| Summary: | 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.
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