The dissertation is aimed to reveal species diversity and taxonomic structure of lichenicolous fungi, as well as their host specificity, interaction between fungus and host, distribution in the steppe zone of Ukraine. Critical taxonomic revision of three lichenicolous genera was provided. Culture characteristics were studied for a few taxa.
The total list of lichenicolous fungi was prepared according to references based previous records, own collections and observations, revised material from CWU, KHER, KW-L and KW-M herbaria. It includes 155 species of lichenicolous fungi and 13 species of lichenicolous lichens. Among them, 96 species (or 57.1 % of total number) have been registered for the territory of Ukrainian steppe zone for the first time. Didymocyrtis trassii, Pleospora xanthoriae, Roselliniella lecideae, Trichoconis hafellneri and Zwackhiomyces polischukii were described as new for science species. 41 species of lichenicolous fungi and 3 species of lichenicolous lichens were for the first time reported to Ukraine, 9 species were new to Western Europe and 3 species were new to Europe.
The analysis of the taxonomic structure of lichenicolous mycobiota showed that the Dothideomycetes (80 species) is the most diverse class. Arthoniales, Dothideales, Collemopsidiales, Hypocreales, Lichenotheliales, Mycosphaerellales, Pleosporales and Verrucariales are orders with the largest number of species. Stigmidium (10 species), Zwackhiomyces (8), Lichenostigma (7), Lichenoconium (7), Pronectria (6) and Arthonia (5) are the species richest genera of lichenicolous fungi in the steppe zone of Ukraine. Co-domination of the genera Lichenostigma and Lichenoconium can indicate features of regional steppe lichenicolous mycobiota.
The host specificity of lichenicolous fungi was investigated. 79.7 % of examined species related to one lichen genus, as well as 20.3 % or 34 species can infect more than two host genera. Xanthoria (18 species of lichenicolous fungi was observed), Lecanora (17), Caloplaca (15), Cladonia (12) and Aspicilia (11) are the most hospitable lichen genera in the steppe zone of Ukraine. Our data confirm the hypothesis about the relation between lichen biota and mycobiota. The Lichenicolous Index of examined mycobiota was calculated. There is 0.32 (the ratio of 168 fungi species to 528 host species) and can be rated as high. This Index suggests that the lichenicolous mycobiota of the steppe zone of Ukraine has been studied at an adequate level in comparison with other regional mycobiotas.
Lichenicolous fungi are a very heterogeneous group by the type of fungus-host interaction. Some of them have interaction with lichen phycobiont (105 species) and mycobiont (64 species) as well. Our data confirm the hypothesis that most lichenicolous fungi are the commensals (92 species in our material).
Lichens are consortia of different organisms with determinant core (alga cells) and a few consort levels formed by several fungal organisms that interact with the core and among themselves. We analyzed the infection of one lichen thalli with several lichenicolous fungi. According to the results of the analysis, the scheme of consortial relationship of Xanthoparmelia conspersa and Xanthocarpia crenulatella with lichenicolous fungi was modeled.
Some of the lichenicolous fungi are confined to growth in wet conditions and show features of seasonality. 14 species (9.1 %) of Ascomycota (mostly from the order Hypocreales) are ephemeral fungi.
Lichenicolous fungi are important components of lichen communities. The influence of lichenicolous fungi to Xanthoparmelietum pokornyi Khodosovtsev 2011, Amandineo punctatі-Xanthorietum parietinae Khodosovtsev et al., 2017, and Parmelietum somloensis V. Wirth 1995 community was monitored and identified. As a result, it was found that a significant influence on the spatial structure of these communities is exerted by aggressive lichenicolous fungi, which infect dominant lichen species.
Сultures on artificial nutrient medium of Acremonium and Didymocyrtis were obtained. A culture of lichenicolous fungus "Phoma candelariellae" was obtained for the first time. These cultures allowed to establish the morphological features of the colonies, as well as identified the sequences of the ITS region of ribosomal DNA, which is an important component for further taxonomic studies of these genera.
110 species of lichenicolous fungi and lichens (65.4 % for total number) were found within protected territories. Lichenicolous fungi as a separate specific group of organisms can be protected from loss of species diversity due to several factors. Firstly, the protection of host lichens is an important part of achieving this goal. Secondly, an important method of their conservation is the protection of valuable habitats with a significant diversity of lichens.
