Detection and molecular characterization of phytoplasmas infecting Rosmarinus officinalis L

Rosemary (Rosmarinus officinalis L.; Lamiaceae family) is a common and attractive evergreen shrubby species growing wild in the Mediterranean area, but cultivated for aromatic, ornamental and medicinal purposes. The interest towards this species is strongly arising, due to biological activities of essential oils extracted from leaves and flowers. In the Spring of 2011, symptoms of yellowing, necrotic spots, leaf rolling and stunting were observed on rosemary plants cultivated at three commercial aromatic growers of “Piana di Albenga” (Liguria region); in 2012 other plants showing witches’ broom symptoms were collected in the same area. In order to verify phytoplasma presence and to determine their identity, asymptomatic and symptomatic samples were tested by applying a direct PCR assay with universal primers P1A/P7A, followed by nested-PCR using primers F1/B6 or R16F2n/R2. Only from symptomatic samples expected length bands were obtained and RFLP analyses using restriction enzyme Tru1I allowed to classify phytoplasmas as belonging to ribosomal group 16SrXII-A (stolbur) in 2011 samples and 16SrI-B (aster yellows) in 2012 samples. Phytoplasma finding in rosemary represents the first report in this species. Considering that Liguria is the most important region for aromatic plants production, for a rapid and efficient eradication of this disease it is necessary to eliminate all symptomatic plants that could play an important role in the epidemiology of stolbur and aster yellows, as well as vectors (leafhoppers) and weeds, using suitable mechanical methods. Specific phytoplasma control of mother-plants before their vegetative propagation is also a necessity to prevent economic losses in rosemary crops.