Viral particles obtained from a single tobacco plant were used to initiate an evolution experiment in A. thaliana Ler plants. Seven independent lineages were founded. Each lineage consisted on 10 plants. Twenty-one dpi, positive infections were confirmed by Western blot hybridization using an anti-coat protein antibody (data not shown). One of the infected plants from each lineage was randomly chosen to be the source of viral particles for infecting the next batch of plants. This basic transfer protocol was serially repeated every three weeks. In six out of seven cases, lineages went to extinction as a consequence of decreases in viral loads beyond the threshold value that ensures efficient transmission. The only surviving lineage was maintained for 17 serial passages (hereafter TEV-At17). The viral load reached by TEV-At17 21 dpi, was 2138.386134.08 LFU/mg. In other words, TEV-At17 accumulation was ,44-fold larger than the value estimated for the ancestral TEV (two-sample t-test, t 43 = 15.58, P,0.0001). Not only more viral particles were produced per gram of infected tissue, but also the infectivity of TEV-At17 was 100% (95% CI: 77.91-100%) and significantly larger than for the ancestral TEV (Binomial test, 1-tailed P,0.0001). Furthermore, symptoms induced by TEV-At17 were more severe (Figure 1 ), including stunting, vein clearing and leaf deformation.