Association of Candidatus Phytoplasma asteris with little leaf disease of desert rose

Desert rose (Adenium obesum) of the Apocynaceae family, is an exotic ornamental plant from warm climates, grown for its attractive fleshy stem, leaves and bright colourful flowers. Little leaf like symptoms (Fig. 1) were observed in May-August 2006 on two plants that were being maintained in a house garden at Lucknow, India. Symptoms included phyllody and excessive development of internodes resulting in little leaves. To assay for the association of phytoplasma with the little leaf symptoms, total DNA was isolated from infected leaf tissues and from an apparently healthy plant. PCR was performed with P1/P6 universal primers specific to the 16S rRNA gene (Deng & Hiruki, 1991. In addition, nested PCR was carried out with primers R16F2n/R16R2n (Gundersen & Lee, 1996) using the first round PCR product as the template. DNA fragments of the expected sizes (~ 1.5 kb and 1.2 kb respectively) were obtained from the infected plant samples but not from the apparently healthy one. The identity of the PCR amplicons was confirmed by Southern blot hybridization using a probe prepared from a clone of the chilli little leaf phytoplasma reported earlier (GenBank Accession no.DQ343288), which showed strong hybridization under high stringency conditions.

The 1.2 kb amplicon was sequenced and the sequence data deposited in GenBank (Accession no. EF159729). The sequence shared 99% similarity with the 16S ribosomal RNA gene of Barley deformation, Aster yellows, Valeriana yellows, Onion yellows, Silene virescence and Chilli little leaf phytoplasmas (GenBank Accession nos. AY734453, AY665676, AY102274, AP006628, AY744070 and DQ343288 respectively), which belong to Candidatus Phytoplasma asteris (16SrI Aster yellows group).

A literature survey revealed reports of natural infection of desert rose with Cucumber mosaic virus (Baker et al., 2003) and Tomato spotted wilt virus (Adkins & Baker, 2005), but not with phytoplasma. To our knowledge this is the first report of Candidatus Phytoplasma asteris associated with little leaf disease of desert rose in India or elsewhere.