Big vein of lettuce a virus disease transmitted by the fungus

Big vein of lettuce is a disease well known to lettuce growers in California and Arizona. The disease is characterized by coarse chlorotic bands along the leaf veins, as shown in photo, and by a delay in maturity and a reduction in head size. The disease does not kill lettuce plants and marketable crops are produced in spite of big vein infections. During the winter and spring when lettuce is shipped from the Imperial and Salinas valleys and big vein is severe, salad bowls across the country commonly contain lettuce leaves with big vein symptoms.