Biochemical and physiological aspects of brown blotch disease of Agaricus bisporus

Pseudomonas tolaasii is a bacterium endemic to the compost beds where commo n mushroom (Agaricus bisporus) is cultivated. Under some environmental cond itions still not well-determined, but influenced by temperature and relativ e humidity, the bacterium can become pathogenic and provoke the brown blotc h disease. This review describes the interaction between P. tolaasii and A. bisporus that results in the appearance of brown spots on the mushroom cap s, typical symptoms of the disease. Firstly, P. tolaasii is studied, the ch anges in pathogenicity are explained, the compounds that provoke the damage are enumerated as well as Various experimental methods to identify the pat hogenic form of the bacteria. Secondly, mechanisms involved in the formatio n of the brown colour on the A. bisporus caps upon infection are briefly me ntioned, taking into account the enzymes that catalyse the reaction, their mechanism, substrates and reaction products. Afterwards, a detailed descrip tion of the infection process is presented step by step, starting by the ch emotactical attraction, fixation, secretion of the toxins, membrane breakdo wn, effect of the toxin on mushroom polyphenol oxidases and on the discolou ration reaction. A possible mechanism of infection is hypothesised at the m olecular level. Finally, the strategies tested until now to control the dis ease are discussed. (C) 1999 Federation of European Microbiological Societi es. Published by Elsevier Science B.V. All rights reserved.