Scientists at Oregon State University want to find out if preharvest sprays with calcium or salt can improve the shipping quality of sweet cherries.
Dr. Yan Wang, postharvest physiologist at the Mid-Columbia Research and Extension Center in Hood River, hopes ultimately to find the best ways to apply calcium and sodium chloride (salt) to minimize postharvest splitting, pitting, stem browning, and acid loss for Skeena, Sweetheart, Lapins, and Regina cherries.
During the Washington Tree Fruit Research Commission’s cherry research review in November, Wang explained that cherries with a high calcium content tend to ship better and have better storage potential, and cherries that are susceptible to pitting, such as Van, normally have a lower calcium content than cherries that resist pitting, such as Regina.
For the calcium tests, he will apply calcium chloride at rates of 0, 0.2 percent, and 0.4 percent each week between fruit set and harvest (six times).
He’ll also test a two-application treatment at straw stage and one week before harvest, and a two-application treatment two weeks and one week before harvest.
The calcium will be applied with a pressurized hand-gun sprayer, with four single-tree replications per treatment.
To identify the best source of calcium, he’ll compare calcium chloride, calcium nitrate, and calcium propionate sprayed at a 0.2 percent rate two weeks and one week before harvest.
In the second and third years of the project, he’ll then test the optimal spray protocol in grower orchards on Skeena, Sweetheart, Lapins, and Regina cherries. Fruit from the orchard tests will be harvested, hydrocooled, passed through a test packing line, packed in a modified-atmosphere packages, and stored for two to three weeks.
Wang will look at the effect of the treatments on fruit growth, fruit size, yield, and return bloom, as well as on fruit quality (firmness, size, soluble solid content, acidity, anthocycanin and total antioxidant capacity) and decay.
Wang said that researchers working with other plants have found that preharvest sprays of sodium chloride (salt) can induce formation of cuticle lipids, which make the skin less permeable to water. On cherries, it could potentially reduce moisture loss, minimizing postharvest splitting and pitting and keeping the stems green.
Wang’s preliminary studies in 2013 with Lapins and Regina showed that sodium chloride sprays on whole trees can improve cherry quality, but he said the effectiveness will depend on application rates and timings.
Wang plans to test sodium chloride applications at four rates (0, 30, 60, and 120 parts per million) applied every week between fruit set and harvest (six times).
After determining the best rate, he will test two more treatments—applications at straw color stage and then one week before harvest, and applications two and one week before harvest.
As with the calcium tests, in the second and third years of the project, he will test what appears to be the optimal rate and frequency in grower orchards. •