Assessment of the variability for tolerance to powdery mildew in grapevine germplasm from La Rioja.

Fungal diseases such as powdery mildew are a major problem in grapevine cultivation worldwide. Although many American species are resistant to powdery mildew, most resistances are quantitative and have been difficult to introduce in European cultivars, due to the difficulty in selecting for both resistance and berry quality traits. European grapevine is susceptible to the disease, but European varieties show important differences with regard to the degree of tolerance. Conservation and characterization of local grapevine varieties are becoming important issues, as the importance of preserving genetic variability for agronomic traits and for resistances to biotic and abiotic stresses has been realized. A germplasm collection has been established in Rioja, Spain. Seven minor varieties together with 'Grenache' and 'Carignan', have been evaluated for the degree of tolerance against the fungus using a whole leaf assay in the lab. The quantification of the response to powdery mildew infection could allow the identification of natural sources of tolerance to the disease within V. vinifera germplasm.