First report of a 'Candidatus Phytoplasma asteris' isolate associated with a little leaf disease of pigeon pea in India

Pigeon pea (Cajanus cajan; family Fabaceae) is a protein-rich pulse crop, cultivated for its nutritive value. India contributes over 80% of world production and 77.5% of the global hectarage (Ahlawat et al., 2005). Pigeon pea plants growing in an experimental field at NBRI, Lucknow in 2005 were found with typical phytoplasma symptoms that included little leaves, shortening of internodes and petioles giving a bunchy appearance and whole plant stunting.

DNA was extracted from infected leaves (0.5 g) and used in a simple PCR with phytoplasma 16S rDNA primers P1/P6 (Deng & Hiruki, 1991). This resulted in the production of a band of approximately 1.5 kb, from all 3 samples with symptoms but not from an apparently healthy sample. The PCR products were used as templates in a nested PCR using primers R16F2n/R16R2 (Gundersen & Lee, 1996) giving a product of around 1.2 kb. This amplicon was cloned, sequenced, with the sequence deposited in Genbank (Accession No. DQ343287). Blast analysis showed the highest (99%) similarities with Ash witches'-broom (AY566302), Hydrangea phyllody (AY265219), Maize bushy stunt (AY265208), Epilobium phyllody (AY101386) and Onion yellows (AP006628); all members of the 16SrI Candidatus phytoplasma asteris group (IRPCM Phytoplasma/Spiroplasma Working Team-Phytoplasma taxonomy group, 2004). The isolate did not share any similarity with members of the phytoplasma 16SrIX (Pigeon pea witches'-broom) group. This is the first record of pigeon pea little leaf disease in India and the first report of an isolate of 'Candidatus Phytoplasma asteris' infection of pigeon pea.