Evaluation of resistance to downy mildew in grape varieties grown in a Spanish collection

The genotypic diversity maintained in grapevine repositories can provide an invaluable source of resistance to diseases. Resistance to downy mildew (Plasmopara viticola) of most main and minor grapevine varieties grown in Spain was evaluated in the germplasm collection at "El Encin" (IMIDRA, Madrid). Resistance assessment using the leaf disc technique was compared with the results of field evaluations of natural infected plants according to OIV452-1 and OIV452 descriptors, respectively. A good correlation was found among both methods. Results ranged from very low to high levels of resistance to fungal infection, with most varieties showing high levels of susceptibility, as expectable in Vitis vinifera varieties, but some of them (usually those originally collected from humid temperate regions in Spain) were found to be less susceptible.