EN
All morphological parts of sweet flag (calamus), particularly rhizomes are used not only as a herbal material, but also in confectioner and cosmetic industry. Both quantity and quality of the material which may be obtained exclusively from natural stands are determined by the fungi accompanying the plant’s vegetation. Hence, in the years 2005−2006 research was conducted to determine the diversity of mycobiota which induce chlorosis and necrosis of calamus leaves. It was found that phyllospherae of calamus is colonized by 24 taxa. Ramularia aromatica and Ascochyta acori were the two most often isolated monophagous agents of necrosis. Polyphagous facultative parasites included Fusarium sporotrichioides and Epiccocum nigrum, Alternaria alteranta and A. tenuissima. It is also important that there was the discovery of the presence of Athelia rolfsii and Fusarium incarnatum which are polyphagous species causing destruction of the tissue in tropical and subtropical climate. Due to biochemical activity of most of the isolated species and their ability to induce production of toxins, the content of active substances in calamus may be reduced and consequently diminishes its market value.