Rarity of Pseudomonas agarici on Edible Mushrooms Associated with Susceptibility to Biological Competition.

Taxonomically diverse Pseudomonas species induce bacterial blotch of edible mushrooms around the world. Pseudomonas tolaasii, [Pseudomonas gingeri], and Pseudomonas agarici are dominant mycopathogenic pseudomonads in mushroom production farms. In this study, among 216 mycopathogenic bacterial strains isolated from edible mushrooms in Iran, 96 strains were identified as Pseudomonas spp., while only three strains were preliminarily identified as P. agarici. Multilocus sequence analysis showed that only one strain (FH2) authentically belonged to P. agarici, while the other two strains either belonged to [P. gingeri] or represented a unique phylogenetic clade. The three strains also differed from each other in phenotypic characteristics e.g., production of fluorescent pigment and the reaction to tolaasin produced by P. tolaasii. Pathogenicity assays under controlled environment showed that the symptoms induced by authentic P. agarici were far less severe than those caused by the predominant species P. tolaasii. Furthermore, co-inoculation of P. agarici with three bacterial pathogens that are prevalent in Iran on mushroom caps i.e., P. tolaasii, Ewingella americana and Mycetocola sp. resulted in the development of combined symptoms representing characteristics of both pathogens. Antibiosis assay showed that tolaasin-producing strains of P. tolaasii could inhibit the growth of P. agarici, while tolaasin-negative strains of the same species were unable to do so. This led us to the hypothesis that the inhibitory effect of P. tolaasii on P. agarici is driven by tolaasin production in the former species. This inhibitory effect also associated with the rarity of P. agarici in natural conditions.

Ewingella americana: An Emerging Multifaceted Pathogen of Edible Mushrooms.

Mycopathogenic bacteria play a pivotal role in the productivity of edible mushrooms grown under controlled conditions. In this study, we carried out a comprehensive farm survey and sampling (2018 to 2021) on button mushroom (Agaricus bisporus) farms in 15 provinces in Iran to monitor the status of bacterial pathogens infecting the crop. Mycopathogenic bacterial strains were isolated from pins, stems, and caps, as well as the casing layer on 38 mushroom farms. The bacterial strains incited symptoms on mushroom caps ranging from faint discoloration to dark brown and blotch of the inoculated surfaces. Among the bacterial strains inciting disease symptoms on bottom mushroom, 40 were identified as Ewingella americana based on biochemical assays and phylogeny of 16S rRNA and the gyrB gene. E. americana strains differed in their aggressiveness on mushroom caps and stipes, where the corresponding symptoms ranged from deep yellow to dark brown. In the phylogenetic analyses, all E. americana strains isolated in this study were clustered in a monophyletic clade closely related to the nonpathogenic and environmental strains of the species. BOX-PCR-based fingerprinting revealed intraspecific diversity. Using the cutoff level of 73 to 76% similarity, the strains formed six clusters. A chronological pattern was observed, where the strains isolated in 2018 were differentiated from those isolated in 2020 and 2021. Taken together, due to the multifaceted nature of the pathogen, such a widespread occurrence of E. americana on mushroom farms in Iran could be an emerging threat for the mushroom industry in the country.

Rhizosphere Bacterial Composition of the Sugar Beet Using SDS-PAGE Methodology

ABSTRACT The rhizosphere zone has been defined as the volume of soil directly influenced by the presence of living plant roots or soil compartment influenced by the root. During the growing season of 2014, the rhizobacteria of 23 sugar beet plants sampled from 12 sites in the west and north west of Iran were inventoried. Using a cultivation-dependent approach, a total of 217 bacteria were isolated from the rhizosphere. The bacterial isolates were tentatively grouped and documented based on polyacrylamide gel electrophoresis of whole-cell proteins and were found to represent 43 different protein electrotypes. The majority of the fingerprint types were found only on a single occasion. Fifty-nine percent of the strains belonged to the five bacterial species and identified as Stenotrophomonas maltophilia, Pseudomonas fluorescens, Pseudomonas aeruginosa, Stenotrophomonas rhizophila and Serratia marcescens. Minor occurring fingerprint types were identified as Flavobacterium spp, Erwinia spp, Acetobacter spp, Agrobacterium spp, Enterobacter spp, Aeromonas spp and Bacillus spp.