‘Candidatus Liberibacter Solanacearum’ Is Unlikely to Be Transmitted Spontaneously from Infected Carrot Plants to Citrus Plants by Trioza Erytreae

SIMPLE SUMMARY: The potential transmission of the bacterium ‘Candidatus Liberibacter solanacearum’ from infected carrot plants to citrus plants by the African citrus psyllid (Trioza erytreae) should be considered and therefore studied, because this psyllid is an efficient vector of citrus huanglongbing disease (associated to bacteria from the same genus). The aim of this study was to assess the bacterium transmission by three different ways: dodder, grafting and the African citrus psyllid. Additionally, the feeding behavior and oviposition of this psyllid were also evaluated. The bacterium was only transmitted from carrot plants to citrus plants through dodder, although the infection was not established. The African psyllid could settle and oviposit in carrot plants, but it was not able to complete its life cycle on them. This psyllid acquired and transmitted the bacterium from carrots to carrots but was not able to transmit it to citrus plants. In conclusion, after having assessed all relevant possibilities by experimental transmissions from infected carrot plants to citrus plants, the bacterium was transmitted but not established. Our data suggest that the bacterium transmission to citrus plants by the African citrus psyllid is unlikely. ABSTRACT: Bacteria belonging to ‘Candidatus Liberibacter spp.’ are associated with various severe diseases in the five continents. The African citrus psyllid Trioza erytreae (Hemiptera: Triozidae) is an efficient vector of citrus huanglongbing-HLB disease, absent in the Mediterranean basin. This psyllid is currently present in the islands and mainland Portugal and Spain, where the prevalence of ‘Ca. Liberibacter solanacearum’ (CaLsol) associated to a carrot disease is high. Trioza erytreae normally feeds on citrus plants but has also been observed on other crops. It would be a great concern to the Mediterranean citrus industry if T. erytreae could transmit this bacterium from carrots to citrus and cause disease; therefore, the transmission of CaLsol from carrot plants to citrus plants was experimentally assessed. Although CaLsol was initially detected on receptor citrus plants in transmission assays by dodder and budding, the infection was not established. The feeding behavior by electrical penetration graphs and oviposition of T. erytreae on carrot plants versus citrus plants was evaluated. Trioza erytreae only reached the phloem in citrus plants. However, it was able to acquire CaLsol from infected carrots but unable to transmit it to citrus plants. CaLsol was detected in some carrot plants immediately after 7 and 14 days (inoculation access period), but it was not detected after one month. Trioza erytreae was unable to complete its life cycle on carrot plants. In conclusion, the efficient vector of bacteria associated to huanglongbing was unable to transmit CaLsol from carrot to citrus plants, but it acquired and transmitted the bacterium from carrot to carrot plants with low efficiency.