During a disease survey conducted in 2009 in Alaska, one potato plant (Solanum tuberosum) with symptoms characteristic of aster yellows, such as apical leaves rolling inward, leaves turning yellow or purple, and presence of aerial tubers, was found in a commercial field. Total DNA was extracted from leaves, stems, and roots of the symptomatic and symptomless plants with a DNeasy Plant Mini Kit (Qiagen, Valencia, CA) according to the instructions of the manufacturer. A nested PCR was carried out with the first round primer pair P1/P7 followed by second round primer pair R16F2n/R16R2 (1,3). An approximate 1.2-kb PCR product was amplified from the symptomatic plant, but not symptomless plants. The PCR products from R16F2n/R16R2 were digested using restriction enzymes AluI, BfaI, BstUI, HhaI, HpaI, KpnI, MseI, and RsaI. The restriction fragment length polymorphism (RFLP) patterns were compared with those from known phytoplasma strains (1) and they matched the patterns for aster yellows subgroup B (16SrI-B). After P1/P7 amplification, the nested PCR product of primer pair P1A/16S-SR (2) was purified with a MiniElute Gel Extraction kit (Qiagen), sequenced by GENEWIZ (South Plainfield, NJ), and the sequence data analyzed by iPhyClassifier software (4). The results indicated that the sequence (GenBank Accession No. HQ599231) had 99.65% similarity to ‘Candidatus Phytoplasma asteris’ reference strain (GenBank Accession No. M30790). The RFLP similarity was identical (coefficient 1.00) to the reference pattern of 16Sr group I, subgroup B (GenBank Accession No. NC 005303). To our knowledge, this is the first report on the molecular identification of aster yellows phytoplasma associated with potatoes in Alaska. The source of the phytoplasma and pathway of disease transmission is currently under investigation.
References: (1) I.-M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998. (2) I.-M. Lee et al. Int. J. Syst. Evol. Microbiol. 54:337, 2004. (3) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996. (4) Y. Zhao et al. Int. J. Syst. Evol. Microbiol. 59:2582, 2009.
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