The Pseudomonads Associated with Bacterial Canker and Decline of Hazelnut (Corylus avellana L.)

Abstract

Bacterial canker and decline, caused by Pseudomonas avellanae, is seriously damaging the hazelnut cultivation in central Italy and in northern Greece. Surveys carried out in the other main areas of cultivation in Italy ascertained the presence of strains similar to P. syringae pv. syringae van Hall. In these areas severe epidemics of bacterial decline were not observed. The taxonomic relationships among the pseudomonads associated with hazelnut decline and the other plant pathogenic Pseudomonas spp. has been established by using a collection of more than 200 strains by means of ARDRA, repetitive PCR fingerprints using ERIC, REP and BOX primer sets with UPGMA analysis, 16S rRNA gene sequencing as well as by analysis of fatty acid methyl ester and whole-cell protein profiles, and by pathogenicity tests. P. avellanae belongs to genomospecies 8, sensu Gardan et al., which also includes P. s. pv. theae and P. s. pv. actinidiae. P. avellanae shows a pathogenicity restricted to Corylus avellana and is very virulent to hazelnut germplasm. The P. s. pv. syringae-like strains isolated from hazelnut fit well with the main features of the pathovar, including the presence of the syrB gene. A population found in Piedmont appears different from the P. s. pv. syringae-like strains when analysed by fatty acid profiling. In addition, the strains do not have the syrB gene and show a very restricted pathogenicity. This population might be a new pathovar within the P. syringae complex.