Effect of Secondary Metabolites of Tomato (Solanum lycopersicum) on Chemotaxis of Ralstonia solanacearum, Pathogen of Bacterial Wilt Disease

The chemotactic activity of the pathogen of bacterial wilt disease, Ralstonia solanacearum, was tested against 30 aromatic acids and plant hormones infused on filter discs in bioassays on agar plates. 4-Hydroxycinnamic acid (p-coumaric acid) and 4-hydroxybenzoic acid were strong chemoattractants, 3,4-dihydroxybenzoic acid (protocatechuic acid) and jasmonic acid were weak attractants, and 2-hydroxybenzoic acid (salicylic acid) showed both attracting and repelling activity depending on dose. Examination of the dose dependency revealed that the ED50 for 4-hydroxycinnamic acid and 4-hydroxybenzoic acid was 0.08 and 0.39 mu mol/disc, respectively. 2-Hydroxybenzoic acid showed chemoattractant activity at 0.33 mu mol/disc but chemorepellent activity at 3.3 mu mol/disc, and bacterial random motility was activated at 1.0 mu mol/disc and bacterial activity was suppressed at 33 mu mol/disc. Although water-soluble attractants including amino acids and organic acids have been previously investigated, this is the first report of hydroxylated aromatic acids (HAAS) as chemoattractants of R. solanacearum.