MOLECULAR CHARACTERIZATION OF 'CANDIDATUS PHYTOPLASMA PRUNORUM' ISOLATES IN CACOPSILLA PRUNI INSECT VECTOR

'Candidatus Phytoplasma prunorum' (16SrX-B subgroup), the causal agent of European stone fruit yellows (ESFY), occurs in all Italian stone fruit-growing areas. Recently, a molecular characterization based on the non ribosomal tuf gene of 'Ca. P. prunorum' detected in infected plants, revealed the presence of two different groups of isolates ('type a' and 'type b') with a defined geographical distribution. To verify whether this differentiation occurred also in phytoplasmas present in the vector Cacopsylla pruni and to correlate the presence of the two types of isolates in insects and infected orchards, a molecular characterization of phytoplasmas from C. pruni specimens was carried out. Individuals were captured in ESFY-affected orchards located in northern Italian regions (Lombardia, Trentino, Friuli Venezia Giulia, and Emilia Romagna) both on cultivated and wild Prunus species. Total DNA from 66 infected individuals was submitted to the amplification of a phytoplasma tuf gene fragment and then analyzed by RFLP. Single infections of both isolates were identified in C. pruni specimens confirming their differentiation also inside the vector. As to the geographical distribution of the 'a' and 'b' types, previously defined in the investigated areas, only 'type a' was found in insects collected from orchards in Emilia Romagna and Friuli Venezia Giulia, while both types were detected in individuals from Lombardia and Trentino. Moreover, in these last two regions, the percentage of C. pruni specimens infected by 'type a' was prevalent (92.3% and 80.0%, respectively), in agreement with the infection rate of the same isolates detected in the corresponding orchards.