Ecology-based analysis of a recent association between Spartium junceum and 16SrV phytoplasma

An outbreak of Spartium witches' broom (SWB) in Sicily prompted efforts to identify and characterize associated phytoplasmas. Over 80 samples of Spartium junceum and around 270 individuals of the potential vector Livilla spectabilis were collected and analysed. Single and mixed infections of 16SrV and 'Candidatus Phytoplasma spartium' were dectected in Spanish-broom samples and for the first time in L. spectabilis. The 16SrV isolates were further characterized by multilocus sequence typing (MLST) to determine their phylogenetic relationship with Flavescence dorée phytoplasma (FDp) and to evaluate the risk of host-jump to grapevine. Phylogenetic analysis of most of analysed genes in MLST approach grouped S. junceum 16SrV-C isolates with FDp isolates infecting grapevine and Scaphoideus titanus. Notably, phylogenetic analysis of vmpA gene clustered the S. junceum isolates with FDp genotypes transmitted by S. titanus. This study extends the knowledge of SWB epidemiology with particular focusing on the possible risk of 16SrV host jump from Spanish broom to grapevine. Spanish broom was identified as a reservoir and potential inoculum source of phytoplasmas that cause severe disease on cultivated crops. Furthermore, involvement of the L. spectabilis psyllid in the epidemiology of this 16SrV-C phytoplasmas is postulated, although in the absence of in vivo transmission trials. The study further confirms the high ability of phytoplasmas to adapt to new hosts and vectors, a feature doomed to determine new phytosanitary emergencies.