Splash dispersal of spores of Pseudocercosporella capsellae (white leaf spot) from oilseed rape leaves of different inclination, flexibility and age
1992
Fitt, B.D.L. (Rothamsted Experiment Station, Harpenden (UK). Inst. of Arable Crops Research) | Inman, A.J. | Lacey, M.E. | MacCartney, H.A.
Spore dispersal gradients were fitted well by exponential models in three experiments when simulated rain fell on to oilseed rape leaves infected by Pseudocercosporella capsellae (white leaf spot). Regressions of number (ln) of spores on distance from the source generally accounted for over 90% of the variance. Gradients were steepest, with the smallest half-distances (5.0 - 5.5 cm), when the sources were younger, detached leaves placed horizontally on nylon mesh. Half distances were 6.9 cm for younger leaves inclined at 30 degrees C to the horizontal, 7.5 cm for older detached leaves placed horizontally and 8.5 - 10 cm for lower or upper leaves remaining attached to plants. Droplet size categories with the greatest numbers of spore-carrying droplets dispersed from a source were 0 -200 mig diameter (43% of the droplets) and 200 - 400 mig (30%), respectively, for the younger and older horizontal detached leaves. The number of spores per droplet increased similarly with increasing droplet size for both sources, from 1.5 spores per droplet for the 0 - 200 mig droplets to c. 22 spores per droplet for droplets over 1000 mig in diameter. The number of spores dispersed decreased exponentially with time, with half-life of 2 - 5 min., estimated by regression of number (ln) of spores on time. The efficiency of dispersal, as estimated by the proportion of the spores present in a source which were dispersed in splash droplets, was greater for younger (50% dispersed) than for older (9%) horizontal detached leaves, greater for upper (43%) than lower (2%) attached leaves and greater for horizontal (78%) than inclined (49%) or flexible (39%) detached leaves
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