The investigations were carried out in 2001-2003 at plantations of highbush blueberry under different habitat conditions of southeastern region of Poland. The aim of the work was to determine health status of 11 highbush blueberry cultivars cropped in the plantations, to identify the composition of fungal species colonizing stems, and to recognize the Topospora myrtilli morphology, its living requirements and the possibility of growth control. The estimation of health status was performed

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... ly on the plantations in two periods of a plant vegetation cycle , i.e. in spring during bud swelling and in autumn when leaves fall down. The percentage of bushes with the symptoms of stem canker and the share of stems with disease symptoms in a bush were determined. The fungi were isolated from infected stems with artificial culture method. Three types of disease symptoms were distinguished: spots on stems, from which mainly T. myrtilli was isolated, widespread stem necrosis inhabited by Phomopsis archeri and necrosis of stem tops caused by Botrytis cinerea. Moreover, the following isolates of fungi were obtained: Cytospora, Phoma, Fusarium, Alternaria and Seimatosporium vaccinii, Myxothyrium lepideum and Sordaria fimicola. Topospora myrtilli was identified as the most dangerous pathogen of highbush blueberry stems in the studied region, on the base of occurrence frequency and significant harmfulness. The cultivars 'Jersey', 'Earlyblue' and 'Bluecrop' were considerably susceptible to T. myrtilli. 'Bluejay', 'Darrow' and the above-mentioned cultivars were found susceptible to fungi causing widespread necrosis. The pathogen colony growth was investigated in the temperature range from-10°C to +28°C. Vegetative growth of the pathogen occurs from +2°C to +28°C. The optimum for T. myrtilli mycelium growth is between +18°C and +22°C. Conidial spores are formed at +22°C. The temperature +28°C limits the development of mycelium and stops sporulation. At-10°C the growth of mycelium is limited but the fungus does not lose its vitality.