Sweet potato research yields new Canadian option

Radiance variety provides short growing season with top yield production

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The future is looking sweet for a Canadian variety of succulent orange-fleshed potato that’s a winter dinner table staple.

Valerio Primomo, a Vineland Research Station scientist and vegetable breeder spoke about the development of Radiance, a variety of sweet potato with a short growing season during the Ecological Farmers Association of Ontario’s 2020 virtual conference.

Why it matters: An Ontario-developed variety of sweet potato can help expand the market for Ontario growers.

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The Vineland research program, which included a partnership with Louisiana State University, spent the better part of the last decade testing sweet potato seeds for one that would perform well in Canada.

Primomo said they screened approximately 3,000 seeds supplied by LSU, propagating about 500 to 600 a year in the greenhouse and using the small tubers to cull varieties at an early stage based on the colour of flesh they produced.

“Our target was a deep orange colour,” said Primomo. “That’s what the primary market is looking for, the main retailers Loblaw and Sobeys, that’s probably 80 per cent of the market.”

The remaining 20 per cent is aimed at the Asian market and consumers looking for unique colours, such as cream-coloured flesh with purple skin or peach colours.

Retailers like access to unique varieties because they can charge a premium price for them, said Primomo.

In the second stage, five to 10 cuttings from the top 100 or 200 varieties were transplanted into the field where they were propagated and again narrowed down based on uniform elliptical shape, size and skin colour.

Only varieties meeting those criteria were cured and stored as seed potatoes for the third stage where they were sprouted out, and used in larger field-testing of three replications of about 20 plants in Ontario and a site in Nova Scotia.

Slips from the top five selections were trialled across Canada, along with Covington and Orleans as controls, to assess how climate, soil variation and growing conditions would affect yield and to test for sugar and dry matter content at 11 trial sites across Prince Edward Island, Nova Scotia, Quebec, Ontario, Manitoba and British Columbia between 2014 and 2017.

Primomo said in the 2015 Canadian yield trials, Radiance exhibited excellent yields against its competitors, including the commercial varieties leading to it being chosen for further development over the next three years.

“Yield is very crucial for commercial growers,” said Primomo. “Radiance actually out-performed Covington and Orleans year after year.”

Traditionally, organic and commercial growers have favoured Covington or Orleans strains, which have a growing season of 120 and 131 days respectively, he said.

Radiance has a growing season of 111 days and ticks two major boxes: it’s ideal for the shorter growing season of Canada and it can be harvested in time for Canadian Thanksgiving.

“In addition to that, when harvested Radiance has a deep orange colour,” he said. “Whereas Covington, when you harvest it much earlier, it still has this imperfect colour…it’s a yellow and an orange, which is what retailers are not looking for.”

Radiance again outperforms the others in single plant yields by at least 20 per cent, with uniform colour, shape, size and preferred flavour compared to the other commercial varieties, he said.

Radiance with its rich orange flesh was chosen eight out of 10 times during Loblaw’s study on consumer preferences.

The challenge in Canada is now that there is a breeding program, who will produce slips for commercial use?

Primomo said the partnership with LSU gave them access to the university’s resources for virus index material but they won’t produce the slips.

Most producers won’t go past the G3 generation before returning to virus index material through tissue culture to acquire a virus clean material for slip production because seeds begin to accumulate viruses year-over-year.

Primomo is optimistic there are greenhouse propagation opportunities in Canada and to that end Vineland produced a manual — Sweet Potato Slip Production in Canadian Greenhouses, to assist those interested in propagating slips.

“We found it’s important to establish a slip production industry here in Canada,” he said. “And some of the Ontario growers actually prefer this.”

Primomo said there is a cost associated with shipping slips from North Carolina and sometimes the product arrives late or runs the risk of not arriving at all. That hasn’t happened yet, he said, however, COVID-19 restrictions came closest to shutting down shipments and many producers received their slip materials late.

Radiance has been commercially available for three years, he said.

About the author

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Diana Martin

Diana Martin has spent more than two decades in the media sector, first as a photojournalist and then evolving into a multi-media journalist. Five years ago she left mainstream media and brought her skills to the agriculture sector. She owns a small farm in Amaranth, Ont.

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