First report of Grapevine leafroll associated virus-4 strain 5 in Italy

Leafroll is one of the most harmful viral diseases affecting grapevine worldwide. Historically, a dozen of viruses, named grapevine leafroll-associated viruses (GLRaVs), belonging to genera Closterovirus and Ampelovirus (Family Closteroviridae), have been found associated with the disease. Recent studies showed that GLRaV-4, -5, -6, -Pr, Deand -Car are in fact strains of the same virus species prompting taxonomic and nomenclatural revision of these viruses. Among these viruses, GLRaV-4 strain 5 has been reported from many viticultural areas in the world. In 2012-2013, surveys for virus detection disclosed the identification of GLRaV-4 strain 5 in 768 samples collected in Tuscany. The virus presence was ascertained by real-time (RT)-PCR. GLRaV-4 strain 5 was found in 2 samples (0.63% rate, 2012) and in 4 samples (1.16%, 2013) in cvs Sangiovese and Canaiolo. Further molecular analysis revealed that one infected vine hosted a single GLRaV-5 infection, while other infected vines were infected with multiple viruses, including GLRaV-3, GVA, GFkV and GRSPaV. The GLRaV-4 strain 5 sequences obtained from the positive samples shared 96% nucleotide identities with the corresponding fragment of a reference GLRaV-5 isolate (GenBank accession No. JX559639.1). The nucleotide sequence was deposited in GenBank as accession No. KM252726. To the best of our knowledge this is the first report of the occurrence of GLRaV-4 strain 5 in Italian vineyards.