Page 214 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

*[P21] EVALUATION OF THE HOST SPECIFICITY OF VERTICILLIUM LONGISPORUM IN WESTERN
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CANADA. Lidan Gao , Haitian Yu , Godfrey Chongo , Stephen E. Strelkov , and Sheau-Fang Hwang .
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1 Department of Agricultural, Food and Nutritional Sciences, University of Alberta, Edmonton, AB, Canada,
T6G 2P5; and BASF Canada Inc., Saskatoon, SK, Canada, S7K 3J9
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Correspondence to: lg@ualberta.ca

Verticillium longisporum is a soilborne fungal pathogen that causes Verticillium stripe of canola (Brassica
napus). This study evaluated the host specificity of V. longisporum on eight crops of economic
significance in western Canada: canola, wheat, barley, pea, lentil, faba bean, soybean, and potato.
Inoculations were conducted under greenhouse conditions, with each crop represented by 2 to 4
cultivars. Compared to the controls, inoculated treatments showed variable reductions in height and
emergence across all crops. Soybean and lentil were the most severely affected, experiencing height
reductions ranging from 83% to 94% for soybean, with emergence declining by 85% to 95% compared
with the non-inoculated control. Principal component analysis indicated that wheat, barley, pea, and faba
bean showed somewhat more tolerance to V. longisporum infection, experiencing smaller reductions in
emergence and plant height. No signs or symptoms of disease were visible on barley or wheat.
Nonetheless, the emergence of wheat, along with canola, lentil and faba bean, was significantly delayed
compared to the non-inoculated controls. Symptoms of infection were most pronounced on canola, pea,
and potato, although assessments of disease severity are still underway. Preliminary results suggest that
several crop species may serve as hosts of V. longisporum in western Canada.

[P22] BALANCING SELECTION COMPLICATES MANAGEMENT OF CLUBROOT AND (POSSIBLY)
OTHER PROBLEM DISEASES. Bruce D. Gossen , A. Sedaghatkish and M. R. McDonald . Saskatoon
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Research and Development Centre, Agriculture and Agri-Food Canada, Saskatoon, SK, Canada; and
2 Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada
Correspondence to: bruce.gossen@agr.gc.ca

Balancing selection occurs when multiple alleles are retained over time in a population, usually at very
low frequency. Evidence is accumulating that Plasmodiophora brassicae Wor., the cause of clubroot in
Brassica spp., retains many complete genotypes at low frequency. This likely occurs because the
dominant genotype suppresses host resistance, facilitating host infection by other phenotypes. This
retention of entire genotypes may explain the rapid breakdown of single-gene resistance to clubroot.
Genotypes that can overcome the resistance may already be present in the pathogen population at low
frequency. When a new host resistance gene is deployed, intense selection for virulent phenotypes would
occur. The pathogen can produce billions of spores per infected plant, so clubroot can increase rapidly
even from a low starting point. Stacked resistance genes or rotation of resistant cultivars in combination
with crop rotation, which reduces spore populations by 90–99% over 2–3 years, could substantially
reduce the risk of resistance breakdown. In addition, we suggest that the definition of balancing selection
be expanded to include situations where one genotype / species ‘opens the door’ to less virulent
genotypes, allowing them to infect a host. This may occur among AG groups of Rhizoctonia solani or
among Pythium / Globisporangium spp. Isolation from rotting roots often yields many genotypes /
species, only a few of which are aggressive on healthy roots. It appears likely that infection of a root by
one genotype provides an opportunity for related pathogens to colonize the dying root and thus be
maintained in the microbial population.

[P23] DO NEMATODES GET AROUND? A CASE OF SOYBEAN CYST NEMATODE IN A MANITOBA
FIELD. Fernanda Gouvea Pereira , Nazanin Ghavami , Jason Voogt , and Mario Tenuta . Department of
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Soil Science, University of Manitoba, Winnipeg, Manitoba, Canada; and Field to Field Agronomy Inc.,
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Miami, Manitoba, Canada
Correspondence to: Fernandagouveap@gmail.com

Soybean Cyst Nematode (SCN) is a devastating pathogen known for causing significant yield losses in
soybean and certain dry bean varieties across North America. Although SCN was first identified in
Manitoba in 2019 with low cyst populations, a subsequent investigation in July 2021 revealed an SCN
symptomatic soybean field with cyst-laden roots in the Rural Municipality of Thompson. The affected area
surrounded the field entranceway for machinery. Detailed soil sampling in the affected area was
conducted in a grid patten (6 m x 10 m) covering 1,680 m . Molecular analysis confirmed the cysts to be
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