Lettuce big-vein virus

Lettuce big-vein virus (LBVV), taxonomically classified as a member of the genus Varicosavirus, is a significant pathogen affecting lettuce crops globally. The virus is exclusively transmitted through the soil-borne fungus Olpidium brassicae, which acts as an obligate vector by introducing viral particles into the root system of the lettuce plant during infection.

The primary host for this disease is cultivated lettuce (Lactuca sativa). It is particularly problematic in greenhouse operations and indoor hydroponic systems. The virus thrives where high humidity levels and specific temperature ranges support the life cycle of the fungal vector, leading to widespread infections in commercial production facilities.

The clinical symptoms of the disease are diagnostic: veins on the leaves become excessively enlarged, translucent, and pale. This gives the leaf blade a distinctively crinkled, puckered, or blistered appearance, which is why the condition is commonly referred to as "big vein." Affected plants exhibit stunted growth and fail to form heads of commercial quality, leading to significant economic losses.

The disease cycle is heavily influenced by environmental factors. The fungal vector produces resting spores that remain viable in the soil for several years, even in the absence of a host crop. Infection risk increases significantly when soil temperatures remain within the 10°C to 18°C range, which is optimal for the mobility and infection cycle of Olpidium brassicae zoospores.

Integrated management is essential for controlling this disease, as there are no direct chemical treatments to eradicate the virus once the plant is infected. Management strategies focus on:

• Steam sterilization or chemical fumigation of soil;
• Use of virus-resistant lettuce cultivars;
• Effective water management and drainage improvement in hydroponics;
• Strict sanitation protocols to prevent the movement of contaminated soil.