Page 198 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

Studies have shown that high nitrogen availability can increase the severity of infection by obligate plant
parasites. In clubroot disease, caused by the obligate soilborne parasite Plasmodiophora brassicae,
nitrogen has been reported to affect the resistance of Brassica napus, but only for specific cultivar/isolate
interactions. In addition, nitrogen is also an essential element for plant growth, including root architecture
and development. The aim of this project is to determine if changes in Brassica root system development
associated with nitrogen application affect clubroot response. In the first phase of this study, variable
levels of nitrate were assessed for impact on root architecture in four Brassica genotypes grown
hydroponically, which helped to identify three nitrogen concentrations ideal for characterizing genotype
and nitrogen effects on roots. Three software packages for conducting root analyses were compared to
identify the best program for the evaluation of complex root systems. A potting system was then
developed to evaluate clubroot resistance under variable levels of nitrogen without artificially modifying
the early stages of root development. Fifty Brassica genotypes, selected for their root architecture
diversity, were screened against the resistance-breaking pathotype 3A of P. brassicae. The genotypes
with the highest modulation of resistance level by nitrogen fertilization was selected with the future
objective of testing the effect of root architecture modification on clubroot response, independently of the
nitrogen effect on plant defense. This study will help to identify and quantify the potential impact of root
architecture on clubroot resistance.

*[O188] EFFECTS OF FREEZE AND THAW TEMPERATURE CYCLES ON THE SURVIVAL OF
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1
PLASMODIOPHORA BRASSICAE RESTING SPORES. K. Holy , B. D. Gossen , and M. R. Mcdonald .
1 Department of Plant Agriculture, University of Guelph, 50 Stone Rd. E, Guelph, ON N1G 2W1, Canada;
2
and Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science
Place, Saskatoon, SK S7N 0X2, Canada
Correspondence to: kholy@uoguelph.ca

Clubroot disease, caused by Plasmodiophora brassicae (Woronin), can cause substantial yield loss in
several economically important Brassica crops. After host maturity, the ‘clubbed’ roots remain in the soil
and release resting spores back into the surrounding soil. The spores can remain viable in the soil for
many years. Repeated freeze-thaw cycles under controlled conditions reduced spore viability by up to
85%, but natural cycles in the field have not been examined. A field trial was conducted at the Ontario
Crops Research Centre – Bradford during the winter of 2022–2023. Clubs were buried at 10–15 cm
depth, which would be the typical depth for clubbed roots, or placed on the soil surface to assess the
effect of natural freeze-thaw cycles. A control treatment was maintained in a freezer at -20°C. Plastic
mesh bags were used to closely mimic natural conditions, allowing the clubbed material to interact with
the soil. Temperature sensors were placed in bags from each treatment. The number of freeze-thaw
cycles was vastly different between the buried treatment (2 cycles) and the soil surface treatment (32
cycles) during the winter season. Spore viability was assessed using an Evans Blue vital stain and
confirmed in a bioassay on susceptible canola (Brassica napus line ACS N39). Evans Blue staining
showed that the frozen control and buried club treatments maintained 94% spore viability in the spring of
2023, whereas the soil-surface clubs had only 54% spore viability. In the bioassay, inoculation with spores
from clubs from the soil surface produced clubroot severity of 79% compared to clubs that were buried
(91%) or maintained in a freezer (94%). These results strongly suggest that freeze-thaw cycles reduced
both resting spore viability and subsequent infection success. The study was repeated in 2023–2024 and
results are being assessed.

*[O189] UNRAVEL TO BUILD: PTEROCARPAN BIOSYNTHESIS FROM LEGUMES TO
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HETEROLOGOUS HOSTS. Audrey Cote , Brandon Saltzman , and Mehran Dastmalchi . Department of
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1
Plant Science, McGill University, 21111 Lakeshore Road, Ste-Anne-de-Bellevue, QC, Canada, H9X3V9
Correspondence to: audrey.cote@mail.mcgill.ca

Pterocarpans are specialized metabolites, characteristic of legume species (Fabaceae), associated with
plant defence response. Pterocarpans are classified as phytoalexins, as they are often biosynthesized in
response to abiotic or pathogenic stresses. Therefore, they have potential as antimicrobial or protective

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