243 Bacterial Species Associated to Brown Spots of Hazelnut in Central Italy: Survey, Isolation and Characterization J.R. Lamichhane, A. Fabi and L. Varvaro Department of Science and Technology for Agriculture, Forestry, Nature and Energy (DAFNE), Tuscia University via San Camillo de Lellis, 01100, Viterbo Italy and Hazelnut Research Center viale Trieste 127, Viterbo Italy Keywords: physiological disorder, quali-quantitative composition, Pseudomonadaceae, Enterobacteriaceae, Xanthomonadaceae, Microbacteriaceae Abstract A disease like physiological disorder of hazelnut known as “brown spots” was thoroughly studied for the first time from the Italian hazelnut growing areas. The quali-quantitative composition of the bacterial microflora associated to the syndrome was investigated. Six bacterial species, belonging to four different families were constantly isolated from the syndrome. On the basis of traditional and molecular assays, the species associated to brown spots were identified as Pantoea agglomerans, Microbacterium schleiferi, Xanthomonas arboricola pv. corylina, Pseudomonas fulva, Pseudomonas putida and Brenneria alni. Quantitative differences, statistically significant, were observed among the species. The populations, expressed as colony forming units per gram of the sample (CFU/g), ranged from a lowest value of 3.6×10 3 to a highest value of 2.7×10 4 respectively for Microbacterium schleiferi and Xanthomonas arboricola pv. corylina. Plant stress, caused by the adverse environmental conditions and inadequate agronomic and cultural practices, was the main cause of the brown spots during which the ubiquitous bacteria rapidly colonize and multiply the weakened plants. This phenomenon can be overcome if good agronomic and cultural practices are adopted. INTRODUCTION Hazelnut (Corylus avellana L.), like many other plant species, is subjected to several attacks of plant pathogens. Among the diseases, so called “moria” or “hazelnut dieback” caused by a bacterial pathogen is the most serious and devastating. The causal agent of moria was previously hypothesized as Erwinia amylovora group of bacteria (Varvaro, 1994; Varvaro et al., 1990) and later as Pseudomonas avellanae (Psallidas) (Janse et al., 1996). Some authors also suggested, on the basis of epidemiological studies by means of Geographic Information Systems (GIS) and geostatistics, that the disease can be better described as of complex origin (Fabi and Varvaro, 2009). Besides moria, which still represents a serious threat along the hazelnut cultivation area in the Province of Viterbo, bacterial blight caused by Xanthomonas arboricola pv. corylina, bacterial twig dieback caused by Pseudomonas syringae pv. coryli, bacterial wilt of twig and branch caused by P. syringae pv. syringae have been reported from different filbert cultivation areas of Italy. Moreover, fungal diseases such as Cytospora canker caused by Cytospora corylicola and fruit gray necrosis caused by a group of Alternaria spp. and Fusarium spp. can cause significant losses when climatic conditions are favorable (Belisario et al., 2004, 2005). In addition to the diseases of plant pathogenic nature, a disease like physiological disorder, which is so far known as hazelnut brown spots, has been frequently found from the Italian hazelnut growing areas. The symptoms of this disorder have been reported for the first time along the branches and trunk of hazelnut from limited areas of Piedmont in Proc. VIII th International Congress on Hazelnut Eds.: P. Grau Beretta and M. Ellena Acta Hort. 1052, ISHS 2014