DETECTION AND MOLECULAR CHARACTERIZATION OF AN ASTER YELLOWS GROUP PHYTOPLASMA ASSOCIATED WITH SOYBEAN AND EVIDENCE OF TWO NEW 16SrI SUBGROUPS IN CUBA

An emerging soybean disease observed in Cuba was investigated in view of the possibility that a phytoplasmas could be involved in its aetiology. Thirty-five soybean plants showing symptoms of stunting, chlorosis, crinkle and aborted seed pods were collected in Las Tunas and Holguin provinces during 2013, and analysed by nested-PCR with primers targeting the 16S ribosomal DNA (16S rDNA). Phytoplasmas were detected in 83% of symptomatic soybean plants. Conventional and virtual RFLP analyses of 16S rDNA sequences revealed the presence of strains of ‘Candidatus Phytoplasma asteris’ (16SrI group). Phytoplasmas belonging to ribosomal subgroup 16SrI-B and two putative new ribosomal subgroups 16SrI-W and 16SrI-Y were identified. Phylogenetic analysis corroborated the RFLP analyses, in which the Cuban strains formed a clade with representative sequences of the 16SrI group. 16SrI-B was the most prevalent subgroup (45% of positive samples) and mixed infections of different subgroups were observed (10% of the positive samples). The partial 16S rDNA sequences of three strains showed 99% nucleotide identity to several GenBank sequences of group 16SrI phytoplasmas, including a phytoplasma associated with a soybean disease in Brazil. This is the first report of a phytoplasma belonging to the 16SrI subgroup occurring in soybean in Cuba.