Aetiology of peach and sweet cherry leaf spot and twig canker in Montenegro

During the surveys of stone fruit orchards in 2017 and 2018, yellow, convex and mucoid bacterial colonies were isolated from peach and sweet cherry samples showing leaf and fruit spot and twig necrosis. We selected 37 g negative, HR positive strains. They were strictly aerobic, oxidase negative and catalase positive, hydrolyzed esculin and did not grow at 37°C. PCR analysis with primers XapY17-F and XapY17-R produced a single band of 943 bp. Based on the BOX-PCR profile, ten strains were selected for amplification and sequencing of the gyrB gene using Parkinson et al. (2007) primers. Obtained partial DNA sequences showed that 8 strains share 98.97 to 99.71% of gyrB sequence identity with Xanthomonas arboricola pv. pruni (Xap) pathotype strain ICMP51. The remaining two strains showed 100% identity to gyrB gene of Xap peach and apricot strains from Hungary and peach in Italy. Pathogenicity was tested by spraying shoots, and by infiltration of leaves and fruits of 'Royal Time' peach and 'Stella' sweet cherry with the suspension (10⁷ CFU mL^‑1 in SDW) of the strains, in three replicates. Lesions appeared on all inoculated plant material within 4 to 11 days after inoculation. The strains isolated from peach and sweet cherry in Montenegro were identified as Xanthomonas arboricola pv. pruni.