Epidemiology of European stone fruit yellows in Germany: the role of wild Prunus spinosa

A nationwide monitoring with regard to the presence and distribution of ‘Candidatus Phytoplasma prunorum’ and its vector, Cacopsylla pruni, has been carried out in Germany between 2013 and 2017. In total, 286 sites with cultivated and wild Prunus species were surveyed. 806 plant samples covering 94 administrative districts in all 13 federal area states and one city-state were analysed by PCR. Furthermore, 3108 C. pruni were caught in 63 districts and tested for ‘Ca. P. prunorum’. European stone fruit yellows was found mainly in symptomatic apricot, plum, almond and peach but also for the first time in Germany in sweet cherry. Non-symptomatic infections were detected in 437 randomly sampled P. spinosa at 104 sites without any stone fruit growing nearby representing a natural infection rate of 14%. The vector C. pruni was found on all P. spinosa plants at 62 sites spread across Germany. The infection rate of C. pruni was 1–2% regardless whether the insects were caught in stone fruit growing areas or at wild habitats. Our results strongly indicate that ‘Ca. P. prunorum’ is widespread in all natural habitats in Germany and that wild P. spinosa represent a major source of infection in stone fruit orchards. A representative sample of 1164 individuals of C. pruni captured at 100 sites was molecularly typed: all but one insect were of B-type, the one which is the proven vector of ‘Ca. P. prunorum’. C. pruni A-type was detected for the first time in Germany near the French border.