Grape Powdery Mildew

The causative agent of the disease is the ascomycete fungus Erysiphe necator, whose anamorph stage is known as Oidium tuckeri. The pathogen affects all green parts of the plant, including leaves, young shoots, inflorescences, and clusters. A characteristic sign of the infection is a grayish-white powdery coating that develops mainly on the upper side of the leaf, as well as the appearance of 'flag shoots,' which are stunted and have deformed leaf blades.

Infection of berries at early stages leads to their desiccation, while late infection causes the berry skin to crack, exposing the seeds. On mature vines, traces of the mycelium appear as irregular dark brown spots. In grapevine breeding for resistance to this pathogen, specific loci designated with the prefix Ren (e.g., Ren3, Ren9) and Run1, introduced from Muscadinia rotundifolia, are used, and research is ongoing into knocking out susceptibility genes such as MLO-7.