Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The common beech (<jats:italic>Fagus sylvatica</jats:italic> L.) is the main forest-forming species in Slovakia and its share accounts for over 31% of the total forest area in this country. Recently, there are more and more reports of the deterioration of the health of this species in Europe, incl. as a result of the action of pathogens of the genus <jats:italic>Phytophthora</jats:italic>. The aim of this study is to confirm the presence of pathogens of the genus <jats:italic>Phytophthora</jats:italic> in beech forests in Slovakia. Ten plots in central and western Slovakia were selected for the study. The presence of: <jats:italic>P. x cambivora</jats:italic>, <jats:italic>P. cactorum</jats:italic>, <jats:italic>P. plurivora</jats:italic>, <jats:italic>Globisporangium macrosporum</jats:italic>, and <jats:italic>G. heterothallicum</jats:italic> was confirmed in the samples taken. A pathogenicity test was performed to confirm Koch’s postulates. After three months, the plants were gently taken out, and then: the pathogen was reisolated from the roots to confirm its presence in the tissues, the root systems were scanned and the image was analyzed with WinRhizo software, and finally the roots were dried to obtaining dry biomass. Additionally, during the course of the experiment, the degree of infection of the plants was assessed weekly in order to calculate the area under the disease-progress curve. The conducted research showed the greatest threat from <jats:italic>P. x cambivora</jats:italic>. In this variant, the symptoms of plant dieback were observed the fastest, as well as the pathogen, compared to the control variant, significantly damaged the root systems.</jats:p>