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Postharvest Pathology and Mycotoxins

Effect of Inoculum Concentration and Salt Solutions on Biological Control of Postharvest Diseases of Apple with Candida sp.. R. J. McLaughlin, Research plant pathologist, United States Department of Agriculture, Agricultural Research Service, North Atlantic Area, Appalachian Fruit Research Station, Kearneysville, WV 25430; M. E. Wisniewski(2), C. L. Wilson(3), and E. Chalutz(4). (2)(3)Research plant pathologists, United States Department of Agriculture, Agricultural Research Service, North Atlantic Area, Appalachian Fruit Research Station, Kearneysville, WV 25430; (4)Research plant pathologist, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel 50250. Phytopathology 80:456-461. Accepted for publication 18 October 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1990. DOI: 10.1094/Phyto-80-456.

Two osmotolerant strains (87 and 101) of the yeast, Candida sp., were tested for ability to reduce lesion development in Golden Delicious apple after challenge with 10⁵ or 10⁴ conidia per milliliter of the postharvest pathogens Botrytis cinerea and Penicillium expansum. Lesion size and frequency of Botrytis rot were significantly less in fruit pretreated with aqueous suspensions of strains 87 and 101 (10⁷ and 10⁸ colony-forming units [cfu]/ml) as compared with controls pretreated with water. Significant, but marginal, reduction of Penicillium rot was observed in treatments with these yeasts at 10⁸ cfu/ml. Biological control of Botrytis rot was enhanced when wounds were treated with strain 87 at 10⁷ cfu/ml in 2% (w/v) aqueous solutions of CaCl₂, KCl, and CaCO₃, as compared with aqueous suspensions of the strain alone. Salt solutions applied to wounds without yeast cells did not reduce rot. The ability of the salt solutions to enhance control with yeasts was not related to the osmotic potential of the solutions. Calcium chloride was the most effective salt. Yeast strains differed slightly in their response to calcium chloride; a 1% concentration enhanced biocontrol with strain 87, whereas a 2% concentration was necessary to enhance control with strain 101. Calcium chloride facilitated control of Botrytis rot with yeast populations as low as 10⁶ cfu/ml. Decay due to Penicillium expansum also was significantly reduced when fruit were treated with strains 87 and 101 in the presence of calcium chloride.