For fruit producers, compromised skin appearance — like a bruise on an apple, for example — usually results in reduced market value. Targeting the reasons behind fruit disorders and diseases could help producers modify growing strategies and increase profits.
A newly released study, published in the American Society for Horticultural Science, found that “skin spots,” a disorder commonly found in Elstar and Golden Delicious apples, usually appear on the apples’ skin after the fruit has been transported or moved from storage.
In the study, corresponding author Mortiz Knoche explains that skin spot comprises patches of small, brownish spots that are caused by the death of individual epidermal and hypodermal cells underlying microcracks in the fruit cuticle.
Previous reports suggested that apples are susceptible to skin spot if they are poorly colored, from dense canopies, grown in wet years, or have been harvested late. But the research team investigated the relationship between surface water on fruit, the formation of microcracks in the fruit cuticle, and the severity of the skin spot and found that most skin spots and microcracks were already present by harvest time and before storage.
Analyses showed that increasing fruit surface wetness by overhead sprinkling helped increase both the severity of the spotting and the cuticle microcracking.
“The severities of both increased significantly during storage. Surface wetness between 14 and 44 days after first bloom had no effect on the severity of skin spot compared with dry, control fruit but markedly increased the surface area percentage of the skin that was russeted,” Knoche said.
Essentially, the scientists confirmed there is no skin spotting or russeting when the apple surfaces are kept dry.
This is a photo of an 'Elstar' apple with skin spot. The disorder was linked to late season wetness on the fruit. (Photo courtesy of Moritz Knoche)