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First Report on Molecular Detection of Phytoplasmas in Papaya in Cuba

Phytoplasmas and rickettsias have been associated with recent nonviral papaya diseases (1,2). Forty leaf samples with symptoms similar to papaya bunchy top (PBT) (1) and Australian papaya diseases (2) were collected from surveys done in Cuban papaya areas of Havana and Villa Clara provinces. Thirty nine plants showed typical PBT symptoms, while 35 plants also exhibited symptoms previously described for phytoplasma diseases (2) such as yellowing, crinkling, necrosis and deformation of older leaves, phyllody, virescence, short internodes, reduced latex flow, stunted crown leaves, and abscission of the fruit. Samples were evaluated by transmission electron microscopy, nested polymerase chain reaction (nPCR) with 16S ribosomal RNA phytoplasma primers SN910601/DH6-R16F2n/R16R2, PCR with rickettsial succinate dehydrogenase gene (sdhA) primers PBT1/PBT2, HaeIII, RsaI, and AluI enzyme restriction, and phytoplasma intergenic sequence analyses. Rickettsia PCR amplifications of 750 bp were obtained for samples with PBT symptoms, while the 35 phytoplasma-infected samples yielded amplifications of 1,250 bp. Restriction profiles and a 98% homology in the intergenic sequence (GenBank Accession No. AY257547) confirmed the presence of apple proliferation phytoplasma group. Electron microscopy analysis evidenced the presence of particles similar to rickettsia and phytoplasma pleomorfic bodies in more than 50% of samples analysed. Also, those similar to potyvirus and rhabdovirus were observed in 22.5%. To our knowledge, these results are the first report on the molecular detection of phytoplasmas in papaya in Cuba and suggest a possible concomitance among phytopathogens detected.

References: (1) M. Davis et al. Curr. Microbiol. 36:80, 1998. (2) K. Gibb et al. Plant Dis. 80:174, 1996.