EFFECT OF WOUND MOISTURE ON THE BIOCONTROL BY CANDIDA-OLEOPHILA OF GRAY MOLD ROT (BOTRYTIS-CINEREA) OF APPLE

The effect of moisture on the growth and performance of Candida oleophila, an antagonistic yeast considered for the biocontrol of storage diseases of fruits, was studied with various indirect methods on wounds of mature apples stored at 18 degrees C. Typically, introduced populations of C. oleophila increased about 32 times during the initial 24 h following their introduction to fresh wounds, and remained stable afterwards. Air-drying the wound surface for 24 h before application of C. oleophila significantly reduced growth of the yeast. Conversely, fresh wounds wetted with water four times daily had higher populations on days 2 and 4, but not on day 1. The incubation of fresh wounds at two different relative humidity levels (58 and 95%) had no effect on yeast growth. Candida oleophila effectively reduced the development of gray mold rot caused by Botrytis cinerea when applied to wounds two hours before the pathogen. The biocontrol of gray mold rot was more effective when C. oleophila was applied to fresh wounds rather than one-day-old wounds. However, one-day-old wounds were less susceptible to infection by B. cinerea than were fresh wounds. It is concluded that moisture becomes rapidly limiting for yeast growth as the wound surface dries, and possibly causes population levels to stabilize after the initial increase 24 h following yeast introduction to fresh wounds. For this reason, the application of C. oleophila should follow the occurrence of wounding as soon as possible in order to obtain optimal disease control during storage.