Biological and molecular features of ‘Candidatus Phytoplasma prunorum’ associated with a severe outbreak in apricot

European Stone Fruit Yellows (ESFY) outbreaks have recently become quite common in stone fruits, especially apricots, where the disease can severely damage production, resulting in economic losses. Since there is scarce knowledge about the disease, this study evaluated some biological and molecular aspects of ‘Candidatus Phytoplasma prunorum’ (16SrX-B) associated with ESFY by analyzing 30 symptomatic plants from a severely infected apricot orchard in Italy. In particular, resistance induction by Plasma Activated Water (PAW) was evaluated and genetic variability in the phytoplasma strains was searched through a multigenic study. In addition, the presence of potential insect vectors was investigated and cultivation trials of phytoplasma and other possible bacterial agents in artificial media were conducted. The results showed that PAW treatments did not affect the presence of phytoplasmas, nor the symptom severity in plants, and despite the different symptomatology observed in the orchard, no ‘Ca. P. prunorum’ variants were identified. Moreover, despite the growing number of symptomatic plants in the orchard, none of the potential vector species analyzed were positive for phytoplasmas. Finally, cultivation trials showed that it was not possible to isolate ‘Ca. P. prunorum’ on the artificial medium, however, Pseudomonas species were isolated and identified.