Abstract:
Phytoplasmas are associated with many plant diseases. In palms, lethal bronzing disease,
Texas Phoenix palm decline, and coconut lethal yellowing decline are some of them. In Sri Lanka,
coconut leaf wilt decline has been reported in the Weligama area of the Southern province, and
the disease is called Weligama coconut leaf wilt disease (WCLWD). Unlike other phytoplasma
diseases of palms, WCLWD shows slow disease progress. Pathogen detection entirely relies on
nested polymerase chain reaction (PCR). However, inconsistencies in pathogen detection have been
experienced, i.e., symptomatic plants often produce negative results. The objectives of this study were
to reconsider the choice of primers and to determine the best sampling tissue types for consistent
detection of the pathogen. Among the six universal primer combinations tested, P1/Tint nested with
fU5/rU3 produced consistent results. BLASTn searches of the sequences showed 99–100% similarity
to sugarcane white leaf disease (SWL) or grassy shoot (SGS) disease-causing phytoplasma. The
optimized nested PCR protocol was successful, with the minimum success rating of 88% and 100%
specificity. Midribs of milky white bud leaf samples were the best tissue type for rapid detection.
Systemic movement of the pathogen and a tentative latent period were also reported. The findings
are helpful in the early detection of the disease.
