Fungi that grow on leaf surfaces alternate between a life cycle phase on the leaf, a transport phase in the atmosphere, and growth on another leaf of the same host or host of species, on a different host species, or on some other substrate. Essentially nothing is known quantitatively about the demography of these fungi in situ. The ultimate goal of this research is to produce a model for the yeast-like fungus, Aureobasidium pullulans, on apple leaf surfaces. To provide the foundation for the demographic study, the further development of molecular methods to track all epiphytic members of the A. pullulans population in situ is proposed. Second, to discriminate introduced from background populations, the (GUS) gene from E. coli will be installed into A. pullulans thereby allowing the detection of fungus chromogenically or fluorogenically in situ. Live versus dead cells will be confirmed independently by a vital staining method. The system will be evaluated and modelled under controlled and uncontrolled systems and then used to test the hypothesis that "source" areas (growth>immigration; and growth>death + emigration) exist for A. pullulans on leaves at different positions within the tree canopy. The project has implications for both basic ecology (community processes and structure) and for the biological control of plant pathogens.
