Prevalence of Blackleg and Pathogenicity Groups of Leptosphaeria maculans in North Dakota

Abstract

Blackleg, caused by Leptosphaeria maculans, was first reported on canola (Brassica napus) in North Dakota in 1991. In 2003, L. maculans strains of previously unreported pathogenicity groups (PG) were discovered in the region. Since then, however, little has been known about the prevalence of L. maculans in the state. The objectives of this study, therefore, were to characterize the prevalence of blackleg and of L. maculans PGs in North Dakota. Prevalence was assessed in 2004, 2007, and 2009 in 572 fields. PG determination for 216 L. maculans isolates retrieved from blackleg symptomatic stems during that period was achieved on a set of B. napus differential cultivars. Blackleg prevalence increased from 28% in 2004 to 63 and 74% in 2007 and 2009, respectively. Similarly, the number of fields with blackleg incidences >30% increased from 4% in 2004 to 12 and 23% in 2007 and 2009, respectively. In all years, PG-4 was the predominant group, while PG-2, once predominant, accounted for <2% of isolates. Increase in the prevalence and incidence of blackleg as well as the frequency of virulent PGs over the last 10 years is a serious threat to the canola industry of the region.

Rapid identification of the Leptosphaeria maculans avirulence gene AvrLm2 using an intraspecific comparative genomics approach

“…AvrLm2 genotypes are: (i) currently absent in Europe and found only for two isolates obtained before 1975 (Balesdent et al ., ; Stachowiak et al ., ; this study); (ii) rare in Australia with only one isolate of 65 showing the AvrLm2 phenotype (Dilmaghani et al ., ; this study); (iii) common in current and older populations from western and eastern Canada, but not in Ontario (Dilmaghani et al ., ; Kutcher et al ., , ), and becoming increasingly less common through southern Manitoba and North Dakota (Chen and Fernando, ; Nepal et al ., ); and (iv) prevalent in Mexican populations (Dilmaghani et al ., ) (http://onlinelibrary.wiley.com/doi/10.1111/mpp.12228/suppinfo). Adaptive mechanisms used by fungi to escape R gene recognition have been analysed in detail for those Avr genes which have been submitted to cognate R gene selection in either agronomic practice or experimental fields, namely AvrLm1 (Gout et al ., ), AvrLm2 (this study), alleles AvrLm4 (Parlange et al ., ) and AvrLm7 (Daverdin et al ., ) of AvrLm4‐7 and AvrLm6 (Fudal et al ., ).…”

Association mapping in Brassica napus (L.) accessions identifies a major QTL for blackleg disease resistance on chromosome A01

“…In the 1990 and early 2000s, PG-2 strains of L. maculans were predominant in North Dakota with strains of PG-3 and PG-4 accounting for less than 5 % (Bradbury et al 2007). By 2009, strains of PG-3 and PG-4 had become predominant and PG-2 constituted less than 3 % of the population (Nepal et al 2014). Strains of PG-4 represent a serious threat to the canola industry of the state as they are more aggressive than PG-3 and PG-2 (Franceschi and del Rio 2014) and are capable of infecting plants carrying resistance genes Rlm1, Rlm2 and/or Rlm3 (Nepal et al 2014).…”

Co-localisation of the blackleg resistance genes Rlm2 and LepR3 on Brassica napus chromosome A10

“…Kutcher et al (2010) noted that the only avrLm2 isolates detected in their survey were collected in southern Manitoba in 2003–2005. Another survey also found avrLm2 isolates both in Alberta, Manitoba and directly south across the Canada/US border in North Dakota [ 54 ] and a recent report suggests nearly all L. maculans in North Dakota would be virulent on Rlm2 varieties [ 55 ]. Clearly relying on Rlm2 as the single resistance source for a canola variety would be foolhardy.…”