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

Abstract

BackgroundAgaricus bisporus is the most widely cultivated and consumed mushroom worldwide. Pseudomonas ‘gingeri’ is the only pathogenic causative agent of ginger blotch in A. bisporus. Current research on mushroom pathogenic biotoxins is limited to P. tolaasii, which causes brown blotch, while understanding of P. ‘gingeri’ is lacking. Therefore, identifying the toxins produced by P. ‘gingeri’ and evaluating their toxicity on A. bisporus is essential for understanding its pathogenic mechanisms.ResultsA pathogenic bacterium isolated from fruiting bodies of A. bisporus with ginger blotch was identified as P. ‘gingeri’, and its main toxin identified as 2',4',6'‐trihydroxyacetophenone monohydrate, also known as monoacetylphloroglucinol (MAPG). Its first known extraction from a mushroom pathogen is reported here. MAPG at 250 μg/mL significantly inhibited the host's mycelial growth, increased branching, caused the structure to become dense and resulted in folds appearing on the surface. An MAPG concentration of 750 μg/mL MAPG leds to mycelial death. P. ‘gingeri’ had high MAPG production in medium containing 0.1 mol/L of either glucose and mannitol (4.30 μg/mL and 1.85 μg/mL, respectively), and mycelia were inhibited by 69.6% and 41.1%, respectively. The MAPG content was significantly lower in other carbon source media.ConclusionThis work first provides a detailed description of the structure and virulence of the P. ‘gingeri’ biotoxin, which has implications for understanding its pathogenic mechanism and for exploring precise control strategies for A. bisporus ginger blotch disease, such as the development of MAPG inhibitory factors.This article is protected by copyright. All rights reserved.

Elucidating the role of monoacetylphlorogulcinol in the pathogenicity of Pseudomonas ‘gingeri’ against Agaricus bisporus

“…The differences among various treatments were assessed using SPSS 27 software based on analysis of variance (ANOVA). 9 All numerical values for the results were reported as mean ± standard deviation (SD). Graphs were created using GraphPad Prism software.…”

“…2.1 Sample treatment and collection MAPG (92.3 mg) was extracted from the fermentation broth of P. 'gingeri' using a previously described method and stored at −20 °C. 9 The preparation of the toxin solution and peeling of mushroom caps followed the procedures outlined in previous studies. 9 Mushroom caps were peeled and treated with 20 μL of 125, 250, and 500 μg/mL MAPG, resulting in final doses of 2.5, 5, and 10 μg of MAPG.…”

“…9 The preparation of the toxin solution and peeling of mushroom caps followed the procedures outlined in previous studies. 9 Mushroom caps were peeled and treated with 20 μL of 125, 250, and 500 μg/mL MAPG, resulting in final doses of 2.5, 5, and 10 μg of MAPG. A solvent containing 6.5% dimethyl sulfoxide (DMSO) served as the control (CK).…”

“…Each mushroom was divided into five inoculation sites, which were appropriately labeled. 9 Six mushrooms were used for each treatment, and all treatments were placed in sterile culture dishes. The dishes were then incubated at 20 °C under 85-90% humidity for 24 h. Tissue samples from the inoculation sites of the mushrooms (approximately 40 mg per site) were immediately frozen in liquid nitrogen and stored at −80 °C for subsequent analysis.…”

“…[4][5][6] P. 'gingeri' is the sole pathogenic factor responsible for the ginger blotches on A. bisporus, with the blotch size increasing as the mushroom fruiting body matures, leading to severe symptoms. [7][8][9] Inoculating 1 × 10 4 CFU of P. 'gingeri' per gram of casing soil (wet weight) can trigger an outbreak of the disease. 7 Moreover, this pathogen can cause ginger discoloration during storage, further compromising the quality of A. bisporus.…”