In recent decades, one of the biggest threats to forest ecosystems has been the extremely rapid spread of invasive organisms (pathogens, insects, etc.). Invasive species are moving into new territories and causing huge economic and ecological losses as a result of climate change and intensive international trade. One such invasive pathogen is the fungal microorganism Ophiostoma (Ascomycota), which causes Dutch Elm Disease (DED) in ash (Ulmus L.). Over the last 100 years, this disease has destroyed millions of ash trees worldwide. The studies have shown that hybridisation occurs between genes in O. novo-ulmi subspecies. Therefore, it is assumed that the pathogens have a high potential to form increasingly aggressive hybrids that displace less aggressive hybrids, as is the case with O. ulmi, which is no longer found in some countries, or is very rare and episodic.
According to recent studies in Lithuania, only one species of O. novo-ulmi has been identified so far, i.e. O. novo-ulmi ssp. novo-ulmi subspecies and the two-subspecies hybrid O. novo-ulmi ssp. novo-ulmi x ssp. americana. However, it is still unclear how they are formed, how and from where they spread (O. novo-ulmi ssp. americana has never been detected). Studies have also been published on differences in mycobiota between healthy and DED-damaged trees, but these have relied only on the occurrence of traits attributed to DED, without assessing which subspecies and/or hybrid is dominant, and whether this might also have influenced differences in mycobiota in damaged plants. Therefore, more detailed and extensive studies are needed, as this work is expected to compare the characteristics of pathogens found in the country. The PhD research would build knowledge on the epidemiology of the disease and the biological and ecological characteristics of the disease agent(-s). Molecular studies would investigate the properties of the pathogen populations, providing more information on population structure, hybridisation and other properties, as well as more information on the biology of the pathogen and possible routes of spread.