Hwang: Effect of Crop Rotation on Canola Seedling Blight and Soil Pathogen Population Dynamics
Date: October 2007
Term: 2 years
Status: Completed
Researcher(s): Dr. Sheau-Fang Hwang, H. Ahmed and G.D. Turnbull, Alberta Agriculture and Food, Edmonton; S. E. Strelkov, Department of Agricultural, Food & Nutritional Science, University of Alberta; H.R. Kutcher, Agriculture and Agri-Food Canada, Saskatoon
SaskCanola Investment: $10,000
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
Diverse crop rotations are known to reduce the quantity of soilborne pathogens, while the continuous planting of any crop increases diseases and pests specific to that crop, causing a reduction in the yield. This study confirmed that diversity in crop rotation can reduce disease pressure caused by soilborne pathogens, however, an integrated management approach needs to be utilized for economic disease management.
Long-term crop rotations have been used as a standard practice to reduce disease pressure in field crops. Diverse crop rotations are known to reduce the quantity of soilborne pathogens, while repeated cultivation of a susceptible crop can lead to increased populations of many pathogens.
With more producers adopting direct seeding and early seeding of hybrid and specialty canola varieties, losses to seedling blight and damping off of canola has exceeded 10% at some locations. In 2005 and 2006, over 20% of fields surveyed in central Alberta suffered from poor seedling establishment.
Among the numerous soilborne pathogens, Fusarium, Pythium and Rhizoctonia are persistent, recurrent problems causing canola seedling blight and dampening off, reducing crop stand establishment in the Canadian prairies. Seed treatment with fungicides is not always effective for the control of soilborne diseases and integrated, sustainable disease management options are desirable. The purpose of this study was to determine the impact of long-term crop rotations on soil pathogen populations and on the growth parameters of canola on soil collected from rotation experiments.
Study sites were located on long-term crop rotation experiments established in the late 1990s at the Agriculture and Agri-Food Canada Research Stations at Scott and Melfort. The crops included in the long-term rotations were canola, flax, pea and wheat. The rotations were continuous canola, continuous field pea, canola-wheat, pea-wheat, pea-canola-wheat, canola-wheat-pea-wheat and canola-wheat-flax-wheat.
At both sites, Fusarium was the predominant soilborne pathogen, followed by Pythium and Rhizoctonia. In the study, canola seedling emergence and growth generally increased with increased diversity of the crop rotations, while the populations of soilborne pathogens declined with increased crop diversity in rotation. A greenhouse study also indicated seedling emergence and growth parameters, including root vigour, shoot weight, root weight, seedling height and plant height, were greater in both of the diverse 4-year crop rotations (canola-wheat-pea-wheat and canola-wheat-flax-wheat). Similarly, the soil pathogen populations were reduced in the soil following 4 diverse crop rotations as compared to more intensive rotations.
This study reinforces previous findings and concludes that the spectrum of soilborne pathogens responds to crop rotation and environment. As well, canola seedling growth is affected by which soilborne pathogens are present and by their relative abundance.
For example, continuous cropping, particularly of pea, resulted in higher populations of Pythium and Fusarium, and in most cases, lower seedling emergence and growth. Populations of Rhizoctonia did not show consistent trends among the rotation types.
Overall, the research suggests that diverse crop rotations may reduce the populations of Fusarium, Pythium and Rhizoctonia in the soil and may contribute to improve the overall growth of canola. Canola yields in shorter crop rotations were reduced due to the combined effect of aggravated weed and disease pressure. Therefore, diversity in crop rotation can reduce disease pressure caused by soilborne pathogens. Crop rotation alone may not be effective for disease management, and an integrated approach including varietal resistance, herbicide tolerance, timing of seeding and other cultural practices, as well as fungicides need to be utilized for economic and effective disease management.
Scientific Publications
Hwang, S.F., Ahmed, H., Turnbull, G.D., Gossen, B.D., Kutcher, R.H., Strelkov, S.E., and Howard, R.J. 2008. Effect of crop rotation on canola seedling blight and soil pathogen population dynamics. Can. J. Plant Pathol: 30: 369.
Hwang, S. F., H.U. Ahmed, B.D. Gossen, H.R. Kutcher, S.A. Brandt, S.E. Strelkov, K.F. Chang, and G.D. Turnbull. 2009. Effect of crop rotation on the soil pathogen population dynamics and canola seedling establishment. Plant Pathology Journal 8 (3): 106-112.