Identification and partial characterisation of Lettuce big-vein associated virus and Mirafiori lettuce big-vein virus in common weeds found amongst Spanish lettuce crops and their role in lettuce big-vein disease transmission

The potential role of 10 frequently occurring weed species found amongst Spanish lettuce crops as host plants for the two viruses associated with the lettuce big-vein disease, Lettuce big-vein associated virus (LBVaV) and Mirafiori lettuce big-vein virus (MLBVV), was studied. The results showed that both viruses can infect naturally growing Sonchus oleraceus (common sowthistle) plants, the unique susceptible species detected among the analysed weeds. The sequences of the coat protein (CP) genes of the LBVaV and MLBVV isolates recovered from S. oleraceus plants were determined. Phylogenetic studies revealed a very close relationship between the CP sequences from these weed isolates and those from Spanish lettuce. Moreover, we showed that S. oleraceus can act as a source of lettuce infection by means of Olpidium brassicae, the vector fungus of both viruses.