The interrelationships between plants and rhizosphere bacteria are strongly dependent on the quality and quantity of root exudates. The ability to colonize roots is crucial for pseudomonads to function as biological control agents of root- and soil-borne pathogenic microbes. The multiplication of rhizosphere bacteria is restricted in the presence of simple phenolic compounds, which are components of the resistance mechanisms of plants to pathogens. Caffeic acid is a phenolic compound, which is commonly found in wheat tissues. It is prone to oxidation into o-quinones, which are toxic to microorganisms. The aim of the present study was to determine whether the ability of microorganisms to resist caffeic acid and its oxidation products could play a role in the early colonization of wheat seedlings. Among the fluorescent pseudomonads that we have studied, strain PSR114 is one of the most efficient colonizers of wheat seedlings during the first 48h after seed germination, and it is particularly resistant to products resulting from the spontaneous oxidation of caffeic acid. This strain was isolated from the rhizosphere of oilseed rape and identified as being closely related to Pseudomonas proteolytica through the analysis of 16S rRNA and rpoB gene sequences. At pH 7.0, this strain grew intensively in the presence of 1.50mgmL-1 of caffeic acid. Its multiplication was partially reduced in the presence of oxidized caffeic acid at concentrations above 0.21mgmL-1, and completely inhibited at concentrations above 0.38mgmL-1. A Tn5 transposon mutant of PSR114 had lower level of resistance to the oxidation products of caffeic acid, as well as reduced capacity to colonize wheat seedlings when compared to the wild type strain. This work demonstrates that resistance to oxidation products of caffeic acid can be important for successful bacterial colonization of wheat seedlings.