| Summary: | Downy mildew, caused by the biotrophic oomycete <i>Plasmopara viticola</i>, is one of the most serious grapevine diseases. The development of new varieties, showing partial resistance to downy mildew, through traditional breeding provides a sustainable and effective solution for disease management. Marker-assisted-selection (MAS) provide fast and cost-effective genotyping methods, but phenotyping remains necessary to characterize the host–pathogen interaction and assess the effective resistance level of new varieties as well as to validate MAS selection. In this study, the <i>Rpv</i> mediated defense responses were investigated in 31 genotypes, encompassing susceptible and resistant varieties and 26 seedlings, following inoculation of leaf discs with <i>P. viticola</i>. The offspring differed in <i>Rpv</i> loci inherited (none, one or two): <i>Rpv3-3</i> and <i>Rpv10</i> from Solaris and <i>Rpv3-1</i> and <i>Rpv12</i> from Kozma 20-3. To improve the assessment of different resistance responses, pathogen reaction (sporulation) and host reaction (necrosis) were scored separately as independent features. They were differently expressed depending on <i>Rpv</i> locus: offspring carrying <i>Rpv3-1</i> and <i>Rpv12</i> loci showed the strongest resistance response (scarce sporulation and necrosis), those carrying <i>Rpv3-3</i> locus showed the highest levels of necrosis while <i>Rpv10</i> carrying genotypes showed intermediate levels of both sporulation and necrosis.
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