Identification of Lettuce big-vein associated virus and Mirafiori lettuce big-vein virus Associated with Lettuce Big-Vein Disease in Slovenia

Lettuce big-vein disease (LBVD) is an important disease of lettuce (Lactuca sativa L.) worldwide. Two viruses are reported to be associated with the disease, Lettuce big-vein associated virus (LBVaV) and Mirafiori lettuce big-vein virus (MLBVV). The majority of publications shows that MLBVV is the causal agent of LBVD, but two plants with big-vein symptoms and infected only with LBVaV were found by Roggero et al. (2). Lettuce plants with big-vein symptoms were observed in a greenhouse in Ljubljana and in a private garden near Sežana. Chlorotic vein banding with deformations of leaves were observed and the plants were generally smaller than those without symptoms. The seedlings at the first location were grown in sterilized soil and showed no such symptoms. Six symptomatic plants and two seedlings without symptoms from the first location and three symptomatic plants from the second location were analyzed for the presence of LBVaV and MLBVV. Total RNA was isolated from 50 mg of lettuce leaf tissue with a RNeasy plant mini kit (Qiagen, Chatsworth, CA). Multiplex reverse transcription-PCR with primers VP248 (5'-CGCCAGGATCTTTGATCCATCTG-3') and VP249 (5'-TTGCGACATGTTCCTCCTCATCG-3') for LBVaV, VP286 (5'-TATCAGCTCACATACTCCCTATCG-3') and VP287 (5'-CAACTAGCTCAGAATACATGCAG-3') for MLBVV, and VP383 and VP389 for internal control (1), was performed. Mixed infections with MLBVV and LBVaV were detected in four plants and only MLBVV was detected in two plants from the first location. None of the viruses was detected in the two seedlings without symptoms. Mixed infections with MLBVV and LBVaV were detected in all analyzed plants from the second location. According to these results, only MLBVV could be correlated with observation of disease symptoms. To our knowledge, this is the first reported association of MLBVV and LBVaV with big-vein disease in Slovenia. MLBVV was the only virus found in all samples with big-vein symptoms. References: (1) J. A. Navarro et al. Phytopathology 94:470. 2004. (2) P. Roggero et al. Eur. J. Plant Pathol. 109:261, 2003.