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

Abstract

Growth inhibiting substances of unknown origin found in the nutrient solution nourishing growing cucumber plants were isolated and identified. The growth 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 diethyl ether soluble fraction, but not in others. 2. The active substances in the above fraction analyzed by GC/MS method were identified as:benzoic acid, p-hydroxybenzoic acid, 2,4-dichlorobenzoic acid and phthalic acid. 3. The above substances were assayed for their activity on cucumber seedlings by adding various concentrations to the nutrient solution. 2, 4-dichlorobenzoic acid exhibited the strongest inhibitory activity;others were very weak. 4. 2, 4-dichlorobenzoic acid at 2 μmol · liter-1 in nutrient solution had no effect on plant growth but it lowered fruit yield and shortened fruit harvesting period, compared with the control. Any inhibition was eliminated by adding activated charcoal to the nutrient solution. 5. Thus, 2, 4-dichlorobenzoic acid, the most effective inhibitor in the nutrient solution nourishing growing cucumber plants can be eliminated by adding activated charcoal.