Identification of phytoplasmas in olive trees infected with Xylella fastidiosa in Salento (Italy).

Sampling was carried out in four olive grove localities in May, July and September 2018 in Lecce province (Italy) to compare the performance in the detection of Xylella fastidiosa presence in olive trees among PCR on three genes and qPCR[1]. The X. fastidiosa targets were the sigma RNA polymerase (primers RST31/33), the housekeeping gene lacF (primers lacF/R) and the hypotethical protein XF1100 (primers 272-1-int/272-2-int). The comparative screening results indicate that the qPCR and the PCR with primers RST31/33 were the most reliable methods for the pathogen detection, irrespectively from the sampling time and the locality. Morevoer considering that in several cases the CT values were very border line (35), the conventional PCR resulted a more suitable method for the confirmation of the presence of the bacterium. Further analyses on the same DNA extracts were performed to verify the possible presence of phytoplasmas and were carried out by nested PCR on 16S ribosomal gene followed by RFLP and/or sequencing analyses[2]. In a number of olive tree samples from one locality that were positive to X. fastidiosa (CT values from 32 to 35) or (in one case) negative with all the detection systems employed, the presence of phytoplasmas classified in subgroups 16SrI-B (‘Candidatus Phytoplasma asteris’-related) and 16SrX-B (‘Ca. P. prunorum’-related) was detected. The 16SrI-B phytoplasmas were already detected in olive in Italy[3], while the 16SrX-B are detected for the first time. The phytoplasma detection in the olive plants is indicating a possible active role of the Xylella insect vectors in the transmission of both bacteria that should deserve further studies for clarification