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First Report of Phytoplasma Infection of Grasses in Singapore

In September of 2005, patches of Cynodon dactylon showing symptoms of bleached leaves were first observed in an open field in Singapore. Samples were collected from this site, from which total DNA was extracted with a Qiagen DNeasy kit (Catalog No 69104) and analyzed for phytoplasma DNA by a PCR assay with phytoplasma universal primer pairs P1/PTint (3). Resulting PCR products were each diluted 1:30 with sterilized distilled water and used in nested PCR with primer pair R16F2n and R16R2 (1). Twenty-five C. dactylon samples were assessed by this means, of which eight of eight with bleached leaves and four of seventeen symptomless samples tested positive. Widened disease surveillance identified the grasses, Axonopus compressus and Paspalum conjugatum, with similar bleached leaf symptoms in December 2006 and May 2007, respectively. Twenty-three of fifty-three A. compressus and six of twenty P. conjugatum samples were detected as positive for phytoplasma infection with the above PCR methods. A comparative analysis of sequences derived from the three grass hosts determined that the phytoplasma infecting C. dactylon (Genbank Accession No. EU234510) was most similar (>99%) to ‘Candidatus Phytoplasma cynodontis’ (GenBank Accession No. AB052871.1), whereas those detected in A. compressus (Genbank Accession No. EU234511) and P. conjugatum (Genbank Accession No. EU234512) were most similar (>99%) to the Brachiaria white leaf phytoplasma (GenBank Accession No. AB052872.1) (2). To our knowledge, this is the first report of phytoplasmas in C. dactylon, A. compressus, and P. conjugatum in Singapore.

References: (1) I. M. Lee et al. Int. J. Syst. Evol. Microbiol. 48:1153, 1998. (2) C. Marcone et al. Int. J. Syst. Evol. Microbiol. 54:1077, 2004. (3) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996.