore resistance can be overcome.

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Effect of overcoming resistance

• Varieties with a number of minor genes
  (polygenic) may lose resistance gradually.
• Varieties with single major genes can go from
  resistant to susceptible very quickly.
• Some varieties have lost resistance quickly
  others have never lost resistance.
• The 2009 blackleg ratings have Reduced
  Resistance warnings.

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Effect of overcoming major gene verse polygenic
resistance
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Sylvestris resistance overcome - 2003
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What do we know?
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1st Learning

• Durability to blackleg differs between regions

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What have we learnt

• NSW no issue in last 5 years

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SA issues
regional climate seasonal conditions canola
intensity
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High risk indicators

• Higher rainfall regions.
• Intensive canola production.
• Growing the same cultivar for the third year or
  more in a row.
• Proximity to last years canola stubble.

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2nd Learning

• Canola cultivars can regain blackleg resistance

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Reduced blackleg in Surpass501TT
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Surpass 501 TT 2002-2007
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3rd Learning Blackleg pathotypes can be
specific in their virulence
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Blackleg can be reduced by not over using the
same resistance
2008
2007
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Blackleg severity when sown into different
stubble sources
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4th LEARNING

• We can identify problems before they occur on a
  large scale
• but are sure to miss some

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2009 Isolate from Hyola50 _at_ Coulta (EP) (high
blackleg severity in 2008)
BravoTT
Hyola50
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5TH LEARNING

• Blackleg is all speed but little puff

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Canola on canola
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500m away from stubble
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1000m away from stubble
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Isolation distance required
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Potential new blackleg Mangt
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Known factors that influence blackleg severity

1. Annual rainfall (mm)
2. Autumn rainfall total
3. Month sown
4. Canola intensity on farm
5. Cultivar Blackleg rating
6. Jockey or Impact seed dressing
7. Dist to 1 year old stubble
8. Dist to 2 year old stubble
9. Dist 1 yr old stubble of same cultivar
10. Dist 2 yr old stubble of same cultivar
11. Years of same cultivar sown in a row

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Severity factor weighting
Blackleg risk severity factor Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score
9 8 7 6 5 4 3 2 1 Your score
Rainfall lt550 gt500 gt450 gt400 gt400 gt350 gt300 gt250
Canola intensity lt20 20 15 10 5
Blackleg rating VS S-VS S MS-S MS MR-MS MR R-MR R
Dist to stubble 0 100 250 500 gt500
Years of same cultivar lt3 Years 3 years
Total score Total score
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Lake Bolac
Blackleg risk severity factor Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score Individual factor score
9 8 7 6 5 4 3 2 1 Your score
Rainfall lt500 gt500 gt450 400 gt400 gt350 gt300 gt250
Canola intensity lt20 20 15 10 5
Blackleg rating VS S-VS S MS-S MS MR-MS MR R-MR R
Dist to stubble 0 100 200 300 400 500 gt500
Years of same cultivar lt3 Years 3 years 2 1 0
Total score Total score 34
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Clear cut Genotypes
Resistance gene Resistance gene Resistance gene Resistance gene Resistance gene Resistance gene Resistance gene Resistance gene Resistance gene Resistance gene
Variety Rlm1 Rlm2 Rlm3 Rlm4 Rlm5 Rlm6 Rlm7 Rlm8 Rlm9 RlmS
Wesbrook - - - - - - - - - -
TAPAROO - - - - - - - - -
Oscar - - - - - - - - -
46C76 - - - - - - - - -
Thunder TT - - - - - - - - -
BLN3347 - - - - - - - - or H -
Karoo - - - - - - - - -
Dunkeld - - - - - - - - -
Wesroona - - - H (75) - - - - - -
Tl1Pinnacle - - - - - - - -
Tarcoola - - - - - - - -
Tornado TT - - - - - - - -
AV Garnet - - - - - - - -
Ripper - - - - - - -
Surpass400 - - - - - - - ?
Rocket CL ? ? ? ? ? ? ? ? ? ?
Dune ? ? ? ? ? ? ? ? ? ?
Oasis CL ? ? ? ? ? ? ? ? ? ?
Sahara CL ? ? ? ? ? ? ? ? ? ?
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New blackleg rating system

• Numerical 1 - 9 has been replaced with alpha R to
  VS scale.
• The alpha scale is consistent with other crop
  disease rating scales including cereals
• BUT.

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New canola blackleg rating system

• Cereals
• R immune
• Canola
• R does not imply complete immunity

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Blackleg resistance rankings
R May get leaf lesions May get some internal infection
MR Will get leaf lesions Will get some internal infection Some external canker Some plant death (high disease pressure situations)
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Blackleg resistance rankings
MS Will get leaf lesions Will get internal infection Will get external canker Plant death (moderate to high disease pressure situations)
S If sown in moderate disease pressure situations plant death may be severe
VS If sown in moderate disease pressure situations plant death may be extremely severe