Diseases

Downy mildew — bulb onion

Allium cepa L.

An obligate fungus-like disease caused by the oomycete Peronospora destructor, affecting all aerial organs of the onion. The disease manifests as a diffuse systemic infection or a secondary local lesion characterized by a grayish-violet coating.

In the reference 48 varieties crop Onion, where this is mentioned in the description.

The causal agent of the disease is the oomycete Peronospora destructor (syn. Peronospora schleideniana). The pathogen is highly specialized to the genus Allium and affects the leaves, scapes, and seeds of the bulb onion. The infection manifests as a systemic lesion where the mycelium penetrates the growing point, causing curling and yellowing of the leaves, or as local chlorotic spots that become covered with downy sporulation under high humidity conditions.

Completely immune onion varieties do not exist; however, breeding efforts are focused on utilizing the resistance gene Pd1, derived from the wild species Allium roylei. To identify this gene in the breeding process, molecular markers such as DMR1 are employed, and in professional documentation, the level of resistance to the pathogen is designated by the code Pd.

General information about the subject — on the page Downy mildew.

Sources8

Varieties of Onion mentioned in the description

Selection based on the description text, not on official evaluation: these data are absent from registers. For specific variety details, please refer to its profile.