Myrtus communis: nuovo ospite di fitoplasmi in Sardegna.

Myrtus communis L., a bushy species of Mediterranean maquis, covers thousands of hectares in Sardinia (Italy). It is found from the coast to the interior of the island and in different soils and climatic zones. The berries and the leafy biomass are used in the food industry and, in the present case in the production of liquors. These liquors are Red Mirto, which is made from cold infusions of the berries in hydro-alcoholic solution, and White Mirto, which is made in the same way but using the young leaves. These products are very popular with around three million bottles a year being sold, and have a growing market. Given the species importance for the regional economy, many studies have been made in recent decades which have increased our knowledge of the process of domestication by defining the best cultivation techniques. Nowadays many cultivars which have been selected for their productive characteristics are available in the nurseries. In this context the sanitary status of the plants is of great importance. In 2003, during field studies comparing the performance of different cultivars, a severe series of symptoms was observed. The syndrome, although prevalent in certain cultivars, affected the majority of the plants, and was characterised by significant vegetative anomalies. These were a yellowing of the leaves showing also witches’-broom aspects, and strong microphyllia. The basal vegetation was prostrate and abnormally striped. As the epidemic developed, the previously mentioned alterations quickly spread from some plants to other on the rows, and, over a period of two years, to the entire plot, although the seriousness of the infection varied from plant to plant. These symptoms could be related to phytoplasmas infection resembling those mentioned by Camele et al. (1996). Studies aimed to assess the phytoplasmas presence were carried out in the autumn of 2004 on six samples of vein tissue from affected plants collected from two different fields. The plant DNA was extracted and amplified in direct PCR with universal primers (P1/P7), in nested PCR with F1/B6, and in a second nested PCR with R16F2n/R2 (Gundersen et al., 1996). The amplified products digested with TruI allowed to identify 16SrIII-B phytoplasma (reference strain Clover yellow edge) on one sample and 16SrX phytoplasma group, on the others. To confirm these results the F1/B6 products were further amplified in nested PCR with R16(X)F1/R1. The RFLP analyses with RsaI and SspI, allowed to identify the phytoplasmas as belonging to the 16SrX-A subgroup (reference strain Apple proliferation). A further nested PCR with R16(I)F1/R1 on the F1/B6 template, after RFLP with TruI, showed that 16SrXII-A phytoplasmas were present, in mixed infection with 16SrX-A, in two samples. This is the first time, as far as we know, that phytoplasmas 16SrIII-B, 16SrX-A and 16SrXII-A are detected on Myrtus communis. Epidemiological and molecular studies are in progress towards designing the possibility to contain further disease spreading.