From lettuce (Lactuca sativa) leaves with big-vein symptoms, two viruses associated with lettuce big-vein, Mirafiori lettuce virus (MiLV) and Lettuce big-vein virus (LBVV), were isolated. To make clear which virus is really associated with big-vein symptoms expression, the effect of the growth temperature for lettuce, on the serological detection of the two viruses and symptom expression was analyzed. At 27°C, LBVV was detected in the leaves, but neither the big-vein symptoms nor MiLV were observed. When the growth temperature was decreased to 18°C, big-vein symptoms appeared and MiLV was detected in the leaves.
