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Traditionally, <i>Pseudomonas syringae</i> has been viewed as a crop pathogen and consequently research has focused on strains isolated from crops. However, sampling precipitation, snow pack, leaf litter, and surface water has revealed an immense genetic diversity of <i>P. syringae</i> in these non-agricultural substrates. Interestingly, very close relatives of the tomato pathogen <i>P. syringae</i> pv. <i>tomato</i> (Pto) have been found among the <i>P. syringae</i> in these non-agricultural substrates. Some of these strains are as aggressive on tomato as Pto under laboratory conditions. Multilocus sequence typing and analysis of selected virulence genes show that these environmental Pto-like strains share identical alleles with Pto at some loci and that recombination between Pto-like strains and Pto has occurred during evolution of Pto. The implications of these findings for crop pathogen emergence and evolution will be discussed.<p><p>Keywords: