Assessment of the Virus Infections Occurrence in New Established Plum and Sweet Cherry Orchards in Transylvania, Romania

Sixteen plum and eleven sweet cherry newly established commercial orchards in Transylvania, Romania, were the subject of the survey during the vegetative periods of 2020-2021 in order to assess the occurrence of different virus infections. Two blocks of 200 trees from each orchard were monitored by visual observation for virus-like symptoms, especially for Plum pox virus (PPV) in plum orchards. Twenty trees of each plum orchard were then sampled and tested for serological detection of PPV, Prune dwarf virus (PDV), Prunus necrotic ringspot virus (PNRSV), Apple chlorotic leaf spot virus (ACLSV), Apple mosaic virus (ApMV) and Myrobalan latent ringspot virus (MLRSV). Similarly, ten trees of each sweet cherry orchard were sampled and tested for the presence of PDV, PNRSV, ApMV, ACLSV, PPV, Arabis mosaic virus (ArMV), Cherry leaf roll virus (CLRV), Raspberry ringspot virus (RpRSV), Strawberry latent ringspot virus (SLRSV) and Tomato black ring virus (TBRV) by serologic assays. Additionally, a few sweet cherry trees suspected to be infected by Little cherry virus-1 (LChV-1) were tested by molecular assay. Unexpectedly, no plum orchards were found to be free of PPV. The average level of PPV infection was 32%. PNRSV occurred in 8.1% and PDV in 1.2% of sampled plum trees. Four out of ten viruses were detected in sweet cherry sampled: PDV (3.6%), ACLSV (0.9%), RpRSV (0.9%) and TBRV (0.9%). No infection with ACLSV, ApMV and MLRSV in plum and PPV, PNRSV, ApMV, ArMV, CLRV, SLRSV and LChV-1 in sweet cherry was detected. Mixed infections occurred at 4.8% in plum, and at 0.9% in sweet cherry trees sampled. The average occurrence of viruses in plum and sweet cherry orchards surveyed in Transylvania was determined at 41.3%, and 6.3% respectively. Overall results revealed a critical situation especially in regards to PPV infections making the success of fruit production in the most surveyed plum orchards quite problematic. Virus infections level in the younger sweet cherry orchards were significantly lower.