Proceedings of the 7th International Conference on Mushroom Biology and Mushroom Products (ICMBMP7) 2011 Section: Pests and Diseases 452 RECENT ADVANCES ON BACTERIAL DISEASES OF CULTIVATED MUSHROOMS IACOBELLIS NICOLA SANTE Dipartimento di Biologia, Difesa e Biotecnologie Agro Forestali, Università degli Studi della Basilicata Viale Ateneo Lucano, 10, 85100 Potenza Italy Iacobellis@Unibas.it ABSTRACT Recent studies on bacterial diseases of cultivated mushrooms in southern Italy showed that brown blotch of Agaricus bisporus and the yellowing of Pleurotus ostreatus, caused by Pseudomonas tolaasii, are actually complex diseases since, besides P. tolaasii, which may be considered the main causal agent of the above diseases, also P. reactans and not yet characterised fluorescent pseudomonads appear to participate to the expression of the diseases symptoms. Furthermore, P. reactans appears to be the causal agent of P. eryngii yellowing. Strains of P. tolaasii produce tolaasin I and II (Tol I and Tol II) and five minor analogs called tolaasins A-E). Tolaasins are involved in the pathogen virulence causing membranes lysis through biosurfactant activity and transmembrane ion channel formation for which a barrel-stave mechanism has been proposed. Furthermore, strains of P. tolaasii produce in vitro an array of volatile substances which are apparently involved in the virulence of the producers and the pathogen/mushrooms interaction. Strains of P. reactans produce the White Line Inducing Principle (WLIP) which causes the brown discoloration of A. bisporus tissues though at lesser extent than tolaasin I. The loss of WLIP production by avirulent morphological variants of P. reactans supports its role in the pathogen virulence. The formation of avirulent variants in the cultures of P. reactans strains appears to be responsible for the attenuation/loss of virulence and this may tentatively explain why the pathogenicity of P. reactans was neglected and/or not well understood in the past. A comparative evaluation of Tol I and WLIP on blood red cells and artificial lipid vesicles demonstrated a detergent-like mechanism for WLIP. REP-PCR analysis showed that P. reactans, on the contrary of P. tolaasii, is not a genetically uniform group. Keywords: Agaricus bisporus; Pleurotus ostreatus; Pleurotus eryngii; Pseudomonas tolaasii; Pseudomonas “reactans”. INTRODUCTION World production of cultivated mushrooms is growing and, in fact, from 1,500,000 tons in 1985 [1] it rose to 3,206,738 tons according to FAO data in 2007, with China as the first world producer followed by United States of America and several European Countries. The Italian annual production of cultivated mushrooms is about 90.000 tons [2], and the most cultivated mushroom is the button mushroom Agaricus bisporus (Lange) Imbach followed by the oyster mushroom Pleurotus ostreatus (Jacq. ex Fr) Kum and a few other mushroom species including the king oyster mushroom (cardoncello) P. eryngii (DC ex Fr). Cultivated mushrooms are attacked by a number of fungal and bacterial diseases that may cause significant production losses [3, 4, 5]. These occurrences are due to environmental conditions to which the mushroom cultivation is generally carried out. Though reliable data in this respect are not available, it is believed that the bacterial diseases are the main causes of product loss [3]. Several bacterial diseases of cultivated mushrooms of the genus Agaricus and Pleurotus are caused by fluorescent pseudomonads [5]. This is the case of brown blotch