BACTERIAL BARK CANKER ON ENGLISH WALNUT

The bacterial canker caused by Brenneria nigrifluens (syn. Erwinia nigrifluens) has been observed in several English walnut orchards located in the north, central and south of Italy. The disease attacked the bark of trunks and scaffold branches of young and mature trees. Commonly, symptoms consisted in dark brown to blackish roundish blotches from which a dark liquid oozed from late spring to fall. Early indication of canker formation was the development of sunken areas. Removing the surface of the bark, lesions appeared as longitudinal blackish streaks affecting the inner bark, the cambium and the outer layer of xylem. Cankers were commonly deeper and more severe than those reported in USA, resembling symptoms caused by B. rubrifaciens, the agent of deep bark canker. Usually, well managed trees success¬fully healed cankers by producing abundant callus tissue, whilst weak trees with numerous infected areas declined and died. Symptomatic trees were observed in Veneto, Piedmont and Campania regions. Positive isolations were obtained from humid blotches. Preliminary results on the susceptibility of several Juglans species to Brenneria nigrifluens artificial inoculation are reported.