Hollman, K.B.

Hwang, S.F.

Manolii, V.P.

Strelkov, S.E.

English

eCommons@USASK

Virulence and pathotype characterization of Plasmodiophora brassicae populations collected from clubroot resistant canola cultivars in Western Canada 2018

University of Saskatchewan Research Archive

Virulence and pathotype characterization of Plasmodiophora brassicae populations collected from clubroot resistant canola cultivars in Western Canada 2018K.B. HOLLMAN1*, S.F. HWANG1,2, V.P. MANOLII1, AND S.E. STRELKOV11I1Department of Agriculture, Food, and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5, Canada; and (S.F.H.) Crop Diversification Centre North, Alberta Agriculture and Forestry, Edmonton, AB, T5Y 6H3, Canada.INTRODUCTION RESULTSOf the 124 samples submitted, 1 of the 6 samplessubmitted from Manitoba, had overcome resistance andwas a confirmed new pathotype. Of the 10 samplessubmitted from Saskatchewan, no samples showedevidence of resistance breakdown. Of the103 samplessubmitted from Alberta, 87 of the samples had overcomeresistance and were confirmed new pathotypes.METHODSCanola roots with typical clubroot symptoms were collected from 124 fields from Alberta, Manitoba and Saskatchewan in 2018 where CR cultivars had been planted. Resting spores of P. brassicae were extracted from multiple clubbed roots  of each field. The concentration of P. brassicae resting spores in filtrates from symptomatic root tissue homogenates was measured with a hemocytometer (VWR, Mississauga, ON) and adjusted to 1 107spores mL-1 with sterile deionized water. The resulting spore suspension was used to inoculate 1-week-old seedlings of 13 host genotypes from the Williams, Somé et al., and CCD set, which had been germinated on moistened filter paper in glass Petri dishes. The plants grew for 6 weeks under greenhouse conditions. They were harvested, washed and rated on a 0-3 scale.  Based on the unique virulence pattern they produced on the CCD set (Table 1), a letter was assigned to distinguish a unique pathotype. The experiment was arranged in a randomized design, with 4 repetitions per host, and 12 seedlings per repetition. CONCLUSIONA total of 88 fields with confirmed resistance breakdownin 2018 is the most new virulent pathotypes confirmed ina single year (Fig 4, Fig 5). Most new pathotypes in 2018can be characterized as pathotype 3A on the CCD set(Fig 3). The results suggest that the loss or erosion ofresistance continues to become more widespread inAlberta, and that pathotype 3A should be included inresistance screening activities.REFERENCESClubroot, caused by Plasmodiophorabrassicae Wor., is an importantsoilborne disease of canola (Brassicanapus L.) and other crucifers. Themanagement of clubroot in Alberta,Canada, relies heavily on the plantingof clubroot resistant (CR) canola. Thefirst CR canola cultivar was releasedonto the Canadian market in 2009, butby 2013, resistance breakdown hadbeen documented in two fields.Currently, a loss or erosion of clubrootresistance had been confirmed in acumulative total of 170 fields acrossAlberta, likely as a result of pathotypeshifts in the P. brassicae population.Most field isolates capable ofovercoming resistance are classified aspathotype A on the Canadian ClubrootDifferential (CCD) Set. Sincepathotype A is a variant of pathotype 3on the system of Williams, it is knowncommonly as pathotype 3A.Knowledge of pathotype composition isimportant for guiding resistancebreeding activities, and continuedmonitoring of the performance of CRcanola cultivars was carried out in2018.CCD3H 3D 3A 5X 5L 8E 8N 8P2 18 42641041920501001502002502013 2014 2015 2016 2017 2018# OF FIELDSYEAR# of fields where new pathotypes confirmedDISCUSSIONSomé et al.P2 P3Williams3 5 8The widespread emergence of new pathotypes brings aserious threat to Canadian oilseed farmers. Continuedpathotyping efforts are crucial in understandingdistribution, and identifying most common newpathotypes, for example pathotype 3A, as a focus forbreeding efforts. CR canola is the most effective defensetool for farmers against clubroot, however with thecontinued spread of new pathotypes in which nocommercially available resistant cultivars exist,management strategies must be tailored to preventfurther spread and infection.Old PathotypeNew PathotypeACKNOWLEDGEMENTSCollaborators, students and staff from the University of Alberta; Alberta Agriculture and Forestry; Canola Agronomic Research Program (Alberta Canola Producers Commission, Manitoba Canola Growers Association, SaskCanola); Growing Forward 2, Canadian agricultural partnership between Canola Council of Canada and Agriculture and Agri-Food Canada; Clubroot Steering Committee; Industry, municipalities, Agriculture Companies, and Farmers who submitted samples for the project.-Strelkov SE, Hwang SF, Manolii VP, Cao T, Feindel D. 2016a. Emergence of new virulence phenotypes of Plasmodiophora brassicae on canola (Brassica napus) in Alberta, Canada. Eur J Plant Pathol. 145:517–529.-Strelkov SE, Hwang SF, Manolii VP, Cao T, Fredua-Agyeman R, Harding MW, Peng G, Gossen BD, Mcdonal MR,Feindel D. Virulence and pathotype classification of Plasmodiophora brassicae populations collected from clubrootresistant canola (Brassica napus) in Canada. Can J Plant Pathol. 40: 284-298. -Somé A, Manzanares MJ, Laurens F, Baron F, Thomas G, Rouxel F. 1996. Variation for virulence on Brassica napus L. amongst Plasmodiophora brassicae collections from France and derived single-spore isolates. Plant Pathol. 45:432–439.-Williams PH. 1966. A system for the determination of races of Plasmodiophora brassicae that infect cabbage and rutabaga. Phytopathology. 56:624–626.Figure 1: Galls from a field with an old pathotypeversus galls from a field with a new pathotypeFigure 1: 2018 pathotype designation based on Somé et al., Figure 2: 2018 pathotype designation based on WilliamsFigure 3: 2018 pathotype designation based on the CCD setFigure 4: # of new pathotypes found in new fields from 2013-2018Figure 5: Distribution of new pathotypes found from 2013-2018Table 1: Pathotype classification scheme on the hosts of the CCD set Old Pathotype

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Virulence and pathotype characterization of Plasmodiophora brassicae populations collected from clubroot resistant canola cultivars in Western Canada 2018

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