The purpose of the present paper was to find oud about the population of bacteria collonizing hazel-nuts with black spotted symptoms of the pericarp and darkening and softening of the nucleus. Moreover, pathogenic abilities of the selected bacterial isolates towards these organs were estimated. The object of the studies conducted in the years 2000–2002 consisted of hazel-nuts, cultivar Hall’s Gigant, with the above mentioned symptoms, orginiating from commercial plantations in Motycz and Końskowola. The bacteria were isolated from diseased hazel-nuts each year, in June and August, and among the population obtained, 42 representative cultures were chosen, which were used in physiological, biochemical and pathogenicity tests. It was shown that 3 isolates of Erwinia spp., 4 isolates of Bacillus spp. and 3 of Pseudomonas fluorescens could damage the fruitsets and fruit of hazel. The effectiveness of infection was considerably higher after inoculation of young and injured organs. Erwinia spp. were recognized as a potential pathogen of hazel-nuts. It seems that pectinolytic isolates of Bacillus spp. and Pseudomonas fluorescens might be recognized as facultative parasites which have the abilities to damage hazel-nuts in favourable conditions.

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