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Effects of an Interaction Between Inoculum Density and Temperature on Germination of Puccinia allii Urediniospores and Leek Rust Progress

Controlled environment experiments were conducted to study the effects of inoculum density, temperature, and their interaction on germination of Puccinia allii urediniospores and infection of leek leaves. Percent germination of P. allii urediniospores and percent branching of germ tubes increased with 3 density of urediniospores and approached a plateau for densities above ≈20 spores cm^-2 of leaf area. Percent germination was highest at 12 to 21°C, a wide-range temperature optimum. Branching occurred at temperatures ranging from 5 to 25°C, but there were few germ tubes branching at 25°C. P. allii successfully infected leek leaves at temperatures ranging from 7 to 22°C. The number of pustules produced increased with urediniospore density on leek leaves. At low spore densities, pustule production was little affected by temperature; at higher spore densities, pustule production was greatest between 9 to 11°C, and numbers of pustules decreased greatly with temperature increasing above this optimum. Latent period was affected by temperature, with latent period being shortet between 19 and 22°C, and latent period increasing when temperature decreased. Latent periods became ≈1.8 days shorter for every 10-fold increase in spore density. The rate of pustule production increased with increasing spore density on leaves and was greatest between 11 to 14°C. Computer simulation of leek rust progress based on the found relationships suggested that at optimal temperatures the development of leek rust epidemics may be little affected by initial spore density and density caused by each pustule, but that at sub- and supra-optimal temperatures the development is greatly affected by these variables.