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Oral: Viral Diseases


Factors that influence the structure of Citrus tristeza virus populations.
S. HARPER (1), S. Cowell (2), W. Dawson (2) (1) Department of Plant Pathology, University of Florida, U.S.A.; (2) Department of Plant Pathology, University of Florida, U.S.A.

A virus infection of a host is not a discrete, static entity, but a dynamic population whose members interact with one another and with their host to persist and spread. We have been using populations of Citrus tristeza virus (CTV) strains to examine this phenomenon, and have found that under constant conditions, the population structure will stabilize to an equilibrium defined by the host. This led us to ask what determinants, other than the host, can define a population, and what factors can cause a shift in population structure. Here we examined the effect of (a) inducing stress on the host through drought, high temperature, and by inducing systemic acquired resistance through the application of salicylic acid (SA), and (b) the addition of Citrus tatter leaf virus (CTLV) and Citrus leaf blotch virus (CLBV). We found that the structure of a CTV population comprised of three strains showed no significant change between treated and non-treated plants when exposed to drought or treated with SA, nor did the addition of CTLV or CLBV. Only exposure to approximate Florida summer temperatures (36°C day/25°C night) caused a change in structure, decreasing virus titer in a strain-specific and host-specific manner. Knowledge of the factors that determine population structure will aid in developing methods to manipulate populations and prevent disease.