Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/1996
Publication Date: N/A
Citation: Interpretive Summary: Rust fungi cause serious diseases of wheat, oat, and barley. Typically, there are many races in rust populations in regions where these crops are grown. Crop varieties resistant to some of these races may not be resistant to others. To help plant breeders decide which races are most important to breed varieties against, we need to learn more about competition between rust races. Prior to our research, no method had been developed to analyze competitive ability of rust races in relation to rust disease severity levels. We studied competition between two races of the wheat stem rust fungus and identified the key qualities of rust races that determine their success in competition with other races in plants infected with mixtures of races. This information will be useful not only in predicting changes in rust races in major cereal producing regions of the U.S., but also in analyzing interactions between other types of microorganisms. Our method may be useful for determining abilities of Biocontrol microorganisms to competitively exclude plant pathogens from plant surfaces. Thus, our research will enhance both the effectiveness of breeding for resistance and success of Biocontrol of plant diseases. Both approaches will increase the stability of U.S. crop production while reducing the need for pesticides to control plant diseases.
Technical Abstract: Inter- and intra-strain competitive interactions and their effects on fitness were quantified for coexisting strains of Puccinia graminis f.sp. tritici (Pgt) on wheat leaves. Two components of fitness in Pgt, number of uredinia formed per leaf and number of spores produced per leaf per day, were quantified for two Pgt strains alone and in a 1:1 mixture over a range of inoculum densities. A mathematical model was developed to describe the relationships between uredinial formation and inoculum dose, and between spore production and uredinial density. From the single-strain data, values of the following parameters were estimated for both strains: infection efficiency of spores, carrying capacity for uredinia on leaves, sporulation efficiency of uredinia and maximum sporulation capacity. For the mixed-strain data, the single-strain to which each strain reduced the fitness of the other relative to intra-strain competitive effects. These competitive effects, quantified by competition coefficients for uredinial formation and spore production, provide density-independent measures of the competitive abilities of the strains. Strain SR41 had greater competitive ability than SR22 for both uredinial formation and sporulation, even though SR22 formed more uredinia and produced more spores at all densities in single-strain inoculations. Despite the greater competitive abilities of SR41, strain SR22 maintained higher relative fitness in mixed infections at all densities in terms of both uredinia formed and spores produced. However, the fitness advantage of SR22 over SR41 was not as great at high population densities.