https://doi.org/10.37229/fsa.fja.2026.09.24

Powdery mildew, caused by the obligate ascomycete Erysiphae necator Schw., remains a primary threat to viticulture worldwide. This study evaluated the susceptibility of several grapevine cultivars to powdery mildew and investigated the potential of various chemical compounds to enhance biochemical resistance under field conditions. Among the assessed cultivars, King Ruby exhibited the highest disease severity, followed by Thompson Seedless, whereas Prime and Starlight displayed the greatest resistance. The results demonstrated a significant reduction in total chlorophyll content in infected leaves compared to healthy ones, revealing a consistent inverse correlation between chlorophyll levels and disease intensity across all cultivars. Conversely, proline accumulation increased significantly following infection; resistant cultivars (Prime, Starlight, and Crimson) maintained the highest proline levels, while King Ruby and Thompson Seedless recorded the lowest. Regarding fruit quality, healthy berries from Prime and Starlight cultivars showed superior Total Soluble Solids (TSS%) compared to Thompson Seedless. Conversely, the highest Titratable Acidity (TA%) was observed in Thompson Seedless and King Ruby. Field treatments revealed that all tested chemicals significantly mitigated powdery mildew severity on the susceptible cv. King Ruby compared to the control. Calcium silicate, Potassium silicate, and Ataclawed demonstrated the highest efficacy, while micronized sulfur, calcium carbonate, and potassium bicarbonate showed moderate suppressive effects. Notably, all treatments enhanced the average fruit yield (kg/vine), with potassium bicarbonate and Ataclawed yielding the highest results. Furthermore, biochemical assays confirmed that all treatments stimulated the activities of defense-related enzymes, specifically peroxidase (PO) and polyphenol oxidase (PPO), alongside a marked accumulation of total phenolic content. These findings suggest that silicate-based compounds and Ataclawed offer promising, eco-friendly alternatives for integrated powdery mildew management in vineyards.