The third and final day of the International Fruit Tree Association’s 68th annual conference in Rochester, New York, on Feb. 19 covered a lot of topics, including the postharvest disorder bitter pit, a recurring problem in Honeycrisp and other varieties.
Chayce Griffith, a graduate student and research assistant in Michigan State University professor Todd Einhorn’s lab, discussed some of the lab’s latest bitter pit findings.
Researchers have known for some time that calcium deficiency plays a role in bitter pit, but the Einhorn lab has shown that incidence of the disorder is related to fruit growth rate during a crucial period.
Bitter pit starts in the xylem, the vascular tissue that transports water and dissolved minerals throughout the fruit. Unlike other minerals such as potassium and magnesium, calcium can only move through the xylem. If the xylem breaks down, calcium can’t spread through the fruit, and bitter pit is more likely to develop, Griffith said.
In more susceptible varieties, xylem function gradually declines as the season progresses and eventually breaks down completely — and xylem can’t be repaired. So, the fruit is still growing but it isn’t getting the calcium it needs.
The earlier the breakdown, the more susceptible a cultivar is to bitter pit. In Honeycrisp, xylem breaks down between five and eight weeks after full bloom, a period of rapid growth, he said.
Keeping the xylem as functional as possible for as long as possible is critical to reducing bitter pit incidence. Scientists know that slowing fruit growth rate early in the season can help preserve xylem function, Griffith said, but more research is needed on the best ways to achieve it.
—by Matt Milkovich
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