Response of Pseudomonas tolaasii,the causal agent of mushroom brown blotch disease to the volatile compounds produced by endofungal bacteria

Volatile organic compounds (VOCs) produced by bacteria have significant potential to control phytopathogens. In this study, the VOCs produced by endofungal bacteria Pseudomonas sp. Bi1, Bacillus sp. De3, Pantoea sp. Ma3 and Pseudomonas sp. De1 isolated from wild growing mushrooms were evaluated in vitro for their antagonistic activity against Pseudomonas tolaasii Pt18, the causal agent of mushroom brown blotch disease. The gas chromatography–mass spectrometry (GC–MS) analysis revealed that strains Pseudomonas sp. Bi1, Pseudomonas sp. De1, Bacillus sp. De3 and Pantoea sp. Ma3 produced eight, sixteen, nine, and twelve VOCs, respectively. All antagonistic endofungal bacteria produced VOCs which significantly reduced brown blotch symptoms on mushroom caps and inhibited the growth of P. tolaasii Pt18 at the varying levels. Scanning electron microscopy revealed severe morphological changes in cells of P. tolaasii Pt18 following exposure to the VOCs of Pseudomonas sp. Bi1 and De1. Furthermore, The VOCs produced by endofungal bacteria significantly reduced swarming, swimming, twitching, chemotaxis motility and biofilm formation by P. tolaasii Pt18 cells, which are essential contributors to pathogenicity. This is to first report about the inhibition effects of VOCs produced by antagonistic bacteria on virulence traits of P. tolaasii. Our findings provide new insights regarding the potential of antibacterial VOCs as a safe fumigant to control mushroom brown blotch disease.

     

Role of CheY1 and CheY2 in the Chemotaxis of <Emphasis Type="Italic">A. tumefaciens</Emphasis> Toward Acetosyringone

Agrobacterium tumefaciens has a chemtaxis operon, which includes orf1, orf2, cheY1, cheA, cheR, cheB, cheY2, orf9, and orf10. In-frame deletions of cheY1 and cheY2 were constructed and the chemosensory behavior of the mutants was examined on swarm plates and in a chemotaxis assay toward acetosyringone. The cheY2 mutant (C1/delY2) showed impaired chemotactic capabilities in both swarming and chemotaxis assays. The effect of lacking CheY1 on chemotaxis is less severe than that of CheY2, under the conditions studied.     

Occurrence of Alfalfa Bacterial Stem Blight Disease in Kurdistan Province, Iran

During spring and summer of 2004 and 2005, a new disease of alfalfa was observed for the first time in some areas of the Kurdistan province in Iran. Symptoms were initially yellowed area on leaves, within which water‐soaked, irregular spots developed. These spots eventually coalesced to produce large necrotic areas. Symptoms on petiole and stem include water‐soaked lesions, which later turned brown. Gram negative and rod‐shaped bacteria were isolated from infected tissues. From the results of LOPAT tests (levan production, oxidase reaction, potato soft rot, arginine dihydrolase and tobacco hypersensitivity) and other phenotypic, biochemical and physiological properties investigated, the causal bacterium have been identified as Pseudomonas syringae pv. syringae. Pathogenicity of selected strains was confirmed by injecting a bacterial suspension into leaf tissue from the underside of leaves.