The interaction between tomato and Pseudomonas syringae pv. tomato (Pst) is a well-developed model for investigating the molecular basis of the plant immune system. There is extensive natural variation in Solanum lycopersicum (tomato) but it has not been fully leveraged to enhance our understanding of the tomato-Pst pathosystem. We screened 216 genetically diverse accessions of cultivated tomato and a wild tomato species for natural variation in their response to three strains of Pst. The screen uncovered a broad range of previously unseen host symptoms in response to Pst, and one of these, stem galls, was found to be simply inherited. The screen also identified tomato accessions that showed enhanced responses to flagellin in bacterial population assays and in reactive oxygen species assays upon exposure to flagellin-derived peptides, flg22 and flgII-28. Reporter genes confirmed that the host responses were due primarily to pattern recognition receptor-immunity. This study revealed extensive natural variation in tomato for susceptibility and resistance to Pst and will enable elucidation of the molecular mechanisms underlying these host responses.Key Words: Bacterial speck disease, flagellin, natural variation, NLR-triggered immunity, patterntriggered immunity, plant immunity, PRR-triggered immunity Abramovitch RB, Janjusevic R, Stebbins CE, Martin GB. 2006. Type III effector AvrPtoB requires intrinsic E3 ubiquitin ligase activity to suppress plant cell death and immunity. Proc Natl Acad Sci USA 103: 2851-2856. Abramovitch RB, Kim Y-J, Chen S, Dickman MB, Martin GB. 2003. Pseudomonas type III effector AvrPtoB induces plant disease susceptibility by inhibition of host programmed cell death. EMBO J 22: 60-69. Arredondo CR, Davis RM. 2000. First report of Pseudomonas syringae pv. tomato race 1 on tomato in California. Plant Disease 84: 371. Bao Z, Meng F, Strickler SR, Dunham DM, Munkvold KR, Martin GB. 2015. Identification of a candidate gene in Solanum habrochaites for resistance to a race 1 strain of Pseudomonas syringae pv. tomato. The Plant Genome 8: 10.3835/plantgenome2015.3802.0006. Buell CR, Joardar V, Lindeberg M, Selengut J, Paulsen IT, Gwinn ML, Dodson RJ, Deboy RT, Durkin AS, Kolonay JF, et al. 2003. The complete genome sequence of the Arabidopsis and tomato pathogen Pseudomonas syringae pv. tomato DC3000.