Influences of phenolics isolated from the nutrient solution nourishing growing cucumber (Cucumis sativus L.) plants on fruit yield

Growth inhibiting substances of unknown origin found in the nutrient soluti on nourishing growing cucumber plants were isolated and identified. The gro wth inhibitors were absorbed on activated charcoal and extracted therefrom by an organic solvent. These extracts were partitioned into four fractions with different solvents. 1. The inhibiting activity for cucumber plants was detected in the acidic d iethyl ether soluble fraction, but not in others. 2. The active substances in the above fraction analyzed by GC/MS method wer e identified as:benzoic acid, p-hydroxybenzoic acid, 2, 4-dichlorobenzoic a cid and phthalic acid. 3. The above substances were assayed for their activity on cucumber seedlin gs by adding various concentrations to the nutrient solution. 2, 4-dichroro benzoic acid exhibited the strongest inhibitory activity;others were very w eak. 4. 2, 4-dichlorobenzoic acid at 2 mu mol . liter(-1) in nutrient solution h ad no effect on plant growth but it lowered fruit yield and shortened fruit harvesting period, compared with the control. Any inhibition was eliminate d by adding activated charcoal to the nutrient solution. 5. Thus, 2, 4-dichlorobenzoic acid, the most effective inhibitor in the nut rient solution nourishing growing cucumber plants can be eliminated by addi ng activated charcoal.