16SrV phytoplasmas in grapevine and hazelnut. Epidemiology of Flavescence dorée and hazelnut decline in Slovenia: geographical distribution and genetic diversity of the associated 16SrV phytoplasmas

Flavescene dorée (FD) phytoplasma from 16SrV-C and -D subgroups are causing severe damage to grapevines throughout Europe. This phytoplasma is transmitted between grapevines by the sap-sucking insect Schapoideus titanus. European alders and clematis serve as perennial plant reservoirs for these phytoplasma strains, and recently it was found that the host range of phytoplasmas of subgroup 16SrV-C also extends to hazelnuts. In Slovenia, hazelnut orchards are declining due to 16SrV phytoplasma infections, and large populations of the leafhopper Orientus ishidae have been observed in these orchards. To characterise the genetic diversity of 16SrV phytoplasma in grapevine, hazelnut, and insect vectors, we performed nucleotide sequence analysis of the map gene. In this search for map genotypes, we also discovered new ones - one in grapevine and four in hazelnut . Analysis of additional genes allowed us to assign them to the VmpA-III cluster, which includes strains compatible with S. titanus transmission. Our results confirm the presence of FD-related strains in hazelnuts, and these strains are most probabily transmitted from one shrub to another by O. ishidae.