First report of 'Candidatus Phytoplasma asteris' (16SrI group) associated with colour-breaking and malformation of floral spikes of gladiolus in India

Gladiolus is an important ornamental plant, grown in the floriculture industry in India. More than 100 cultivars are maintained at NBRI, Lucknow. During January-February 2008, gladiolus plants (cv. Pacifica) exhibited symptoms of severe leaf stripe, colour-breaking, yellowing and malformation of flower spikes with stunted growth, small-sized corms and poorly developed root system (Fig.1). The disease incidence was low (3.2%), however the severity of symptoms imposed a threat for neighbouring plants by rapid disease spread. Similar symptoms have been previously reported on gladiolus, associated with a 16SrI phytoplasma, ‘Candidatus Phytoplasma asteris’ (Kamińska et al, 1999; Pfleger & Gould, 2002). Therefore, a phytoplasma infection was suspected.

Total DNA was extracted from 100 mg of leaf, flower and corm of infected and healthy gladiolus and indexed by nested PCR using phytoplasma universal primers specific to the 16S rRNA gene: P1/P6 (Deng & Hiruki, 1991) and R16F2n/R16R2 (Gundersen & Lee, 1996). This yielded amplicons of ~1.2 kb in two out of two infected leaves (Fig. 2a) and leaf, flower and corm of one severely infected plant (Fig 2b), but not in the single healthy plant tested. Two amplicons from infected leaves were directly sequenced and consensus data deposited in GenBank (Accession No. FJ491455). BLAST analysis revealed the highest identity of 97% with members of group 16SrI, confirmed by phylogenetic analysis (Fig. 3); this suggests the occurrence of a possible new ‘Candidatus Phytoplasma’ species. This is the first report on the association of 16SrI group, ‘Ca. Phytoplasma asteris’ with a disease of gladiolus in India.