Verticillium Wilt in Canola

 
 
Verticillium wilt in canola, caused by Verticillium longisporum, was detected in Manitoba in 2014 and this was the first case of this disease on an oilseed crop in North America. This disease is common in northern Europe and is the number one disease of oilseed crops in Sweden.
 
Host crops
 
The complete host range of V. longisporum is still unknown, but many other brassica crops like broccoli, cabbage, mustard, and cauliflower are also hosts.
 
Biology
 
Verticillium longisporum overwinters in the soil as microsclerotia, small masses of fungal cells that are hard and compact. These structures are capable of surviving in the soil for 10 to 15 years, but the number of viable microsclerotia will decline over time.
 
Microsclerotia germinate after stimulation by root exudates from host plants. The fungus then infects the plants via the roots, most often at the seedling stage. As the plant grows, the fungus spreads upward through the xylem tissue.
 
Symptoms of damage 
 

Symptoms of Verticillium wilt in canola most often appear near the end of the season as the plants begin to ripen.

While the stem is still green, a vertical yellow or brown band extending up one side of the stem may be visible.

 

As the plant fully ripens, the outer layer of the stem epidermis peels back to reveal black microsclerotia just below the surface.



These microsclerotia appear as black pepper-like spots that are visible to the naked eye. If a cross-section of an infected stem is examined under a microscope, microsclerotia will also be visible in the inner pith tissue representing the colonization of the vascular tissue by the fungus.

Scouting techniques

The best time to scout for Verticillium wilt in canola is at swathing, but it is even possible to identify this disease after harvest as microsclerotia will continue to develop on the stubble. Infected plants will become more obvious after harvest as they will turn grey-black as they senesce.

Control tips

There are no foliar or seed treatment fungicides currently registered for control of Verticillium wilt in canola. In addition, there is no host resistance in canola varieties at this time for V. longisporum.

In northern Europe, where this disease has been an important issue for more than 30 years, it is recommended that growers leave three years between canola crops. This allows the pathogen populations to naturally decline in the soil, but, due to the long-lived microsclerotia, rotation alone is not enough to manage this problem effectively.

As V. longisporum is a soil-borne pathogen, biosecurity practices can help mitigate the spread of this disease on- and off-farm. Biosecurity practices include equipment and tool sanitation, controlling off-farm traffic, monitoring seed/feed/fertilizer sources, and developing an on-farm biosecurity plan.

For more information contact your GO representative.

References

Gladders, P. 2009. Relevance of verticillium wilt (Verticillium longisporum) in winter oilseed rape in the UK. Home-Grown Cereals Authority: Research Review No. 72.

Inderbitzin, P. & K.V. Subbarao. 2014. Verticillium systematics and evolution: How confusion impedes Verticillium wilt management and how to resolve it. Phytopathology 104: 564-574.

Johannson, A. 2006. Verticillium longisporum, infection, host range, prevalence and plant defence responses. Licentiate thesis. Swedish University of Agricultural Sciences, Uppsala.