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Postharvest Pathology and Mycotoxins

Postharvest Discoloration of the Cultivated Mushroom Agaricus bisporus Caused by Pseudomonas tolaasii, P. ‘reactans’, and P. ‘gingeri’. J. M. Wells, U.S. Department of Agriculture, ARS, Eastern Regional Research Center, 600 East Mermaid Lane, Philadelphia, PA 19118; G. M. Sapers(2), W. F. Fett(3), J. E. Butterfield(4), J. B. Jones(5), H. Bouzar(6), and F. C. Miller(7). (2)(3)(4)U.S. Department of Agriculture, ARS, Eastern Regional Research Center, 600 East Mermaid Lane, Philadelphia, PA 19118; (5)(6)University of Florida, Gulf Coast Research & Education Center, Bradenton 34203; (7)Sylvan Foods, Inc., Worthington, PA 16262, Current address: 148 Holl Road, Cabot, PA 16023. Phytopathology 86:1098-1104. Accepted for publication 17 June 1996. 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, 1996. DOI: 10.1094/Phyto-86-1098.

A postharvest discoloration of the cultivated mushroom Agaricus bisporus in Pennsylvania was associated with three pathotypes of fluorescent pseudomonads. Pathotype A strains caused pitted, dark-brown blotches on mushroom caps, formed precipitates in agar (‘white line’ reactions) with Pseudomonas tolaasii strain ATCC 14340 (reclassified as P. ‘reactans’), were phenotypically like P. fluorescens biovar V, and fit descriptions of P. tolaasii. Pathotype B strains caused pitted, yellow-brown, sometimes slimy lesions on mushrooms, formed no ‘white line’ reactions, were phenotypically like P. fluorescens biovars III and V, and fit descriptions of P. ‘gingeri’. Pathotype C strains caused mild, light-brown discoloration on mushrooms with little tissue collapse, formed ‘white line’ reactions with P. tolaasii ATTC 33618 (type strain), had P. fluorescens biovar III and V phenotypes, and fit descriptions of P. ‘reactans’. Isolations from mushroom casing material yielded all pathotypes including both pathogenic and nonpathogenic strains of P. ‘reactans’ with distinguishing phenotypic or chemical characteristics. Cellular fatty acid analysis suggested pathogenic strains of P. ‘reactans’ were more similar to P. tolaasii and P. ‘gingeri’ than to saprophytic strains of P. fluorescens, and nonpathogenic strains were more similar to saprophytic P. fluorescens than to P. tolaasii or P. ‘gingeri’.