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The research was carried out in a mushroom farm, College of Agriculture, Tikrit University, five microelements were tested, namely, iron, manganese, molybdenum, Zinc and boron, and a combination of these five elements, in addition biological agent, Pseudomonas fluva, to control of the brown blotch disease caused by pathogenic bacteria Pseudomonas tolaasii on the edible mushroom Agaricus bisporus. The results showed that all the treatments of the micro-elements as well as the growth-promoting bacteria P. fluva led to a significant superiority in the higher productivity of A. bisporus fruit bodies compared to the treatment of the pathogenic bacteria P. tolaasii only. The highest productivity of the fruit bodies was reached in the treatment of the elements mixture with beneficial bacteria P. fluva, which amounted to 2675.6 g / 20 kg compost, with a biological efficiency of 79.59%. At the level of elements, molybdenum (without bacteria) and with P. fluva outperformed the other elements by recording the highest productivity of 2533.2 and 2527.4 g / 20 kg compost with a biological efficiency of 80.26 and 79.0% , respectively, compared to the lowest productivity of 1404.3 g / 20 kg compost with a biological efficiency of 45.7 in the pathogenic bacteria P. tolaasii. The results showed that all treatments of the elements individually and in combination led to a significant decrease in the infection rate, no infection rate was recorded in the treatments of the elements mixture with the presence of pathogenic bacteria P. tolaasii with beneficial P. fluva compared to the highest infection rate of 32% in the treatment of P. tolaasii.

• Susceptibilities of Pleurotus ostreatus to brown blotch disease (BBD) are analyzed. • Morphological and structural changes exist between BBD resistant/sensitive strains. • Molecular mechanism of resistance to BBD in P. ostreatus are elucidated. Pleurotus ostreatus is among the most frequently cultivated and consumed mushrooms worldwide. However, brown blotch disease (BBD) caused by the pathogenic bacterium Pseudomonas tolaasii severely impacted its quality and production. In this study, we selected the BBD-resistant strain HP36 and the BBD-sensitive strain HP801 from twenty P. ostreatus strains. Obvious morphological and ultrastructural differences between the two strains were observed at 12 h, 24 h and 72 h after Ps. tolaasii infection. At 24 h, a large area of brown-yellow blotch appeared on the pileus of HP801 and with Ps. tolaasii almost completely overgrowing the pileus. In contrast, few bacteria and no obvious symptoms were found on the pileus of HP36. At 72 h, the cell wall and nuclei and mitochondria were seriously damaged in HP801 while no obvious deformity was observed in HP36. In the infected pileus, transcriptome analysis identified 153 and 2,189 differentially expressed genes for HP36 and HP801 respectively. Further bioinformatic analysis showed that genes encoding oxidation–reduction enzymes, cell wall degradation, heat shock proteins and protein kinases were significantly more differentially expressed after infection in HP801 than in HP36. The results suggested that Ps. tolaasii infection impaired the capacities of HP801 for stress sensing and signal transduction, oxidation resistance and protein modification, resulting in cellular and organelle damages. Together, our results provided insights into the molecular mechanism of resistance to BBD in P. ostreatus and suggested potential strategies for controlling BBD and improving mushroom production and quality by selecting and breeding the resistant strains. [Display omitted] [ABSTRACT FROM AUTHOR]

The natural antimicrobial peptide, epsilon-poly- l -lysine (ε-PL), is widely acknowledged as a food preservative. However, its potential in managing bacterial brown blotch disease in postharvest edible mushrooms and the associated mechanism remain unexplored. In this study, concentrations of ε-PL ≥ 150 mg L−1 demonstrated significant inhibition effects, restraining over 80% of growth and killed over 99% of Pseudomonas tolaasii (P. tolaasii). This inhibition effect occurred in a concentration-dependent manner. The in vivo findings revealed that treatment with 150 mg L−1 ε-PL effectively inhibited P. tolaasii -caused brown blotch disease in Agaricus bisporus (A. bisporus) mushrooms. Plausible mechanisms underlying ε-PL's action against P. tolaasii in A. bisporus involve: (i) damaging the cell morphology and membrane integrity, and increasing uptake of propidium iodide and leakage of cellular components of P. tolaasii ; (ii) interaction with intracellular proteins and DNA of P. tolaasii ; (iii) inhibition of P. tolaasii -induced activation of polyphenol oxidase, elevation of antioxidative enzyme activities, stimulation of phenylpropanoid biosynthetic enzyme activities and metabolite production, and augmentation of pathogenesis-related protein contents in A. bisporus mushroom s. These findings suggest promising prospects for the application of ε-PL in controlling bacterial brown blotch disease in A. bisporus. [Display omitted] • ε-PL significantly inhibited the growth of Pseudomonas tolaasii in vitro. • ε-PL effectively reduced bacterial brown blotch disease in postharvest A. bisporus. • ε-PL disrupted membrane integrity and led to cellular leakage of P. tolaasii. • ε-PL could likely disturb intracellular DNA and proteins of P. tolaasii. • ε-PL induced disease resistance against P. tolaasii in postharvest A. bisporus. [ABSTRACT FROM AUTHOR]

