Are the “bois noir” - associated phytoplasmas molecularly differentiable from stolbur phytoplasmas infecting other species?

Phytoplasmas of stolbur group affect a wide range of wild and cultivated plants, and are mainly transmitted by polyphagous planthoppers of the Cixiidae family. In vineyards, grapevine-affecting stolbur phytoplasmas are associated with “bois noir” (BN) disease and are transmitted by Hyalesthes obsoletus Signoret, but in wine-growing areas where H. obsoletus is absent, the presence of stolbur phytoplasma may entail the existence of alternative vectors. Based on actual and virtual RFLP analyses of PCR-amplified 16S rDNA sequences a number of subgroups had been described in the stolbur group, and molecular characterization on a number of its genes show growing evidences of variability related with strain differentiation. Biological complexity of stolbur phytoplasmas is also proved by the existence of numerous herbaceous hosts and diverse insect vectors. The question about host specificity is still open for stolbur as well as for the majority of described phytoplasmas. Characterization of BN phytoplasma populations was performed by multilocus sequence analysis and intriguingly, distribution patterns indicated a diverse prevalence of different populations in the geographic areas investigated (Contaldo et al., 2009; 2011; 2012). Selected BN strains were therefore compared with a number of stolbur strains from other plant host species as well as from H. obsoletus on secY and (st)amp genes in order to verify strains differentiation behaviours.