BIOASSAY EVALUATION OF THE POTENTIAL ALLELOPATHIC EFFECTS OF GARLIC (ALLIUM SATIVUM L.) ROOT EXUDATES ON LETTUCE AND CUCUMBER

Two experiments were carried out to assay the allelopathic effects of garlic root exudates on seed germination and seedling growth of lettuce and cucumber. In the first experiment, a hydroponic method was adopted to collect garlic root exudates to simulate the natural secretion. Both the primary aqueous solution and different concentrations (10%, 12.5%, 25%, 50% and 100%) of the three different organic extracts of petroleum ether (PE), ethyl acetate (EA) and methanol (MA) were tested for lettuce. The results indicated that the primary aqueous solution showed a significant suppressive effect on germination and root length, but a stimulative effect on antioxidant enzyme activities in lettuce. The three organic extracts showed dose-dependent effects, and the frequency of inhibition amplified with increasing concentration of exudate extract. During comparative intensity evaluation of three different organic extracts, the activity of PE extract demonstrated the highest allelopathic reaction for seed germination and root morphology. The second experiment was conducted to eliminate the microbial effects, which might degrade the allelochemicals in the root exudates. Then, a biological test under an aseptic condition was directed to verify the allelopathic effect of garlic root exudates on cucumber. The results exhibited that garlic root exudates had a significant inhibitory effect on the germination of cucumber, but a dose-dependent effect on the growth of cucumber seedlings, thus confirming the results of the first experiment. These results provided a theoretical basis for further research into the identification of putative allelochemicals in garlic root exudates.