SUMMARY

During 2001-2005, 54 bacterial strains were isolated from the rhizosphere and phyllosphere of hazelnut trees with symptoms of dieback. The bacteria were screened by in vitro agar plating assays for possible bio-logical control of hazelnut dieback. Two of the bacteria inhibited the growth of the hazelnut dieback-associated pathogens, Pseudomonas avellanae and Pseudomonas sy-ringae pv. coryli. The antagonistic bacteria were identi-fied as Pseudomonas fluorescens and Bacillus megateri-um according to phenotypic characters and 16S rDNA sequencing. Key words: Natural antagonists, biological control, organic agriculture, bacterial pathogens, hazelnut. Since the 1980s, an emerging bacterial disease of hazelnut has caused severe damage, leading to the re-moval of a large number of diseased trees in several dis-tricts in the province of Viterbo (central Italy), the largest and most important hazelnut production area in Italy. Due to rapid death of entire branches of infected trees the disease was called “Moria”, or hazelnut dieback (HD) (Varvaro et al., 1990). Infected trees have light-green to yellowish leaves in the spring, and by ear-ly summer, the leaves wither and branches die suddenly. Leaves commonly remain attached into winter. Brown cankers appear on many branches and exposed xylem tissue has brown streaks. Diseased trees without healthy canopies generally produce new suckers but these usu-ally die within 2-3 years. The causal agent of HD was originally described in Greece as Pseudomonas syringae pv. avellanae (Psallidas, 1977) and re-classified as Pseudomonas avellanae, by Janse et al. (1996). P. avellanae was identified as the agent of HD in Italy (Scortichini et al., 1994). Addition-ally, both P. syringae pv. coryli (Pc) (Scortichini et al., 2005) and P. syringae pv. syringae (Ps) (Scortichini et al., 2002) were shown to be associated with HD in Italy