Aim: The aim of the survey was to investigate if the grafting type influences the foliar expression of Esca during summer.Methods and Results: Observations were conducted on plots distributed in two French winegrowing regions (two different climatic regions) with two varieties (Cabernet-Sauvignon in the Bordeaux region and Mourvèdre in Provence). Three grafting types were compared: Omega graft, Whip and Tongue graft, and full cleft graft. For both varieties, we found a significant effect of the type of grafting on the foliar development of Esca symptoms. Full cleft grafted plots showed a significantly lower percentage of Esca foliar symptoms than the other two modalities, which were not significantly different from one another. Concerning Omega grafted plots, a significant difference in the rate of Esca foliar symptoms was highlighted compared to full cleft grafted plots, with a higher rate on Omega grafted plots, but these plots were also younger.Conclusions: The study established, for the first time, the difference between full cleft field grafted plots and Omega and Whip and Tongue grafted plots, revealing a higher incidence of Esca on the latter types of grafting.Significance and impact of the study: The spread of mechanical graft could be one of the factors explaining the increasing incidence of Esca in vineyard. Introduction Grapevine trunk diseases including Eutypa dieback, Esca and Botryosphaeria dieback are among the most destructive diseases affecting established vineyards. They have been reported in most winegrowing regions over the world and are responsible for loss of productivity and vine death. Since 1990, the incidence of Esca has increased drastically affecting nearly 10% of French vineyards (Kobès et al., 2005; Bruez et al., 2013).These diseases attack the vine wood: they cause death of spurs, arms, cordons and sometimes entire vines upon wood colonization by various pathogens (Larignon and Dubos, 1997; Mugnai et al., 1999; Surico et al., 2006; Van Niekerk et al., 2006; Lecomte et al., 2012). The development of necrosis inside the wood greatly hinders the sap flow and can induce a general weakening of the plant. The physiological balance of the plant seems affected when the critical volume of non-functional wood becomes too large (Lecomte et al., 2008; Luque et al., 2009; Maher et al., 2012). A high volume of inner necrosis may then seriously reduce water transport and may impact plant functioning, in particular in water stress conditions. There are actually a large number of pathogens described associated with these diseases and increased knowledge about mechanisms of their development in vine wood (Bertsch et al., 2013). Furthermore, Esca is a complex syndrome (Mugnai et al., 1999; Graniti et al., 2000; Surico et al., 2006) and is still poorly understood unlike Eutypa dieback. The role of Botryosphaeria species in the development of the Esca syndrome is still a matter of debate (Mugnai et al., 1999; Lecomte et al., 2012). Both diseased and healthy adult plants show the same fungi species, suggesting they are normal mycota associated with adult vines (Hofstetter et al., 2012). These pathogens are latent and can become pathogenic under the influence of unidentified factors (Retief et al., 2006; Surico et al., 2004 and 2006). There are no efficient methods for managing these diseases in the vineyard (Bertsch et al., 2009). Attempts to control these fungal diseases are currently based on the use of biological agents, natural molecules, chemical compounds and sanitation methods, alone or in combination (Darrieutort and Lecomte, 2007; Bertsch et al., 2013; Diaz and Latorre, 2013). Nevertheless, they are not yet completely effective and current research is focusing on the factors responsible for disease emergence (Lecomte et al., 2012).Numerous factors are reportedly involved in the development of grapevine wood diseases (Lecomte et al., 2011; Hofstetter et al., 2012; Bruez et al., 2013). The quality of plant material and planting practices, vineyard management strategy and pruning systems are some factors that may influence the proportion of Esca symptoms in mature vineyards (Geoffrion and Renaudin, 2002; Lecomte et al., 2011 and 2012). It has been also shown for instance that young plants from nurseries already contain fungi associated with Esca and Botryosphaeria dieback (Larignon et al., 2007; Larignon et al., 2008; Aroca et al., 2010; Billones-Baaijens et al., 2013). Indeed, the quality of the initial plant material can promote the development of pathogens in grapevine wood. Graft quality is another important criterion for the global quality of plant. Grafted vines showed a higher percentage of symptomatic vines compared to own rooted vines (Andreini et al., 2014). Contrariwise, Fourie and Halleen (2006) showed that machine-grafted graft unions had lower pathogen incidences compared to hand-grafted graft unions in commercial nurseries. The authors explained these results by big grafting w
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