Development of rapid bioassays for the screening of plant grapevine material with regard to Eutypa dieback

Eutypa dieback, caused by the fungus Eutypa lata, is one of the most destructive trunk decline disease that affects grapevine. This disease is particularly severe on the susceptible variety 'Ugni Blanc' which is the most cultivated in the Cognac vineyard. In order to quickly reveal potential differences of susceptibility between clones or selections, reproducible methods should be used. Two approaches were tentatively investigated. One approach was based on the use of vitro-plantlets in lab to get infected tissues as previously described (Camps, 2008). Results showed that the length of necrosis obtained after 1 month-incubation varied between 1-3 mm and were not enough developed to allow a reliable screening whatever the cultivar, the technique or the isolate. The herbaceous nature of the grapevine tissues was supposed to be a difficulty for the lesion development. The second approach was based on the method reported by Peros and Berger (1994) using cuttings to reproduce typical leaf symptoms (necrosis and dwarfing). Some trials were carried out with different clones or varieties showing very low levels of leaf expression and indicating that the success of such procedure may be influenced by several factors (inoculation technique, quantity of mycelium, nitrogen supply). We concluded that there is a need for a highly reliable bioassay which can enable a rapid and a more significant induction of symptoms for providing a reproducible tool to the breeders.