First report of Candidatus Phytoplasma prunorum, the European stone fruit yellows phytoplasma on peach trees on the territory of Canton of Geneva, Switzerland

In recent years, ‘Ca. P. prunorum’, the agent of ESFY was reported from several apricot orchards of Canton of Wallis, the main apricot production region in Switzerland (Genini and Ramel, 2004). The psyllid vector Cacopsylla pruni was also found in several locations in the Lake Geneva area (Ackermann et al., 2006). The presence of the disease and of its proven vector C. pruni at the eastern part of the Lake Geneva area, as well as the existing risk of dissemination of ESFY to other stone fruit orchards along the Lake Geneva are the reasons for which ESFY needs to be studied further. ESFY and its possible dissemination through C. pruni on the territory of Canton of Geneva, bordering France, has never been yet studied. In 2016, visual observations were conducted in several stone fruit orchards near Geneva. Plant material was obtained from peach trees, displaying some of the typical symptoms such premature leaf colouration, leaf-roll, tree decline (Sabaté et al., 2015), in the autumn, when the concentration of the phytoplasma in the upper parts of the trees is the highest. Phloem was prepared from branches and was extracted with a CTAB-based adapted protocol (Lefort and Douglas, 1999). PCR amplification of phytoplasma DNA was achieved with the universal primers: fP1/rP7 (Deng and Hiruki, 1991; Schneider et al., 1995). All positive samples were tested with the ESFY-specific non-ribosomal primers ECA1/ECA2 (Jarausch et al., 1998). Typical symptoms of ESFY, like premature leaf colouration, leaf yellowing with reddish edges, leaf-roll, severe chlorosis, die-back of top branches and partial or, complete decline of the trees (Figure 1) were found in a peach orchard (GPS coordinates: 46°15'17.4"N 6°12'40.7"E) located in the area of Collonge-Bellerive, close to Geneva city. Ten trees were sampled in this orchard. The presence of ‘Ca. P. prunorum’ was confirmed in two of them (Figure 2 and Figure 3). At the beginning of spring 2017, the monitoring of the ESFY symptoms in the infested orchard was resumed. Early bud break was found on the two infected trees and the infection was confirmed again by PCR (Figure 4 and Figure 5). The same symptoms were observed in many trees of this orchard, which correlated with the previous autumn observations. Trapping confirmed the presence of the insect vector Cacopsylla pruni (Bodnár et al., 2018) in the infected area. In order to understand more about the origin and the diversity of ESFY phytoplasma in this area, additional plant and insect samples will be analyzed. The correlation between symptoms and infected plants will be studied further. We report here for the first time on the occurrence of ‘Candidatus Phytoplasma prunorum’ (‘Ca. P. prunorum’) the agent of ESFY on the territory of Canton of Geneva.

The Effect of Phytoplasma Disease Caused by ‘Candidatus Phytoplasma prunorum’ on the Phenological and Pomological Traits in Apricot Trees

‘Candidatus Phytoplasma prunorum’, the causal agent of European stone fruit yellows (ESFY), is one of the most important pathogens causing considerable economic losses in stone fruit orchards. This study evaluated trees infected and noninfected by phytoplasma ESFY of 16 apricot varieties grown in an orchard in Lednice (Czech Republic) between the years 2008-2014. Pomological traits, phenophases, pollen germination and seed viability were analysed as well as the presence of ‘Ca. P. prunorum’ in pollen, flower organs, fruit flesh, immature seeds and seedlings by nested PCR. One of the most detrimental impacts was the decreased fruit set of infected trees which occurred in 12 out of 16 studied varieties reaching an average fruit set decrease of 16.1%. Pollen germination rates also suffered, showing an average decrease by 11.78% in infected trees. In the analysis of some traits, overall significant differences were observed between the infected and noninfected trees. However, for all analysed traits in different varieties, both positive and negative influences of phytoplasma ESFY were observed. The presence of ‘Ca. P. prunorum’ in infected trees was confirmed in flower parts (only in peduncle in 70.2% of cases) and fruit parts (immature fruit flesh in 42.0% and milky kernels in 26.2% of cases), however, neither in seedlings nor in pollen.

Prisutnost fitoplazme 'Candidatus Phytoplasma prunorum' u nasadima marelice u Baranji

Tijekom 2015. godine u Baranji je došlo do masovnog propadanja nasada marelice. Iako sve upućuje da je uzrok pojave smrzavanje, određen broj voćnjaka je pregledan kako bi se u njima utvrdila eventualna prisutnost biljnih bolesti. U osam nasada marelice u Baranji sakupljena su 63 uzorka sa stabala sa simptomima odumiranja te su analizirani na prisutnost patogena 'Candidatus Phytoplasma prunorum', uzročnika europske žutice koštičavog voća. Fitoplazma je utvrđena u četiri od osam nasada, ukupno u 15 od 63 uzoraka (24 %). Masovno propadanje marelice u Baranji tijekom 2015. nije povezano sa zarazom fitoplazme 'Ca. Phytoplasma prunorum', no prisutnost tog patogena potrebno je uzeti u obzir kod uzgoja osjetljivih voćnih vrsta i proizvodnje sadnog materijala na tom području.