The biology and epidemiology of ‘Candidatus Phytoplasma asteris‘ and ‘Candidatus Liberibacter solanacearum’ and their contribution to risk management in carrots

Abstract

Between 2020 and 2021, a total of 18 carrot fields were surveyed in east and west Flanders to monitor ‘Candidatus Phytoplasma’ and ‘Candidatus Liberibacter solanacearum’ presence. While ‘Ca. P. asteris’ was detected in 3 out of 18 sampled carrot fields, ‘Ca. L. solanacearum’ was found in none. Vector monitoring on ‘Ca. P. asteris’ positive sites resulted in the identification of 502 insects, mostly Auchenorrhyncha belonging to the genus Empoasca, Macrosteles, Eupteryx, Fieberiella, Euscelis, Zyginidia, Javesella and Aphrophora, as well as insects belonging to the Psyllidae family. ‘Ca. P. asteris’ presence was demonstrated in specimen from the five first mentioned genera. Subsequently, transmission assays were set up for Empoasca pteridis, Eupteryx aurata, Macrosteles sexnotatus, and Euscelis incisus. Setting up a M. sexnotatus culture failed, and for the other three, ‘Ca. P. asteris’ acquisition was only demonstrated for E. pteridis and E. incisus, however, without demonstrating successful transmission to healthy carrot plants.