Abstract:
Phytoplasmas are cell-wall-less bacteria and known to cause disease in
hundreds of plant species worldwide. Phytoplasma diseases have significant
impact on yields of many important crops including rice (Oryza sativa). Rice
yellow dwarf disease (RYD) continues to be a problem for rice farmers in
many regions of Asia. Infected rice turns pale yellow and gradually starts to
decay and ultimately shows stunted growth and fails to produce grain. RYD
phytoplasma has been classified in RYD 16S-group XI and its closest known
relatives are the phytoplasmas associated with sugarcane white leaf (SCWL),
and sugarcane grassy shoot (SCGS) found in sugarcane. In addition to RYD
phytoplasma, several phytoplasmas infect gramineous plants, including rice
orange leaf (ROL), Bermuda grass white leaf (BGWL), and Brachiaria grass
white leaf (BraWL) phytoplasmas. In Sri Lanka, yellowing and stunting of
rice plants similar to the RYD has been reported and the causal agent is not
identified. Symptoms similar to RYD rice plants were collected from
Monaragala and Weligama areas and positive for phytoplasma when
subjected to nested PCR with phytoplasma universal primers. The amplicons
were sequenced and BLAST search showed that the sequences had >98%
similarity with Bermuda grass white leaf (BGWL) group (16SrXIV).
Phylogenetic analysis based on 16S rRNA gene revealed the clustering with
BGWL groups. Further research is being carried out in order to consolidate
this finding with more samples and additional genes such as secA for better
resolution of phytoplasma grouping.
