Fusarium Wilt of Canada

Fusarium Wilt of Canada
by Dr. Winnie McNabb, Research Scientist, Pioneer Hi-Bred Canola Research

Fusarium wilt of canola has appeared in areas of Western Canada in recent years. It is a devastating disease, capable of causing serious yield losses when susceptible canola varieties are grown on infested soil under stressful conditions.

Caused by fungi in the soil

Two fungi, Fusarium oxysporum spp. conglutinans and Fusarium avenaceum have been identified as the pathogens causing wilt symptoms in canola. The former is considered to be the primary pathogen of this disease. The roles of these two fungi in this disease require further research.

Now reported in all provinces

The disease which was first reported in east-central Alberta and west-central Saskatchewan has now been identified in areas throughout the prairie provinces.

Symptoms of wilt

Initial symptoms of wilt such as yellowing and wilting of leaves may not be readily apparent. Symptoms are most visible during the pod filling stage when the stems, branches and pods turn yellow and then reddish brown. Frequently, symptoms appear on only one side of the stem and progress up the stem and side branches. The vascular tissue has a brown discolouration. Severely infected plants have small shriveled pods and seed set is very poor. Plants remain standing with the root system intact. Drought stress contributes to the severity of symptoms. This disease disrupts the functioning of the vascular system so symptoms are readily visible when water is limiting.

	If plants show signs of discolouration, examine the base of the stem to distinguish between Fusarium wilt and blackleg. Plants with blackleg will be black in cross section of the stem. Heat scorch may be confused with Fusarium wilt when plants are viewed from a distance.
Susceptible variety shows brown discolouration on the stem. Photo courtesy of Ralph Lange, ARC
Susceptible canola variety inoculated with Fusarium wilt demonstrates symptions and discolouration. Pioneer research, Edmonton, Alberta

Disease cycle

Fusarium oxysporum is able to survive in the soil for years. The primary spores germinate and invade via wounds or where lateral roots emerge. The transport of water and nutrients is restricted resulting in tissue death of either part of the plant or the entire plant. Fusarium avenaceum is commonly found in agricultural soils and can survive on infected debris.

Variety selection is best method of control

No chemical control is available to protect canola from the effects of Fusarium wilt. Growing resistant canola is the best way to minimize potential losses from this disease. Pioneer has been evaluating their canola products for resistance at disease nurseries with high levels of infection. A standardized method of evaluating and classifying canola for Fusarium wilt resistance is in the process of being developed through an industry wide consortium.

Pioneer® brand products 45H21 (RR), 46H23 (RR), 46H02, 46A76 (CL) and 43A56 (RR) were resistant to Fusarium wilt at Pioneer testing locations in Alberta as well as consortium trials in Alberta and Saskatchewan. Pioneer Hi-Bred will continue to be actively involved in this collaboration in 2004 to characterize products for Fusarium wilt resistance.