Powdery mildew of Sugar beets

Description. This fungus has a white powdery appearance. It appears on leaves in the summer time. Infection normally begins on older leaves, typically close to the junction between the lamina and petiole, and it develops on both ab- and adaxial surfaces.
Pathogenicity. This pathogen decreases yields in crops by the reduction of chlorophyll in the leaves of plants. This will affect (as was mentioned) the yield and the quality of the seed crops. It also causes leaf and shoot deformities. In the case of Erysiphe betae, entry into the cell is both mechanical penetration and enzymatic degradation of the cuticle and the cell wall.
Plant defenses. The way that plants deal with these enzymes is they have an array of specialized inhibitors that counteract the effects of that specific pathogen. Some of these degrading enzymes include pectin lyases and polygalacturonases. In the case of when the pathogen gets entry through mechanical means the plant in itself doesn’t have much it can do against this kind of attack.