European stone fruit yellows phytoplasmas infecting apricot in Serbia and in Italy cluster mainly in two MLT groups

Introduction European stone fruit yellows is a phytoplasma disease that is quite often associated with death of apricot trees in one or two years. The presence of strains that are differentiable for aggressiveness is reported since very long time (1), however there is not clear diversification among the different ESFY strains also because that are infecting other stone fruits such as plum and peach and occasionally it was also detected in grapevine (2). To verify if the strains infecting apricot in different geographic areas may show differences that are consistent with different environments, strains collected in Serbia and North Italy in 2015 and 2016 were studied. The study was conducted using a multilocus typing approach on three selected genes which were used for wide survey of the phytoplasma in diverse stone fruit species before (3). Materials and Methods After their identification at the 16S ribosomal level 38 and 12 ESFY strains from different areas of Serbia and Emilia-Romagna (North Italy), respectively amplified from symptomatic apricot trees in 2015 and 2016 were selected for further RFLP characterization. Amplicons from ace, imp and secY genes were used as molecular markers (3) by RFLP analyses after nested PCR assays using Tru1I as restriction enzyme. Results and Dıscussıon While the ace gene was almost always amplified (49 out of 50), secY and imp gene were amplified from a lower number of samples (41 and 31 out of 50 respectively). The RFLP analyses allow to verify the overall profiles in the genes studied for 31 samples (19 from Serbia and 12 from Italy), and showed that in the profiles of strains from Serbia three lineages could be distinguished and two of these are also detected in the Italian samples. The third profile was only detected in Serbian samples collected in 2016, while the profiles I and II were identified in both samples from 2015 and 2016. SecY gene amplicons showed little or no variation since only in one case, in a Serbian sample, a diverse profile was identified. Ace gene amplicons showed the highest variability in both countries, however the Serbian samples showed also a profile that was not detected in the Italian samples. Imp gene amplicons showed no polymorphism at all, however the lack of amplification of a number of samples suggests a greater variability possibly on primer annealing sites, since this gene is coding a membrane protein that is under high environmental pressure.