Ecology & Evolutionary Biology
Non Technical Summary
Potato virus Y (PVY) is one of the most serious pathogens of potato crops worldwide, reducing both yield and quality. New recombinant strains of PVY have emerged in recent decades, adapted rapidly to the potato ecosystem, and dominated virus populations over vast geographical areas, including both the United States and the United Kingdom. The overall objective of this proposal is to understand the ecological factors that allow recombinant strains of PVY to emerge, spread rapidly, and become the dominant viruses.
Animal Health Component
Research Effort Categories
Goals / Objectives
The overarching goal of this proposal is to identify ecological factors that allow new emerging viruses to predominate in host communities. To do this, we will evaluate the influence of landscape structure, vector community composition, transmission dynamics, within-host processes, and virus recombination on the emergence and spread of new vector-borne viruses, using the economically important aphid-transmitted Potato virus Y (PVY) as a model system. PVY is one of the most serious pathogens of cultivated solanaceous crops worldwide, reducing both yield and quality. New recombinant strains of PVY have emerged in recent decades, adapted rapidly to the potato ecosystem, and dominated virus populations over vast geographical areas, including both the United States and the United Kingdom. The recombinant strains must have a fitness advantage to be able to emerge rapidly as the dominant virus population, but the ecological factors influencing fitness are not clearly understood and represent an overall objective of this proposal. Our specific objectives include: 1) Determine whether landscape structure influences the composition of the vector community, patterns of PVY transmission, and prevalence of emerging disease. Agroecosystems are embedded in landscapes composed of a variety of ecosystems, including forests and other natural habitats, but agricultural landscapes vary in their composition and complexity. As compared to uniform landscapes, complex landscapes offer a diversity of host plants that may favor some vector species while limiting others, thus changing the species composition of the vector community, altering the spatial and temporal structure of virus communities, and modifying disease dynamics. 2) Quantify the effects of vector community composition and seasonal movement dynamics on the spread of different strains of PVY and prevalence of strain coinfections within a field. We will focus on the differential transmission of pathogens by different vector species. Although most plant viruses are transmitted by more than one vector species, mathematical theory addressing multiple vectors is rare. The spatial dynamics of vector colonization and virus transmission are key to predicting rates of virus spread and the likelihood of coinfection that may lead to recombination. These dynamics are particularly complex in virus systems like PVY, where the virus is transmitted by many aphid species, including species that establish and reproduce on the host plant ("colonizers") and transient species that visit the host but do not reproduce ("non-colonizers"). 3) Evaluate how host traits affect the probability of infection, coinfection and recombination by plant viruses. Both genetic variation among host plants and ontogenetic and physiological changes within hosts leading to mature plant resistance (MPR) can alter the probability of successful transmission and infection. Large differences in MPR between cultivars and virus strains have been demonstrated, but the mechanisms causing these changes are not well understood.
We will evaluate the ecological factors that may lead to virus recombination and emergence using field surveys, experimental sentinel plants, manipulative field experiments, lab experiments and mathematical models to explore PVY dynamics at three scales: the landscape scale, within field scale, and within host scale. Objective 1: We expect increased aphid species diversity in heterogeneous landscape, leading to a decrease in the average transmission efficiency of vectors and reduced spread of PVY. We will address this hypothesis in two contrasting regions of potato production: the heterogeneous landscapes of upstate New York, and the simplified agricultural landscapes of large scale monocultures in central Wisconsin. Vector abundance and diversity will be measured throughout the season using water traps. Plants will be sampled weekly for PVY using ELISA and RT-PCR. For the Wisconsin landscapes, we will compare field-level data on aphid community composition and abundance in varying landscapes with an estimate of the regional species pool based on suction traps. We will use a spatially explicit, agent based modeling platform to ask how landscape composition influences vector abundance, and how vector community composition and landscape structure interact to shape virus dynamics on agricultural landscapes of varying spatial heterogeneity. Objective 2: We will use field and laboratory experiments to address the role of vector community composition on virus emergence. First, manipulative field experiments will be used to determine the effects of the vector community on virus spread and rates of coinfection. Second, a series of lab experiments will explore: 1) the spatial and temporal dynamics of single and mixed strain infections in the plant; 2) how these dynamics influence vertical and horizontal transmission of virus populations; and 3) how genetic heterogeneity of vector populations influence the transmission efficiency and genetic diversity of virus populations. Mathematical modeling will integrate information from empirical and field studies to address how vector community composition and dispersal affect rates of disease transmission and coinfection. Objective 3: Our hypothesis is that MPR is a result of the sink/source status of the inoculated tissue and phloem connectivity between it and tubers. We will investigate phloem entry and connectivity using fluorescent dyes, radiolabelled carbon, and GFP tagged virus in genotypes of potato that differ in virus susceptibility and maturity. The results will be used to develop markers of resistance or susceptibility that can be used in field assays to provide data for predictive models being developed in the other objectives within this proposal. We will use a spatially specific within host model to help determine whether MPR resistance is due to a physical or biochemical mechanism.