Superoxide and hydrogen peroxide levels in apricot trees infected by European stone fruit yellows phytoplasma

The present study was based on a 6-year survey conducted in a Hungarian apricot orchard planted in 2014. Starting in 2019, the spread of European stone fruit yellows (ESFY) disease (causal agent: ‘ Candidatus Phytoplasma prunorum’) was followed in 200 plants by visual inspection of symptoms as well as by molecular analyses. The presence of ‘ Ca . P. prunorum ’ was confirmed in the investigated plant material. Asymptomatic, mildly symptomatic and severely symptomatic trees were present among phytoplasma-infected plants. We performed histochemical staining in leaves of uninfected (healthy) and phytoplasma-infected apricot trees to monitor the accumulation of the reactive oxygen species (ROS) superoxide and hydrogen peroxide. Our aim was to investigate the association of ROS accumulation with phytoplasma infections differing in symptom severity in apricot. We have shown that although ROS accumulation in phytoplasma infected apricot leaves may not be a marker of infection, lower concentrations of the ROS superoxide and hydrogen peroxide could indicate asymptomatic infections.