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Pseudomonas syringae pv. coryli, the Causal Agent of Bacterial Twig Dieback of Corylus avellana

First and second authors: C.R.A.-Istituto Sperimentale per la Frutticoltura, Via di Fioranello, 52, 00040 Ciampino, Roma, Italy; third and fourth authors: C.R.A.-Istituto Sperimentale per la Patologia Vegetale, Via C.G. Bertero, 22, 00156 Roma, Italy; fifth author: Dipartimento di Protezione delle Piante, Università degli Studi di Sassari, Via E. De Nicola, 07100 Sassari, Italy; sixth author: Department of Plant Sciences, University of Oxford, South Park Road, OX1 3RB Oxford, U.K.; seventh and eighth authors: Central Science Laboratory, Sand Hutton, Yo41 1LZ York, U.K.; ninth and tenth authors: Dipartimento di Virologia e Biotecnologie, Istituto Zooprofilattico Sperimentale delle Regioni Lazio e Toscana, Via Appia Nuova, 1411, 00178 Roma, Italy; and eleventh author: Department of Bacteriology, Plant Protection Service, 6700 HC, Wageningen, The Netherlands

Thirty-eight bacterial strains isolated from hazelnut (Corylus avellana) cv. Tonda Gentile delle Langhe showing a twig dieback in Piedmont and Sardinia, Italy, were studied by a polyphasic approach. All strains were assessed by fatty acids analysis and repetitive sequence-based polymerase chain reaction (PCR) fingerprinting using BOX and ERIC primer sets. Representative strains also were assessed by sequencing the 16S rDNA and hrpL genes, determining the presence of the syrB gene, testing their biochemical and nutritional characteristics, and determining their pathogenicity to hazelnut and other plants species or plant organs. Moreover, they were compared with reference strains of other phytopathogenic pseudomonads. The strains from hazelnut belong to Pseudomonas syringae (sensu latu), LOPAT group Ia. Both fatty acids and repetitive-sequence-based PCR clearly discriminate such strains from other Pseudomonas spp., including P. avellanae and other P. syringae pathovars as well as P. syringae pv. syringae strains from hazelnut. Also, the sequencing of 16S rDNA and hrpL genes differentiated them from P. avellanae and from P. syringae pv. syringae. They did not possess the syrB gene. Some nutritional tests also differentiated them from related P. syringae pathovars. Upon artificial inoculation, these strains incited severe twig diebacks only on hazelnut. Our results justify the creation of a new pathovar because the strains from hazelnut constitute a homogeneous group and a discrete phenon. The name of P. syringae pv. coryli is proposed and criteria for routine identification are presented.