Morphological, phenotypic and pathogenicity characters of the bacteria causing blotch on button mushroom in Chaharmahal-o-Bakhtiari province

Bacterial blotch is one of the most important diseases of white button mushrooms (Agaricus bisporus) which results in consumer demand loss at the marketplace. The main aim of this study was identification of bacteria causing blotches in some mushroom cultivation centers of Chaharmahal-o-Bakhtiari province. Mushrooms with cream to brown or black blotches on caps and stems were collected and bacterial isolation was done. The phenotypic characteristics of isolates were investigated. Pathogenicity tests were performed on excised tissue blocks, on intact caps and by injection to stipe of A. bisporus. Some of pathogenic isolates were identified as Pseudomonas tolaasii based on phenotypic characters and detection by Pt1A/1D primer sets in PCR. The others were identified as Ewingella americana based on phenotypic characters, pathogenicity on stipe and the partial sequence of 16S rDNA region. Based on pathogenicity tests, P. tolaasii isolates were divided in two distinct groups: high pathogenic and low/non-pathogenic. These two groups differed in some phenotypic characters such as type and color of colony, HR on geranium and potato rot test. To the authors'' knowledge, it is the first description of low/non- pathogenic isolate of P. tolaasii and the first report of E. americana from Chaharmahal-o-Bakhtiari province.