Presence and spread of stone fruit viruses in Northern Italy

Stone fruit cultivation is very important in the Emilia-Romagna region, as well as in other areas in Northern Italy, in particular in the Trento Province, where extension of sweet cherry (Prunus avium) orchards has been recently increased. Symptoms of fruit necrosis and deformation, necrotic lesions and spots on leaves were observed in both regions. For this reason, regional Plant Protection Services (PPS) carried out a detailed survey in orchards and nurseries in order to avoid the spread of dangerous viral diseases that can cause quality losses and plant decline of fruit trees. During the recent five years, 5480 stone fruit samples were analyzed by ELISA or RT-PCR in the Virology laboratory of PPS, in order to detect Plum pox virus (PPV), Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV) and Apple chlorotic leaf spot virus (ACLSV), both in symptomatic and symptomless samples. Peach cultivars represent the main group of samples (3262), and one third of these were infected by PPV (1008). PPV was the most prevalent infectious agent also in apricot and plum, but it was not detected on cherry. Cherry samples, collected in orchards where fruit showed deformations and discoloration, were found positive for PDV, PNRSV and/or ACLSV. Furthermore, the flexiviridae Cherry virus A (CVA) and Cherry necrotic rusty mottle virus (CNRMV), and the foveavirus Little cherry virus 1 (LChV-1) were also discovered by analyses performed in the Virology Lab of the University of Bologna, using RT-PCR. In Trento Province, the same symptoms on cherry fruit were observed in 2015 and 2016 and a proper investigation was carried out to evaluate the presence of viruses infecting the cherry trees. Samples collected in 13 different orchards (399 in total) were analyzed by ELISA in the Fondazione Edmund Mach Virology Laboratory, resulting in mainly presence of ACLSV and PNRSV. CVA was detected by RT-PCR in some samples