A seedling flood-inoculation assay for the analysis of host signal pathways leading to disease development. A. Disease phenotype of Arabidopsis seedlings flood-inoculated with pathogenic Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) and Pseudomonas syringae pv. maculicola ES4326 (Pm ES4326) at a concentration of 5 × 106 CFU/ml. Mock-inoculated plants were flooded with sterile distilled H2O containing 0.025% Silwet L-77. Photographs were taken 3 dpi. (B, C) Bacterial populations of Pst DC3000 (B) and Pm ES4326 (C) in Arabidopsis were quantified at 0, 2 and 4 dpi. Vertical bars indicate the standard errors for three independent experiments. Asterisks indicate a significant difference from WT Col-0 using a t-test (** = p < 0.01).