Deterioration of dried French prunes is characterized by macerated, wet, sticky areas on the fruit surface and by skin that tends to slip with the slightest pressure. This condition is most often the result of fresh-fruit decay caused by the fungus Rhizopus stoioni/er. The mold is also known as “bread mold fungus” or the “whiskers disease” on fresh market stone fruits, strawberries, and almond hulls. Prune growers have called this type of deterioration of dried prunes “box rot” and have suspected it to be responsible for serious losses.

This research was supported in part by the California Prune Advisory Board. The authors thank employees of Sun Diamond for their technical help in assessing deterioration and Mr. Clarence Paine for drying experimental fruit at the Fairfield dehydrator. The technical advice from Dr. T. Kosuge and technical assistance of Bill Manji, Elaine Bose, Steve Sibbett, Steve Koike, and Bob Hanowell are appreciated.