Hybrid Grapevine Resistance to Downy and Powdery Mildews in Israel Under Warm Middle Eastern Conditions

Vitis vinifera grapevines are susceptible to downy and powdery mildews, requiring 4 to 10 chemical treatments per season in Israel. Resistant grape varieties offer an alternative. Hybrid varieties developed by the Weinbauinstitut Freiburg were introduced in Israel for disease resistance evaluation in different climatic regions through an understanding of the resistance mechanism based on secondary metabolite profiles. Grapevines were planted across four different climatic regions in northern Israel. Key findings: (i) in the laboratory, after artificial inoculation of downy mildew, the susceptible V. vinifera variety Cabernet Sauvignon had six times more Plasmopara viticola sporangia per leaf disc than the hybrid varieties (P < 0.001). For powdery mildew, the susceptible variety had ca. 3 × 10⁴ more spores/cm² leaf area than the hybrid varieties; (ii) in four tested vineyards, located in different climatic zones, downy mildew was only observed on the V. vinifera varieties; up to 4.6 times more powdery mildew incidence was observed on susceptible V. vinifera references than on the hybrid variety Cabernet Carbon, and hybrid varieties Bronner and Prior were only infected with powdery mildew on clusters, up to 33.6 times less than the reference. Souvignier Gris showed no infection in four plots over 3 years; (iii) the hybrid red grapevine varieties Prior and Cabernet Carbon showed significantly higher levels of antifungal response mediators, such as salicylic acid, than the red V. vinifera variety Tempranillo. These elevated metabolite levels correlated with increased resistance to downy and powdery mildews in the hybrids. This study advances our understanding of tolerance mechanisms in hybrid grape varieties and highlights their potential adaptation to Israel's climate in different terroir conditions.