Survey for ‘Candidatus Liberibacter’ spp. and relative putative vectors in north-western Italy

‘Candidatus Liberibacter’ spp. are fastidious, phloem-limited bacteria within the alphaproteobacterial family Rhizobiaceae. Psyllids (Hemiptera: Psylloidea) are the primary vectors of ‘Candidatus Liberibacter’ species, playing an important role for their spread. These phloem-feeding insects acquire the bacteria while feeding on infected plants. ‘Candidatus Liberibacter europaeus’ (CLeu) was first recorded in Italy in plants of the rosaceous family and in psyllids belonging to the Cacopsylla genus. Subsequently CLeu was reported in scotch broom [Cytisus scoparius (L.) Link] plants from New Zealand and UK and the associated psyllid Arytainilla spartiophila Förster (Hemiptera: Psyllidae). While no symptoms have ever been observed on rosaceous plants suggesting that it behaved as endophyte rather than a pathogen, stunting and leaf chlorosis were observed on scotch brooms in New Zealand. Moreover, ‘Candidatus Liberibacter solanacearum’ (CLso) has been found associated with various plant disorders and economic losses in plants from the Solanaceae and Apiaceae families. Recently, it has been reported in Europe, primarily linked to carrots and celery. This situation is seen as a threat which necessitate the investigation of the current status of CLeu, its potential hosts and vectors, and their population dynamics. Furthermore, a serious need for a survey on the CLso presence. Scotch broom plant samples were collected as well as broom psyllids including different ecological niches followed by DNA extraction, conventional PCR tests for CLeu and sequencing of the positive samples. Transmission trials have been conducted including both broom psyllids A. spartiophila and Arytaina genistae Latreille (Hemiptera: Psyllidae), besides, investigating insights on their population dynamics for two consecutive years. Concerning CLso survey, plant and psyllid samples were collected from potato and carrot field, besides, sampling of wild plants from fields’ vicinity and from urban areas. The same detection test procedures were performed using different primers specific for CLso detection. CLeu was detected in plant samples and in both species of broom psyllids. Arytainilla spartiophila proved to be efficiently able to transmit CLeu to healthy scotch broom plants. Arytainilla spartiophila proved to be a univoltine species while A. genistae showed to be bivoltine in the surveyed area. This is the Abstract 2 first report of CLeu presence in scotch broom and its associated psyllids in Italy and specifically in A. genistae worldwide. In potato fields, the psyllid species Bactericera nigricornis Förster (Hemiptera: Triozidae) was the dominant, while Bactericera trigonica Hodkinson (Hemiptera: Triozidae) was the most abundant in carrot fields, followed by Heterotrioza chenopodii Reuter (Hemiptera: Triozidae) ranking as the second most abundant species in both cases. CLso positive samples were found from Daucus carota L., B. trigonica, H. chenopodii, B. nigricornis and Trioza urticae L. (Hemiptera: Triozidae). Sequencing results suggest the detected haplotypes are D and U. It is the first report of CLso in B. nigricornis and H. chenopodii in Italy and specifically of haplotype U in B. nigricornis worldwide. These findings raise concerns about the host range of CLeu and its potential impact of other plant that may host it as well as the potential spread scenarios of CLso and the associated risk of significant economic losses