Molecular characterization of "Candidatus Phytoplasma prunorum" isolates in Cacopsylla pruni insect vector.

Candidatus Phytoplasma prunorum’ (16SrX-B subgroup), the causal agent of the European Stone Fruit Yellows (ESFY), is occurs in all Italian stone fruitgrowing areas. Recently, a molecular characterization on the non ribosomal tuf gene of ‘Ca. P. prunorum’ from infected plants, revealed the presence of two different groups of isolates (‘type a’ and ‘type b’) with a defined geographical distribution. In order to verify this molecular differentiation also in the phytoplasma in the vector Cacopsylla pruni vector and to correlate the presence of the two types of isolate in insects and infected orchards, a molecular characterization of the phytoplasmain C. pruni specimens was carried out. Individuals were captured in ESFY-affected orchards located in northern Italian regions (Lombardia, Trentino and Emilia Romagna) both on cultivated and wild Prunus species. Total DNA from 64 infected C. pruni specimens was submitted to amplification of a phytoplasma tuf gene fragment and then analyzed by RFLP. Single infections of both isolates were identified in C. pruni individuals confirming their differentiation also inside the vector. According 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 while both types were detected in insects coming from Lombardia and Trentino. Moreover, in these latter two regions, the percentage of C. pruni specimens infected by ‘type a’ was prevalent (91,6% and 84,6%, respectively) in agreement with the infection rate of the same isolate detected in the corresponding orchards.