Phenotypic traits of fluorescent pseudomonads causing bacterial blotch of Agaricus bisporus mushrooms and other mushroom-derived fluorescent pseudomonads

Abstract

Fluorescent pseudomonads isolated from diseased Agaricus bisporus mushrooms (bacterial blotch), internal mushroom stipe tissue, and reference cultures were subjected to an array of determinative tests including a recently described white-line reaction. All isolates recovered from fresh, healthy mushroom tissue proved to be in the range of Pseudomonas putida or P. fluorescens types, producing oxidase and arginine dehydrolase with growth at 4 °C, while failing to cause soft rot of potato tissue or to blotch mushroom tissue, produce pigment on King's medium A, or to grow at 41 °C. Significantly, 68 cultures identified as P. fluorescens belonged to biotype G, 35 having a similar nutritional profile, which suggests a unique identity. Six of eight P. tolaasii reference cultures were pathogens but their placement into a defined biotype is speculative. Dissociative tendencies were commonplace with all isolates. The white-line test was employed with P. tolaasii reference cultures. Those which caused blotch had an R reaction, white-line test. Of 90 isolates from diseased tissue, 76 were indicators (I) and 14 nonreactors (NR). The white-line reaction occurred in King's medium B as described and on three additional substrates. Hundreds of isolates responded as expected with either an I or an R reaction even though stored for up to 2 years. Reliable assessment of P. tolaasii pathogenicity using excised pileus tissue required three replicates read following 24 h incubation.