Diversity and distribution of Armillaria species in Dalby Söderskog and Norreskog

Abstract: Armillaria is a genus from the phylum Basidiomycota, which can cause Armillaria root rot disease. Both broadleaves and conifers are hosts for Armillaria. Some Armillaria species are important root and butt rot pathogens, causing mortality and yield reduction in forests. Others have more of a role as a saprophyte, helping to degrade woody substrate and therefore have some ecological importance. Knowing which species of Armillaria is present is important to determine any potential impact in forest regeneration. The aim of this thesis is to study the diversity and distribution of Armillaria species in the forest reserves at Dalby Söderskog and Norreskog in southern Sweden Two different methods were used in this study, one is based on the molecular techniques where the ITS region and EF-1ɑ region of samples’ DNA were amplified for sequencing. The amplified DNA sequences were queried in the Gene bank. The other method is based on the biological species concept which is realized by pairing tests. According to the results, Armillaria gallica, A. cepistipes and additional Armillaria sp. were identified in the study area and A. gallica is dominating. Armillaria gallica is distributed both in Söderskog and Norreskog, while A. cepistipes was only found in Söderskog. The morphology of rhizomorphs of Armillaria in cultures varied among isolate. Two genets were identified using traditional pairing tests and the genet sizes could be large enough to cover the whole study site. The Armillaria species identified in this thesis have an important role as saprophytes, decomposing dead organic matter, but can also behave as facultative parasites if trees are weakened by other stress factors. Several tree species are currently suffering from other biotic stressors (e.g. Hymenoscyphus fraxineus on ash, Dutch elm disease on elm, Phytophthora spp. on beech), which may make tees more susceptible to attack by Armillaria species in the future. However, given the typical lower virulence associated with the identified species at Dalby, any increase in inoculum potential that may affect regeneration in the long-term is probably short-lived.