this paper we use a combination of replicated microcosm experimentation, simple nonlinear modelling and model fitting to analyse and interpret the dynamics of biological control of an economically important plant pathogen, Rhizoctonia solani Kuhn, by a fungal antagonist, Trichoderma viride Pers ex Gray. Rhizoctonia solani is a commonly occurring soil--borne fungus that causes substantial losses due to damping--off of seedlings of many crop and other plants. It can also cause severe loss in mature plants including potatoes, rice and wheat. Biological control of damping--off diseases by species of Trichoderma has been widely advocated (Papavizas, 1985) for horticultural and other crops but commercial success has been marred by marked variability in control, even under strictly controlled conditions. We show that although the biocontrol agent reduces the average amount of disease, the variability amongst replicates is greatly enhanced in the presence of the antagonist. The results are shown to be consistent with predictions from a model in which small differences in host susceptibility, fungal infectivity and control are amplified as the pathogen spreads from initial inoculum in soil and later from plant to plant. The differences are maintained because of interruption of disease progress as a result of a decline in host susceptibility. 2 EXPERIMENT Using simple, repeatable and highly uniform microcosms, we quantified the temporal development of damping-off disease on radish seedlings, Raphanus sativus L., caused by R. solani.
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Kleczkowski et al. (1996) studied this question.