Submitted to: Cost Workshop on Epidemiological Parameters Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/20/1995
Publication Date: N/A
Technical Abstract: Urediniospores of two strains of Puccinia graminis f.sp. tritici were inoculated onto wheat seedlings singly and in a 1:1 mixture at a range of inoculum densities. Inter- and intra-strain competitive interactions were quantified by determining numbers of uredinia and urediniospores produced per leaf at each inoculum density. A mathematical model was developed to relate uredinial formation to inoculum dose and spore production to uredinial density. The parameters infection efficiency, carrying capacity in uredinia per leaf, sporulation efficiency, and maximum sporulation per leaf were calculated from single-strain inoculations. Competition coefficients for uredinial formation and sporulation were calculated by fitting the density response data from mixed-strain inoculations to the model using the four single-strain fitness parameters. Strain SR41, had greater competitive ability than SR22 for both uredinial formation and spore production, but SR22 had greater fitness because of its significantly greater infection efficiency and carrying capacity for uredinia per leaf. Simulations with the model indicated that (1) a fixed advantage in infection efficiency provides a constant fitness advantage from low to high inoculum density; (2) advantages in carrying capacity and the uredinial competition coefficient provide little fitness advantage at low densities, but increasingly contribute to greater fitness at higher densities; (3) the same is true for advantages in maximum numbers of spores that can be produced per leaf and in the competition coefficient for sporulation; and (4) greater sporulation efficiency provides a high fitness advantage at low densities but little or no advantage at high densities.