Résumé
Potyviruses comprise the largest group of plant viruses. They are transmitted mostly by aphids in a nonpersistent manner. Many plant viruses cause severe disease in the host that they infect. Therefore, survival of plant viruses in nature strongly depends on their capacity to spread among new hosts. Most plant viruses require vectors for their transmission. This is attributed to the impermeable cuticle that coats the plant epidermis and cellulose cell walls, preventing entrance of virus particles, in contrast to animal viruses, which enter through natural openings. The association of nonpersistent viruses (NPV) with the vectors is very brief. Therefore, they were believed to be carried passively and were named stylet-borne, for almost half a century. The wide use of mechanical inoculation led to the appearance of virus strains that were highly infective but not transmissible by aphids. Complementation between aphid-transmissible (AT) and nonaphidtransmissible (NAT) strains led to the understanding that the process of transmission of potyviruses is much more complex than simply being carried on the external ridges of stylets, as suggested by van Hoof. This chapter is intended to complement the former reviews on the mechanisms of transmission and to summarize some important biological, biochemical, and molecular findings that may resolve the complexity of potyvirus transmission by aphids.