steve marcroft – marcroft grains pathology, horsham phil salisbury, barb howlett – university of...

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.

Effect of overcoming major gene verse polygenic resistance

01

23

45

67

89

Bla

ck

leg

ra

tin

g

Su

rpa

ss

40

0

Be

ac

on

Sa

pp

hir

e

Riv

ett

e

Kim

be

rle

y

To

rna

do

TT

Released 2004 2005 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

-10

0

10

20

30

40

50

2004 2005 2006 2007 2008

% ex

tra di

seas

e in S

urpa

ss50

1TT

2007 2008

0

10

20

30

40

50

60

70

45Y77 ATR-Beacon AV-Garnet Dune

% b

lack

leg

infe

ction

2007 stubble type

45Y77

0

10

20

30

40

50

60

70

45Y77 ATR-Beacon AV-Garnet Dune

% b

lack

leg

infe

ction

2007 stubble type

ATR-Beacon

0

10

20

30

40

50

60

70

45Y77 ATR-Beacon AV-Garnet Dune

% b

lack

leg

infe

ction

2007 stubble type

AV-Garnet

010203040506070

45Y77 ATR-Beacon AV-Garnet Dune

% b

lack

leg

infe

ction

2007 stubble type

Hyola50

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

Hyola50 BravoTT

Blackleg is all speed but little puff

0

10

20

30

40

50

60

70

80

90

100

0 250 500 750 >850

Distance (m) from canola stubble

% S

ev

ere

inte

rna

l bla

ckl

eg in

fect

ion

6 Months

18 Months

30 Months

Isolation distance required

1. Annual rainfall (mm)2. Autumn rainfall total3. Month sown4. Canola intensity % on farm5. Cultivar Blackleg rating6. Jockey or Impact seed dressing7. Dist to 1 year old stubble8. Dist to 2 year old stubble9. Dist 1 yr old stubble of same cultivar10. Dist 2 yr old stubble of same cultivar11. Years of same cultivar sown in a row

Blackleg risk severity factor

Individual factor score

9 8 7 6 5 4 3 2 1 Your score

Rainfall <550 >500 >450 >400 >400 >350 >300 >250

Canola intensity

<20%

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 >500

Years of same cultivar

<3 Years

3 years

Total score

Blackleg risk severity factor

Individual factor score

9 8 7 6 5 4 3 2 1 Your score

Rainfall <500 >500 >450 400 >400 >350 >300 >250

Canola intensity

<20%

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 >500

Years of same cultivar

<3 Years

3 years

2 1 0

Total score 34

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 ? ? ? ? ? ? ? ? ? ?

Clear cut Genotypes

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

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)

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