Control of blue mold of apples by preharvest application of Candida sake grown in media with different water activity

Unmodified and low water activity (a(w))-tolerant cells of Candida sake CPA-I applied before harvest were compared for ability to control blue mold of apples ('Golden Delicious') caused by Penicillium expansum under commercial storage conditions. The population dynamics of strain CPA-I on apples were studied in the orchard and during storage following application of 3 x 10(6) CFU/ml of each treatment 2 days prior to harvest. In the field, the population size of the unmodified treatment remained relatively unchanged, while the population size of the low-a(w)-modified CPA-1 cells increased. During cold storage, the populations in both treatments increased from 10(3) to 10(5) CFU/g of apple after 30 days, and then declined to about 2.5 x 10(4) CFU/g of apple. In laboratory studies, the low-a, tolerant cells provided significantly better disease control as compared with the unmodified cells and reduced the number of infected wounds and lesion size by 75 and 90%, respectively, as compared with the nontreated controls. After 4 months in cold storage, both unmodified and low-a(w)-tolerant cells of C, sake were equally effective against P. expansum on apple (>50% reduction in size of infected wounds).