BIOASSAY OF DECOMPOSED PRODUCTS OF RAPESEED CAKE USING Lemna paucicostata 6746

The effects of the water extracts of rapeseed cakes undergoing decomposition under different conditions on plant growth were evaluated using Lemna paucicostata 6746 for the bioassays. Half-strength Hutner’s medium was used as the basal medium, to which aliquots of concentrated water extracts were added in the ratio of 1/1,000, and the number of reproduced fronds were counted after 7 days as an index of the growth. Aerobic decomposition of rapeseed cake (1:1 ratio of rapeseed cake to water, w/w) showed a strong inhibitory effect on the growth of L. paucicostata 1 to 4 weeks after the start of the decomposition. In the submerged decomposition (1 : 10 ratio of rapeseed cake to water, w/w), no inhibition was detected in the first weeks, but a strong inhibition appeared after 8 weeks and increased thereafter. The water extracts of the rapeseed cake undergoing decomposition under the submerged condition contained large amounts of fatty acids (acetic, propionic, and butyric acid), which were considered to be the...