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Poster: Diseases of Plants: Disease Detection & Diagnosis


A new ‘Candidatus Phytoplasma pini’-related strain associated with witches’-broom of Pinus spp. is detected in Maryland
S. COSTANZO (1), J. Rascoe (1), Y. Zhao (2), R. Davis (3), M. Nakhla (1) (1) USDA-APHIS-PPQ-CPHST, U.S.A.; (2) USDA-ARS, U.S.A.; (3) USDA-ARS

Phytoplasmas are insect transmitted specialized bacteria that cause devastating diseases in crops and natural ecosystems. Pine trees (Pinus spp.) showing abnormal shoot branching and witches’ broom symptoms in a wooded area of Laurel, Maryland, were examined for the presence of phytoplasmas. Nested PCR assays for amplification of the 16S ribosomal RNA gene (rDNA) sequences were used on pine tree DNA samples to confirm possible association of a phytoplasma with the disease. Comparison of restriction fragment length polymorphism (RFLP) patterns and nucleotide sequence analysis of 16S rRNA gene fragments revealed that several trees were infected by a ‘Candidatus Phytoplasma pini’ -related strain (MDPP). The 16S rDNA sequence of MDPP shares 98.4% similarity with that of the ‘Candidatus Phytoplasma pini’ reference strain reported from Spain (isolate P127). The collective 16Sr DNA F2nR2 RFLP pattern is distinct from the reference patterns of all previously delineated subgroups, and is most similar to that of subgroup 16SrXXI-A with a pattern similarity coefficient of 0.79. Since the similarity coefficient value is lower than the threshold (0.97) for new subgroup recognition, MDPP may represent a new subgroup within the group 16SrXXI. The new subgroup is hereby designated as 16SrXXI-B. To our knowledge, this is the first report of a ‘Ca. Phytoplasma pini’-related strain associated with pine trees in North America and possibly the entire western hemisphere.