Lettuce mosaic virus (LMV) is a typical potyvirus (genus Potyvirus, family Potyviridae), which causes one of the major virus diseases of lettuce crops worldwide. LMV is seed-borne to a low but significant rate (1-10% of the seeds produced by an infected mother plant germinate into infected seedlings). This provides the primary inoculum in lettuce crops. LMV, and thus the mosaic disease, is then spread locally from plant to plant by the feeding stylets of aphids.