Virulent blackleg strains – a cause for concern?

New blackleg strains reinforce need for sound management practices and continued research.

Blackleg is a destructive pathogen in canola in North America and a potentially economically devastating disease world wide. So when new and virulent PG3, PGT and PG4 isolates or races recently appeared in Western Canada and North Dakota, some alarm bells started to sound. Reports from Australia and Europe tell us that blackleg pathogen populations can change quickly and break down the resistance of newly introduced varieties – how concerned should Western Canadian canola growers be?

Visit http://www.prairiecca.ca/members/article_CanolaBlackleg.pdf for the recent research summary titled “The Changing Phase of Canola-Blackleg Populations in Western Canada” from the University of Manitoba.

New blackleg strains a cause for concern?

Derwyn Hammond, Agronomy Specialist with the Canola Council of Canada says, “In the short term growers with a reasonable rotation, using an R rated canola variety should see good suppression.” He adds, “while we’ve found some isolates that would fall into different pathogroups than we have been dealing with in Canada in the past, the proportion of the fungal population those represent is still relatively small and the R rated canola varieties still provide a good level of protection for the most part.”

However, with the increase in canola prices some producers may be tempted to push their rotations, increasing the selection pressure. Hammond advises them to rethink their options, “with tighter rotations there are greater selection pressures for more virulent races in the pathogen population to overcome the blackleg resistance in R rated canola varieties.” Producers could conceivably be their own worst enemy by pushing rotations, feeling confident because they are using an R rated canola variety, and setting the stage for the most virulent strains to build up in their fields and spread to others.

Producers in other countries like Australia and France have seen the devastation of selection pressure at work first hand with some fungal populations shifting to overcome particular resistance genes in a relatively short period of time – just a few years. At that rate it would be difficult for seed breeders to stay ahead of the disease in providing varieties with high levels of resistance to that changing fungal population.

Producers in areas where blackleg is prevalent must stick to sound management practices that include only growing canola every 3-4 years, as well as using R rated Certified canola seed to out-manage disease and be profitable. Results from yield, crop rotation, blackleg resistance studies support crop rotation as a sustainable practice. Click here for Agriculture and Agri-Food Canada summaries for more details on the research:

Confused about R ratings?

Some producers not versed on disease and the spread of pathogens might be confused – doesn’t R stand for resistance to Blackleg? How can there be disease escapes when using an R rated canola variety? Stu Brandt, Manager of Breeding Operations and Plant Breeder at Bayer CropScience explains, “some think a resistant canola variety is like immunity, it’s not, there are no immune canola varieties on the market.” He adds, “Resistance, or R rating, means when you have disease in your field if you had grown the check Westar in the field and it was 100 percent wiped out by the disease, the R-rated variety would be no more than 29 percent wiped out by the disease.”

A producer will likely see, even with the most resistant canola varieties available on the market some symptoms of the disease. Likely those symptoms belong to evolving strains and tight rotations will increase the selection pressure for the disease presence to increase, and fast.

For more information on canola varieties and hybrid blackleg ratings visit http://www.canola-council.org/canola_variety.aspx for information on resistance ratings from the Canola Council of Canada’s PCVT tables or their online database.

How can seed breeders stay ahead?

Brandt confirms that Bayer CropScience is focused on staying ahead of blackleg now and in the future. “It’s a challenging disease, blackleg continues to evolve over time and making new strains meaning a variety with a high level of resistance this year, may not have the same level of resistance next year,” says Brandt. “The only thing you can predict is that it is going to change.”

Bayer CropScience has an extensive and dedicated blackleg research and breeding program, including a blackleg nursery in Australia where they test material with the most virulent blackleg strains known globally. “If in the most severe blackleg country we have good resistance, then we can expect we’ll have strong products here,” adds Brandt. “The goal of plant breeding is to develop a durable, strong resistance to blackleg that won’t just last one or two years but a number of years and we accomplish that mostly by stacking multiple resistant genes.”

Blackleg is an important focus for Bayer CropScience because it is the number one disease in canola and arguably it and Sclerotinia are the two diseases that have the greatest potential for devastating effects on canola yields. The company knows diseases change and a fundamental business focus is to keep their canola breeding program one step ahead.

Learn more about managing blackleg.

Blackleg is sometimes misdiagnosed and confused with other diseases like Sclerotinia or grey stem. Visit http://www.canola-council.org/chapter10c.aspx#ch10c_sec3 for information from the Canola Council of Canada including disease history, symptoms, disease cycle and management.