Honeycrisp apples are among the most popular apple varieties in the United States, and more Honeycrisp apple trees have been planted in recent years than any other variety. Honeycrisp apples are known to be very crunchy compared to other varieties, and partially for this reason, Honeycrisp apples are very susceptible to “Bitter Pit”.
This disorder is caused by Calcium deficiency in fruit. It appears as brown spots under the skin, but these spots typically do not become visible until weeks into storage. Apples may not show any symptoms at harvest or even after months in cold storage, but after a few days of storage at room temperature the brown spots can appear.
A recent study on Honeycrisp apples by Penn State researchers over three years showed that bitter pit is, indeed, caused by low calcium levels in the fruit peels. However, the researchers also observed that this disorder was more common in peels that contained high ratios of nitrogen, potassium and/or magnesium to calcium. This imbalance of minerals in the apples peels was determined to be very important in bitter pit development. Trees that grew fast and had high terminal shoot lengths were also observed to be more susceptible to this disorder.
In order to solve the problem of symptoms showing up during storage, researchers developed a procedure to determine whether or not apples are likely to develop bitter pit. For this test, researchers sampled apples from a harvest, dried their peels and ground them into a powder. This powder was analyzed for Calcium levels. Apples with low Calcium levels were determined to be highly likely to develop bitter pit. This test will help growers determine which apples can be stored safely and which apples should be sold immediately.
If growers are able so sample apples early in the season and determine their risk of bitter pit, they may be able to adjust their growing practices to prevent the disorder. Calcium nutrient sprays are helpful and usually help prevent the disorder. In some areas the prevalence of the disorder may be highly dependent on weather. Hot and dry conditions lead to higher susceptibility of this disorder, and in some weather conditions, Calcium sprays, might not completely solve the problem. A test like the one developed in this study would be very helpful for growers to plan their growing practices and help determine how they will sell, or market their fruit.
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