Phytoplasma infection in prized linden Tilia platyphyllos var. laciniata: is 'laciniata' a valid botanical variety?

Abstract

Linden (Tilia platyphyllos var. laciniata) trees growing in Kaunas Botanical Garden and in the parks of Verkiu (Vilnius) and Belvederis estates in Lithuania exhibit laciniated, deformed leaves and yellowing of the veins. These trees had been planted in the parks, for the beauty of their “cut-out-elongated leaves”, as a new variety of linden. However, use of the polymerase chain reaction (PCR), primed by phytoplasma universal primer pairs to amplify 16S rRNA gene sequences, followed by restriction fragment length polymorphism (RFLP) analysis, revealed that these linden trees were infected by phytoplasma strains belonging to subgroup 16SrI-B and to a new subgroup designated 16SrI-V, in the ‘Candidatus Phytoplasma asteris’ species of wall-less bacteria. The strains were further characterized by ribosomal protein gene sequence analysis. The experimental results have rekindled discussion of the possibility that a prized cultivar displaying unusual morphotype might be an invalid taxon. Is linden with laciniate-leaved branches a valid taxon (botanical variety), or simply a plant that has abnormal leaf morphotype caused by infection with a tiny wall-less bacterium?