Molecular characterization of Pseudomonas from Agaricus bisporus caps reveal novel blotch pathogens in Western Europe

Tanvi Taparia,John G Elphinstone,Jan Van Der Wolf,Ralph Noble,Edward Haynes,Marjon Krijger

doi:10.1186/s12864-020-06905-3

Abstract

BackgroundBacterial blotch is a group of economically important diseases affecting the cultivation of common button mushroom, Agaricus bisporus. Despite being studied for more than a century, the identity and nomenclature of blotch-causing Pseudomonas species is still unclear. This study aims to molecularly characterize the phylogenetic and phenotypic diversity of blotch pathogens in Western Europe.MethodsIn this study, blotched mushrooms were sampled from farms across the Netherlands, United Kingdom and Belgium. Bacteria were isolated from symptomatic cap tissue and tested in pathogenicity assays on fresh caps and in pots. Whole genome sequences of pathogenic and non-pathogenic isolates were used to establish phylogeny via multi-locus sequence alignment (MLSA), average nucleotide identity (ANI) and in-silico DNA:DNA hybridization (DDH) analyses.ResultsThe known pathogens “Pseudomonas gingeri”, P. tolaasii, “P. reactans” and P. costantinii were recovered from blotched mushroom caps. Seven novel pathogens were also identified, namely, P. yamanorum, P. edaphica, P. salomonii and strains that clustered with Pseudomonas sp. NC02 in one genomic species, and three non-pseudomonads, i.e. Serratia liquefaciens, S. proteamaculans and a Pantoea sp. Insights on the pathogenicity and symptom severity of these blotch pathogens were also generated.ConclusionA detailed overview of genetic and regional diversity and the virulence of blotch pathogens in Western Europe, was obtained via the phylogenetic and phenotypic analyses. This information has implications in the study of symptomatic disease expression, development of diagnostic tools and design of localized strategies for disease management.

Highlights

Bacterial blotch is a group of economically important diseases affecting the cultivation of common button mushroom, Agaricus bisporus
Pathogenicity of isolates 102 bacterial isolates were tested for their ability to cause bacterial blotch symptoms on fresh mushroom caps (Fig. 1). 6 out of the 17 strains that belonged to international culture collections could cause blotch symptoms
Out of the 85 bacterial isolates recovered from blotched mushroom tissue, 55 isolates caused mild to severe symptoms in the pathogenicity cap test

Summary

Introduction

Bacterial blotch is a group of economically important diseases affecting the cultivation of common button mushroom, Agaricus bisporus. The casing soil introduces pathogenic microbes into mushroom farms, including blotch causing Pseudomonas species [5,6,7]. The genus Pseudomonas is one of the most complex genera of Gram negative bacteria due to its large size of 114 species [8] They form a major proportion (~ 40%) of the total culturable bacteria obtained from casing soil in mushroom farms [9]. While some of these are essential for stimulating the pinning of button mushrooms (e.g. P_putida) [1, 10], others are detrimental to crop health (e.g. P_tolaasii) [11, 12]

Objectives

Methods

Results

Discussion

Conclusion