Isolation and characterisation of two potent growth inhibitory substances from aqueous extract of Bangladeshi rice cultivar BR17

Allelopathy and allelopathic substances in high yielding Bangladeshi rice cultivar BR17 were investigated. An aqueous extract of BR17 rice (Oryza sativa L.) inhibited the seedling growth of cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), alfalfa (Medicago sativa L.), timothy (Phleum pratense L.), crabgrass (Digitaria sanguinalis L.), ryegrass (Lolium multiflorum L.), barnyardgrass (Echinochloa crus-galli [L.] Beauv.) and Echinochloa colonum (L.) Link. Increasing the extract concentration increased the inhibition. These results suggest that BR17 may possess allelopathic potential and allelopathic substances. The aqueous extract was purified and two growth inhibitory substances were isolated and identified by their ¹H-NMR spectral data as 3-oxo-α-ionol and 9-hydroxy-4-megastigmen-3-one. The concentrations required for 50% growth inhibition of 3-oxo-α-ionol were 2.51 and 2.15 μM for cress roots and hypocotyls, respectively, and 16.3 and 134 μM for barnyardgrass roots and shoots, respectively. The concentrations required for 50% growth inhibition of 9-hydroxy-4-megastigmen-3-one were 0.49 and 0.25 μM for cress roots and hypocotyls, respectively, and 30.2 and 180 μM for barnyardgrass roots and shoots, respectively. These results suggest that 3-oxo-α-ionol and 9-hydroxy-4-megastigmen-3-one may contribute to the growth inhibitory effects of BR17 and may play important roles in allelopathy of BR17.