The acquisition of new hosts, or host range expansion, provides a virus with more opportunities for transmission and survival, but may be limited by across-host fitness trade- offs. A major cause of across-host trade-offs in viruses is antagonistic pleiotropy, that is, different phenotypic effects of mutations in different host environments, a Genotype x Environment interaction. In addition, epistasis (a Genotype x Genotype interaction) also may play a role in generating across-host fitness trade-offs. Relevant cases of host range expansion are the emergence of viruses in new host species and resistance-breaking (RB), in which viruses acquire the capacity to infect otherwise resistant plant genotypes. Negative effects of resistance-breaking mutations on within-host virus multiplication have been documented for several plant viruses. However, understanding virus evolution requires analyses of potential trade-offs between different fitness components. In this work we have analysed if there are trade-offs, and what are the causes, associated to the acquisition of new host species or genotypes in tobamoviruses that infect pepper crops.