EVALUATION OF SOME BACTERIAL ANTAGONISTS FOR BIOLOGICAL CONTROL OF FIRE BLIGHT DISEASE
E. Gerami, N. Hassanzadeh, H. Abdollahi, A. Ghasemi, A. Heydari
Antagonistic activities of 120 epiphytic bacterial isolates against Erwinia amylovora were evaluated under laboratory and orchard conditions. Samples were collected at three stages of plant growth during 2009. The hosts were chosen from diseased and healthy pome fruit and stone fruit trees in Alborz, Isfahan and Neishabur regions of Iran. Two in vitro tests including antibiosis and immature fruit assay were performed to identify effective bacterial antagonists. Out of 21 strains, four representative strains encoded Kgh1, Abp2, E11 and E10 showed maximum growth inhibition, growth rate and stability in inhibition. Identification of four bacterial antagonists was confirmed by sequencing their 16S rDNA and performing common biochemical tests. These strains were identified as Pseudomonas fluorescens (E10), Pantoea agglomerans (Abp2), Pseudomonas putida (E11) and Serratia marcescens (Kgh1). Some complementary tests were then conducted to check their antagonistic activity against Erwinia amylovora on pear blossom. In all evaluation procedures, biocontrol effects of Pantoea agglomerans Abp2 and Pseudomonas fluorescens E10 were more promising than those afforded by Pseudomonas putida E11 and Serratia marcescens Kgh1. A one-year field experiment was also carried out on a partially susceptible domestic pear cultivar in an infested orchard in the Karaj region of Iran. The selected bacteria were applied twice at 20% and 80% of blooming. The results showed 46.9% disease occurrence in control plants, while the antagonistic bacteria reduced the disease between 23 and 60%. The field trial the most effective antagonist was P. agglomerans Abp2, while the least effective was S. marcescens Kgh1.