Pseudomonas syringae pv. coryli (pv. nov.), the causal agent of bacterial twig dieback of Corylus avellana L

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 repetitivesequence-
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.