Biological Control of Fire Blight Disease Caused by Erwinia amylovora on Apple

Fire blight is a devastating bacterial disease of apple and pear trees in Turkey. In this study, biological control of fire blight disease caused by Erwinia amylovora was investigated by using 564 putative antagonistic bacterial and yeast isolates obtained from apple, pear and quince blossoms. Among 564 isolates obtained, 7 yeast and 92 bacterial isolates caused inhibition zones between 1.33 and 19.7 mm in Petri tests. Putative antagonist isolates also reduced the disease severity on immature pear slices by 11-78%, while they reduced the disease severity on flowering shoots by 8-58%. Suppression of fire blight disease development in an apple orchard (cultivar [cv.] "Gala" and "Golden Delicious") was studied by comparing two promising antagonistic bacterial isolates (PBAL10 and KAD3), two bioprotection products (Serenade Optimum, Bayer, Hillcrest, Auckland, New Zeland and Blossom Protect, BIO-FERM, Herzogenburg, Austria), copper fungicide and antibiotic on apple flowers. In the apple blossoms (cv. "Gala"), the copper fungicide had the greatest effectiveness (99.0%). Serenade SC reduced the disease by 95.0%. Bacterial isolate PBAL10 significantly reduce the disease severity by 89.5% and isolate KAD3 suppressed severity by 88.5%. Both bacterial isolates were more effective than commercial bioprotection product Blossom Protect (87.0%) and streptomycin sulphate (86%). In the "Golden Delicious" cultivar's blossoms, bacterial isolate PBAL10 (94.5%) and KAD3 (91.0%) suppressed blossom infections more effectively than Blossom Protect (89.5%), the copper product (77%) and streptomycin sulphate (91.5%). Bacterial isolates PBAL10 and KAD3 were identified as Bacillus mojavensis and Pseudomonas chlororaphis ssp. aurantiaca by MALDI-TOF MS. Thus, biological control with local antagonistic bacteria, Bacillus mojavensis and Pseudomonas chlororaphis ssp. aurantiaca has been considered to be an eco-friendly and useful approach for disease management in the apple blossom period.