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Title: New 16Sr subgroups and distinct SNP lineages among grapevine Bois noir phytoplasma populations

item Zhao, Yan
item Davis, Robert

Submitted to: Annals of Applied Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2008
Publication Date: 4/1/2009
Citation: Quaglino, F., Zhao, Y., Bianco, P.A., Wei, W., Casati, P., Durante, G., Davis, R.E. 2009. New 16Sr subgroups and distinct SNP lineages among grapevine Bois noir phytoplasma populations. Annals of Applied Biology. 154:279-289.

Interpretive Summary: Grapevine plants in Europe are seriously affected by a disease known as bois noir (black wood). The disease has been attributed to a species of phytoplasma. Phytoplasmas are tiny bacteria that, unlike most bacteria, lack a rigid cell wall. They are spread from plant-to-plant by insects, leafhoppers, that feed in the major food-conducting tissues (phloem) located in the veins of plants. The bois noir disease has been spreading rapidly and extensively during the past few years, inflicting heavy impacts on the wine industry in Europe. This research was initiated to gain base information concerning the genetic variation among bois noir phytoplasma in different regions and vineyards of Italy. We found that bois noir phytoplasma includes varied strains that can be identified on the basis of molecular genetic markers. Two previously unknown subgroups of bois noir phytoplasma strains were designated, and several tentative new subgroups were identified. This work provides information needed for further research to learn whether genetic changes in the bois noir phytoplasma may be related to increasing spread and damaging effects of the bois noir disease. The study opens new opportunities for in-depth studies of the distribution of grapevine-associated phytoplasma strains in weeds, insect populations, and grapevines from different geographic areas. Results of the study will be of interest to diagnostics laboratories, viticulturists, and plant pathologists involved in devising means to stem the spread of bois noir disease.

Technical Abstract: Bois noir (BN) is an insect-transmitted grapevine yellows disease caused by phytoplasmas belonging to the stolbur subgroup 16SrXII-A. In Italy, increasing prevalence of stolbur phytoplasma strains in vineyards suggests progressive spread of the disease and potential for heavy impacts on the wine industry. In this work, we investigated the genetic diversity of stolbur phytoplasma strains in BN phytoplasma populations. Nucleotide sequences of 16S rRNA genes from stolbur phytoplasma strains affecting vineyards in the Lombardy region of Italy, and stolbur phytoplasma 16S rDNA sequences retrieved from GenBank, were subjected to virtual RFLP analysis. Calculation of virtual restriction similarity coefficients revealed the presence of new subgroups in group 16SrXII (stolbur phytoplasma group). Newly confirmed subgroups 16SrXII-F (XII-F) and XII-G, and tentative subgroups XII-H, XII-I, and XII-J, as well as known subgroup XII-A, were from grapevines; three additional tentative new subgroups (XII-K, XII-L, and XII-M) were from other plant hosts. In addition to recognition of new stolbur phytoplasma subgroups, nucleotide sequence alignments identified no less than nine genetically distinct 16S rDNA SNP lineages from grapevine, indicating a high degree of genetic heterogeneity within BN phytoplasma populations. The present study opens new opportunities for in-depth studies of the distribution of grapevine-associated 16SrXII phytoplasma strains in weeds, insect vector populations, and grapevines from vineyards located in different geographic areas.