The main goal of the thesis was to analyse the occurrence of the fungus Dothistroma pini Hulbary and its mating types in Slovenia. Together with Dothistroma septosporum (Dorogin) M. Morelet, it causes Dothistroma needle blight, a disease whose intensity and distribution have been increasing over the past two decades and is now widespread across the country, especially in black pine stands of the Karst region. In the first part of the study, we analysed molecular data from 165 archived samples collected between 2011 and 2022 by the Department of Forest Protection of the Slovenian Forest Institute, in which at least one of the target pathogens was detected. The result is a database of confirmed locations of D. pini and D. septosporum and the occurrence of D. pini mating types. We found that D. pini is generally present in Slovenia, although its population is smaller and more spatially restricted compared to D. septosporum. The MAT1-2 mating type of D. pini is predominant; however, the MAT1-1 type was also detected more frequently than previous studies indicated. In the second part of the study, we conducted needle loss assessments and sampled 15 symptomatic pine trees at three selected sites (Pivka, Divača, Pliskovica) where D. pini had previously been confirmed. Molecular analyses reconfirmed the presence of D. pini at all three sites, predominantly with MAT1-2 and a single detection of MAT1-1 mating type in a sample from Pivka. In the third part of the study, we isolated six pure cultures of D. pini directly from sporulating symptomatic needles. All cultures were molecularly confirmed as D. pini with the MAT1-2 mating type.
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