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A late blight early-warning system

During the 2014 growing season, a new late blight spore-trapping project was initiated in Alberta that may offer growers another tool for delaying the spread of late blight in the province.

Melanie Kalischuk, an instructor at Lethbridge College, says the study was designed to provide Alberta growers advanced warning about the presence or absence of Phytophthora infestans, the pathogen that causes late blight. In Western Canada, late blight can occasionally cause devastating losses for potato and tomato growers.

According to Kalischuk, P. infestans has two mating types. If both are present in a region, sexual reproduction of this pathogen can occur and this can result in genetic recombination. “We are lucky in Alberta because presently we have only one of the mating types,” she explains.

The sexual form of the pathogen, known as an oospore, also has the ability to survive in the soil for many years, complicating management control practices. “Therefore, we want to avoid sexual reproduction of this pathogen,” Kalischuk says. “Avoiding the occurrence of both mating types in the province is important.”

P. infestans requires a living, unprotected host, as well as precise environmental conditions, including moisture and lower temperatures, for infection. As part of this pathogen’s complex life cycle, it produces a spore type referred to as “sporangia.” Sporangia is usually spread via living infected plant tissue in fields, cull piles or weeds. “Sporangia can also become airborne, allowing us to monitor for the occurrences of this pathogen by taking air samples,” Kalischuk says. “Last summer, a series of eight volumetric spore traps were set up in strategic locations throughout the province to monitor air samples for the spores causing late blight disease.”

The study was headed up by Kalischuk and students at Lethbridge College, with assistance from Michael Harding and Ron Howard with Alberta Agriculture and Rural Development at Brooks, and Lawrence Kawchuk at Agriculture and Agri-Food Canada’s Lethbridge Research Centre. Funding for the study was provided by Potato Growers of Alberta (PGA), Alberta Crop Industry Development Fund, Cavendish Farms, Lamb Weston and Crop Production Services. The PGA also supported the study by disseminating spore-trap counts to growers in real-time.

Kalischuk and her team set up two types of spore traps – a rotor rod trap, which had to be checked daily, and a UK-made trap called a Burkard 7-Day Recording Volumetric Spore Trap. Burkard traps are lightweight units that contain built-in vacuum pumps to sample airborne particles continuously, with the particles adhering to coated tape on a clockwork-driven drum inside the unit. Traps can be left for up to seven days before they need to be checked by researchers.

The traps were set up at the edges of farmers’ fields, or just west of fields, because late blight spores tend to travel east to west. The
researchers found that once spore levels spiked in the traps, they had about a 10- to 16-day window before late blight appeared in nearby fields.

“Although this study is in its early stages and more testing is required to quantify pathogen load, last year we were able to observe an increase in the number of air-borne sporangia that correlated with an infection in the field that appeared 10 to 16 days later,” Kalischuk says.

Terence Hochstein, executive director of the PGA, says the study did exactly what they’d hoped it would: it provided growers with an early warning about the advancing spread of P. infestans so they could tighten up their existing spray programs and stay ahead of the pathogen. “We first had a major detection of the traps on about July 20. Our first reported incident was Aug. 5,” he says.

But Kalischuk says the benefit of the study goes beyond immediate payoffs for growers. “Another important component of this study is to identify hot-spots for infection and then to educate people in these areas on practices that can help eliminate late blight,” she says. “A number of years ago, Alberta potatoes had an economic advantage because late blight was rare in the province. With this project we are helping to bring back the Alberta advantage.”

The project will also help growers design more effective management regimes, Kalischuk claims. Growers have to watch environmental conditions to stay on top of late blight management, but the late blight spore-trapping project will deliver concrete data about pathogen pressure. “Typically the best strategy to reduce the chance of getting late blight is to remove cull or compost piles, where the pathogen can live, and avoid planting infected seed,” Kalischuk says. “Now, with this additional information about the pathogen, farmers will also be able to use preventative rather than reactive fungicide spray programs.”

With one year of positive results, Hochstein and Kalischuk are looking ahead to the future. The project will continue this year, with support from new industry partners, as well as an expanding network of interested growers. Hochstein says there is demand for the spore trap information to become even more readily available to growers.

He underscores the importance of the project in giving growers a measure of control in late blight management, echoing Kalischuk’s claim that it offers a preventative, proactive approach to late blight.

“We’re constantly looking for ways to reduce or eliminate late blight in Alberta. Our growers – and the entire industry – are very proactive with that. It’s a community disease and we’re doing our best to fight it.”

September 11, 2015  By Julienne Isaacs