Peng: Survey and Evaluation of Soil Microbes for Clubroot Control on Canola

Date: February 2010
Term: 3 years
Status: Completed
Researcher(s): Gary Peng and Bruce Gossen, Agriculture and Agri-Food Canada (AAFC), Saskatoon SK, Steve E. Strelkov, Department of Agricultural, Food and Nutritional Science, University of Alberta, Sheau-Fang Hwang, Alberta Agriculture and Rural Development, Edmonton AB, Mary Ruth MacDonald, Department of Plant Agriculture, University of Guelph
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: ACPC, CCC

Project Summary

Clubroot of canola, caused by the pathogen Plasmodiophora brassicae (Pb), is an emerging threat to canola production in western Canada. In 2008, researchers initiated a three-year study to assess microbial biofungicides as well as indigenous soil microorganisms for control of clubroot on canola. The study found that the biofungicides Serenade and Prestop, and synthetic fungicides Allegro and Ranman showed efficacy against clubroot of canola only in controlled conditions. Continued research in microbial formulations and delivery approaches will be required to improve performance and practicality of these products in canola cropping systems. There is a potential to use these products with R cultivars for enhanced clubroot control and resistance stewardship. As well, highly efficacious microbes identified from indigenous canola roots represent a new source of clubroot control agents.

Clubroot of canola, caused by the pathogen Plasmodiophora brassicae (Pb), is an emerging threat to canola production in western Canada. First discovered near Edmonton in 2003, the disease had been found in more than 450 fields in Alberta by 2009, and the pathogen was confirmed present in soil from a Saskatchewan field. Until 2009, all commercial canola cultivars were highly susceptible and there was a lack of practical control options against clubroot in canola. The first resistant canola cultivar became commercially available in 2009, although the resistance was only against certain races of the pathogen.

Researchers initiated a three-year study in 2008 to assess microbial biofungicides as well as indigenous soil microorganisms for control of clubroot on canola. There were two main objectives: 1) to assess selected microbial fungicide products for clubroot control on canola; 2) to isolate and evaluate soil microbes of canola roots indigenous to the Canadian prairies for clubroot control. Overall, researchers hoped that effective microbial products or agents could be used as a component in integrated clubroot control on canola.

Study I. Evaluate efficacy of microbial fungicides in controlled conditions

Selected biofungicides were applied in both controlled and field trials to determine the most effective treatments or treatment combinations. Selected biofungicides were initially applied as a soil drench and the synthetic fungicides Allegro and Ranman were also included for comparisons. All products were applied as a soil drench at 25 ml/plant (equivalent to 12,500 L/ha), with the biofungicides applied at 5% concentrations and chemical fungicides at 1x label rates. Promising products were further evaluated at varying label-rate concentrations and soil drench volumes, as a seed treatment and later in combination with resistant cultivars. For the seed treatment, canola seeds were immersed in a product solution/suspension for 5 minutes and air dried for 1 hour prior to seeding.

This study showed that in a controlled environment, the biofungicides Serenade and Prestop, and synthetic fungicides Allegro and Ranman were highly effective under moderate disease pressure, reducing the severity of clubroot on canola by 85–100%. Product rates appeared to be important while soil-drench volumes (500 to 12,500 L/ha) were less critical. These products, however, can sometimes be less efficacious or ineffective under extremely high disease pressure. As expected, the efficacy of seed treatments was lower than that of soil drenches. Seed treatment showed the potential of a practical delivery approach but more work is required. Several resistant canola cultivars/lines reduced the impact of clubroot significantly. Resistance and fungicides or biofungicides may be used in combination for synergy to enhance clubroot control and aid in resistance stewardship.

Study II. Survey and evaluate indigenous soil microbes for clubroot control

A total of 5,152 soil microbial isolates were collected from canola roots in Alberta and Saskatchewan, and screened for potential clubroot control using a tiered system. About 390 isolates were selected and tested against clubroot on canola. Three fungal endophytes showed high efficacy (>75%) while several fungal and bacterial isolates reduced clubroot by more than 50%. These candidates may be assessed further for potential development.

Study III. Efficacy of selected fungicides/biofungicides in field conditions

During the 2009 crop season under field conditions, two canola trials were carried out in Alberta, and one canola and one Chinese-cabbage trial (a model system to mimic canola) were conducted in Ontario. All products were delivered as a liquid in furrow at 500 L/ha. In each trial, resistant (R) and susceptible (S) cultivars were used. Environmental conditions, including a spring drought in Alberta and poor soil moisture conditions after harvest impacted the trials.

In Ontario, the results of the study on Chinese cabbage showed that the fungicide treatments reduced clubroot severity by 54% to 84% when compared to the untreated S-cultivar control and there was no substantial difference among the products used. Cultivar resistance was significant in all trials assessed, often reducing clubroot damage by > 90% when compared to S cultivars.

Overall, the study found that the biofungicides Serenade and Prestop, and synthetic fungicides Allegro and Ranman showed efficacy against clubroot of canola only in controlled conditions. Delivery of these products as liquid was only an initial step for efficacy assessment and continued research in microbial formulations and delivery approaches will be required to improve the performance and practicality of these products in canola cropping systems. There is a potential to use these products with R cultivars for enhanced efficacy of clubroot control as well as for resistance stewardship, and this use will require the development of more effective and practical biofungicide formulations (granules or seed dressing) first.

Scientific publications.

Peng, G, B.D. Gossen, S.E. Strelkov, S.F. Hwang and M.R. McDonald. 2009. Efficacy of selected biofungicides for control of clubroot on canola. Canadian Journal of Plant Pathol. 31:146-146 (abstract).

Peng, G, B.D. Gossen, S.E. Strelkov, S.F. Hwang and M.R. McDonald. 2009. Evaluation of biofungicides for control of clubroot on canola. Soil and Crops. University of Saskatchewan, CD Rom. 15pp.

Peng, G, B.D. Gossen, S.E. Strelkov, S.F. Hwang and M.R. McDonald. 2009. The potential for microbial control of clubroot on canola. In: Proceedings of Kunming International Clubroot Workshop, pp. 7-16. September 16-19, 2009, Kunming, China.

Peng, G, B.D. Gossen, S.E. Strelkov, S.F. Hwang and M.R. McDonald. 2010. Effect of microbial and synthetic fungicides in combination with resistant crop cultivars for managing clubroot (Abstr.). Canadian Journal of Plant Pathol. 32 (in press).

Full Report PDF: Survey and Evaluation of Soil Microbes for Clubroot Control on Canola