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Significance

Oilseeds are one of the most valuable agricultural crops in world trade. Oilseed rape (Brassica napus, B. rapa, and some other Brassica species) ranks third in the world among the oilseed crops, and production is increasing faster than for any other. Oilseed rape was first cultivated in Asia and the Mediterranean and was used as a source of cooking and lighting oil. Canola (Figure 1) is a type of oilseed rape defined by erucic acid levels lower than 2% in the oil (so the oil is edible) and less than 30 mol/g of glucosinolates in the meal (so it can be fed to livestock).

Figure 1

Blackleg is the most important disease of oilseed rape, including canola, with a potential to devastate the crop. It also is an important disease of cabbage and some other brassica (crucifer) crops including broccoli, Brussels sprouts, cauliflower, rutabaga, and turnip.

Yield losses of up to 100% due to blackleg have been recorded in oilseed rape. In Australia in the 1970s, the rapeseed industry was completely destroyed by epidemics of blackleg. Blackleg on canola crops in the U.S. first occurred in Kentucky in 1989, about three years after the crop was introduced. Some fields had 100% losses with nearly every plant lodging and dying (Figure 10).

Figure 10

Blackleg is currently the most important disease of canola in western Canada. The disease first appeared in 1975, and the first widespread occurrences of severe basal stem canker were recorded in central Saskatchewan in 1982. The disease quickly spread to the neighboring provinces and is now endemic in most canola growing regions of the western Canadian prairies.

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