Abiotic Factors Affecting Vector-Borne Plant Pathogen Complexes: Elevated CO2 and the Barley Yellow Dwarf Pathosystem

Changes in atmospheric CO₂ are known to influence plant physiology, subsequently affecting the nature of their interactions with their biotic environment. Barley yellow dwarf virus (BYDV), one of the most widespread and damaging viruses of small grains, is transmitted by cereal aphids and has a broad range of cultivated and uncultivated hosts from the Poaceae family. Here, we examined the effects of elevated CO₂ on plant physiology, <i>Rhopalosiphum padi</i> L. performance, and the accumulation of BYDV (strain BYDV-PAV) in winter wheat (<i>Triticum aestivum</i> L.), foxtail barley (<i>Hordeum jubatum</i> L.), and green foxtail (<i>Setaria viridis</i> (L.) Beauv.). A growth chamber experiment was conducted under ambient (420 ppm) and elevated CO₂ (700 ppm) with aphid-infested and uninfested plants. Elevated CO₂ significantly increased total plant biomass in all species but did not affect aphid survival or reproduction. The root biomass of winter wheat and foxtail barley, but not green foxtail, increased under elevated CO₂. However, no significant effect of aphids/BYDV was detected on total plant biomass. Transpiration rates varied with host plant and aphid presence but were not affected by CO₂ level. Total water-soluble carbohydrate concentration was unaffected by CO₂ or aphids. BYDV-PAV accumulation varied by host plant species, with winter wheat having the highest virus titer, followed by foxtail barley and green foxtail. Virus titers were increased under elevated CO₂ in all host plant species. We demonstrated that uncultivated grasses are important reservoirs for both BYDV-PAV and the <i>R. padi</i> vector and suggested that elevated CO₂ may enhance virus accumulation across the evaluated host plants. This underscores the need to consider the role of non-crop hosts in developing management plans and/or predicting BYDV dynamics in small grains.