Effect of okara extracts on seedling growth of five plant species

We examined the efficiency of different solvents (water, methanol, acetone) to extract potential allelochemicals from okara and their effect on the root growth of cockscomb, barnyard grass, false daisy, lettuce, sesame. Ten % methanol (10% methanol in water), designated as water extract and methanol extract drastically inhibited the root growth of plants than acetone extract. Root growth of sesame was most inhibited, followed by barnyard grass, cockscomb, lettuce and false daisy. Extracts inhibited the root growth of plants in a concentration-dependent manner. Thus okara contained water-and methanol-soluble allelochemicals inhibitory to root growth of test plants. Methanol extract was most inhibitory to shoot growth, followed by acetone extract and water extract. Shoot growth inhibition followed the order: Sesame > lettuce > barnyard grass > false daisy > cockscomb. The interactions among plant spp., extraction solvent and extract concentration were significant (P < 0.05). In cockscomb and false daisy, 30 g eq./l of water extract was most stimulatory to shoot growth, followed by 10 g eq./l and 3 g eq./l. In contrast, 100 g eq./l of water was similar to control. These results suggested that okara contained water- and methanol-soluble allelochemicals with selectivity of plants.