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

 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

 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

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

Blackleg risk severity factor Individual factor score Your score Rainfall <550>500>450>400 >350>300>250 Canola intensity <20%20%15%10%5% Blackleg rating VSS-VSSMS-SMSMR- MS MRR-MRR Dist to stubble >500 Years of same cultivar <3 Years 3 years Total score

Blackleg risk severity factor Individual factor score Your score Rainfall <500>500>450400>400>350>300>250 Canola intensity <20%20%15%10%5% Blackleg rating VSS-VSSMS-SMSMR- MS MRR-MRR Dist to stubble >500 Years of same cultivar <3 Years 3 years 210 Total score 34

Resistance gene VarietyRlm1Rlm2Rlm3Rlm4Rlm5Rlm6Rlm7Rlm8Rlm9RlmS Wesbrook TAPAROO Oscar C Thunder TT BLN or H- Karoo Dunkeld Wesroona---H (75%) Tl1Pinnacle Tarcoola Tornado TT AV Garnet Ripper Surpass ?+ Rocket CL?????????? Dune?????????? Oasis CL?????????? Sahara CL?????????? Clear cut Genotypes

 Numerical 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