Studies on mechanisms of splash dispersal of spores, using Pseudocercosporella herpotrichoides spores

Abstract

Simulated raindrops, 4 or 5 mm in diameter, fell 13 m onto target water films, with Pseudocercosporella herpotrichoides spores incorporated into either drops or targets. Resulting splash droplets were collected on fixed photographic film and numbers of droplets, spore-carrying droplets and spores determined. The patterns of dispersal of splash droplets, spore-carrying droplets and spores with distance and droplet size were similar for 4 mm and 5 mm incident drops with spores incorporated into either targets or drops. Numbers of droplets, spore-carrying droplets and spores decreased with increasing distance from targets and none were collected at 1 m. However, more spores were dispersed by 5 mm than by 4 mm drops and with spores in targets than with spores in incident drops. Whereas most splash droplets were in the smallest size category (0–100 μm), most spore-carrying droplets were 200–400 μm and most spores were in droplets with diameter greater than 1000 μm. Regressions of square root (number of spores) on droplet diameter were significant (p < 0.001) in all cases. The slopes of regression lines were greater when spores were in targets than when they were in incident drops. Splash droplets were collected up to a height of 70 cm, with most between 15 and 20 cm. The dye experiment showed that most splash droplets contained liquid from both incident drop and target film.