Interrelations between alien and native foliar fungal pathogens and woody plants in Siberia.
This article presents the results of 15-year observations of alien and native foliar fungal pathogens and woody plants in Siberian arboreta and urban ecosystems and discusses the possibility of using these data to determine how the pathogenic mycobiota of woody species was formed under Siberian conditions. In total, 121 species of pathogenic micromycetes affecting the leaves of woody plants in botanical gardens and city and belonging to 2 divisions, 14 orders, and 46 genera have been revealed. Most of these species belong to the Ascomycota division (86.8%). The Basidiomycota division is represented by fungi from the order Pucciniales. Among all observed pathogens, 21 species belong to powdery mildew fungi, 15 species belong to rust fungi, and 84 species represent anamorphic fungi. A study of 108 woody plant species growing in Siberian cities has revealed 101 species of leaf pathogens, while 158 woody plant species growing in arboreta have been inhabited by 105 pathogen species. All fungal species revealed during this study, except for three species (Mycopappus alni, Venturia acerina, and Phyllosticta westendorpii), have been observed in Siberia earlier. However, some fungus-host plant associations are apparently new to science, suggesting that complexes of cryptic species differing in their host range and geographic range may occur. The main sources for tree mycobiota formation in Siberia include the invasion of pathogens together with alien plant species, the transition of pathogens from native to alien plant species, the enhancement of a pathogenicity of saprotrophic fungi, and the expansion of fungi onto new hosts. The majority of pathogens (65-75% of the total number of revealed fungi) locate on native plants. Alien plants are infected mainly by (native) pathogens. Only eight pathogen species have been introduced in Siberia with alien plants; three of them originate from the Far East (Cercospora gotoana, Phyllosticta phellodendricola, and Erysiphe palczewskii), while five are of European origin (Cladosporium syringae, Phyllosticta vincae-minoris, Erysiphe syringae, Erysiphe alphitoides, and Erysiphe berberidis). In Siberia, the lateness of phenological phases of plants originating from mild climatic zones, may be favorable for the development of fungal pathogens, such as Erysiphe alphitoides, causing the powdery mildew of oak trees.