Blackleg resistance has been available in commercial canola varieties since the early 1990s. A shift towards increasingly virulent strains of the blackleg fungus has resulted in the breakdown of resistance in many traditional canola varieties. Increasing canola acreage and shortened rotations have contributed to this.
Not all R-rated varieties provide the same level of blackleg protection and an R-rating does not mean the variety is immune to blackleg or resistant in all geographies. An R-rating of an older variety was established against blackleg strains that may no longer be prevalent, whereas newer R-rated hybrids have been tested against current strains of the fungus and provide good protection against blackleg in the majority of locations. Numerical ratings are not a preferred indicator of resistance as they are derived from performance at specific locations against specific blackleg strains in specific years and may not reflect how the variety performs across a range of geographies.
There are two types of resistance genetics for combatting blackleg disease:
1. Quantitative resistance – complex of multiple minor genes, each with a small impact. Plants with quantitative resistance may still get infected, but they have the ability to slow down the progression of the disease and thereby reduce its severity.
2. Qualitative resistance – a more specific form of resistance where plants with a particular R gene respond to a particular strain of blackleg. If that strain of blackleg changes or evolves, the R gene no longer triggers the required plant defense.
Multigenic resistance simply refers to more than one resistance gene. All varieties sold in Western Canada rely on multiple genes for blackleg resistance. What differentiates the level of protection is the particular combination of resistance genes which determine how a variety performs across a range of environments and against a range of blackleg strains.
Plant breeders are in a race to stay ahead of blackleg by incorporating more effective resistance genes into canola hybrids. The challenge is to identify effective R genes that work well against the current predominant blackleg strains. The best and most durable blackleg resistance is derived from a combination of both solid quantitative resistance plus strategic use of effective major R gene resistance.
Coreen Franke, R&D Pathology Research, Nutrien Ag Solutions
Nutrien Ag Solutions varieties are tested thoroughly across Western Canada and Proven Seed has a leading line-up of new R-rated varieties. PV 533 G has consistently demonstrated exceptional blackleg resistance effective against current prevalent strains of the fungus. The next generation of hybrids from Proven Seed, including new PV 540 G, offer world-class protection with our continued evolution of blackleg resistance genetics.
Since it was first reported in Alberta in 2003, clubroot has been on the move, and is becoming a serious threat to canola production across all three prairie provinces. The pathogen has also shown a high potential for adaptation, especially in regions with intensive canola production and shortened rotations, and there are now many new pathotypes to be concerned about. Clubroot resistant varieties are essential tools to help delay establishment and manage the disease, but they are only one piece in an effective clubroot management plan. Of course, preventing clubroot from showing up on your farm is the ideal strategy, but if the disease does turn up on your farm, it can be managed with the right knowledge and the right tools.
REDUCE THE RISK OF INTRODUCING CLUBROOT ON TO THE FARM: Clubroot spores move with soil, so anything you can do to prevent infested soil from moving around will reduce the risk of clubroot being introduced on to your farm. Restrict soil transfer by cleaning vehicles, equipment, tools and footwear between fields.
EARLY DETECTION: Scout often. Know the symptoms and check your fields regularly. The earlier the disease is detected, the better the chance you will have to manage it.
MINIMIZE SOIL DISTURBANCE AND MOVEMENT: If you do identify clubroot in a field, practice reduced tillage to help prevent the clubroot spores from spreading within that field. Reduced tillage will also help decrease the movement of spores by wind and water. The key to successful management is to keep the clubroot spores localized and their numbers low.
ELIMINATE HOSTS: Control volunteers and cruciferous weeds that can act as hosts for clubroot – keep your fields clean between canola crops. Each time a susceptible host is grown in the presence of the disease, clubroot spores multiply, making management more difficult.
ROTATE CROPS: Once you have clubroot, you cannot eradicate it, but you can manage the spore load. Keeping spore numbers low is essential for successful management. A two-year break between canola crops can significantly reduce the number of viable resting spores in the soil. Grow Clubroot Resistant varieties in a minimum 1 in 3 rotation, and only in fields where spore loads have been reduced. If there is no break to reduce the number of viable spores in the soil, the pathogen can shift rapidly making the resistance genetics in your CR variety ineffective.
GROW CLUBROOT RESISTANT VARIETIES: Clubroot resistant varieties are not immune, but highly restrict the development of clubroot symptoms. A single-gene (First Generation) CR variety will protect against the predominant clubroot pathotype in western Canada. A multi-genic (Second Generation) CR variety will give extra protection against some additional virulent pathotypes that may be present in the field, but Second Generation varieties are not likely to be resistant to ALL pathotypes, and therefore must be always used wisely in an integrated clubroot management plan. When used in rotation, CR varieties can offer durable resistance to clubroot.
LEADERS IN CLUBROOT PROTECTION – PROVEN SEED’S GOT YOUR BA