POSTHARVEST DISCOLORATION OF THE CULTIVATED MUSHROOM AGARICUS-BISPORUS CAUSED BY PSEUDOMONAS-TOLAASII, P-REACTANS, AND P-GINGERI

A postharvest discoloration of the cultivated mushroom Agaricus bispor us 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. 'reac tans'), were phenotypically like P. fluorescens biovar V, and fit desc riptions of P. tolaasii, Pathotype B strains caused pitted, yellow-bro wn, sometimes slimy lesions on mushrooms, formed no 'white line' react ions, were phenotypically like P. fluorescens biovars III and V, and f it descriptions of P. 'gingeri'. Pathotype C strains caused mild, ligh t-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 pat hotypes including both pathogenic and nonpathogenic strains of P. 'rea ctans' with distinguishing phenotypic or chemical characteristics. Cel lular Fatty acid analysis suggested pathogenic strains of P. 'reactans ' were more similar to P. tolaasii and P. 'gingeri' than to saprophyti c strains of P. fluorescens, and nonpathogenic strains were more simil ar to saprophytic P. fluorescens than to P. tolaasii or P. 'gingeri'.