Evaluation for powdery mildew resistance in grapevine (Vitis venifere L.) parental germplasm under In-vitro and natural field conditions

Powdery mildew (PM) caused by Erysiphe necator Schwein [(syn. Uncinula necator (Schweinf.) Burrill.] is an ascomycete biotrophic fungus of grapevine, leading to substantial yield and economic losses in infected crop. Thirty-four genotypes of Vitis vinifera L., including commercial varieties and hybrids, two genotypes of V. champini, three interspecific hybrids of Vitis species and two wild indigenous Himalayan species, namely V. parviflora and V. jacquemontii were assessed for resistance to powdery mildew using the leaf disc method in-vitro with E. necator isolate and in the field under natural condition during 2022 and 2023. Significant differences in the scores among the grape genotypes were observed in both in-vitro and field conditions. Resistance evaluation under both conditions classified V. parviflora, 110R, Coudere 1613, Dogridge, St. George and V. vinifera cultivars like Male Hybrid, Pusa Navrang, Blank Prince and Merlot as resistant sources, which can serve as valuable donor parents for breeding programs. Correlation analysis illustrated the negative correlation between disease severity index (DSI) and temperature (r = -0.50 (max), r = -0.48 (min)), rainfall (r = -0.07) and a positive correlation with relative humidity (r = 0.42). In-vitro inoculation, Organisation Internationale de la Vigne et du Vin Descriptors (OIV) scores (7 days post inoculation (dpi)) showed a negative correlation with hyphal area percentage (r = -0.90) and a positive correlation with necrosis (r = 0.86) indicating the resistant genotypes showing necrosis at the infection site and thus restricted the pathogen growth.