Evidence of resistance to the downy mildew agent Plasmopara viticola in the Georgian Vitis vinifera germplasm

Grapevine downy mildew, caused by Plasmopara viticola, is one of the most important diseases at the international level. The mainly cultivated Vitis vinifera varieties are generally fully susceptible to P. viticola, but little information is available on the less common germplasm. The V. vinifera germplasm of Georgia (Caucasus) is characterized by a high genetic diversity and it is different from the main European cultivars. Aim of the study is finding possible sources of resistance in the Georgian autochthonous varieties available in a field collection in northern Italy. The resistance levels to P. viticola were estimated both by experimental inoculations and by disease assessment in field conditions in a multi-year activity. Of the 93 tested accessions, 'Mgaloblishvili N' showed a constant resistant behaviour, by reducing the disease severity and the pathogen sporulation. High levels of leaf hair density did not always associate with reduced disease gravity in experimental inoculations, confirming that this kind of preformed barrier is not completely efficient in preventing pathogen infections.