The bacterial pathogen Pseudomonas tolaasii severely damages white button mushrooms by secretion of the pore-forming toxin tolaasin, the main virulence factor of brown blotch disease. Yet, fungus-associated helper bacteria of the genus Mycetocola (Mycetocola tolaasinivorans and Mycetocola lacteus) may protect their host by an unknown detoxification mechanism. By a combination of metabolic profiling, imaging mass spectrometry, structure elucidation, and bioassays, we found that the helper bacteria inactivate tolaasin by linearizing the lipocyclopeptide. Furthermore, we found that Mycetocola spp. impair the dissemination of the pathogen by cleavage of the lactone ring of pseudodesmin. The role of pseudodesmin as a major swarming factor was corroborated by identification and inactivation of the corresponding biosynthetic gene cluster. Activity-guided fractionation of the Mycetocola proteome, matrix-assisted laser desorption/ionization (MALDI) analyses, and heterologous enzyme production identified the lactonase responsible for toxin cleavage. We revealed an antivirulence strategy in the context of a tripartite interaction that has high ecological and agricultural relevance. [ABSTRACT FROM AUTHOR]

Brown blotch disease (BBD) caused by Pseudomonas tolaasii is one of the most devastating diseases of Pleurotus spp. worldwide. Breeding for resistant strains is the most effective method for controlling BBD. To identify resistant germplasm for BBD management, 97 strains comprising 21 P. cf. floridanus, 20 P. ostreatus, and 56 P. pulmonarius were screened by two different methods; namely, inoculation of the pathogen on the mushroom pileus (IMP) and on the spawned substrate (IMSS) under controlled conditions. Out of the 97 strains screened, 22 P. pulmonarius, and four P. cf. floridanus were moderately resistant to BBD using the IMP method. Eleven P. pulmonarius, six P. cf. florida, and one P. ostreatus strains were highly resistant to BBD using the IMSS method. All of the 97 strains showed varying degrees of susceptibility using the IMP method, but eight strains were completely resistant using the IMSS method. Combining these two methods, five strains were highly resistant (four P. pulmonarius and one P. cf. floridanus) and 11 were moderately resistant (eight P. pulmonarius and three P. cf. floridanus). The resistance sources to P. tolaasii identified in P. pulmonarius and P. cf. floridanus could be used for further breeding of Pleurotus spp.

Brown blotch disease of mushroom caused by Pseudomonas tolaasii , often results of severe damage to mushroom tissues. In this study, the biocontrol mechanisms mediated by endofungal bacteria Pseudomonas sp. De1, Bacillus sp. De3, Pseudomonas sp. Bi1 and Pantoea sp. Ma3 previously isolated from wild growing mushrooms against Pseudomonas tolaasii Pt18 were demonstrated. Our results provide evidence that all bacterial strains can colonize mycelia of Agaricus bisporus. All endogungal bacteria except Pseudomonas sp. Bi1 contained one or more genes encoding antibiotic production. The non-volatile compounds of endofungal bacteria significantly inhibited the biofilm formation by P. tolaasii Pt18. Results showed that all strains except Pantoea sp. Ma3 are capable of detoxify tolaasin, a major virulence factor produced by P. tolaasii Pt18. We also showed that all endofungal bacteria tested were able to significantly decrease the browning symptoms of pretreated-mushroom caps compared to inoculated caps with P. tolaasii alone. AbPPO3 gene expression levels in mycelia and fruiting bodies of A. bisporus significantly increased after P. tolaasii Pt18 inoculation. Our findings indicated that The relative expression level of AbPPO3 gene decreased in the mushroom mycelia and fruiting bodies pretreated with Pantoea sp. Ma3 and Pseudomonas sp. Bi1 strains, and the levels were significantly lower than mushroom tissues treated with P. tolaasii Pt18 alone. Overall, the findings presented in this study revealed the efficacy of the selected endofungal bacteria in biocontrol activity against P. tolaasii and the possible use of these strains as a safe microbial agents in mushroom brown blotch disease management. • The non-volatile compounds of endofungal bacteria significantly inhibited the biofilm formation by P. tolaasii. • Endofungal bacteria belongs to Pseudomonas, Bacillus and Pantoea genus significantly reduced mushroom brown blotch symptoms. • Bacillus and Pseudomonas strains detoxify tolaasin produced by Pseudomonas tolaasii under in vivo conditions. • The relative expression level of AbPPO3 gene decreased in the mushroom tissues pretreated with endofungal bacteria. [ABSTRACT FROM AUTHOR]

Brown blotch disease (BBD) caused by Pseudomonas tolaasii is one of the most devastating diseases of Pleurotus spp. worldwide. Breeding for resistant strains is the most effective method for controlling BBD. To identify resistant germplasm for BBD management, 97 strains comprising 21 P. cf. floridanus, 20 P. ostreatus, and 56 P. pulmonarius were screened by two different methods; namely, inoculation of the pathogen on the mushroom pileus (IMP) and on the spawned substrate (IMSS) under controlled conditions. Out of the 97 strains screened, 22 P. pulmonarius, and four P. cf. floridanus were moderately resistant to BBD using the IMP method. Eleven P. pulmonarius, six P. cf. florida, and one P. ostreatus strains were highly resistant to BBD using the IMSS method. All of the 97 strains showed varying degrees of susceptibility using the IMP method, but eight strains were completely resistant using the IMSS method. Combining these two methods, five strains were highly resistant (four P. pulmonarius and one P. cf. floridanus) and 11 were moderately resistant (eight P. pulmonarius and three P. cf. floridanus). The resistance sources to P. tolaasii identified in P. pulmonarius and P. cf. floridanus could be used for further breeding of Pleurotus spp. [ABSTRACT FROM AUTHOR]