Influence of rainfall and temperature on the expression of leaf symptoms in vines affected by grapevine leaf stripe disease (esca complex).

The dynamics of the leaf symptom expression on vines affected by grapevine leaf stripe disease (GLSD) have not yet been fully elucidated to date. In recent years, several studies investigated the mechanisms involved in the expression of the leaf symptom. This study investigated influence of climatic conditions in leaf symptom expression. Daily rainfall and temperature data for 21 consecutive years(1994 to 2014) from two vineyards were analysed to assess the influence of climatic conditions on foliar symptom expression. These vineyards are located in Abruzzo, in central Italy and vines in both vineyards were 15 years-old in the first year of investigation.For each vineyard and year, rainfall and temperature data collected for each single month or different combinations of months were correlated with the incidence and severity of foliar symptoms which were assessed in September, where maximum symptom expression was usually observed. Rainfall in April to July showed some correlation with the foliar symptom expression, appearing July the most important month for the correlation between rainfall (ranging from 0 to 174.2 mm) and symptom. The correlation assessed in the 1994–2007 period was not longer noticed when the age of those same vineyards increased (2008-2014). Symptomatic vines showing high symptom severity died over the years with a mortality incidence of 22% in 2003 and 20% in 2005, at Giulianova and Controguerra, respectively. However, the mortality decreased significantly from 2006 in both vineyards. In 2008–2014, when a reduced correlation between rainfall and symptom was observed, a decrease of severity and incidence of leaf symptom expression was noticed in both vineyards. The temperature would not seem to have effect on the foliar symptom expression.