Outbreak of Blackleg in Canola in North Dakota is Caused by New Pathogenicity Groups

Abstract

In 2009, a blackleg outbreak was detected in canola fields of North Dakota. The disease, which is caused primarily by the fungus Leptosphaeria maculans, was observed in 88 of 99 fields scouted with 39 fields having incidences >30%. The mean blackleg incidence in these 39 fields was 61% (range 50 to 84%). Fifty nine L. maculans isolates were retrieved from 20 of these 39 fields and classified in five pathogenicity groups (PG) using a set of three differentials cultivars. PG-4 was the pathotype most commonly isolated from these fields with 51% of all isolates, followed by PG-3 with 25% and PG-T with 8% of isolates. Only 3% of the isolates belong to PG-2, a pathotype that was previously considered the most prevalent in the region. Increased prevalence of these new pathogenicity groups represents a threat to the canola industry in the state. Accepted for publication 20 January 2012. Published 10 April 2012.