On November 11th starting at 10:00 doctoral student Liina Jürisoo will be defending her thesis „Distribution of and damages by Dutch elm disease agents in Northeastern Europe."
As elsewhere in the world, elms in Northeastern Europe are threatened by Dutch elm disease (DED), which is one of the most devastating diseases of the elms. The aim of the doctoral thesis was to investigate the spread of Dutch elm disease, its agents and their impact on the health status of different elms, vectors and the health of the elms in different habitats in Estonia and North-West Russia.
The results of the work demonstrated that U. glabra is more susceptible to DED than U. laevis and elm hybrids. Therefore, we recommend to use U. laevis rather than U. glabra in landscaping. Elm hybrids may be promising in green areas, but they still need to be tested before they can be widely used in the conditions of Northeastern Europe.
DED is known to have caused damage to Estonia's elms since 1930s. First, the pathogen was Ophiostoma ulmi which has now been replaced by a new species, Ophiostoma novo-ulmi. In Europe the European subspecies (subsp. novo-ulmi) and to a lesser extent the North American subspecies (subsp. americana) are both the causal agents of DED in Estonia; however, the latter was detected only in Northwestern Estonia, incl. Hiiumaa island. As the American subspecies of DED is more aggressive than the European one, it causes the mortality of elms at a faster rate as was the case in North Estonia. In the current work the presence of an aggressive hybrid of this pathogen was also proved for the first time in Estonia in 2020. At the same time, our investigations demonstrated that the pathogen´s hybrids between subspecies are even more aggressive as revealed by their significantly faster growth in pure cultures. The reason may be the poor health status of elms in Russia where these hybrids were particularly often detected.
Additionally, in this work it was found that Xyleborinus saxesenii and Xyleborus dispar are new potential vectors for DED. This is clear evidence of wider spread potential of DED and greater risk to elms.
Supervisor is prof. Rein Drenkhan and opponent is Dr. Nicola la Porta (FE M Research and Innovation Centre, Italy). Abstract is available in Library of Estonian University of Life Sciences DSpace archive.