Resistance to downy mildew in wildly growing Eurasian Vitis vinifera L. grapevines

Plasmopara viticola (Berk. & M. A. Curtis) Berl. & De Toni, the causal agent of downy mildew, affects both cultivated and wild grapevine. Wild species of the genus Vitis L. are reliable sources of resistance to many of the diseases that affect cultivated grapevines. For this reason, it is important to study wildly growing (typical wild and feral) accessions belonging to V. vinifera L. The aim of this research was to study the levels of resistance to P. viticola of 57 Georgian wildly growing grapevine accessions by leaf disc method. The data were collected over eight years, from 2014 to 2021. Different degrees of resistance have been detected, ranging from susceptible (8.8% of accessions), low resistance (8.8% of accessions) moderate resistance (22.8%), and resistance (12.3% of accessions). Resistance of the 33,3% of the tested accessions was unstable and varied from susceptible to resistance across the years. Among resistant wildly growing grapevine genotypes, there are several accessions with a high density of the trichomes, although the data showed that the density of prostrate and erect hairs of the leaves is not correlated with the resistance trait. A large number of resistant genotypes among wildly growing grapevines suggests that in its natural habitat more resistant forms to downy mildew survives in the process of natural selection. Further studies are needed to characterize the plant-pathogen interaction and the mechanism of resistance of the wild accessions, although the resistant accessions, such as Tedotsminda 07, Tedotsminda 09, Tedotsimda 10 can be interesting for the breeding purposes in the future.