Diseases

Downy mildew — lettuce

Lactuca sativa L. var. crispa L.

A fungal disease of lettuce caused by the oomycete Bremia lactucae. It manifests as yellowish spots on the leaves and white sporulation on the underside, rapidly progressing to tissue necrosis.

In the reference 18 varieties crop Leaf lettuce, where this is mentioned in the description.

The causative agent of the disease is the obligate oomycete Bremia lactucae Regel. Symptoms of infection include the appearance of angular yellowish spots on the upper side of the leaf blade, bounded by veins. On the underside of the leaf, a characteristic whitish, downy growth develops in the affected areas, consisting of conidiophores and conidia. Under cool, high-humidity conditions, the affected areas quickly turn brown and undergo necrosis, while young plants may show a latent form of infection with significant growth retardation.

The pathogen is characterized by high genetic variability, and its populations are represented by numerous races designated by codes such as Bl:38EU–Bl:41EU. To combat the disease, lettuce breeding utilizes specific Dm resistance genes inherited from wild species of the genus Lactuca. The presence of these genes provides variety resistance to specific races of the pathogen, the monitoring of which is carried out by specialized international committees.

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

Sources8

Varieties of Leaf lettuce 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.