Bacterial Brown Pit, a New Disease of Edible Mushrooms Caused by Mycetocola sp.

Abstract

From September to December 2018, commercial button mushroom (Agaricus bisporus) farms in central Iran were surveyed to monitor the causal agent(s) of browning and blotch symptoms on mushroom caps. In addition to dozens of pseudomonads (i.e., Pseudomonas tolaasii and Pseudomonas reactans), six slow-growing gram-positive bacterial strains were isolated from blotched mushroom caps. These bacteria presented as creamy white, circular, smooth, nonfluorescent, and shiny colonies with whole margins resembling members of Microbacteriaceae (Actinobacteria). All of the actinobacterial strains were aggressively pathogenic on cut cap surface of two edible mushrooms (i.e., A. bisporus and Pleurotus eryngii), inducing brown pit symptoms 48 h postinoculation. The strains did not induce symptoms on the vegetables tested (i.e., carrot, cucumber, and potato), and they did not affect the growth of mycelium of tested plant-pathogenic fungi (i.e., Acremonium sp., Fusarium spp., and Phytopythium sp.). Phylogeny of 16S ribosomal RNA and multilocus sequence analysis of six housekeeping genes (i.e., atpD, dnaK, gyrB, ppK, recA, and rpoB) revealed that the bacterial strains belong to the actinobacterial genus Mycetocola spp., whereas the species status of the strains remains undetermined. Mushroom-associated Mycetocola species were previously reported to be capable of detoxifying tolaasin, a toxin produced by P. tolaasii, whereas the strains isolated in this study did not show tolaasin detoxification activities. Altogether, this is the first report of a mushroom disease caused by an actinobacterial species, and “bacterial brown pit” was assigned as the common name of the disease.

Lessons on fruiting body morphogenesis from genomes and transcriptomes of Agaricomycetes

“…Agaricomycete fruiting bodies (mushrooms) are, due to the concentration of biomass, attractive targets of predators, parasites and pathogens. Accordingly, these structures are known to be subject to grazing by slugs, to infestations with larvae of phorid and sciarid flies and to infections by bacteria and molds ( Wood et al 2004 , Krivosheina 2008 , Lakkireddy et al 2020 , Hamidizade et al 2020 ). Since mushrooms are the sexual reproduction organs and a considerable investment in terms of resources and energy, Agaricomycetes have evolved several strategies for the protection and defence of these structures ( Künzler 2018 ).…”

Ginger blotches on Agaricus bisporus due to monoacetylphloroglucinol production by the pathogen Pseudomonas ‘gingeri’

“…Mushroom ginger blotch samples were collected from mushroom farms in Guangxi, China, to isolate pathogenic bacteria. Using the method described by Hamidizade et al ., 19 spotted mushroom tissues were rinsed three times with sterile water on an ultra‐clean bench. After air drying, tissue (approximately 5 × 5 mm) from the onset and disease‐health junction was taken and placed in 2‐mL sterile Eppendorf tubes to which 1 mL of sterile water was added.…”

Bacterial ring rot of potato caused by Clavibacter sepedonicus: A successful example of defeating the enemy under international regulations

“…When typical ring rot symptoms and oozing are observed on potato tubers, the disease can readily be confirmed by direct application of gram-staining or/and a serological test of the tuber exudates, in which a positive result is the presence of gram-positive bacterial cells or specific antigen, respectively (Manzer & Slack, 1979). The colony colour and pigmentation on solid media, for example YPGA, NBY agar, and YDC, is a useful diagnostic characteristic for coryneform plantpathogenic bacteria (Davis, 1986;Hamidizade et al, 2020;Osdaghi et al, 2020b;Vidaver, 1982). Despite all the other plant-pathogenic coryneform bacteria, C. sepedonicus is usually nonpigmented on solid media (Carlson & Vidaver, 1982).…”