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Isolation of potential new biocontrol strains from the blossom of Malus trilobata against the fire blight pathogen Erwinia amylovora

Background: Fire blight is a contagious disease that affects members of the Rosaceae family, caused by the bacteria Erwinia amylovora, which invades apple trees via their blossom.

Methods: In this study, using culture dependent methods, we isolated for the first time the microorganisms colonizing the blossom of the wild apple tree, Malus trilobata, in Lebanon. A total of 94 strains from the blossoms of trees originating from two regions, Ain Zhalta reserve and Dhour EL Choueir, were isolated. Genetic analysis of the strains revealed a wide and interesting variety of microorganisms quite different from those isolated from Malus domestica blossom. Direct and indirect inhibition assays of the isolates against E. amylovora were conducted.

Findings: While some strains belong to species known for their antibacterial activity, two new strains with interesting inhibitory activity against E. amylovora, have not been previously described. The first strain is a fungi, Saccothecium sp., inhibiting E. amylovora growth due to antimicrobial metabolite production and nutrient competition. As for the second strain, a bacterium, Mycolicibacterium sp., it inhibits E. amylovora growth via diffusible antimicrobial. In addition, novel strains potentially competing with E. amylovora for nicotinic acid and nicotinamide were identified such as Filobasidium sp., Rhodotorula sp. and Acinetobacter sp.

Conclusion: We report here two new isolates from the blossom of Malus trilobata with high potential of biocontrol activity against E. amylovora either via secondary metabolites production and/or by competition at nutrient level.

Author(s): Elie KHOURY 1, Antoine ABOU FAYAD2,3,4 , Dolla KARAM SARKIS5 , Mireille KALLASSY AWAD1*

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