Symptom evolution following the emergence of maize streak virus

Abstract 

For pathogens infecting single host species evolutionary trade-offs have previously been  demonstrated between pathogen-induced mortality rates and transmission rates. It remains unclear, however, how such trade-offs impact sub-lethal pathogen-inflicted damage, and whether these  trade-offs even occur in broad host-range pathogens. Here, we examine changes over the past 110  years in symptoms induced in maize by the broad host-range pathogen, maize streak virus (MSV).  Specifically, we use the quantified symptom intensities of cloned MSV isolates in differentially  resistant maize genotypes to phylogenetically infer ancestral symptom intensities and check for  phylogenetic signal associated with these symptom intensities. We show that whereas symptoms  reflecting harm to the host have remained constant or decreased, there has been an increase in how extensively MSV colonizes the cells upon which transmission vectors feed. This demonstrates an  evolutionary trade-off between amounts of pathogen-inflicted harm and how effectively viruses  position themselves within plants to enable onward transmission.  Impact statement  Phylogenetic analyses demonstrate an evolutionary trade-off between the amount of harm inflicted by a broad host-range virus and how effectively the virus positions itself within plants to enable onward transmission.