Steve Marcroft – Marcroft Grains Pathology, Horsham
Phil Salisbury, Barb Howlett – University of Melbourne
Trent Potter - SARDI

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.



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.




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.
2005
Tornado
TT
2004
Kimberley
Released
Rivette
Sapphire
Beacon
Surpass
400
0 1 2 3 4 5 6 7 8 9
Blackleg rating
Effect of overcoming major gene verse polygenic resistance
2006

Durability to blackleg differs between
regions

NSW no issue in last 5 years
regional climate seasonal
conditions canola intensity




Higher rainfall regions.
Intensive canola production.
Growing the same cultivar for the third year
or more in a row.
Proximity to last year’s canola stubble.

Canola cultivars can regain blackleg
resistance
% extra disease in Surpass501TT
50
40
30
20
10
0
2004
-10
2005
2006
2007
2008
2007
2008
70
60
% blackleg infection
60
% blackleg infection
ATR-Beacon
70
45Y77
50
40
30
20
50
40
30
20
10
10
0
0
45Y77
ATR-Beacon
AV-Garnet
45Y77
Dune
AV-Garnet
% blackleg infection
% blackleg infection
60
50
40
30
20
10
0
45Y77
ATR-Beacon
AV-Garnet
2007 stubble type
AV-Garnet
Dune
2007 stubble type
2007 stubble type
70
ATR-Beacon
Dune
Hyola50
70
60
50
40
30
20
10
0
45Y77
ATR-Beacon
AV-Garnet
2007 stubble type
Dune
 We
can identify problems
before they occur on a large
scale
◦– but are sure to miss some
Hyola50
BravoTT

Blackleg is all speed but little puff
Isolation distance
required
% Severe internal blackleg infection
100
90
6 Months
80
18 Months
70
30 Months
60
50
40
30
20
10
0
0
250
500
750
Distance (m) from canola stubble
>850
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Annual rainfall (mm)
Autumn rainfall total
Month sown
Canola intensity % on farm
Cultivar Blackleg rating
Jockey or Impact seed dressing
Dist to 1 year old stubble
Dist to 2 year old stubble
Dist 1 yr old stubble of same cultivar
Dist 2 yr old stubble of same cultivar
Years of same cultivar sown in a row
Individual factor score
Blackleg risk
severity
factor
Rainfall
9
8
7
6
5
4
3
<550
>500
>450
>400
>400
>350
>300
<20%
20%
15%
10%
MS-S
MS
MRMS
MR
500
>500
Canola
intensity
Blackleg
rating
Dist to
stubble
Years of
same
cultivar
VS
S-VS
S
0
100
250
<3
Years
2
1
>250
5%
R-MR
R
3
years
Total score
Your
score
Individual factor score
Blackleg risk
severity
factor
Rainfall
9
8
7
6
5
4
3
<500
>500
>450
400
>400
>350
>300
<20%
20%
15%
10%
Canola
intensity
Blackleg
rating
Dist to
stubble
Years of
same
cultivar
S-VS
S
MS-S
MS
MRMS
MR
0
100
200
300
400
500
>500
3
years
1
Your
score
>250
5%
VS
<3
Years
2
2
R-MR
R
1
0
Total score
34
Clear cut Genotypes
Resistance gene
Variety
Wesbrook
TAPAROO
Oscar
46C76
Thunder TT
BLN3347
Karoo
Dunkeld
Rlm1
-
Rlm2
-
Rlm3
+
+
+
-
Rlm4
+
+
+
+
Rlm5
-
Rlm6
-
Rlm7
-
Rlm8
-
Rlm9
- or H
-
RlmS
-
Wesroona
Tl1Pinnacle
Tarcoola
Tornado TT
AV Garnet
Ripper
Surpass400
Rocket CL
Dune
Oasis CL
Sahara CL
+
+
?
?
?
?
+
?
?
?
?
+
?
?
?
?
H (75%)
+
+
+
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
+
+
+
+
+
?
?
?
?
?
+
?
?
?
?



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….

Cereals
– R = immune

Canola
– R = does not imply complete immunity
May get leaf lesions
 May get some internal infection
R

MR

Will get leaf lesions
 Will get some internal infection
 Some external canker
 Some plant death (high disease pressure situations)
Will get leaf lesions
 Will get internal infection
 Will get external canker
 Plant death (moderate to high disease pressure situations)
MS

S

VS

If sown in moderate disease pressure situations plant death
may be severe
If sown in moderate disease pressure situations plant death
may be extremely severe