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Title: REVISED SUBGROUP CLASSIFICATION OF GROUP V PHYTOPLASMAS AND PLACEMENT OF FLAVESCENCE DOREE-ASSOCIATED PHYTOPLASMAS IN TWO DISTINCT SUBGROUPS

Author
item Davis, Robert
item Dally, Ellen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Flavescence doree is one of the most serious diseases known to affect grapevines. It was first reported in 1957 in France. In recent years, the disease has been spreading in regions in Europe, including Italy where heavy losses have been experienced in commercial vineyards. The cause of the disease is a tiny microbe, known as phytoplasma, that is transmitted from plant to plant by leafhopper insects that feed on the veins of grapevine leaves. To combat this disease, it is important to be able to detect and to accurately identify the phytoplasma that is the cause. In this work, we analyzed the nucleotide sequences of 16S rRNA genes from the flavescence doree phytoplasma and of closely related phytoplasmas. The results of our study document unique characteristics of the 16S rRNA genes in these phytoplasma, and provide a revised classification in which the flavescence doree phytoplasma is distinguished from phytoplasmas that are associated with other plant diseases. This information should aid efforts to improve the accuracy of detection and identification of the flavescence doree and related phytoplasmas.

Technical Abstract: The subgroup classification of phytoplasmas in 16S rRNA group 16SrV (elm yellows phytoplasma group) was revised and extended on the basis of enzymatic RFLP analysis of rDNA and analysis of putative restriction sites in nucleotide sequences. A 1.85 kbp fragment of the ribosomal (r) RNA operon from flavescence doree (FD) phytoplasma strain FD70 from France was amplified and cloned, and its nucleotide sequence determined (GenBank acc. no. AF176319). Placement of FD70 in subgroup V-C was verified by analysis of the amplified DNA and of the cloned sequence. Alder yellows phytoplasma was classified in subgroup V-C on the basis of analysis of GenBank sequence Y16387. Hemp dogbane phytoplasma strain HD1, a member of subgroup V-C, was distinguished from other subgroup V-C phytoplasmas by putative restriction site differences in the 16S-23S rRNA spacer region. Previously published FD phytoplasma sequence X76560 differed from AF176319 by nucleotide substitutions in at least eight positions and by differences in restriction sites for HpaII, MseI and Tsp5091. Therefore, the X76560 phytoplasma was classified in a new subgroup designated V-D. Based on similar analyses of 16S rDNA GenBank sequence Y16395 from Rubus stunt phytoplasma, this phytoplasma was classified in a new subgroup, V-E. The revised classification was supported by sequence similarities, group 16SrV-characteristic sequences, and a phylogenetic tree constructed on the basis of 16S rDNA sequences. The data were consistent with the concept that alder yellows and flavescence doree FD70 phytoplasmas belong to the same taxon.