Occurrence of phytoplasma diseases of papaya in Sri Lanka
A study to investigate the association of phytoplasmas with different syndrome in Sri Lanka was carried out during 2011 and 2013 with sampling performed in major papaya-growing areas representing different agro-ecological zones. Samples from symptomatic and asymptomatic plants were collected from papaya and nested polymerase chain reaction (nested-PCR) was employed for characterization, using phytoplasma generic primers that amplify regions of the 16S rRNA gene. With the R16F2n/R16R2 primers in nested PCR, amplicons of 1.2 kbp were obtained from dieback symptomatic papaya samples of Monaragala suggesting that phytoplasmas are associated with papaya dieback in Sri Lanka. No PCR products were observed for asymptomatic plants and other diseased papaya samples obtained from other locations indicating that probably any other pathogen or undetectable titer of phytoplasmas involved in these diseases. Other phytoplasma specific primers fU5-rU3 also gave amplifications of 880 bp with DNA extracted from dieback symptomatic papaya samples of Monaragala. The partial 16SrDNA sequences of the six representative phytoplasma isolates shared 100% sequence identity with each other which were collected from three consecutive years. BLAST analysis revealed 99% sequence identity with that of phytoplasmas of group 16SrI ('Candidatus Phytoplasma asteris'). Outbreak of dieback generally occurs between December and March is appeared to be associated with weather conditions and the cultivar 'Sinta' is more susceptible than others. No consistent incidence pattern was evident for other diseases. In general, dieback and bunchy top diseases are quite abundant in Monaragala and only found in Monaragala whilst yellow crinkling, mottling and mosaic diseases are equally distributed in the rest of the areas in Sri Lanka.
Abeysinghe, S., Kumari, W.G.S.M., Arachchi, I.M.M. and Dickinson, M. (2016). Occurrence of phytoplasma diseases of papaya in Sri Lanka. Acta Hortic. 1111, 25-30
Carica papaya, Group 16SrRNA I, aster yellows, dieback