Effect of nutrient amendment and osmoadaptation in blossom colonizationof pome fruit trees and efficacy of biocontrol of Ervinia amylovora


Abstract: The efficacy of Pseudomonas fluorescens EPS62e in the biocontrol of Erwiniaamylovora, the causal agent of fire blight disease, depends on the colonization of plant surfaces.A procedure to increase cell survival in the phyllosphere was developed consisting of nutrientamendment, osmoadaptation and their combination. Glycine and Tween80 were selected asappropriate substrates to add as nutrient complements in the formulation of EPS62e, bothnutrients are used by EPS62e and not by E. amylovora strains. Colonization and survival ofEPS62e on detached flowers studies were performed in controlled environmental conditions. Athigh RH population levels of EPS62e remains stable and were not affected by the treatments.Whereas at low RH, population levels of EPS62e fall down and an enhancement of their survivalin the nutrient amended and osmoadapted was observed. Population dynamics of EPS62e in fieldconditions were assessed by real-time PCR and CFU-counting methods. Values obtained by bothmethods were quite correlated and population levels of EPS62e decreased to steady-state andreach values around 106 CFU/blossom in the standard application and were significantly higher,around 107 CFU/blossom, in nutrient amended also in osmoadapted treatment and especially inthe combined treatment. Finally, the efficacy in the control of fire blight infections under fieldconditions was also assessed and the best treatment was the combination of nutrient amendmentwith the osmoadaptation.

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