First report of a 16SrI, ‘Candidatus Phytoplasma asteris’ isolate affecting eggplantand Mikania sp. in Bangladesh

Solanum melongena known as eggplant or brinjal, is a popular cash crop for Bangladeshi farmers. In April 2008, symptoms similar to those previously described for brinjal little leaf disease (BLL) were observed in eggplants brought to the rural plant clinic in Kaliganj (Fig. 1). Disease incidence was up to 45%, with the yield per plant reduced by 90%. A nearby weed (Mikania sp., Asteraceae) also showed early symptoms of phytoplasma infection displaying small yellow and distorted leaves (Fig. 2).

Leaf samples from symptomaticand symptomless eggplants and Mikania, were collected and analysed by the Global Plant Clinic. Total DNA was extracted and assayed in a nested PCR with universal phytoplasma 16S rRNA primers P1/P7 and fU5/rU3. No PCR amplicons were produced by symptomless samples, but products of expected size (~880 bp) were obtained from four out of five eggplants, and one of the four Mikania samples.Amplicons were purified, cloned (pGEM-T Easy Vector, Promega) and sequenced (http:/www.dnaseq.co.uk). All 16S rRNA eggplant phytoplasma sequences had 100% identity with each other, and a representative sequence was deposited in GenBank (Accession. No. EU921446). The Mikania sequence (EU921447) shared 99% identity with that from eggplant, and both shared the highest identity (99%) with members of group 16SrI, ‘Candidatus Phytoplasma asteris’, also confirmed by phylogeny analysis (Fig. 3). This group has been associated with eggplant dwarf in Japan (Okuda et al., 1997), additionally supporting its occurrence in South-East Asia. A 16SrVI, ‘Ca. Phytoplasma trifolii’-phytoplasma was previously found to be associated with BLL symptoms in Gajipure, Bangladesh (Siddique et al., 2000). However, no 16SrVI phytoplasmas were found associated with symptoms in Kaliganj, which is 175 km south of Gajipure, suggesting that geographic location and vector distribution is important for the group of phytoplasma associated with disease of brinjal and that these cannot be distinguished by symptom development.

The detection of a similar phytoplasma in Mikania suggests this as an alternative reservoir for the 16SrI phytoplasma, so its elimination from fields and borders is recommended to help reduce disease incidence. To our knowledge, this is the first record of a ‘Ca. Phytoplasma asteris’-related strain associated with BLL and Mikania in South-East Asia, including Bangladesh.