Aaron Brinkman | ALES Graduate Seminar

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree. This is an ALES MSc Final Exam Seminar by Aaron Brinkman. This seminar is open to the general public to attend.

Zoom Link: https://ualberta-ca.zoom.us/j/96095008739?pwd=I0bXLJ4WiLxmA4pV9027eVr4WFqy9J.1

MSc with Drs. Stephen Strelkov and Sheau-Fang Hwang     

Thesis Topic: Cultivar mixtures for the management of Plasmodiophora brassicae in canola

Abstract:

Clubroot, caused by the obligate parasite Plasmodiophora brassicae, is a major soilborne disease affecting canola (Brassica napus, oilseed rape) and other brassicas in Canada and worldwide.  Disease management largely depends on the use of clubroot-resistant canola cultivars.  However, the extensive cultivation of resistant varieties has led to the emergence of resistance-breaking pathotypes of P. brassicae. In this study, mixtures of the susceptible (S) canola cultivar ‘Westar’ and the resistant cultivar ‘P501L’ in various ratios (S:R – 0:30, 3:27, 7:23, 15:15, 23:7, 30:0) were evaluated for their effects on P. brassicae virulence, pathotype composition, and resting spore production over multiple cultivation cycles. Briefly, the cultivar mixtures were grown in a potting medium inoculated with either a field isolate representing P. brassicae pathotype 3H or a combination of single-spore isolates of pathotypes 3D and 3H in a 1:10 ratio, over three consecutive 7-week cycles under greenhouse conditions.  Clubroot severity was assessed at the end of each cycle, and in planta P. brassicae resting spore production was quantified using microscopy. The concentration of resting spores remaining in the potting medium was determined through quantitative PCR analysis. The virulence of P. brassicae populations recovered from each treatment was evaluated on selected hosts of the Canadian Clubroot Differential (CCD) after the first two cultivation cycles, while pathotype designation and full virulence assessments were conducted on the complete CCD set after the third cycle.  The cultivar mixtures showed lower clubroot severity and resting spore production compared to susceptible monocrops but were less effective compared to a resistant monocrop. No interactions were observed between the resistant and susceptible cultivars, with each cultivar behaving independently as either a resistant or susceptible monocrop.  Assessment of P. brassicae virulence and pathotype designations revealed shifts in most mixtures, typically toward more aggressive pathogen strains.  Based on these findings, binary mixtures of resistant and susceptible canola cultivars cannot be recommended as a substitute for a resistant monocrop. However, further testing with additional cultivars and cultivation cycles, along with field studies, is needed to draw definitive conclusions.