Abstract :
At the beginning of October 1992 and 1993, healthy adult and young
trees of hazelnut, cultivars Tonda Gentile Romana and Nocchione,
were inoculated with a Pseudomonas syringae pv. avellanae strain
through leaf scars located midway from the tip of the twig. In adult
trees, the systemic migration and the population level of the pathogen
were monitored during autumn and wmter by means of weekly to
monthly isolation and countings. In young plants, the possible displacement
of the bacterium was checked in May by sampling different
sites of the plant. At each sampling, the presence of internal and external
symptoms was carefully assessed. During the 2-year study, the results
on migration and symptom development were consistent between the
cultivars. Until the end of February. P.s. pv. avellanae colonized for
approximately 45 mm, only the trait of the twig below the site of
inoculation. At that time the population level ranged, in the farthest
point reached by the pathogen, from 4.1 to 5.6 = lOʹcfu 3 mm of twigportion.
During March the pathogen was recovered from the tip of the
twig. The first sign of disease was noticed in November as brown
discolouration of the epidermis near the site of inoculation as well as
internal necrosis ofthe vascular tissue. In young trees. P.s. pv. avellanae
from the twig reached the branches, collar and roots from where it
also colonized the branch which did not carry an inoculated leaf scar.
Extensive twig dieback was noticed during April, whereas in June, most
of the adult trees inoculated in autumn with approximately 25 000 cells
of the pathogen, randomly distributed in 25 sites of the crown, wilted
completely. The role of leaf scars as a favourite site of penetration
exploited by the pathogen as well as phytosanitar>ʹ measures are
discussed.
