How to use spore testers for sclerotinia

Sclerotinia stem rot management relies on fungicides, for the most part, and several new spore density measurement tools are also available to help growers pinpoint if and when to spray.

Clint Jurke, Canola Council of Canada agronomy director, wants growers to understand that these tools provide some of the information needed. Results of these tests answer the first of two questions about disease risk: Are the spores in the field at the time of flowering? But it doesn’t answer whether present and projected environmental conditions are right for infection.

“If you are going to spray, you need to do it at 20 to 50 per cent bloom, but for the pathogen to move from the petals to the stem and cause disease, you need the following conditions to persist over the next two to three weeks: temperatures 15 to 25°C and high levels of moisture on the petals. That means your pants will get wet as you walk through the field in the afternoon,” Jurke says. “If conditions are drying up and look to stay dry, the pathogen will of course still be there but will stop growing and not cause disease.”

Jurke believes the canola industry is still working out how to position these tests in terms of spray decision-making, but says that any of these tools “are better than what we had five years ago.”

Petal tests

Quantum Genetix in Saskatoon has offered the Q-protect sclerotinia test since 2016, and general manager Heather Deobald says it continues to grow in popularity. To test with Q-protect, users collect three petals from eight plants over five sites in the field. Q-protect reports the percentage of plants infested with sclerotinia spores from each collection site as well as the overall percentage of plants infested in the field. The percentage of plants infested correlates to the risk of developing sclerotinia stem rot.

To help growers interpret test results, Quantum Genetix has a mobile app with a simple colour-coded “risk barometer”.

“The app helps quantify the risk of yield loss so that it can be compared to the cost of disease protection,” says Deobald. “Even though disease may occur, the cost of spraying may be equal to or higher than the cost of yield loss in some scenarios so the farmer may be better off not spraying. Alternatively, the app can illustrate how necessary spraying is when the cost of yield loss is much higher than the cost of spraying. With the ability to compare yield estimates, cost of spraying and risk of disease, farmers get an in-depth picture of their situations.”

Farmers also utilize the reporting of sites to target spraying, perhaps only spraying at sites that showed a moderate to high sclerotinia presence. Farmers could also only target areas of high yield or moisture content if sclerotinia is present at those sites.

Discovery Seed Labs has offered a sclerotinia petal test for two years and has also seen its use increasing. “We are going to limit the number of kits that are sold each season to ensure that we can meet the tight required turnaround time for customers to receive their results,” says Jason Danielson, business manager at Discovery Seed Labs. “We expect in the next year or two to be sold out of kits for each testing year.”

Danielson says the feedback on the kits has been very positive, with customers really liking the added specificity of results when kit results are combined with the company’s sclerotinia calculator. “Some of our customers have used the kits in their research programs and were very impressed with how closely the kits were able to predict disease presence in the field,” he says.

Test results show notable variability from field to field, with very low to very high presence of the spores. “The variability in results from different fields really demonstrates the importance of collecting the information of your specific fields of interest and combining the spore percentage with weather data to make an informed decision about whether or not to spray,” Danielson says.

Spore trapping tool

For 20 years, Canadian horticulture crop producers have used systems that trap fungal spores in the air and identify pathogens present and their amounts. These are now coming to canola crops. In 2018, a system called Spornado Sampler was commercialized in Ontario. It has been used in Alberta on wheat and barley (for fusarium head blight) and canola (for sclerotinia).

Spornado units placed in a field trap spores in a “sample cassette”. Growers or agronomists send the cassettes by courier to 20/20 Seed Labs in Nisku, Alberta. DNA analysis identifies the types and amounts of trapped spores. Growers are provided with a risk level of low, medium or high.

Eleanor McBain is a Masters student working with AAFC pathologist Kelly Turkington on spore collection. This image shows her set up, including Spornado, rotorod and weather stations, in one of her fields in Alberta in 2020.

Studies underway

Kelly Turkington, plant pathologist with Agriculture and Agri-Food Canada (AAFC) at Lacombe, Alberta, and his team trying various tools to measure spore load before and during canola flowering. They are pairing Spornado units with “rotorods”, devices that measure the amount of S. sclerotiorum DNA per unit of time per unit volume of air. Turkington says the Rotorod has been used in research trials as far back as the 1970s and is currently mainly used in Canada for crop research and to monitor pollen levels for air quality determination.

“There isn’t much research info on the Spornado and its results in relation to sclerotinia risk and need for fungicide,” Turkington says. “Thus we are looking at its utility in terms of stem rot pathogen spore trapping and risk assessment.”

As part of the study, they are also using quantitative polymerase chain reaction (qPCR) DNA tests to test canola petals in collaboration with Alberta Agriculture’s plant health lab, and commercial DNA-based petal tests from Discovery Seed Labs and Quantum Genetix. “Our focus is to relate variation in spore load in relation to weather conditions and crop growth stage and how this impacts disease risk and fungicide application response,” Turkington says. For fungicide response, they are studying single versus dual applications and early versus late applications.

In another research project, Xiujie Li, a senior research scientist at InnoTech Alberta, is working on a sensor that could provide quick results in the field. Li has developed a prototype hand-held bio-sensor that is now capable of detecting even a single S. sclerotiorum spore. It was field-tested this summer and the design is being modified to filter out non-desired materials.