Identification of a phytoplasma from the aster yellows group infecting purple coneflower (Echinacea purpurea) in Slovenia

Purple coneflower (Echinacea purpurea) of the Asteraceae family, is a perennial flowering plant native to eastern North America which is widely grown as an ornamental and medicinal plant. Since 2002, phytoplasma-like symptoms have been observed in several gardens in the Savinja valley in Slovenia. Disease incidence (5-30 %) has varied between years and increases with plant age. The symptoms seen include plant weakness, leaf yellowing, and floral malformations particularly virescence and phyllody (Fig.1).

For molecular identification of the pathogen, the total DNA was isolated from samples of several parts of an infected plant and from a plant without symptoms using a CTAB protocol (Kump & Javornik, 1996). PCR was carried out using three universal 16S rDNA-specific primers P1/P7, Fu5/Ru3 and R16F2n/R16R2. All three primer pairs gave a single PCR products from tissue with symptoms, with the expected lengths of ~ 1.8, 0.9, and 1.2 kbp, but no products from samples from plants without symptoms. All PCR products were TA cloned (Promega T-easy), sequenced and assembled into a single sequence of a total length of 1840 bp, which was deposited in GenBank (Accession No. EU416172). A blast search revealed 100% sequence identity for the entire contig with poa stunt phytoplasma (DQ640502) and clover phyllody phytoplasma strain CPh (AF222066) sequences, both belonging to the 16SrI-C subgroup of the aster yellows group (AY). Other matches with high sequence similarities (98-99%) also belonged to aster yellows phytoplasma members, e.g. onion yellows phytoplasma (AP006628.2), epilobium phyllody phytoplasma (AY101386), silene virescence phytoplasma (AY744070) and to the Czech strain of purple coneflower phyllody phytoplasma (EF546778).

Phytoplasmas belonging to the AY group have been previously identified in purple coneflower in the USA, Canada (Stanosz et al., 1997; Lee et al., 2008) and in the Czech Republic. This is the first report of detection of an isolate of ‘Candidatus Phytoplasma asteris’ (subgroup 16SrI-C) infecting purple coneflower in Slovenia.