SYMPTOM EXPRESSION AND DISEASE OCCURRENCE OF A YELLOWS DISEASE OF GRAPEVINE IN NORTHEASTERN ITALY

A severe yellows type disease of grapevine (GYD) has been detected in various regions of Italy since 1982. One of the most susceptible cultivars is Chardonnay. Symptoms of GYD are indistinguishable from those described for flavescence doree (FD) in France. In northeastern Italy, the spread of GYD is not correlated with the presence of the leafhopper Scaphoideus titanus, a vector of FD. A 6-yr trial was carried out to acquire information on the epidemiology of GYD in northeastern Italy and on the effect of GYD infection on grapevines. The presence of an active vector(s) was demonstrated by exposing young, healthy grapevines, cultivar Chardonnay, to natural inoculations. The minimum incubation period for GYD did not exceed 5 mo. Infected Chardonnay grapevines protected in an insect-proof plastic screenhouse showed a transitory recovery (i.e., remission of symptoms followed by symptom reappearance). The length of the symptomatic period was quite variable when it was not influenced by reinfection; and the plants protected from reinfection gradually, but not completely, recovered.