Submitted to: Microbial Ecology International Symposium
Publication Type: Book / Chapter
Publication Acceptance Date: 1/19/1999
Publication Date: N/A
Technical Abstract: We have developed mathematical models for intra- and inter-strain competitive interactions among multiple localized infections of the biotrophic plant parasite Puccinia graminis in wheat leaves. In the infection model, the leaf is composed of a defined number of potential lesion sites, in which only one infection per site can mature and sporulate. In the sporulation model, all infections in a leaf compete for a pool of resources within the leaf for spore production. In inoculations with single parasite strains, we measured the following parameters: infection efficiency, maximum number of infections per leaf, parasite sporulation efficiency per lesion, and maximum sporulation supported by leaves. From mixed-strain inoculations, we determined competition coefficients for effects of each strain on the other during infection and spore production. Strain SR22 showed superior infection efficiency, carrying capacity for infections per leaf, and maximum sporulation supported per leaf in single-strain tests. The fitness advantage of SR22 was tempered, however, by the greater competitive ability of strain SR41, which reduced both infection by SR22 spores and sporulation by SR22 infections in leaves with mixed parasite populations. In the model, superior infection efficiency produces a fitness advantage that is independent of density, but fitness advantages associated with other parameters are density dependent. Fitness effects for competition coefficients not equal to 1.0 are both density and frequency dependent. Our methods for analyzing competitive ability are applicable to other plant parasites.