Abstract
Flavescence dorée (FD) is a European quarantine disease of grapevine caused by FD phytoplasma (FDp) transmitted by the leafhopper of North American origin Scaphoideus titanus. The disease affects the most important viticultural regions of Europe and all wine-growing regions of Serbia. Unlike the insect vector, the pathogen is native to Europe and associated with several wild host plants among which alder trees as the main source of two out of three map genetic clusters of pathogen variants (Map-FD1 and FD2). Heretofore, the FDp epidemic in Serbian vineyards was thought to be monotypic, i.e., caused by the single genotype of the Map-FD3 cluster, M51, and correlated with clematis as the natural source plant. This study aimed to provide data on genetic diversity, through map and vmpA gene typing, and insights into ecological properties of epidemiological cycles driving the epidemic outbreaks of FD in Serbia today. Map genotyping of 270 grapevine isolates collected from 2017 to 2019 confirmed M51 as autochthonous genotype widespread in all wine producing regions of Serbia and the dominant FDp epidemic genotype in most of the districts (75%, 202/270 isolates), except in north Serbia where multiple outbreaks of M12 Map-FD3 were recorded (54 isolates). Tree of heaven is reported as a new FDp plant reservoir for the Serbian vineyards, hosting the M51 genotype, along with clematis. An outbreak of a new endemic Map-FD3 genotype M144 was documented in grapevine samples from east Serbia (5 isolates), correlating with previous findings of the same genotype in clematis. In addition, single grapevine infections with five new Map-FD3 genotypes (M150-M154) were recorded in central Serbia, thus indicating high endemic potential for new outbreaks. The vmpA typing placed all Map-FD3 isolates into the VmpA-III cluster, i.e., Vectotype III. Finally, we found direct evidence that at least two FDp endemic genotypes, M89 and M148, of the Map-FD2/VmpA-II have escaped from alders and propagated in the grapevine-S. titanus pathosystem in Serbia (Vectotype II). Our findings confirm the high complexity of the FDp ecological cycle and provide evidence of a unique, autochthonous Balkan epidemiology sourced endemically.
Highlights
Flavescence dorée (FD) is a quarantine disease of grapevine caused by Flavescence dorée phytoplasma (FDp; taxonomic subgroups 16SrV-C and 16SrV-D) which has first emerged in the vineyards of south-western France in the 1950s [1]
All three genotype clusters are occurring in Italy, Croatia, and Hungary [8,11,12,13,14,15] while Map-FD2 and FD3 are present in Slovenia and Austria [16,17]
The number of characterized FDp isolates per each district was determined in order to give a representative overview of genetic diversity of the pathogen strains in vineyards on the whole territory of Serbia
Summary
Flavescence dorée (FD) is a quarantine disease of grapevine caused by Flavescence dorée phytoplasma (FDp; taxonomic subgroups 16SrV-C and 16SrV-D) which has first emerged in the vineyards of south-western France in the 1950s [1]. The FD disease has a severe impact on productivity of affected vineyards, as well as on landscape management, which has caused significant economic losses in several European countries [3]. Based on genotyping of the epidemiologically informative house-keeping gene map [7,8], the FDp is comprised of variants within three genetic clusters namely MapFD1 (16SrV-C, reference strain FD70), FD2 (16SrV-C and 16SrV-D, reference strains FD92 and FD-D), and FD3 (16SrV-C, reference strain FD-C). These clusters are accompanied with specific vector and reservoir plant-associated epidemiology or geographic distribution. In Serbia, solely the Map-FD3 (FD-C) is present [8,18,19,20]
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