Fusarium head blight in western Canada
By Randy Clear and Susan Patrick, Mycology, Grain Research Laboratory, Canadian Grain Commission
Revised January 25, 2010 (History)
Fusarium head blight (FHB) is a fungal disease that may infect a number of crops in Canada – wheat, barley, oats, rye, corn, canary seed and forage grasses. However, the crops most affected are wheat, barley and corn.
Fusarium head blight is not a new disease. It was identified over 100 years ago, in 1884, in England. It was first called wheat scab, and later, tombstone disease, because of the chalky, lifeless appearance of the infected kernels.
Fusarium head blight has occurred in eastern Canada and the United States for many years. Losses from FHB in eastern Canada date to at least the early 1940's. Fusarium graminearum was first identified in Manitoba in 1923, but no serious outbreaks were reported until 1984. Since then, surveys in western Canada conducted by the Canadian Grain Commission’s Grain Research Laboratory have found F. graminearum in an ever-expanding area, now reaching into northern British Columbia.
F. graminearum is only one of many species of Fusarium, but it is considered the most important one in Canada because of the impact it has on yield and grain quality, its ability to produce several different toxins, and its abundance in eastern Canada and the eastern prairies.
In eastern Canada, it appears to be well established in all the cereal growing areas. In western Canada, F. graminearum is found most frequently in the black soil zone. This zone is also the area of highest rainfall on the prairies. Infection is associated with rainfall during the flowering stage. The infection is spread by wind, but the pathogen is also spread by planting infected seed.
This picture shows wheat seed on filter paper with the reddish colony of Fusarium growing on the seed surface and discolouring the roots and shoot.
FHB results in the production of visibly damaged seeds called FDK, as well as infected seeds which don't display visible symptoms of infection. These non-symptomatic seeds usually outnumber the FDK by a considerable margin. Planting infected seeds can result in a second disease called seedling blight.
FDK have also been called scabby, or tombstone. These names describe the appearance of wheat kernels affected by FHB. Such kernels are shriveled and chalky white.
The earlier in the life cycle of a kernel that FHB strikes, the greater its effect. In this picture, the kernels were infected at progressively later stages of development. The three on the left are chalky white and covered with diminishing amount of the thread-like growth of mycelia of the fungus. The one furthest on the left has not gone through the combine, that is why there is so much more mycelium evident. The fourth seed is more vitreous, but has a trace of mycelium at the germ. The last two seeds on the right look normal, but they too are infected.
This photograph shows 4 wheat kernels, each a chalky white colour and slightly shriveled. A couple kernels also display a slight pink in the crease due to the growth of Fusarium.
The seven rye seeds shown are chalky white and slightly shriveled. One of them has a bright orange fungal structure called a sporodochia covering about one-fifth of the seed surface.
Two oat seeds are shown. One with the purplish-black, urn-shaped surface encrustation formed by F. graminearum and one with the bright orange sporodochia encrusting part of the seed surface formed by a number of Fusarium species.
One barley seed with the purplish-black, urn-shaped surface encrustation formed by F. graminearum.
Four species in North America can cause FHB.
Three species in North America are routinely found to produce it.
Two of these produce DON (vomitoxin).
These pictures show two stages in the life cycle of F. graminearum. The imperfect stage is called F. graminearum and the perfect stage is called Gibberella zeae. Both stages can occur together.
The orange encrustation of spores called sporodochia on the wheat head.
Conidiospores are formed in sporodochia.
Ascospores are formed in perithecia.
Asci containing ascospores.