Oregano (Origanum vulgare) clonal lines O-1 and O-5 generated via tissue culture were treated with Pseudomonas Z strain and polydye R-478. Pseudomonas Z strain was isolated from naphthalene-contaminated soil and is a known degrader of naphthalene. In this study, Pseudomonas Z strain was investigated for its ability to prevent a plant tissue culture condition known as hyperhydricity. Many polysaccharide producing Pseudomonas species are capable of preventing this detrimental condition. Previous studies have shown that some Pseudomonas strains enhance the total phenolic content of plants while preventing tissue culture induced hyperhydricity. Polydye R-478 was used to treat oregano clonal lines O-1 and O-5 in combination with Pseudomonas Z strain to investigate the possibility that a known naphthalene degrader would enhance the plant's tolerance to other aromatic compounds. Pseudomonas Z strain was able to prevent hyperhydricity in O-1 and O-5 while eliciting a stress response mechanism associated with total phenolic content of the plant. When plants were treated with a combination of Pseudomonas Z strain and polydye R-478, responses varied between the two clonal lines. Clonal line O-1 appears to be a hardier line with a high tolerance to bacterial stress, whereas O-5 is initially affected greatly by bacterial stress, but the shoot cultures that survive are tolerant. (C) 2002 Published by Elsevier Science Ltd.