Psedomonas tolaasii, the causal agent of brown blotch on buttom mushroom is one of the most delimiting factor in Agaricus bisporus production. To assess the antibacterial activity of essential oil / extracts of chamomile (Chamaemelum nobile) on P. tolaasii, many diseased samples were collected from mushroom producing centers of Tehran province and screened for bacterial agents. In total 14 local bacterial cultures were selected. The suspected P. tolaasii isolates were characterized and pathogenicity tests were fulfilled. Likewise, chamomile plant samples were obtained from Shiraz city. Extractions were made by macerating 3 g/ml from each sample in both water and three organic solvents (acetone, methanol and ethanol). The essential oil was extracted by hydro-distillation method using the device Clevenger. The antibacterial effects of EO, water and organic extractions and four antibiotics i.e. tetracycline, erythromycin, gentamycin and penicillin were evaluated on both NA and KB agar media. Among the four serial dilutions of essential oil(1,0.1,0.01.0.001 gr/ml) ,one conc. Extracts(0.3 gr/ml) and four antibiotics at concentrations of 0.01,1and 10 mg/ml, the most efficient results were obtained with methanol extract and pure EO under laboratory condition. GC/MS analysis showed the high percentage (58.8%) of a-bisabolol oxide A in plant compounds spectra indicating its significant role in antibacterial activity of Chamaemelum nobile plants.
