Genetic variability of Alder yellows phytoplasma in Alnus glutinosa in its natural Spreewald habitat

The genus ‘Candidatus Phytoplasma’ comprises wall‐less bacteria colonizing the phloem of plants and insect tissues. Phytoplasmas are associated with diseases in over 1000 plant species worldwide, including many important crops as well as forest trees. Alder yellows (AldY) phytoplasma, which frequently infects Alnus spp., is closely related to the economically important phytoplasma causing Flavescence dorée (FD) in grapevines. In a natural habitat (Spreewald, Brandenburg, Germany), 57 Alnus glutinosa (black alder) trees were examined for phytoplasma infection in summer 2013. No phytoplasma typical infection‐associated symptoms such as yellowing and decline were observable in this natural swamp‐alder area. Amplification followed by a restriction fragment length polymorphism, and a sequence analysis of the 16S rDNA, allowed for the detection of AldY phytoplasmas in all examined trees and their assignment to the taxonomic group 16SrV‐C. Additional analyses of the non‐ribosomal marker gene methionine aminopeptidase (map) revealed diverse strains as well as mixed infections with closely related AldY strains, and the strains were assigned to phylogenetic clusters closely related to German Palatinate grapevine yellows, AldY or FD strains. The results confirmed that AldY phytoplasmas infection in A. glutinosa is prevalent. The results also indicate a presence of an established phytoplasma population in chronically infected black alder.