Purple Coneflower Is a Host of the Aster Yellows Phytoplasma.

The perennial plant purple coneflower (Echinacea purpurea (L.) Moench, Asteraceae) is native to open woods and prairies of the eastern U.S. and is gaining popularity as a garden and roadside ornamental. It is propagated both by seed and by division of established plant crowns. During late summer 1996, three of seven purple coneflower plants located in a residential garden in Dane County, WI, exhibited symptoms associated with diseases caused by phytoplasmas. These plants had been established from seed in spring 1995. Stems were thickened and brittle. Leaves were slightly twisted and drooped, and flower parts lacked normal pigmentation. Petals of ligulate flowers were narrow. Clusters of short, thin stems bearing sterile, dwarfed, distorted, green heads had grown from the receptacles of severely affected flower heads. A presumptive fluorescence test with 4',6-diamidino-2-phenylindole staining was positive for phytoplasmalike bodies in phloem sieve elements in the midveins of leaves from a symptomatic plant. Nested polymerase chain reaction (PCR) amplification of extracted DNA with phytoplasma-specific oligo-nucleotide primer pairs (1,2) confirmed the presence of phytoplasmas in this plant. Based on restriction fragment length polymorphism analysis of the PCR products, the associated phytoplasma was identified as phytoplasma 16S rRNA group I (aster yellows [AY] and related phytoplasmas), subgroup A. This is the first report of a host of the AY phytoplasma in the genus Echinacea. Because no attempt was made to transfer the phytoplasma via leafhoppers, the potential for purple coneflower to be a source of inoculum is unknown. References: (1) D. E. Gunderson and I.-M. Lee. Phytopathol. Mediterr. 35:144, 1996. (2) I.-M. Lee et al. Phytopathology 84:559, 1994.