3. Results and discussion
The affected plants showed various kinds of malformation of vegetative and floral parts. The affected vines showed conspicuous tufts of malformed branches giving a witches broom appearance with yellowing symptoms (Fig. 1a). The stalk of affected spike increased in length, the bracts and the flowers were transformed into small leaf like structures and floral buds of the affected spikes were transformed into small branches with nodes and internodes similar to fruiting laterals (Fig. 1b). Malformed fruiting laterals produced aborted flower buds/small leaf like structures. DNA extracted from these malformed budtips was used as template in PCR. In the case of first round PCR, use of primers SN910601/P6 failed to yield visible amplified DNA fragments either from infected or healthy tissues of black pepper. This could be due to the presence of DNA concentration below the detection limit in ethidium bromide-stained agarose gel. When the first round PCR products were reamplified in the nested PCR using primers R16F2n/R16R2, a DNA fragment of 1.2 kb was obtained in the diseased black pepper samples and a known phytoplasma positive sample (periwinkle little leaf) but not in asymptomatic plants (Fig. 2). This DNA fragment was cloned and its nucleotide sequence determined. The sequence was deposited in GenBank and its accession number listed in Table 1. The sequenced region which contained 1230 bases was compared with corresponding region of phytoplasma isolates belonging to different groups from different hosts and regions (Table 1). Comparative sequence analyses showed that the black pepper phytoplasma shared maximum sequence identity (98.7–99.4%) with phytoplasma isolates belonging to aster yellows group (16Sr I) (Table 2). In contrast, black pepper phytoplasma showed an identity ranging from 87.0 to 88.0% with seven members of elm yellows group (16Sr V) used for comparison. Identities among different members within a group was >98% (Table 2). The identities of black pepper phytoplasma with 13 other groups and other undesignated groups (Table 1) were in the range of 88–96% (not shown). Phylogenetic tree constructed using these sequences also revealed that among phytoplasmas, black pepper phytoplasma was most closely related to the members of 16S rDNA group I (aster yellows) forming one cluster that is well separated from other groups (Fig. 3).