Where do spores go? Rain-splash patterns using surrogate dye.
Microorganisms are incredibly difficult to trap, identify and enumerate efficiently and quickly. This makes it difficult to study incursions of new pathogens and the spread of existing ones effectively. Finding efficient ways of overcoming these difficulties is essential to guide monitoring protocols, control or mitigate spread, or find potential areas for eradication after incursions. We investigated the use of a fluorescent dye, PTSA (1,3,6,8-pyrenetetrasulfonic acid), to explore patterns of rain-splash dispersal of Neonectria ditissima spores. Spores mixed with PTSA dye were released in pear and apple trees within orchards and in an artificial setting using a marquee. Spores and dye were released from a central point source 2.5 m above ground and recaptured in a number of rain traps at ground level and within the tree canopy. It was often very difficult to detect low numbers of recaptured spores, with zero counts found at any distance from the release point. Data points were highly variable, as expected given the range of field conditions, but a clear relationship between dye and spores caught in rain traps under various scenarios was obtained. These results show the merit of PTSA tracer dye as a tool to quantify potential dispersal patterns of microorganisms in an actual landscape of interest with various rainfall scenarios.