Wageningen Agricultural University, Wageningen, The Netherlands

Background and objectives
Spores of many fungal plant pathogens are dispersed in rain-splash droplets and consequently cause new infections within a crop [1]. A rain simulator often is used to study the dispersal of infectious units and the effects of rain, canopy and surface are assessed. The resulting data sets are being used to test a recently developed mathematical model for dispersal of plant pathogens by rain splash.

The model incorporates the main mechanisms underlying the spatial spread of spores from a point source, that is: the probability per time unit of a spore being hit by a raindrop and splashed away; the probability per splash of being removed from the process; and a function for the spatial distribution of splashed spores.

Using these mechanisms, the effects of different crop characteristics on splash dispersal can be studied. We assume that spores can occupy four different sites in a crop, that is, the ground between plants, the ground underneath plants, leaves and fruit. Incorporating the above-mentioned mechanisms, a transition matrix is derived representing transition probabilities between the different sites in a canopy. To obtain reasonable parameter values for these transition probabilities, experiments are being performed using the rain tower facility at Rothamsted experimental station (Harpenden, UK). Oilseed rape plants infected with light leaf spot P. brassicae is the first system under study.

Previous field experiments showed that both horizontal and vertical dispersal of P.brassicae plays an important role in the spread of disease within the canopy [2]. Data analysis showed that both the dynamics of the pathogen and the growth dynamics of the plant play an important role in potential disease development. Therefore, the purpose of this study was to develop a model that included both plant growth and splash dispersal of infectious units. This model will give further insight in spore movement within a plant canopy under different environmental conditions.

1. Madden, LV, 1992. Advances in Plant Pathology, 8, 39-79.
2. Inman, AJ, Fitt, BDL, 1992. Brighton Crop Protection Conference-Pest and Diseases, 6c-25, 681-686.