The Effect of Within-host Virus Population Growth and Interspecific Competition on Aphid Transmission and Population Structure of Barley Yellow Dwarf Virus

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Barley yellow dwarf virus (BYDV) (Luteoviridae) species PAV and PAS are ecologically similar in that they share aphid vectors and host species, but in agricultural fields in New York State we found that the prevalence of PAV was three times greater than that of PAS. To determine if differences in within-host population growth rate affect vector transmission efficiency, disease spread and the distribution of virus types in the host community, this study evaluated the biological characteristics of PAV and PAS species isolates in common agricultural hosts and the outcome of competitive interactions between species in mixed infections. In singly infected plants, PAS population size was 20% greater than that of PAV at 8 days post inoculation (DPI), but by 33 DPI the population size of PAV was 10% greater than that of PAS. In doubly infected plants, by 33 DPI the population size of PAV was 40% greater than that of PAS. There was no difference in the transmission efficiency of PAV and PAS by Rhopalosiphum padi from singly infected plants at 30 DPI. But when transmission assays were performed 60 DPI, the transmission success of PAV was significantly greater than that of PAS. The greater transmission efficiency of PAV at late stages of infection did not translate to greater spread of PAV isolates in barley, oat or wheat plots in the field experiment. In the field, the susceptibility of plants significantly declined 18 days post plant emergence, suggesting that the development of resistance as plants matured may have arrested virus spread before asymmetry in the distribution of PAV and PAS could occur. In general, disease spread further in wheat than oat or barley plots. Taken together these results suggest that the identity of host species and vector population dynamics in relation to the availability of susceptible hosts are key determinants of the disease prevalence in the host community. Virus multiplication within hosts may influence the relative abundance of PAV and PAS in natural populations if there is a greater likelihood of virus transmission at different stages of host infection.
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virus competition; luteovirus; aphid transmission
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dissertation or thesis
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