Effects of fluorescent Pseudomonas spp. isolated from mushroom cultures on Lecanicillium fungicola Roeland L. Berendsen a,⇑ , Stefanie I.C. Kalkhove b , Luis G. Lugones b , Johan J.P. Baars c , Han A.B. Wösten b , Peter A.H.M. Bakker a a Plant–Microbe Interactions, Department of Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands b Molecular Microbiology, Department of Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands c Plant Breeding, Plant Research International, Droevendaalsesteeg 1 , 6708 PB Wageningen, The Netherlands highlights " Bacterial strains were isolated from mushroom cultures. " Pseudomonas spp. were dominant and screened for in vitro antagonism of L. fungicola. " In vitro, L. fungicola is sensitive to competition for iron and antibiosis. " None of the antagonistic strains effectively controlled dry bubble disease. " The insensitivity of dry bubble disease to biological antagonism is discussed. graphical abstract article info Article history: Received 14 May 2012 Accepted 30 July 2012 Available online 7 August 2012 Keywords: Lecanicillium fungicola Agaricus bisporus Mushroom pathogen Antagonistic bacteria Pseudomonas Dry bubble disease abstract Dry bubble disease, caused by Lecanicillium fungicola, is a serious economic problem in the cultivation of the white button mushroom. Biological control of the disease would meet the mushroom industry’s efforts to minimize the use of chemicals. A total of 160 bacterial strains were isolated from colonized cas- ing and screened for in vitro antagonism of L. fungicola. Fifty-three isolates inhibited L. fungicola in vitro. Using BOX-PCR, the 53 antagonistic isolates were grouped in 18 unique genotypes. Further characteriza- tion based on the 16S rDNA identified all isolates as Pseudomonas spp. Using previously characterized Pseudomonas isolates and their mutants it was determined that L. fungicola is sensitive to both sidero- phore-mediated competition for iron and production of antibiotics. However, when tested for disease suppression, none of the Pseudomonas spp. strains isolated from colonized casing effectively controlled dry bubble disease. The insensitivity of dry bubble disease to direct biological antagonism and the impli- cations for biological control of mushroom diseases are discussed. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Lecanicillium fungicola (Preuss) Zare and Gams (synonyms: Ver- ticillium fungicola (Preuss) Hassebrauk, Verticillium malthousei (Pre- uss) Ware) causes dry bubble disease and is a serious and economically important problem in commercial production of the white button mushroom, Agaricus bisporus. Depending on the time point of infection, disease symptoms can vary. Small necrotic lesions on the caps of the fruiting bodies develop when mush- rooms are infected late in development. Infections at earlier time points lead to partially deformed fruiting bodies called stipe blow-out or totally deformed and undifferentiated masses of mushroom tissue, the so called dry bubble (North and Wuest, 1993). Annual costs of L. fungicola infections for mushroom growers are estimated at 2–4% of the total revenue. Control of 1049-9644/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.biocontrol.2012.07.012 ⇑ Corresponding author. Fax: +31 30 253 2837. E-mail address: r.l.berendsen@uu.nl (R.L. Berendsen). Biological Control 63 (2012) 210–221 Contents lists available at SciVerse ScienceDirect Biological Control journal homepage: www.elsevier.com/locate/ybcon