Variability of the 16S-23S rRNA gene internal transcribed spacer in Pseudomonas avellanae strains

The 16S-23S rRNA gene internal transcribed spacer region (ITS1) from 34 strains of Pseudomonas avellanae and some strains of Pseudomonas syringae pathovars was amplified and assessed by restriction fragment length polymorphism (RFLP) using 10 restriction enzymes. In addition, the ITS1 region of four representative P. avellanae strains was sequenced and compared by the neighbour-joining algorithm with that of P. syringae pathovars. Two main groups of P. avellanae strains were observed that did not correlate with their origin. The ITS1 region sequencing revealed a high similarity with the P. syringae complex. One group of P. avellanae strains showed high similarity to P. s. pv. actinidiae and P. s. pv. tomato; another group showed similarity with P. s. pv. tabaci and P. s. pv. glycinea. Two strains clustered with P. s. pv. pisi. The difficulties to unambiguously classify the strains associated with hazelnut decline in Greece and Italy are discussed.