Notes on distribution of Scaphoideus titanus and “flavescence dorée” phytoplasmas in Tuscany
Abstract: In the last decade, the monitoring of Scaphoideus titanus Ball and of the “flavescence dorée” (FD) phytoplasmas, conducted by the Regional Plant Health Service of Tuscany and some technical and scientific institutions, highlighted a rather broad distribution of the leafhopper, not recorded till now only in the south-western provinces of Livorno and Grosseto, and on the contrary, a presence of FD, at epidemic risk levels, merely in some wine-growing areas of the Massa Carrara and Lucca provinces. In order to deepen the knowledge on Auchenorrhyncha fauna associated with grapevine yellows in Tuscany, surveys were conducted in several vineyards of the “Chianti Classico” area in the years 2007-2012. In 45 vineyards located in the territories of Castellina in Chianti, Radda in Chianti e Castelnuovo Berardenga (Siena), one to three monitoring stations, characterized by agronomic and cultural parameters, were set up with yellow sticky traps exposed from the second half of June to the middle of September. During 2009-2012 a similar survey was conducted in 31 wine farms located at Panzano, Greve in Chianti (Florence). The surveys pointed out an increasing trend in S. titanus population density in the monitored areas, despite the mandatory treatments against the leafhopper. The percentage of positive records in the Senese area increased progressively from 25% in 2007 to settle at around 60% in 2009-2012; in the Florentine districts stations involved in captures moved from 95.78% in 2009 to 98.97% in 2012. The distribution of S. titanus seemed mainly influenced by microclimatic factors and the origin of the propagation materials confirming previous findings. This increasing trend of the cicadellid spread to date has not been followed by an increasing presence of FD. In 2012-2013 other surveys were carried out in a wine growing area of Massa Carrara province, involved in FD infections in 2009, in order to clarify epidemiological aspects of grapevine yellow diseases. This agroecosystem was characterized by agronomical and environmental parameters and intensively sampled. Surveys, including the assessment of the Auchenorrhyncha vectors of grapevine yellows, are still in progress. Molecular studies have revealed that in the face of a fairly limited population of S. titanus, a very high percentage of plants are infected by FD. Molecular characterization on the 16Sr gene of FD strains obtained from 2009 and 2012 samples, showed that all belonged to FD-C. However the RFLP characterization on the SecY gene highlighted a polymorphism typically reported in FD-D. This finding shows the possibility to early identify the appearance of new FD strains and allows to manage FD in time.