Plant-virus-vector interaction: grapevine fanleaf virus in Tunisia

This review of the literature on Fanleaf disease, illustrated by fieldwork in Tunisia, is important in view of the destructive nature of the disease and the interaction between the virus strains and the different species of nematodes that are its vector. Two nepoviruses are associated with the disease: Grapevine Fan Leaf Virus (GFLV) and Arabis mosaic virus (ArMV). Xiphinema index and Xiphinema italiae, which reproduce parthenogenetically, are vectors of GFLV, whereas Xiphinema diversicaudatum, with predominantly sexual reproduction, is the vector of ArMV. The determinants of transmission specificity of these nepoviruses by their natural vectors are located on the virus capsid protein.The study of the incidence of fanleaf disease in northern Tunisia shows that Grombalia has the highest infection rate (71% for both GFLV and ArMV) followed by Rafraf (45% for GFLV and 38% ArMV). Despite its geographical and environmental similarity to Grombalia, Takelsa had infection rates statistically closer to those of Rafraf. This same trend was observed in the correlation between disease symptomatology and the genetic diversity of isolated GFLV strains. The study of virus-nematode interaction showed GFLV in 93% of the Xiphinema samples analyzed. No ArMV was found, largely due to the absence of the specific vector in Tunisia.