| Microbial colonization patterns on the phylloplane have been described, but it is not known how these patterns develop or if they are maintained. By use of an experimental system consisting of the adaxial surface of apple leaves and the yeast-like fungus Aureobasidium pullulans (Ap), the development of micro-scale phylloplane colonization patterns was studied throughout the 2003 and 2004 growing seasons in an orchard. The total counts/mm2 on midveins, other veins, and interveinal regions were enumerated weekly, and by 7 July 2003 and 7 June 2004, total Ap counts/mm2 were significantly higher ( P < 0.05) on midveins and other veins compared to interveinal regions. This pattern remained consistent thereafter.; Some possible causal factors for the colonization pattern were investigated in the field. Because Ap densities were low on interveins, the hypothesis was explored that the veinal colonization pattern was caused by immigration differences to sites. At two periods in 2004, green fluorescent protein-tagged (GFP) blastospores were applied to hydrogen peroxide- and water-treated foliage of orchard trees. Individual leaves were re-sampled by a semi-destructive method immediately after inoculation (t0), and about one, two, and three weeks later. At t0 there were no significant differences in counts/mm2 on veinal (excluding the midvein) and interveinal sites, but at all points thereafter, densities were significantly higher on veins. There were no significant differences between peroxide- and water-treated leaves in either trial. The veinal colonization pattern developed in the absence of immigration.; Finally, the effect of rainfall on an established GFP-Ap population was investigated by non-destructive sampling during three rain events in 2004. Blastospores were produced immediately after each rain with significant increases overall, at all leaf microsites. When population data were examined on an individual leaf basis, rain led to significant increases on some leaves and decreases on others. This indicated that some blastospores likely convert to SCC and contribute to the established population. |
