Interactions between Fusarium culmorum and its potential biocontrol agent, Trichoderma harzianum, in a packed-bed, continuous-flow column reactor

The interaction between the filamentous fungi Fusarium culmorum and Trichoderma harzianum was studied. A continuous-flow column reactor analogous to a soil column was used to provide a unidirectional flow of nutrients and solid support particles to which the fungi could attach. Such a system gave rise to a heterogeneous distribution of microorganisms and concentration gradients, and thus exhibited the most significant physical characteristics of the the soil. In columns inoculated with both fungal species, a succession in population dominance was observed. F. culmorum was the dominant organism at the beginning of the experiment; however, it was gradually replaced by T. harzianum. To analyze the results obtained from the dual culture columns, a mathematical model was developed. Three functions representing interaction between the two species were tested to determine which represented the experimental results most accurately. The best qualitative fit was obtained with a model incorporating Monod kinetics and making logistic limitation off. culmorum a linear function of the population density of T. harzianum. The implication of combined experimental and mathematical evidence was that the interaction between the two species was not solely competition for a single resource; the population of T. harzianum had a direct effect on that off. culmorum. (C) 1997 Elsevier Science Inc.