Vineyards of southern France and northernPhytoplasmas are phloem-restricted wall-less bacteria pathogenic to many plant species worldwide (37, 52). Phytoplasmas can be spread both by hemipteran insect vectors (63) and by vegetative multiplication of infected-plant material. Controlling phytoplasma-induced diseases in perennial crops depends on field surveys and implementation of prophylactic sanitary measures requiring sensitive and specific detection of phytoplasmas in plants. Genetically different phytoplasmas can infect the same plant species; therefore, precise identification and typing of phytoplasma strains are necessary to ascertain the causes and origin of new outbreaks and predict the route of disease spread.Vineyards in southern France, northern Italy, and Spain are affected by the flavescence dorée (FD) phytoplasma, a quarantine pathogen of grapevine (7,8,16,24). The classification of phytoplasmas, which are uncultivable and currently described under the provisional genus "Candidatus Phytoplasma," is mainly based on 16S rRNA gene phylogeny, genomic diversity, and plant and insect host ranges (32,36,59). The FD phytoplasma belongs to the 16SrV taxonomic group (36). Members of this group share high 16S rRNA gene sequence similarity (34, 38), but the group consists of phytoplasmas with an important variety of specific biological niches restricted to woody perennial hosts. "Ca. Phytoplasma ulmi" is responsible for yellows of elm species in North America and Europe (38) and "Ca. Phytoplasma ziziphi" is the agent of jujube witches'-broom and cherry lethal yellows in Asia (34,38). In Europe, other phytoplasmas of group 16SrV are mainly infecting grapevine (23,43), alder (46,51), blackberry (26,50), Spartium, and eucalyptus (44,45). Most of the insect vectors naturally disseminating group 16SrV phytoplasmas have been identified. The elm yellows phytoplasmas are transmitted in North America by Scaphoideus luteolus (Van Duzee) (5) and in Europe by Macropsis mendax (Fieber) (15), whereas FD phytoplasmas are specifically transmitted by Scaphoideus titanus (Ball) (53, 58) and rubus stunt phytoplasma by Macropsis fuscula (Zetterstedt) (26). Phytoplasmas associated with Palatinate grapevine yellows (PGY) and alder yellows (AldY) are both transmitted by the alder leafhopper Oncopsis alni (Schrank) (41, 42) and were classified as members of the group 16SrV on the basis of their high 16S rRNA gene and secY sequence similarity to the corresponding genes of FD phytoplasmas (2, 3).The genomic diversity in this phytoplasma group was recently examined. Sequence and restriction fragment length polymorphism (RFLP) analysis of the 16S rRNA genes and the 16S-23S intergenic spacer allowed differentiation of two differ-* Corresponding author. Mailing

Flavescence doré e (FD) is a European quarantine grapevine disease transmitted by the Deltocephalinae leafhopper Scaphoideus titanus. Whereas this vector had been introduced from North America, the possible European origin of FD phytoplasma needed to be challenged and correlated with ecological and genetic drivers of FD emergence. For that purpose, a survey of genetic diversity of these phytoplasmas in grapevines, S. titanus, black alders, alder leafhoppers and clematis were conducted in five European countries. Out of 132 map genotypes, only 11 were associated to FD outbreaks, three were detected in clematis, whereas 127 were detected in alder trees, alder leafhoppers or in grapevines out of FD outbreaks. Most of the alder trees were found infected, including 8% with FD genotypes M6, M38 and M50, also present in alders neighboring FD-free vineyards and vineyard-free areas. The Macropsinae Oncopsis alni could transmit genotypes unable to achieve transmission by S. titanus, while the Deltocephalinae Allygus spp. and Orientus ishidae transmitted M38 and M50 that proved to be compatible with S. titanus. Variability of vmpA and vmpB adhesin-like genes clearly discriminated 3 genetic clusters. Cluster Vmp-I grouped genotypes only transmitted by O. alni, while clusters Vmp-II and-III grouped genotypes transmitted by Deltocephalinae leafhoppers. Interestingly, adhesin repeated domains evolved independently in cluster Vmp-I, whereas in clusters Vmp-II and-III showed recent duplications. Latex beads coated with various ratio of VmpA of clusters II and I, showed that cluster

No abstract