'Candidatus phytoplasma solani' genotypes associated with potato stolbur in Serbia and the role of Hyalesthes obsoletus and Reptalus panzeri (hemiptera, cixiidae) as natural vectors

A progressive spread of stolbur-associated symptoms observed in potato fields in Serbia over the past few years initiated the study on disease epidemiology and transmission pathways performed during 2013 and 2014. Inspection of potato fields on 12 localities in northern Serbia revealed high incidence (60 % of symptomatic plants) and wide dispersal (100 % of inspected localities) of 'Candidatus Phytoplasma solani'. A qualitative analysis of Auchenorrhyncha fauna in affected potato fields identified 16 species, however only Hyalesthes obsoletus, Reptalus panzeri and R. quinquecostatus tested positive for 'Ca. P. solani'. Multilocus typing of strains associated with field collected potato plants and insects had been performed to identify the propagation scenario underlying the threatening epidemics. Combined analyses of the tuf, stamp and vmp1 genes detected ten genotypes, seven of which were shared by the potato plants and insects, confirming their interaction, with no clear species-specific association of certain 'Ca. P. solani' genotypes with plausible insect vectors. Semi- field experiments with naturally 'Ca. P. solani'-infected H. obsoletus and R. panzeri confirmed the ability of both species to successfully transmit the pathogen to potato plants and induce symptoms characteristic of stolbur disease. The third putative vector R. quinquecostatus shared genotypes of 'Ca. P. solani' with potato plants and other two cixiids, and though not tested in this study should not be ruled out as a potential vector. Our study revealed rather complex epidemiology of potato stolbur in Serbia involving several possible routes of horizontal transmission and provided experimental evidence for two natural planthopper vectors.