Revisiting cross-protection in the form of antagonism: The case of Papaya mosaic virus protecting papaya plants against Papaya ringspot virus

Cross-protection has been defined as the initial inoculation of a mild strain of a virus protecting plants against a severe strain. As the elucidation of the mechanisms that underlie this phenomenon evolves, we propose that this concept extends to the use of different species of viruses, where a mild species [Papaya mosaic virus (PapMV), a potexvirus] protects against other severe species [Papaya ringspot virus (PRSV), a potyvirus] in papaya plants.