Competition and stability in plant mixtures in the presence of disease.

A deterministic mathematical model is developed for competition between two plant species (or genotypes) in the presence of a host-specific pathogen capable of attacking one of the species only. The complexity of the plant-plant-pathogen interaction precluded precise mathematical description of all possible long-term outcomes. However, extensive computer simulation shows that stability is not an inevitable consequence of the differential interaction, rather, the outcome depends greatly upon the growth rates and relative competitive abilities of the plant species and on the transmission efficiency of the pathogen and its effect on individual host plants. The model confirmed the general validity of previous intuitive arguments but clearly indicated that the occurrence of inflected yield curves is not a sufficient indication in itself of long-term stability.