Effects of rain on splash dispersal of fungal pathogens
1997
Madden, L.V.
Dispersal of fungal plant pathogens by rain splash or wind is the critical component in epidemic development of many diseases. Yet, splash dispersal has been infrequently studied compared to wind dispersal, until recently. Over the past 12 years, we have studied the splash dispersal of Phytophthora cactorum and Colletotrichum acutatum at three hierarchical levels: splash from single water-drop impactions, spore transport with simulated rain over small areas, and disease spread in the field with naturally occurring rain. Number of splash droplets produced, number of spores disseminated, and flight distance of the splash droplets all increase with increasing size (and hence velocity and kinetic energy) of impacting raindrops. However, transport distance is very short, generally < 15 cm in each splash event, indicating that deposition of spores on a potential infection site is a result of continual re-splashing of spore-carrying droplets across the soil surface or ground cover, and through the canopy. Thus, characteristics of the ground cover and plant canopy can have a dramatic effect on resulting disease spread; increasing roughness of the surface and leaf area index of the canopy reduce splash dispersal. Very short rain durations (e.g. < 2 min) can result in substantial dispersal, but rain intensity [mm/h] has a complicated (nonlinear) relationship to dispersal, since increasing rain intensity leads to both increased removal of spores from the source but also loss of spores through the soil and canopy.
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