Microfungi in the phyllosphere of <i>Senecio umbrosus</i> Waldst. et Kit., a host species with a narrow ecological niche

Among the biotic factors that limit plant growth, population size, and reproduction, there is a mass appearance of microscopic parasitic fungi. The aim of the study was to determine the spectrum of the microfungi and the degree of leaf surface infection in the ragwort Senecio umbrosus, i.e., one of the Polish red data book species. In 2014–2016, studies on the diversity and dynamics of microfungi were carried out within its population on White Mt, southeastern Poland, where it grows in xerothermic habitats. During three seasons (6 collection series between May and October), 15 microfungal species were identified in total (1–9 species per one collection date, 9 species in each season). Only Coleosporium tussilaginis was present in all study dates, and it accounted for 30–100% of all records of the microfungi. Three hyperparasites were also identified on C. tussilaginis: Cladosporium uredinicola, Ramularia coleosporii, and Alternaria sp. The other taxa were found five (Boeremia exigua, Leptosphaeria ogilviensis), four (Alternaria sp.), or three times (Ascochyta compositarum, Periconia cookei), but the majority of the microfungi were noted twice or only once, depending on meteorological conditions in a given growing season. Among common species of microfungi, we collected Ascochyta compositarum, which is a new species for Poland. Additionally, we found new fungus/host plant combinations for C. tussilaginis.