Soil pH affects growth of destructive fungus in canola
Study suggests producers may need to balance practices to avoid inadvertently trading one crop disease for another.
October 28, 2024 By Bev Betkowski
Becky Wang led a study that is the first to assess how soil pH affects the growth of a destructive fungus emerging in canola crops in Western Canada. (Photo: Supplied)
Soil pH may be an important factor in the growth of a destructive fungus emerging in Western Canadian canola crops, new University of Alberta research shows.
The study — the first to assess how soil’s alkalinity or acidity affects Verticillium longisporum infection in canola — shows that the fungus, which causes a disease called Verticillium stripe, grows quickly and spurs more severe symptoms under neutral to alkaline conditions, meaning high pH.
First found in Manitoba canola crops in 2014, V. longisporum has since been identified in parts of Alberta, Saskatchewan, British Columbia, Ontario and Quebec, and has resulted in yield losses ranging from 10 to 50 per cent.
“That information can give growers an idea of where Verticillium stripe could potentially take hold in their fields, and alerts them to the importance of monitoring soil pH for prevention.”
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The findings may also help explain why the disease is more prevalent in Manitoba, which has more alkaline and neutral pH soil than Alberta and Saskatchewan, Wang notes.
Verticillium stripe damages the plant’s tissues, interfering with uptake of water and nutrients.
A canola plant infected with Verticillium stripe is pictured alongside healthy plants. The fungal disease damages the plant's tissues and interferes with its ability to take up water and nutrients. (Photo: Supplied)
In lab experiments assessing the impact of pH on both the growth of V. longisporum and its virulence in canola, results showed that colonies of the fungus were about 16 per cent greater in diameter at pH levels of 7.4 and 8.6, compared with those at pH 5.5.
Along with that, the symptoms of infection in both seedlings and adult plants generally became more pronounced as soil pH increased, with disease severity at its worst at pH 7.8.
The findings could help inform more integrated strategies for disease management, says Wang, co-author of the study with professors Sheau-Fang Hwang and Stephen Strelkov.
For example, while many of Alberta’s crop soils have pH levels of 6 and lower, that has also meant widespread distribution of clubroot, another important canola disease that prefers acidic soil.
Treatments for clubroot include increasing soil pH by adding lime to the soil, but that could inadvertently increase severity of Verticillium stripe, the study authors note.
Though further research is needed to evaluate the pH sensitivity of a larger collection of V. longisporum strains and to test these effects at the field level, knowing more about the pH sensitivity of this pathogen could aid canola producers and crop scientists in developing “an integrated crop protection plan for canola,” Wang suggests.
That means possibly not liming fields where Verticillium stripe or other canola diseases favoured by an alkaline environment are an issue, she advises. Farmers can also scout their fields for signs of the disease, sanitize field equipment and extend crop rotations — increasing the number of years before growing the same crop again in the same field, to avoid a buildup of pests and diseases.
