Plant pathologists have frequently suggested viruses are parasites of chloroplasts. The investigators will integrate approaches from plant population biology, physiological ecology, and pathology to test the hypothesis that virus infection in leaves of herbaceous plants growing in the shade may limit their ability to acclimate to, and to occupy bright light habitats. A field study in which three species from shaded and sunny habitats will be infected with known viruses has been designed to test the significance of virus interactions with photosynthesis under natural conditions. The species selected, Solanum dulcamara, Plantago lanceolata, and Anthoxanthum odoratum, have all been thought to show ecotypic differentiation with respect to sun and shade, and all are known to carry many viruses under field conditions. It is possible that symptoms of terminal photoinhibition (leaf yellowing in the sun) previously associated with shade ecotypes may reflect the consequences of viral infection. New methods of chlorophyll fluorescence imaging will be developed which can diagnose impaired photosynthesis in virus infected leaves prior to symptom expression. These non-intrusive methods will be used to screen populations of plants for changes in photosynthesis which will be linked to plant growth, fecundity, and survival following infection. Such instrumentation may well find application in horticulture, where virus infection of plants in nursery cultivation is rampant.
