Erwinia Its small size is accordant with its

Erwinia amylovora is a cause of fire blight disease in apple, pear, quince, blackberry, raspberry and many other wild and cultivated rosaceous ornamental plants (Vanneste, 2000). The disease creates sporadically, but it is highly destructive, especially to young fruit trees that may be killed instantly by infections that girdle the trunk or the rootstock.Erwinia amylovora is of great historical importance to phytobacteriologists in that it was the first bacterium clearly demonstrated to cause disease in plants shortly after the pioneering work of Pasteur and Koch on bacterial pathogens of humans and animals in the late 1800s (see Griffith et al., 2003 for the pioneering papers of Burrill, Arthur and Waite). Thus, E. amylovora is justifiably referred to as the ‘premier phytopathogenic bacterium’. Interestingly, the genome of E. amylovora is amongst the smallest of the plant pathogenic bacteria sequenced so far, at only 3.89 Mb (Sebaihia et al., 2010). Its small size is accordant with its lack of plant cell-degrading ways, which are frequent to most other phytopathogenic bacteria, e.g. cell walldegrading enzymes and low-molecular-weight poisonous substance. Its most important pathological tools seems to be part of the hrp pathogenicity island and the exopolysaccharides amylovoran and levan (Oh and Beer, 2005). The type III secreted proteins DspA/E and HrpN are necessary to pathogenicity (Bocsanczy et al., 2008), whereas about 20 additional proteins that secrete or modulate the expression of Hrp proteins also play a role. Amylovoran and levan are involved in biofilm formation and pathogenicity (Koczan et al., 2009). Genomes of several strains and species is closely related to E. amylovora have become available . Bioinformatic comparisons undoubtedly will reveal additional genetic bases for the virulence capability of the fire blight pathogen. HOW TO  TREATE ;Use of essential oils as pesticides or fungicides is safer than chemicals, but it requires plenty of the plant to be effective. Hence, finding the effective compounds of essential oils and their synthesis decreases the problem of preparing the natural compound. The antibacterial effect of Satureja hortensis L., Thymus vulgaris L. essential oils, and their major constituents were determined using the disc diffusion method. These essential  0ils prevented Erwinia amylovora growth (that causes fire blight disease). The essential oils were fractionated using preparative column chromatography (Silica column) and all fractions were tested for their antibacterial activities on this bacterium. Effective fractions were analyzed by GC-MS. Results showed that carvacrol is the effective compound in Satureja hortensis essential oil and has strong antibacterial effect. The effective compounds in Thymus vulgaris essential oil are thymol and carvacrol. Thymol and carvacrol showed a strong antibacterial effect against E. amylovora in the disc diffusion method. These compounds prevented the growth of E. amylovora in sucrose and nutrient agar media(Khodaverdi et al ., 2010).