Spatial epidemiology of a vector-borne plant virus: interactions between landscape, hosts, vectors and an emerging disease of potatoes

Potato is the world's third most important staple food and Potato virus Y (PVY) is the most important virus disease in most potato production systems. In the last few decades recombinant strains of PVY have emerged in Europe and more recently in N America that are spreading and are associated with serious tuber damage. Factors responsible for the emergence and spread of these new strains are unknown but PVY is an ideal system to study the ecology and evolution of this infectious disease because all of the components, the virus, the host and the vector, are relatively well characterised. In this project we will investigate genetic, physiological, ecological, evolutionary and environmental factors as a dynamic network of variables affecting disease spread. We will identify the most important variables and how they influence PVY spread within and between potato plants.

This project addresses the significant challenges to agricultural production posed by changes in climate and the limitations on the use of agrochemicals in Europe. Potato production requires high levels of inputs to ensure high yields of crop for consumption as well as high quality of seed tuber planting material. PVY and many other virus diseases are transmitted by aphids and the changing weather patterns with warmer, drier summers and warmer, wetter winters is resulting in increasing aphid populations with the earlier arrival of aphids into the crops. The information gained will be used to develop quantitative and predictive models of disease risk in different agro-ecosystems and devise strategies for targeted intervention with agrochemicals for improved disease control. PVY infects a wide range of other crops including vegetables, tobacco and fruit and the underlying concepts, models and disease management tools developed in the project will have broad applicability in other agricultural systems.

The UK component will examine mature plant resistance (MPR) to PVY and provide data on aphid phenology. Results will be combined with data collected by the US collaborators on spatial epidemiology and interactions between landscape, hosts and vectors to describe the ecology of this important virus disease and emergence of new strains. MPR has been little studied since the 1980s and while there is evidence that it prevents virus infection in potato tubers in the late growing season and reduces the plants susceptibility, sometimes completely, the mechanism behind MPR remains unknown. Since MPR varies with cultivar and environmental conditions its onset is currently impossible to predict. The main, but poorly tested, hypothesis that we will investigate is that changes in host physiology affect translocation of virus in the phloem from leaves to tubers. We will investigate phloem connections between leaves and tubers, at different stages of development, and the effect of flower and fruit formation on tuber sink strength. The sink/source transition will be manipulated and variation between genotypes will be examined. We will use GFP-tagged virus infectious clones to test whether phloem entry and translocation of PVY varies at different stages or with cultivar. Gene expression in inoculated leaves will be analysed by comparison of microarray data from different virus strains and potato cultivars. Numbers of infected tubers and sprouts of progeny tubers will be tested to assess the potential for transmission to next generation. The goal is to identify physiological and gene expression markers for onset of MPR that can be used in field assays.
Information obtained about virus infection and movement through the plant will help to devise a risk index for different cultivars at key growth stages. Further work in collaboration with other partners will involve validation and optimisation of the markers and their use in predictive models for virus risk.

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