The occurrence of orange leaf phytoplasmas in India has not
previously been reported. However, recently the occurrence of
phytoplasmas in the Cauvery Delta areas and other rice
growing areas were noticed for first time. An extensive survey
has been conducted in the Cauvery Delta, Lower Bhavani
project Delta, Parambikulam Aliyar Delta, Periyar Vaigai
Project Delta and Thamiraparani Delta zones. The plants
exhibited typical symptoms with orange yellow discoloured
leaves which were distributed sporadically in the field
(Fig. 1). The symptoms were suspected to be phytoplasma as
testing for Rice Tungro Disease (RTD) with PCR gave negative
results and the bacterial blight pathogen could not be isolated.
Subsequently we attempted to identify the causal agent by
using nested PCR using phytoplasma specific primers.
Leaf samples were collected from four symptomatic plants
of each of the rice varieties ADT 43, CO 39 and White Ponni
(collected from TNAU farms, Coimbatore district) and BPT
5204 (from the Erode district) and used for the present study. A
modified CTAB method (Warokka et al. 2006) was used for the
extraction of total DNA from leaf samples of rice for detecting
phytoplasmas. Nested-PCR assays with the universal primer
pair P1/P7 followed by the universal primer pair R16F2/R2,
designed to amplify a portion of the 16S rRNA gene (Lee et al.
1993; Gundersen and Lee 1996) were employed. One
microlitre of DNA was used for first round amplification with
primer pair P1/P7 and 0.5 μl of first round product was used as
template in nested-PCR without dilution with phytoplasma
specific primers R16F2n/R16R2. A total of 35 thermal cycles
were carried out which included denaturation for 1 min (2 min
for first cycle) at 94 °C, annealing for 2 min at 50 °C and
extension for 3 min (10 min in final cycle) at 72 °C. DNA
fragments ca. 1.2 kb in size were amplified by nested-PCR
(Fig. 2) from DNA extracts of symptomatic leaves from the
infected plants but not from the DNA of healthy leaves. The
nested-PCR was repeated thrice using the same samples. The
DNA fragments were gel purified using a gel extraction kit
(Qiagen, New Delhi, India) and cloned in plasmid (pGEMT®
vector- Promega). The Plasmid DNAwas directly sequenced in
both orientations at SciGenom Labs Pvt Ltd, Kerala, India and