| Abstract: | The diffusion theory of focus development permits development of a class of related models of different complexity. The basis of the present study is an earlier model which simulates a dual spore dispersal mechanism, consisting of a short-distance and a long-distance mechanism. This model was further elaborated by adding stochasticity and an external directional force simulating wind. Stochasticity was simulated through randomization of lesions produced by spores dispersed by the long-distance mechanism. The model was run twelve times for three values of spore partitioning over the two dispersal mechanisms combined with four values of wind speed. Model responses were sampled at three simulation time values: 40, 90, and 100 days. A major model response was the shape of a single focus, studied through snap-shot pictures of disease severity over the field. Real life phenomena, non-circular mother or central focus with ragged front and daughter foci, were reproduced. Throughout the simulations, maximum disease severity remained at the location of the initial inoculation. However, after all available sites around the centre were exhausted, the geometrical centre of the focus was apparently moved downwind. Number of daughter foci and their relative size were strongly dependent on the spore partitioning over the two dispersal mechanisms. |
