Effect of CaCl(2) and Various Wild Yeasts From Plant Origin on Controlling Penicillium expansum Postharvest Decays in Golden Delicious Apples

The biocontrol potential of four wild yeast strains (Meyerozyma guilliermondii – strain YS-1, Meyerozyma caribbica – strain YS-3, Cryptococcus albidus – strain YS-4, and Cryptococcus sp. – strain YS-5) against Penicillium expansum was studied in vivo (on Golden Delicious apples). The test yeasts were applied to the fruits alone as well as in combination with 2% CaCl(2). Treated apples were stored at room temperature (~21°C) for up to 2 weeks or under refrigeration (3°C) for up to 2 months. Candida oleophila was used as positive biocontrol agent. Biocontrol activities were expressed as percentages of lesion size reduction caused by the test yeasts or by test yeasts + CaCl(2) as compared with decays on apples treated with P. expansum alone. All strains tested during this study showed some degree of biocontrol activity against P. expansum. When the test yeasts were applied alone, they effected moderate pathogen inhibition reducing the decay size by 28% to 52% at day 7 and 11% to 27% at day 14 of incubation at room temperature. When the treated apples were stored at 3°C, lesion size reduction was between 48% and 63% after 1 month and 24% to 41% after 2 months of incubation. Addition of CaCl(2) to yeast suspensions facilitated much higher pathogen inhibition. At room temperature, lesion size reduction ranged between 74% and 77% during the first week. After 2 weeks of incubation, decays on yeast + CaCl(2)-treated apples were still substantially smaller (49%-73% lower) than those on apples treated with P. expansum alone. At refrigeration, lesion size reduction ranged between 76% and 92% in the first month of storage and between 75% and 87% after 2 months of incubation. Decay incidence was 75% to 100% in apples stored at room temperature and 30% to 85% in those kept under refrigeration. The inhibitory activities of the wild yeast strains were similar to those exhibited by C. oleophila for the most part. These strains, when combined with CaCl(2), showed high potential as biocontrol agents against P. expansum on stored apples.