Blackleg Resistance Durability Steve Marcroft Marcroft Grains Pathology

Blackleg Resistance Durability Steve Marcroft – Marcroft Grains Pathology, Horsham Phil Salisbury, Barb Howlett – University of Melbourne Trent Potter - SARDI

How does blackleg overcome resistance n Unlike asexual rusts, blackleg is sexually reproducing n 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 disease cycle

How does blackleg overcome resistance cont. Blackleg spores are all genetically different. When you grow a new resistant canola variety there 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.

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.

Effect of overcoming major gene verse polygenic resistance

Sylvestris resistance overcome - 2003

What do we know?

1 st Learning Durability to blackleg differs between regions

What have we learnt NSW no issue in last 5 years

SA issues regional climate seasonal conditions canola intensity

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 year’s canola stubble.

2 nd Learning Canola cultivars can regain blackleg resistance

Reduced blackleg in Surpass 501 TT

Surpass 501 TT 2002 -2007

3 rd Learning – Blackleg pathotypes can be specific in their virulence

Blackleg can be reduced by not over using the same resistance 2007 2008

Blackleg severity when sown into different stubble sources

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

2009 Isolate from Hyola 50 @ Coulta (EP) (high blackleg severity in 2008) Hyola 50 Bravo. TT

5 TH LEARNING Blackleg is all speed but little puff

Canola on canola

500 m away from stubble

1000 m away from stubble

Isolation distance required

Potential new blackleg Mangt

Known factors that influence blackleg severity 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

Severity factor weighting Individual factor score Blackleg risk severity factor Rainfall 9 8 7 6 5 4 3 <550 >500 >450 >400 >350 >300 <20% 15% 10% MS-S MS 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

Lake Bolac Individual factor score Blackleg risk severity factor Rainfall 9 8 7 6 5 4 3 <500 >450 400 >350 >300 <20% 15% 10% Canola intensity Blackleg rating Dist to stubble Years of same cultivar S-VS S MS-S MS 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 46 C 76 Thunder TT BLN 3347 Karoo Dunkeld Rlm 1 - Rlm 2 - Rlm 3 + + + - Rlm 4 + + Rlm 5 - Rlm 6 - Rlm 7 - Rlm 8 - Rlm 9 - or H - Rlm. S - Wesroona Tl 1 Pinnacle Tarcoola Tornado TT AV Garnet Ripper Surpass 400 Rocket CL Dune Oasis CL Sahara CL + + ? ? ? ? + ? ? H (75%) + + + ? ? ? ? ? ? + + + ? ? ? + ? ?

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….

New canola blackleg rating system n Cereals – R = immune n Canola – R = does not imply complete immunity

Blackleg resistance rankings May get leaf lesions n May get some internal infection R n MR n Will get leaf lesions n Will get some internal infection n Some external canker n Some plant death (high disease pressure situations)

Blackleg resistance rankings Will get leaf lesions n Will get internal infection n Will get external canker n Plant death (moderate to high disease pressure situations) MS n VS n 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