Investigation of the presence of phytoplasmas and ‘Candidatus Liberibacter solanacearum’ in potato and carrot in Belgium, and tracking their (potential) vectors

Several harmful phytoplasmas and bacteria such as Xylella fastidiosa, ‘Candidatus Liberibacter solanacearum’ or fruit crop phytoplasmas are threatening important European crops such as potatoes, olives, apple and pear, with major economic impact. For these pathogens, some phloem and xylem feeding insects have already been identified as vectors or candidate vectors whereas involvement of other Auchenorryncha in the transmission of the diseases has not yet been investigated.
Knowledge on vectors involved, their phytosanitary status in specific areas, their host range, alternative hosts, and influence of abiotic factors on the vector occurrence and disease transmission capacity is fragmented or lacking. A comprehensive scientific insight is indispensable in order to improve risk evaluation and define effective regulation and phytosanitary management strategies adapted to local conditions for this type of vectored plant diseases.
During the first year of an intensive vector survey, a number of widely used trapping methods were compared, proving sticky traps to be the most effective. The vector survey focused on apple proliferation and pear decline phytoplasma infected apple and pear orchards, and a selection of severely phytoplasma (aster yellows; CYP) ravaged carrot fields. In pear, the known vector Cacopsylla pyri was abundantly present as known vector, yet several potential Auchenorrhyncha vectors (e.g. Empoasca decipiens, Eupteryx atropunctata, Orientus ishidae and Fiberiella florii) were identified. In apple, the known psyllid vectors appeared to be rare, yet as also the case for pear, E. decipiens which is known for its phytoplasma vectoring potential, and a number of other Auchenorrhyncha were found in high numbers throughout the growing season. In carrot, the known vector Macrosteles sexnotatus, as well as the CYP experimental vector E. decipiens (most abundant in summer), Zyginidia scutellaris (most abundant in autumn) and other species such as Javesella pellucida and E. atropuncata were found and population dynamics was assessed. In a next step, the potential vectors that were found on infected trees were tested for the presence of the phytoplasmas. So far, nested PCR (16SrRNA, primer pair P1/P7 followed by R16F2/R2 and fU5/rU3) resulted in bands for O. ishidae, but phytoplasma presence further needs to be confirmed.