Genetic diversity, origin, and new hosts of the invasive pathogen Lecanosticta acicola in northern Europe


On January 10 starting at 10:00 doctoral student Marili Vester will be defending her thesis „Genetic diversity, origin, and new hosts of the invasive pathogen Lecanosticta acicola in northern Europe."

Lecanosticta acicola is an ascomycete causing Brown Spot Needle Blight (BSNB) – a foliar disease affecting pine species (Pinus spp.). The disease causes premature needle shedding which leads to reduced growth of the trees and to severe defoliation which may cause death of the infected trees.

The native range of L. acicola is in North America but during the last century anthropogenic activity introduced the pathogen also into Europe and Asia. In Europe, L. acicola was first detected in southern and central regions, but during the current century the disease agent has significantly distributed northward and is now present also in the Baltic states and southern Sweden.

So far, in northern Europe, the disease has mostly affected non-native pine species. Nevertheless, by today, L. acicola has already succeeded to infect native Scots pine (Pinus sylvestris), although so far damage on the P. sylvestris is insignificant and only the trees growing in the immediate proximity to non-native P. mugo have been found to be infected.

The distribution range of L. acicola appears to be expanding also to the western Asia. In this thesis the pathogen was identified for the first time in Turkey and Georgia. In Turkey, the infection of BSNB was found also on Cedrus libani, proving that L. acicola is not only a Pinus-specific pathogen.

Identical genetic strains of the pathogen were found on the distances that the fungus could not spread naturally. Identical strains were found to be shared even between continents, being present in Canada and Germany, but similarly strains were also shared between the countries in Europe. Lecanosticta acicola has reached northern Europe predominantly from pre-existing populations in central Europe and not directly from its native range in America.

Surprisingly high diversity found from the populations in northern Europe is probably the result of repeated introductions from genetically different source populations. Although, by today, both mating types of the fungus are present in northern Europe and probably in some limited areas the sexual reproduction takes place, the clonal reproduction mode dominates in this region. Based on the so far distribution of this pathogen and that the ongoing climate changes support its dissemination, it can be assumed that northwards spread of L. acicola will continue in Europe.

It is important to avoid any further increase in the diversity of pathogens’ populations, that could easily happen if new fungal strains are imported with insufficiently controlled planting material. An increase in diversity could lead to dangerous development of strains with higher virulence or higher suitability to local climate conditions which could result in higher damage to the forest stands.

Supervisor is Prof. Rein Drenkhan and opponent is Dr. Michael M. Müller (Natural Resources Institute Finland). Abstract is available in Library of Estonian University of Life Sciences DSpace archive