Partenaires et organisations internationales
(Anglais)
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AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GR, HR, HU, IE, IL, IT, LT, LV, MK, NL, NO, PL, PT, RO, RS, SE, SI, SK, TR, UK
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Résumé des résultats (Abstract)
(Anglais)
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Fire blight, caused by Erwinia amylovora, is the single most serious threat to apple and pear production in Switzerland and Europe, in both orchards and old-growth landscape trees. Biological control via application of natural antagonistic microorganisms is currently the best alternative to antibiotics. Pantoea agglomerans (syn. = Erwinia herbicola) are among the most adapted antagonists to pome fruit for disease control. Several strains are at different stages of commercial registration for fire blight biocontrol in North America and New Zealand. Efficacy data confirms the high potential benefit of these products. Currently, registration in Europe is hampered by the listing of P. agglomerans as a biosafety level 2 agent based on clinical reports of pathogenicity. This project made great strides to clarify the biosafety realities behind this classification, and to provide a solid basis of scientific knowledge for regulatory decision making. Comparative genetic and phenotypic analysis was completed using a large collection of clinical and biocontrol strains. Molecular phylogenetic analysis (e.g., 16S rDNA; gyrB; pagRI) and newly developed MALDI-TOF MS protein profiling demonstrated a serious problem of misidentification of most clinical strains as P. agglomerans. Total genomic DNA analysis with fAFLP on a sensu stricto group identified a biocontrol-specific band not found in the clinical type strain or any other clinical strain. Unique biocontrol metabolites (e.g., pantocins) were also found to be potential markers. Bioassays with plants (apple, pear) showed that biocontrol strains have higher beneficial activity against plant diseases. Virulence tests using a newly developed phytoparasitic nematode model, murine, and haemolytic models demonstrated that not only do biocontrol strains show no evidence of virulence potential, neither do any clinical strains. Fundamental problems with the biosafety assumption of pathogenicity based solely on clinical reports were identified. Clinical reports refer largely to polymicrobial isolations with no confirmation of causality for P. agglomerans, contrary to the cornerstone of pathology - Koch's postulate. In fact, our virulence tests suggest they do not have pathogenic potential. Identification of isolates is frequently erroneous. Clinical isolates are rarely preserved to properly evaluate these isolates, and contrary to standard microbiological practice. Thus, evidence for lack of pathogenicity has been delivered and critical flaws in clinical reports have been revealed, warranting regulatory re-evaluation of this potentially beneficial group of bacteria for biological control.
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