Symptomless phytoplasmosis of black alder (Alnus glutinosa): a model for host tolerance

Abstract

Phytoplasmas are associated with hundreds of plant diseases worldwide including many economically important crops. These bacteria are limited in their plant hosts to the phloem sieve tubes and are transmitted by phloem sap-sucking insect vectors. Research on these pathogens is hampered by the unavailability of axenic cultures and established cultivation methods despite their importance. Alder yellows (AldY) phytoplasma frequently infects Alnus spp. (black alder), and is closely related to the economically important phytoplasma causing Flavescence doree (FD) in grapevines, a quarantine pathogen. AldY strains had been transmitted to grapevines through an occasional grapevine-feeding vector from alders; consequently, AldY share a common European origin with FD. In contrast to FD, no phytoplasma typical infection-associated symptoms such as yellowing and decline can be observed for AldY. Here, we summarize the current state of the art of phytoplasmosis of black alder (Alnus glutinosa). The symptomless phytoplasmosis might be an interesting model for investigating host tolerance strategies in phytoplasma/host interactions.