Hwang: Effects of Clubroot-Resistant Canola Lines on Soils Infested by Plasmodiophora brassicae
Date: March 2014
Term: 4 years
Status: Completed
Researcher(s): S.E. Strelkov, Department of Agricultural, Food and Nutritional Science, University of Alberta, S.F. Hwang, H. Ahmed, Q. Zhou and G.D. Turnbull, Alberta Agriculture and Rural Development, Edmonton, AB
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
Clubroot poses a serious threat to the canola industry in Alberta and western Canada because of its long-lived spores, its ability to rapidly multiply, and its detrimental effect on canola yields. Researchers in Alberta conducted a four-year study to determine the effects of resistant crops, non-host crop rotations, repeated growth of a resistant cultivar, and mixtures of resistant and susceptible cultivars on soil pathogen population levels. The effect of seedling age and inoculum density on clubroot severity, plant height, and seed yield were also investigated. The results show that effective clubroot management in canola will largely depend on utilization of cultivar resistance and the reduction of viable resting spore populations in the soil.
Clubroot, caused by Plasmodiophora brassicae, poses a serious threat to the canola (Brassica napus, B. rapa) industry in Alberta because of its long-lived spores, its ability to rapidly multiply, and its detrimental effect on canola yields. Clubroot was first identified on canola in Alberta in 2003, and 10 years later the disease had spread to nearly 1500 fields. The disease now presents a major threat to canola production in Alberta, and has recently been identified in the provinces of Saskatchewan and Manitoba, suggesting that clubroot could eventually become widespread in the Canadian Prairies.
Researchers at the University of Alberta and Alberta Agriculture and Rural Development in Edmonton conducted a four-year study from 2010 to 2014 to determine the effects of clubroot-resistant canola lines on soils infested by Plasmodiophora brassicae. The project had several objectives, including determination of:
effects of growing resistant cultivars on clubroot severity in subsequent crops and resting spore population,
effects of volunteer canola on clubroot severity in subsequent susceptible crops,
effects of crop rotation using resistant canola on clubroot severity,
effects of P. brassicae population density on clubroot level in canola,
the relationship between clubroot severity and yield,
the relationship between inoculum production and root hair infection, and
contribution of clubroot galls to soil resting spore populations.
The study included greenhouse trials, mini-plot trials using naturally infested field soil and field trials near Edmonton.
The results from the study show that effective clubroot management in canola will largely depend on utilization of cultivar resistance and the reduction of viable resting spore populations in the soil. High soil populations of P. brassicae significantly reduce plant growth and yield. Clubroot spore populations increase dramatically with the successful formation of clubroot galls within cruciferous plants like canola.
The study found that the repeated cropping of susceptible plants progressively increased spore populations in the soil. The introduction of a susceptible cultivar resulted in greater spore populations, higher disease levels and more root hair infection compared to the resistant cultivar. At the end of the trial comparing four cropping cycles of continuous susceptible plants, continuous resistant plants and three cycles of fallow plus one cycle of susceptible plants, clubroot severity was 10-fold greater in the susceptible cropping sequence relative to the resistant sequence, but there was no difference in severity between the resistant and fallow sequences. (Figure 1)
The study also found that higher proportions of a susceptible volunteer led to higher root weights and disease severity and lower plant heights in a susceptible crop cultivated afterwards. Higher soil populations of viable spores tended to increase root weight in a susceptible crop due to clubroot galls. The higher soil populations also increased disease severity and reduced plant height and seed yield.
The results from the crop rotation experiements showed that four years of continuous canola resulted in greater clubroot severity compared to any other rotation treatment (Table 4). Where a susceptible crop was preceded by three non-host crops, yield, plant height and shoot weight were greater and disease severity was lower compared to the same crop preceded by one, two or three resistant crops. Clubroot severity was greater where the susceptible crop was preceded by three years of resistant crops, compared to a mixture of resistant and non-host crops or to three years of non-host crops. The canola-oat-pea-canola rotation produced a greater seed yield compared to any other treatment.
Table 4: Effect of resistant and non-host crop rotation treatment on growth, clubroot severity and yield of a susceptible cultivar of canola (45H26) in clubroot-infested soils
Data are the means of 12 replicate mini-plots
N =Non-host crop (barley)
R =Clubroot-resistant canola cv. 45H29
S = Susceptible canola cultivar 45H26
The study also found that at high inoculum densities, in naturally infested soil dilutions, yield declined as inoculum density increased. However, variations in inoculum density did not affect clubroot severity. Plant height was not affected by spore densities of 105 spores/cm3, but at higher spore densities plant height declined with increases in spore density. In artificially inoculated growth medium, clubroot severity increased with increasing inoculum density, but there was little effect on yield.
Overall, the study confirms that high soil populations of P. brassicae reduce plant growth and yield. The crop rotation experiments showed that four years of continuous canola resulted in greater clubroot severity compared to any other rotation treatment. Therefore, effective clubroot management in canola will largely depend on utilization of cultivar resistance and the reduction of viable resting spore populations in the soil through good management practices.
Figure 1: Effect of sequential cropping of resistant (‘45H29’, Pioneer Hi-Bred) and susceptible (‘45H26’, Pioneer Hi-Bred) canola cultivars on fresh root weight (A), plant height (B) and index of disease (C) caused by Plasmodiophora brassicae on a final susceptible canola crop. Bars in each cycle topped by the same letter do not differ at P ≤ 0.05.