Pepino mosaic virus and Tomato torrado virus: two emerging viruses affecting tomato crops in the Mediterranean basin

The molecular biology, epidemiology, and evolutionary dynamics of Pepino mosaic virus (PepMV) are much better understood than those of Tomato torrado virus (ToTV). The earliest descriptions of PepMV suggest a recent jump from nontomato species (e.g., pepino; Solanum muricatum) to tomato (Solanum lycopersicum). Its stability in contaminated plant tissues, its transmission through seeds, and the global trade of tomato seeds and fruits may have facilitated the global spread of PepMV. Stability and seed transmission also probably account for the devastating epidemics caused by already-established PepMV strains, although additional contributing factors may include the efficient transmission of PepMV by contact and the often-inconspicuous symptoms in vegetative tomato tissues. The genetic variability of PepMV is likely to have promoted the first phase of emergence (i.e., the species jump) and it continues to play an important role as the virus becomes more pervasive, progressing from regional outbreaks to pandemics. In contrast, the long-term progression of ToTV outbreaks is not yet clear and this may reflect factors such as the limited accumulation of the virus in infected plants, which has been shown to be approximately two orders of magnitude less than PepMV. The efficient dispersion of ToTV may therefore depend on dense populations of its principal vectors, Bemisia tabaci and Trialeurodes vaporariorum, as has been proposed for the necrogenic satellite RNA of Cucumber mosaic virus.