Phoma strasseri was isolated first time from peppermint (Mentha piperita L.) in 2004. These species had not been found in Poland earlier. Biotic interactions between P. strasseri and 16 species of fungi colonizing the phyllosphere of stems and rhizomes of peppermint were determined using the biotic series method and maltose agar MA. The effect of particular fungi species on P. strasseri was expressed as and individual, general and summary biotic effect. Fungi from genera Trichoderma were found out to be the most effective and positive antagonists whereas those of Alternaria alternata, Botrytis cinerea and Rhizoctonia solani – despite the high values of IBE – were considered negative antagonists. Studies on the effect of thermal conditions pointed out that the thermal optimum for the growth of the fungus colonies ranged from 16^oC to 28^oC, while that for the formation of the infectious material from 24^oC to 28^oC. Basing on the ability of P. strasseri to develop in a wide range of temperatures, it was included within the group of eurythermic organisms.

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