AvrPto recognition is a major factor mediating resistance to Pseudomonas syringae pv. tomato (Pst) DC3000 in Bu-22 and Bu-25 Arabidopsis accessions. (a) In planta bacterial growth in Pst DC3000-resistant accessions after infiltration with Pst DC3000, Pst ΔavrPto, and Pst ΔavrPtoB at an inoculum of 5 × 105 colony-forming units (CFU) ml−1. Error bars show ± SE of 3 and at least 7 biological samples for days 0 and 3, respectively. Letters above each bar indicate similar groups as determined with a Tukey HSD test (P < 0.05). Notice that the absence of AvrPto allows Pst to multiply to high titers in both Bu-22 and Bu-25 accessions. (b) Disease symptoms 3 d after inoculation with 5 × 105 CFU ml−1 of Pst DC3000, Pst ΔavrPto, and Pst ΔavrPtoB. Image was composed from accessions’ individual images from a single experiment. Bar, 1 cm.