Petri dish battles may ultimately benefit N.S. onion growers

Adèle Bunbury-Blanchette busy in the lab. (David Kristie photo)

by Emily Leeson
There are some serious, if microscopic, battles underway in petri dishes at Acadia University’s biology department. Different species of fungi are facing off against a common enemy: Fusarium basal rot. When a victor ultimately arises from the lab, then the greenhouse, and then in field trials, it may well change the course of Nova Scotia onion farming.
Caused by the pesky soil-borne fungus Fusarium oxysporum f. sp. cepae (FOC), Fusarium basal rot can have a significant impact on an onion crop. Outbreaks occur in warm weather when the fungal spores in the soil germinate and infect onions planted in the infested fields. Local growers have reported that FOC is overwintering in the soil and spreading between fields.
The disease can affect an onion crop at any stage of development. While some symptoms are visible in the field – infected plants gradually become yellow and then brown, they wilt, and the inside of the onions soften – in most instances, the rot is not apparent until after the crop is harvested and stored. Growers often only see evidence of the problem once stored onions are being prepared for shipment, at which point they must be discarded. 
It’s a problem that impacts onion crops worldwide, but it is a big problem for Nova Scotia’s onion producers in particular.
“It is thought to be related to the humid climate and warm temperatures,” said Dr. Allison Walker, an assistant biology professor at Acadia University in Wolfville, N.S., who is researching biocontrol options to combat the disease in local fields. “The things that make it good for growing crops here also make it good for growing fungi.”
Nova Scotia’s annual onion production represents a farm gate value of approximately $3 million, with a production volume of 9,747 tonnes. Each year, 20 percent of the onion crop is lost to Fusarium basal rot, representing about $600,000 of the farm gate value. 
For Nova Scotia’s four major commercial onion growers, the disease is not a problem to be taken lightly. “It has the capacity to wipe out all of the commercial onion growing in the (Annapolis) Valley,” said Walker. “They’ve had to abandon entire fields when they get infected. Even if they do a seven- to 10-year rotation, they are still seeing the spores existing in the soil.”
Horticulture Nova Scotia has identified the disease as a serious threat to the province’s onion industry. Growers say instances of the disease increase each year. 
Situated amidst the province’s most fertile farmland, Acadia University is actively engaged with the agricultural industry surrounding it. Back in December of 2014, at an event aiming to pair up researchers with expertise in the lab and growers with experience in the field, Walker was connected with Nova Scotia onion growers.
From there, a plan was hatched and funding was arranged. Walker and master’s student Adèle Bunbury-Blanchette were able to get down to the business of investigating what could combat FOC and protect Annapolis Valley onions.
As it turns out, the best way to fight fungus is with fungus. Now two years into the project, Bunbury-Blanchette is testing biocontrol products that are already commercially available along with other beneficial fungi that she’s isolated from local soils. All the options they’re testing are compatible with both organic and conventional farming. 
The process in the lab is just a matter of pairing up each of these fungi with the FOC and making observations.
“I put them both in and see what interactions happen,” said Bunbury-Blanchette. “If it’s a good candidate for a biocontrol option, you’ll see it overgrow the pathogen or the pathogen will have a stress response. In some cases, the biocontrol will completely overgrow it.”
Bunbury-Blanchette is also testing the options on onion seedlings she’s been growing in a greenhouse. She’s able to monitor them for symptoms and see if and when the plants wilt or even fail to germinate. The researchers are also monitoring onions in storage to see what effect the options they’re testing have at that stage. In the spring, the researchers will team up with a local farmer to do field tests.
Eventually, from the pool of 10 biocontrol options they’re investigating, the one with the most promise for real-world use will emerge. With the Acadia team planning for at least one more year of work on the project, the potential benefit to the local agricultural industry is immense.
Another aspect of the project involves finding a molecular diagnostic tool to pick up evidence of the pathogen in soil samples based on its unique DNA sequence, allowing growers to predict which fields are best for onions and which should be avoided.
For researchers like Walker and students like Bunbury-Blanchette, as well as the six other students who have also been working on the project, the opportunity to work with local producers on an industry problem is a unique one.
“They’ve been great to work with because they work really collaboratively,” said Walker, adding that the experience also lends an interesting and accessible narrative to the Acadia team’s academic work. “Applied research makes it easy to tell the story of why what you’re doing is important.”