2.2. Nested PCR
The total genomic DNA was subjected to nested PCR using universal primers designed to amplify a specific sequence within the 16S rDNA of phytoplasmas (Gundersen and Lee, 1996). Primers P6 (5′ CGGTAGGGATCACTTGTTACGACTTA 3′) (Deng and Hiruki, 1991) and SN910601 (5′ CGAAAAAACCTTACCAGGTCTTTG 3′) (Namba et al., 1993) were used for the first round amplification of the 16S rDNAs. For the second round, to amplify an internal fragment of the 16S rDNA, primers R16F2n (5′ GAAACGACTGCTAAGACTGG 3′) corresponding to bases 144–163 and R16R2 (5′ TGACGGGCGGTGTGTACAAACCCCG 3′) corresponding to bases 1365–1386 (Lee et al., 1993) were used. The PCR reaction (100 μl) contained 200 ng each of the primers, 2.5 units Taq Polymerase 1× PCR buffer, 1.25 mM MgCl2 and 10 μM each of the dNTPs. PCR mix (27 μl) containing the above components was added to the tubes containing the template DNA (73 μl) resulting in a final reaction volume of 100 μl. Amplification was performed in an automated thermal cycler (Eppendorf Master Cycler Gradient) programmed for one cycle of 94 °C for 3 min followed by 35 cycle reaction profile involving 30 s of denaturation at 94 °C, 60 s of annealing at 53 °C and 90 s of extension at 72 °C and single cycle of final extension at 72 °C for 10 min for the first round amplification. The reaction product (1 μl) of first round amplification was used as template for the second round of amplification with similar reaction profile except for the annealing step, which was carried out at 56 °C (instead of 53 °C).