Study of the epidemiology of “flavescence dorée”(FD)-related phytoplasmas and potential vectors in a FD-free area
Epidemiological traits of “flavescence dorée” (FD)-related phytoplasmas were studied in Palatinate, a FD-free viticultural area in southwestern Germany. Grapevines with yellows symptoms, alder trees and leafhoppers on alders were sampled and tested for 16SrV-group phytoplasma presence. Genotyping of positive samples was based on the gene map. A high proportion of alder trees was infected by various genotypes including the FD-related genotype M38. About 22% of 330 sampled grapevines were infected with 16SrV-group phytoplasmas, but the map genotyping disclosed only the PGY-type of the 16SrV-C subgroup. The most abundant Deltocephalinae leafhoppers were Orientus ishidae, Allygus mixtus and Allygus modestus. Infection rates by group 16SrV phytoplasmas were 44%, 38% and 41%, respectively, with the predominant map genotype being M38. Allygus spp. and O. ishidae were able to transmit it to either Vicia faba, Alnus glutinosa, or both. A survey in vineyards revealed no evidence for the presence of the FD vector Scaphoideus titanus in spite of its local occurrence in the adjacent Alsace region. Thus, the Palatinate can still be considered free from FD and its vector.