Herbaceous plant hosts as supermodels for grapevine viruses: a historical perspective

Herbaceous plant hosts are essential to grapevine virus research. Such plants offer numerous advantages as experimental hosts of viruses over Vitis species, the natural hosts. They grow faster, have a shorter generation time, and require little maintenance in the greenhouse or growth chamber in comparison with the natural hosts for which experiments are more technically challenging and last substantially longer. Local, pseudo-local, systemic, and pseudo-systemic herbaceous plants have been identified among infected experimental hosts and used for advances in grapevine virology. The discovery pipeline made possible by alternative model hosts has had a tremendous impact on the field. Species of Chenopodium, Nicotiana, Phaseolus, Cucumis, Petunia, and Cuscuta have served to document mechanical or graft transmission of grapevine viruses, fulfill Koch's postulates, study pathogenesis, examine movement, determine replication, purify and observe virus particles, image virions at the atomic level, develop diagnostic assays, characterize vector-mediated transmission, assess defense and counter defense mechanisms, and engineer resistance, among many other critical milestones. Alternative hosts continue to have intrinsic value for discoveries, although many technologies, including high-throughput sequencing, have largely outperformed their use for diagnostic applications. This review focuses on the critical role of herbaceous plant hosts in important discoveries on the biology of grapevine viruses.