Colonization of Apple Wounds by Naturally Occurring Microflora and Introduced Candida oleophila and Their Effect on Infection by Botrytis cinerea during Storage

The colonization of apple wounds by natural microflora and an introduced antagonist, Candida oleophila, was followed at 4 and 18°C. Fresh wounds had initial populations of yeasts, filamentous fungi, and bacteria ranging between 102 to 103 cfu/wound. Colonization at 18°C by the natural microflora was rapid with fungal and bacterial populations increasing to about 104 to 105 and 106 cfu/wound, respectively, within the first 2 to 4 days and changing little afterwards. Aureobasidium pullulans and yeasts (mainly Sporobolomyces roseus) were the dominant fungal wound invaders, while species of Erwinia, Gluconobacter, and Pseudomonas were the most common bacteria isolated. At 4°C, little difference was noted in the composition of the microflora in wounds except for the absence of Gluconobacter sp. and lower populations of A. pullulans. The colonization process was more gradual at this temperature, reaching populations of about 5 × 104 and 105 cfu/wound by day 20 for fungi and bacteria, respectively. Populations of introduced C. oleophila applied at levels of 105 or 106 cfu/wound increased by about one log within 1 day at 18°C and 4 days at 4°C and stabilized thereafter. Introduced C. oleophila outnumbered the natural colonizers, forming a film of cells on the wound surface. Some of the main components of the natural microflora (Erwinia sp., A. pullulans, and S. roseus) coinoculated into wounds with C. oleophila in equal proportions did not have any effect on the establishment of C. oleophila on wounds. However, their introduction to wounds reduced the incidence of gray mold rot at 4°C after 23 days but not 30 days. Erwinia sp. and S. roseus coinoculated on wounds with C. oleophila did not affect the performance of C. oleophila in the biocontrol of gray mold rot, but A. pullulans improved it. Thus, the presence of the naturally occurring microflora of apple wounds does not interfere with the biocontrol of storage rot by C. oleophila and, in some cases, may even be beneficial.