A Canadian research center is working to enhance local table grape growers' competitiveness by increasing the fruit's storability with the use of sulphur pads. 

A team at the Ontario-based Vineland Research and Innovation Centre has been working to adapt the pads that are already established in other parts of the world to the Canadian grape industry, which currently lacks sufficient post-harvest measures to extend the marketing window.

Vineland senior research technician Kimberley Cathline said the season for the Sovereign Coronation variety - a hybrid that is by far the most common in Ontario's Niagara Peninsular - currently ran from around early August to mid-October. However, the market at that time is often saturated with other produce.

The majority of the grapes are shipped to the eastern province of Quebec, with a large proportion starting in Ontario.

"Usually the fruit that comes off first goes to the fresh market and then they would generally try and store what came off later, but typically it would just last a week or two," Cathline told www.freshfruitportal.com.

"So now they want to do that post-harvest storage so they can market the grapes later in the season."

Cathline explained that much of the research that began in the 2013 harvest season had largely been a matter of adapting the pads to the Canadian climatic conditions and the growers' packing system.

"Sulphur is very important in storage, so we wanted to adapt that here to the Ontario climate," she said.

"The pads range in size, but a typical size is 10-13 inches by about 18 inches. Usually it’s going to all depend on the grower, but in general there’s some sort of master or final destination box container which usually contains many of the smaller sale containers or clamshells."

The pads, which were provided by Chilean company Infruta S.A., work by releasing sulphur dioxide when exposed to humidity in the air. The sulphur dioxide then inhibits mould and reduces stem browning until the active ingredient in the pads is depleted, thus making the grapes of marketable quality for longer.

"The two main factors that contribute to reduction of quality are stem browning, which is due to water loss, and the grey mould infection by Botrytis. So sulphur can help with both of those things," Cathline said.

"The problem with detritus is that it thrives at very lower temperatures, so even if you’re storing your grapes at -1°C, you can still have growth of Botrytis. It can still ruin your grapes in a couple of weeks."

In a recent study, Vineland scientists demonstrated that Coronation grapes could be successfully stored at -1°C to 0°C and 90 to 95% relative humidity for at least five weeks using dual release sulphur generating pads - a type of pad which allows a high concentration release for the first 24 hours followed by several months of slow release.

Other grapes used in the study that were stored with no sulphur treatment were said to be 'completely unmarketable' after three weeks.

Following the successful trials using the sulphur pads, the next stage of the research will be to see if room fumigation works with the grapes.

Cathline said a potential hurdle to fumigation was that the Sovereign Coronation variety was part of the Vitis labrusca grapevine species, which performs well in cooler climates but can be a lot more sensitive to sulphur than the much more common Vitis vinifera.

"So I wanted to see if the sulphur-generating pads were even going to work in the first place, because they have a much lower concentration than doing a room fumigation," Cathline said.

"We didn’t see any phytotoxicity [using the pads], and so we think ‘okay maybe now we can move ahead with trying to adapt fumigation to this market’. But it was positive to see that the Vitis labrusca was compatible with the sulphur pads.

"With sulphur there’s always that balance, so you want to get as high a concentration of sulphur as you can without damaging the grapes. Even normal grapes are going to show effects if you go too high with the concentration."

Cathline said she hoped to begin research with the fumigation method this autumn.

"This research was supported and funded by the Ontario Fresh Grape Growers Marketing Board, so the growers are directly involved. We try to only do stuff that is relevant to the industry," she said.

"They're showing interest in wanting to do fumigation, so we're hoping to put in a proposal this season and, if it’s accepted, to begin work with it in this growing season."

Photo: Coronation grapes, courtesy of the Ontario Fresh Grape Growers Marketing Board

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