SCALING AND SPATIAL DYNAMICS IN PLANT-PATHOGEN SYSTEMS - FROM INDIVIDUALS TO POPULATIONS

Components of transmission for primary infection from soil-borne inocu lum and secondary (plant to plant) infection are estimated from experi ments involving single plants. The results from these individual-based experiments are used in a probabilistic spatial contact process (cell ular automaton) to predict the progress of an epidemic. The model acco unts for spatial correlations between infected and susceptible plants due to inhomogeneous mixing caused by restricted movement of the patho gen in soil. It also integrates nonlinearities in infection, including small stochastic differences in primary infection that become amplifi ed by secondary infection. The model predicts both the mean and the va riance of the infection dynamics of R. solani when compared with repli cated epidemics in populations of plants grown in microcosms. The broa der consequences of the combination of experimental and modelling appr oaches for scaling-up from individual to population behaviour are disc ussed.