the study of biological control of pear fire blight caused by erwinia amylovora by some antagonistic bacteria

fire blight is an important worldwide disease of pome fruits that control of which through antibiotics is particularly critical. in this case and in absence of another chemical methods, the biocontrol methods can be considered as the best alternative for control of fire blight. in this study efficacy of 5 isolates of antagonistic bacteria belongs to pseudomonas fluorescens and pantoea agglomerans on fire blight pathogen, erwinia amylovora was investigated in laboratory assays and field experiments. for this purpose antagonist bacteria and the pathogen were isolated from infected and healthy tissues of pear and apple trees in qazvin and tehran provinces. these bacteria were identified by morphological, biochemical and physiological properties. to investigate the efficacy of these antagonists on the growth of fire blight pathogen, laboratory assays were performed such as chloroform test and inhibition zone (antibiosis). all antagonists showed significantly effect on e. amylovora growth in laboratory assays. a field experiment also performed to study of antagonistic effect on blossoms blight of pear trees. in orchard trial, analysis showed that these antagonists significantly reduce the blight on pear blossoms. these treatments decreased the incidence of disease by  55.3%-  86.4% in field experiments. these findings indicated that these five antagonists are effective in biological control of fire blight in both laboratory and orchard situations.