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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-1 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-1 on apples were studied in the orchard and during storage following application of 3 × 10⁶ 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 10³ to 10⁵ CFU/g of apple after 30 days, and then declined to about 2.5 × 10⁴ CFU/g of apple. In laboratory studies, the low-a_w-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 non-treated 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).