Abstract. Fungal diseases have emerged as one of the most critical challenges in viticulture,
significantly reducing grape yield and quality. Among these, downy mildew, caused by the fungus
Plasmopara viticola (Berk. & Berl. & de Toni), poses a severe threat to global grapevine (Vitis vinifera
L.) production, leading to substantial crop losses. The disease not only limits grapevine growth but
also negatively affects the quality of harvested grapes, thereby impacting wine and table grape
industries.
This study aimed to evaluate the resistance of grapevine genotypes to downy mildew through a natural
field survey. Resistance assessments were conducted using the method developed by H.M. Shikhlinsky
(2016) and a refined 5-point scale (as described by Naydenova & Nedov, 1985). To ensure result
accuracy, infected leaf samples from each genotype were microscopically examined, and pathogen
identification was confirmed following Benkena’s methodology (1963). Data obtained from field trials
were subjected to Cluster Analysis to classify the genotypes based on their resistance levels.
The analysis revealed that 3 genotypes were highly resistant, 21 were resistant, 10 were tolerant,
5 were susceptible, and 1 was highly susceptible. Notably, the genotypes Sahibi, Gulabi, and
Tulkuquyrugu were categorized as highly resistant, indicating their potential as valuable candidates
for breeding programs aimed at enhancing resistance to P. viticola. The study underscores the
importance of utilizing highly resistant and resistant genotypes in grapevine breeding initiatives to
mitigate the economic and agricultural impacts of downy mildew.