Natural spread of grapevine viral diseases in temperate climate: the case of a Ligurian vineyard

Abstract

In the last decades efforts have been made in grapevine genetic and sanitary improvement through clonal selection procedures. Considering the high cost of establishing a vineyard, it is crucial that the planting material is, among the various valuable characteristics, free from the most dangerous viruses. However a vineyard planted with certified virus-free material is still subject to viral infection if viruses and their natural vectors are present in the area. The natural spread of viruses in vineyards is related to the environmental characteristics and the knowledge of its patterns in different viticultural areas is important from both a scientific and an economic point of view. A previous research carried out in a vineyard in Piemonte (NorthWestern Italy) showed that the spread of Grapevine virus A (GVA), Grapevine leafroll-associated virus 1 and 3 (GLRaV-1 and GLRaV-3) followed a constant, slow upward trend during the years. We extended the monitoring for the possible spread of viruses in natural conditions to a vineyard in the adjoining region Liguria, that has a warmer climate thanks to the Mediterranean Sea which flanks it. In a single row of the monitored vineyard the spread of GLRaV-3 was relatively fast, reaching a level little below 40 % in 11 years from vineyard planting; in some cases a double infection with GVA was also detected. This trend was confirmed by additional assays performed on vines in other rows of the vineyard. Mealybugs are known as vectors of viruses associated with leafroll and rugose wood complex diseases. According to a previous survey, Liguria is characterized by the presence of several mealybug species and a generally high population level. This may explain the fast spread particularly of GLRaV-3 in the monitored vineyard, although this must be confirmed by further investigations.