Grape Powdery Mildew

The pathogen, the fungus Erysiphe necator, is represented by two main genetic groups. Group A overwinters primarily as mycelium in buds, forming 'flag shoots,' while group B can overwinter as both mycelium and cleistothecia, which increases the survival rate of the infection.

Symptoms include the appearance of 'flag shoots' that are stunted and covered with fungal growth, leaf deformation, poor vine maturation, and damage to inflorescences. When berries are affected, the skin cracks, which opens the way for secondary infections.

Vitis vinifera varieties are mostly susceptible to the pathogen, so breeding relies on the introgression of resistance genes from wild species such as V. amurensis and V. riparia, including the Unr gene. The degree of infection in variety trials is evaluated on a scale from 1 to 9 points.