Viruses at the interface between wild plants and crops

Viruses constitute the largest group of emerging pathogens, and geminiviruses (plant viruses with circular, single-stranded DNA genomes) comprise the major group of emerging plant viruses. With their high potential for genetic variation due to mutation and recombination, their efficient spread by "supervectors" and their wide host range as a group, including both wild and cultivated hosts, geminiviruses are attractive models for the study of the evolutionary and ecological factors driving virus emergence. Since the last four decades, much has been learned about the epidemiological features of geminivirus diseases in crop plants. Nevertheless, knowledge of geminivirus infection in wild plants, and specially at the interface between wild and cultivated plants, is still far from providing a complete view of their ecology, evolution and emergence. In this review, we address the most relevant aspects of geminivirus variability and evolution in wild and crop plants, and of their potential to emerge in crops. Data allow to hypothesize that ecosystem simplification/anthropisation affects the infection dynamics, the virulence and the evolution of geminiviruses, and seems to be a key factor driving their emergence in crops. However, data show that different viruses have their own evolutionary dynamics, even when sharing the same hosts and being transmitted by the same vectors. The level of genetic variability seems to be an intrinsic property of the virus, regardless of host range or co-existence in mixing infection with other viruses. Wild hosts may be categorised into two types: “sealed containers” and “mixing vessels”, with differential roles as virus reservoirs. Mixing vessel hosts could be hubs for transmission and for virus diversification, acting as efficient reservoirs for virus emergence.