Experiments on Splash Dispersal of Fungus Spores

Abstract

SUMMARY: Splash dispersal (first studied by Faulwetter, 1 9 1 7~~ b) is characteristic of many bacterial plant pathogens and slime-spored fungi. The mechanism of splash has been studied in the laboratory under simplified conditions with water drops falling from known heights on to thin films of a suspension of conidia of Fusarium solani spread on horizontal glass surfaces. The resulting splash droplets were caught, counted and measured by the naphthol green B slide method (Liddell & Wootten, 1957). Both the total number of droplets produced and of those carrying spores increased as the film thickness decreased, and as the size and velocity of the incident drop increased.One incident drop 5 mm. in diameter falling on a horizontal film of spore suspension 0.1 mm. thick on a glass surface produced over 5200 splash droplets of which over 2000 carried one or more spores. The sizes of splash droplets ranged from 5 p to about 2400p, and their size distribution was of the log probability type. The median diameter was 70p for all droplets, and 140p for droplets carrying spores. The medium horizontal distances travelled by these droplets in still air was 10 and 20 cm. respectively. Increasing the film thickness to 0.5 and 1.0 mm. reduced the total resulting droplets to 3500 and 2100 (1600 and 500 carrying spores), respectively. Neither median diameter nor median distance of horizontal travel were much altered by varying the diameter of incident drop or film thickness. Droplets of diameters between 164 and 655p tended to travel further than either smaller or larger droplets. Small spores such as those of Gloeosporium album, Colletotrichum lindemuthianum and Nectria cinnabarina were even more readily picked up from suspension than the macroconidia of Pusarium solani.The number of droplets deposited per unit area on a horizontal plane decreased rapidly with increasing distance from point of impact, and in still air few droplets travelled beyond 70 cm.Splash on a twig bearing conidial fructifications of Nectria cinnabarina produced 2OOO spore-carrying droplets, and the sequence of events is shown by high-speed photography.A splash droplet consists of an intimate mixture of liquid from both the i&i-dent drop and the surface film. The larger splash droplets contain spores if either the incident drop or the surface f i l m is a spore suspension. Both raindrops falling at terminal velocity and drops falling more slowly from vegetation may operate the splash dispersal mechanism. Splash in rain or drip from trees may act as a complete dispersal mechanism in still air, or as a ' take-off ' mechanism leading to dispersal by wind. Both functions are important in plant epidemiology.Many fungi have mechanisms liberating their spores into dry air and their dispersal has been studied extensively. Many others produce their spores embedded in mucilage, which, as shown by Stepanov (1935), prevents their removal by wind. Field workers recognize that some of these slime-spored fungi are spread by insects while others may be spread by the actio...

Seasonal changes of leaf surface contamination in beech, oak, and ginkgo in relation to leaf micromorphology and wettability

“…Since raindrops have high kinetic energy they might remove many particles by splashing on impact with the leaf surface. Splashing is not only very effective in contaminating surfaces (Dreicer et al, 1984 ;Foster et al, 1985), but might also be an important factor in the removal of particles from smooth surfaces, as has been shown for the dispersal of fungal spores (Gregory, Guthrie & Bunce, 1959 ;Walklate, McCartney & Fitt, 1989). Especially heavy rain occurring during thunderstorms should be very effective in this respect, and might explain reasonably the decrease in contamination of beech leaves in later summer.…”

Rainfall and crop residue effects on soil dispersion and Beauveria bassiana spread to corn

“…Rainfall is important in dispersal of fungal and plant pathogens (Faulwetter, 1917a,b). In the absence of insects that can act as vectors of fungal spores, rain splash is critical to fungal spore transport (Gregory et al, 1959;Hunter and Kunimoto, 1974;Schub, 1983). However, the influence of these environmental factors on the spread of entomogenous fungi, for the most part, is unknown.…”

Dry Liberation of Fungus Spores by Raindrops

“…Two, when raindrops collide with wet, spore-bearing surfaces, parts of the falling drop and the surface water film become incorporated in splash droplets that contain spores. Many plant pathogens are thus 'splash dispersed', but the process probably adds little to the number of airborne spores because most splash droplets are large and soon deposited (Gregory, Guthrie & Bunce, 1959). Three, wetting fructifications can initiate spore release, for example, ascospores are released by hydrostatic pressure (Ingold, 1953).…”