Virulence and spread ofPlasmodiophora brassicae[clubroot] in Alberta, Canada

Abstract

Clubroot, caused by Plasmodiophora brassicae, has emerged as an important disease of canola (Brassica napus) in Alberta, Canada. Annual surveys from 2005 to 2008 revealed 405 clubroot-infested fields, mainly in central Alberta, but also in the southern part of the province. Within-field surveys suggested that the main mechanism of clubroot spread is through the movement of infested soil on farm machinery, as the frequency of infestation was highest at the field entrances and decreased sharply at distances of 150 and 300 m from the entrance. Characterization of P. brassicae populations from Alberta on the differentials of the European Clubroot Differential (ECD) series, P.H. Williams, and A. Somé et al. revealed that pathotype ECD -/15/12, 3, or P 2 , respectively, is predominant in the central part of the province, a finding consistent with earlier reports. However, novel virulence phenotypes were also observed. Two populations from southern Alberta were classified as pathotype 5 or P 3 on the hosts of P.H. Williams and A. Somé et al., respectively, or as pathotypes ECD -/6/8 and -/4/0 on the ECD set, suggesting independent introductions of P. brassicae to this region or greater diversity than previously thought. Pathogen populations collected from infected canola plants from Quebec and Manitoba also yielded unique virulence patterns but were still virulent on most B. napus hosts, and an Ontario population induced significant disease only on a few of the vegetable differentials. Virulence levels overall were highest for the P. brassicae populations from central Alberta, which may help to explain the rapid increase in clubroot observed in this province. 329Résumé : La hernie, causée par Plasmodiophora brassicae, s'est révélée être une maladie importante du canola (Brassica napus) en Alberta, au Canada. Des enquêtes annuelles menées de 2005 à 2008 ont mis en évidence 405 champs infestés par la hernie, dans le centre de l'Alberta principalement, mais aussi dans le sud de la province. Les enquêtes se limitant à des champs individuels ont suggéré que la propagation de la hernie se fait par le déplacement de sol infesté adhérant à la machinerie agricole, étant donné que la fréquence d'infestation était la plus élevée à l'entrée des champs et décroissait radicalement plus on s'éloignait de l'entrée (150 m et 300 m). La caractérisation des populations de P. brassicae trouvées en Alberta par rapport aux différentiels des séries de l'European Clubroot Differential (ECD), de Williams et de Somé et al. a montré que le pathotype -/15/12, 3 ou P 2 , respectivement, prédomine dans le centre de la province, ce qui concorde avec les rapports antérieurs. Toutefois, on a également observé de nouveaux phénotypes de virulence. Deux populations du sud de l'Alberta ont été classifiées en tant que pathotype 5, ou P 3 , par rapport aux séries d'hôtes de Williams et de Somé et al., respectivement, ou comme pathotypes -6/8 et -4/0 par rapport aux séries de l'ECD. Cela suggère soit des introductions involontaires de P. brassicae dans cette ...

Pathotypes of Plasmodiophora brassicae causing damage to oilseed rape in the Czech Republic and Poland

“…Collectively, a total of nine pathotypes were found in the Czech Republic and Poland using Williams' (1966) classification, with pathotype 7 representing 33 % of all isolates tested from both countries, followed by pathotype 6 (23 %), pathotype 4 (17 %) and other less common pathotypes. This greatly differs from the situation reported in Canada, where the main pathotype found on oilseed rape (canola) was pathotype 3 (Cao et al 2009), which in Poland and the Czech Republic was very rare. Nonetheless, some of the other pathotypes were common to Canada, the Czech Republic and Poland, including pathotypes 2, 4 and 6 (Cao et al 2009).…”

“…This greatly differs from the situation reported in Canada, where the main pathotype found on oilseed rape (canola) was pathotype 3 (Cao et al 2009), which in Poland and the Czech Republic was very rare. Nonetheless, some of the other pathotypes were common to Canada, the Czech Republic and Poland, including pathotypes 2, 4 and 6 (Cao et al 2009). In Canada, pathotype 6 was associated only with cruciferous vegetables.…”

“…Using the evaluation system of Somé et al (1996), 67 % of the populations of P. brassicae in these two countries were classified as P 3 , whilst 27 % were P 1 and a small percentage belonged to P 2 , P 4 or P 5 . This is again is different from the Canadian situation, where pathotype P 2 is dominant (Cao et al 2009). According to preliminary results from a survey in Germany, pathotypes P 1 and P 3 are predominant there as well (Somé et al 1996).…”

Quantitative PCR shows propagation of Plasmodiophora brassicae in Swedish long term field trials

“…The high levels of P. brassicae DNA found in the archived soil samples indicate great potential for transmission of P. brassicae inoculum between fields via infected soil carried by farm equipment (Cao et al 2009;Gossen et al 2014;Strelkov and Hwang 2014). Wind erosion is another important transmission pathway, as substantial amounts of inoculum are present in wind-blown dust from infested fields (Rennie et al 2015).…”

Who is sowing our seeds? A systematic review of the use of plant genetic resources in research

“…Recently, the ECD collection has been utilised by researchers in Canada where clubroot (P. brassicae) is becoming a major problem in brassica crops and spreading quickly across the country (Cao et al 2009). In infected fields, clubroot causes an average yield loss of 11% (Dixon 2009), with some strains infecting 74-100% of a crop (Cao et al 2009).…”