New findings on spartium withches' broom disease

Spartium junceum is an important pioneer species of Mediterranean Basin. Spartium witches' broom (SWB) disease occurs in Italy and Spain. Besides the characteristic symptom, the plants show fasciation, yellowing of twigs, flower malformation and death of the whole plant. Both 'Candidatus Phytoplasma spartii' (16SrX-D) and a phytoplasma member of the group 16SrV-C have been associated to SWB. Since 2010 increasing reports of this syndrome were registered in Sicily region (South Italy) and particularly in the Etna area, a valuable viticultural territory. The rapid spread of the disease suggested the presence of an active vector of the phytoplasma/s. Detection and molecular characterization of phytoplasmas was carried out through analysis of the 16S ribosomal RNA gene amplified by nested-PCR using universal primer pairs on samples of spartium and insects collected. Obtained sequences allowed to classify the detected phytoplasmas, on the basis of virtual RFLP analysis performed by iPhyClassifier, in 16rRNA V-C and X-D groups and subgroups. Further phylogenetic analysis of sec-y gene of 16SrV-C isolates evidenced a homogeneous cluster distinguishable from other reference strains of group 16Sr-V including the flavescence dorée associated phytoplasmas. Among all the insects species collected only one monophagous psyllid of S. junceum (Livilla spectabilis) resulted positive to both phytoplasmas. The epidemic of SWB in Sicily and the finding of a potential vector pose interest on the disease especially in consideration of a potential risk of occasional trasmission of 16SrV-C to grapevine in a region free of flavescence dorée.