which step in the ripening process each measures and that step’s sensitivity to ethylene. In climacteric fruit, such as apples, bananas and tomatoes, ripening is associated with increased ethylene production. Starch clearance, which is ethylene sensitive, occurs early in the sequence of events in the ripening process. The DA meter measures the loss of chlorophyll which occurs later in the sequence. Jason Johnston and colleagues in New Zealand suggested that ethylene response curves may shift for fruit harvested at different maturities, for different cultivars and for fruit exposed to different conditions during growth. Based on their suggestions, the relationship between the DA and starch clearance index values would be expected to vary between apple varieties and different stages of maturity of each. Bill Wolk of BC Tree Fruits has been doing work closely related to Toivonen’s. They plan to work together to develop similar protocols.

“We want to be absolutely sure before recommending that growers switch from using the starch index to a DA meter,” Toivonen said.

Assuming eventual recommendation

of the meter, at the current cost of approximately $4,000 it may prove to be beyond the budget of many producers. “I would see it as a tool for field services with BC Tree Fruits, others

who provide consulting services to independent growers, or large independent growers. On top of the cost, it is important that the user be properly trained on how to collect the data,” Toivonen said.

British Columbia FRUIT GROWER • Summer 2017


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