The aims of the investigation were to identify the fungi causing spots, necrosis or death of plants and the evaluation of pathogenicity of some of them to chrysanthemum plants. During the mycological investigations the fragments of plant roots, stems and leaves were placed on a mineral medium. Over 6080 colonies were obtained. Alternaria alternata, Fusarium spp. and Sclerotinia sclerotiorum were isolated most frequently. The largest numbers of colonies and species of fungi were isolated from cv. ‘Snowdon’. In the second experiment, the pathogenicity of F. oxysporum, F. avenaceum and S. sclerotiorum populations was investigated. Disease index for inoculated plants was compared to chlorophyll fluorescence parameters. For most of isolates of higher pathogenicity, the disease index was correlated with the reduction of plants photosynthetic activity. However, in some cases the damage to the photosystem was more severe than external disease symptoms indicated, suggesting that chlorophyll fluorescence measurements might be helpful in early evaluation of disease severity.

59-70