Comparative impacts of Luteoviridae virus infection on cultivated and wild Poaceae

Background/Question/Methods

While the role of viruses in plant ecology is increasingly recognized, much remains unknown.  In particular, we know surprisingly little about how the effects of virus infection differ between wild perennial plants and more extensively studied annual crop plants. Plants are well understood  to experience trade-offs in allocation to growth and defense, resulting in annual plants that are typically less defended than longer lived perennials.  To what degree do viruses that are pathogenic in crop plants cause negative impacts in better defended wild perennials?  Here we compare the effects of virus infection in annual oats (Avena sativa), and native perennial switchgrass (Panicum virgatum), which exemplify vegetation types between which viruses circulate in Midwestern working landscapes. We focus on three related but genetically distinct virus species in the Barley and Cereal yellow dwarf virus (B/CYDV) group, which has become a model virus system in plant ecology: (i) BYDV-PAV (Luteovirus), a putatively crop-associated virus lacking a silencing suppressor, and (ii) CYDV-RPV and (iii) CYDV-RPS (Polerovirus), which possess silencing suppressors and may be more frequently associated with wild grasses.  All plants were inoculated as seedlings, with one virus or a BYDV/CYDV co-infection, grown under controlled conditions, and assessed for above- and below-ground productivity to determine virus-induced impacts.

Results/Conclusions

As expected, the annual Poaceae crop was substantially more impacted by virus infection than was the native perennial grass. Aboveground infection effects in the native perennial were evident for only one virus. However, all three viruses caused significant dwarfing of root systems in the native, an impact that would remain invisible to a field observer but which is likely to increase plant susceptibility to stress. Even more interestingly, the two types of host plant responded to the different viruses with patterns that suggest that the ability to overcome host silencing—evident only in the CYDV species--was a key virus trait necessary for broader impacts in the perennial plant. Nevertheless, the crop-associated BYDV virus was still able to dwarf the perennial’s root system even though its aboveground impact was limited.  This demonstrates how virus impact (I) on host plant growth depends on the genotype of both host (G_H) and virus (G_V), in addition to the environment (E) (I=G_H x G_V X E). It is imperative in microbial ecology that the diversity of plant viruses (both in genetics and impact) be recognized and more attention focused on the movement of viruses between agricultural and wild plant populations.