Bacterial canker of hazelnut (Corylus avellana L.) in Sardinia (Italy): occurrence of Pseudomonas syringae strains.

Surveys carried out since the end of 1998 in Sardinia, (countries of Tonara, Aritzo, Belvì and Tiana; province of Nuoro), allowed to ascertain severe die-backs in hazelnut (Corylus avellana L.) orchards. Longitudinal cankers were observed along the twigs and the main branches. Sometimes, the death of the whole tree was also pointed out. The hazelnut cultivars recently introduced from the Italian peninsula such as Tonda Gentile delle Langhe was more attacked than the local cultivars which showed only cankers. Isolations were performed in spring and autumn from symptomatic tissues. Fluorescent colonies on King’s et al. medium B revealed their pathogenicity to hazelnut, pepper, tomato and pear seedlings, and, to a lesser extent, to apricot, peach and lemon fruits. The isolates did not incite any sign of disease to lilac and apple. The performing of biochemical and physiological tests allocated the isolates in the Pseudomonas syringae group Ia sensu Lelliott et al. Slide agglutination and ELISA tests carried out using an antiserum towards P. syringae pv. syringae gave positive result. The isolates were also compared with other pseudomonads associated with hazelnut decline by means of repetitive PCR using BOX primer. The comparison revealed that the isolates obtained in Sardinia were different from P. avellanae, the causative agent of hazelnut decline in northern Greece and central Italy, and from the P. syringae pv. syringae strains previously isolated in Sardinia from local cultivars of C. avellana. The isolates herein studied resemble the P. syringae population recently found in Piedmont and isolated from Tonda Gentile delle Langhe. Other studies are under way to confirm these findings.