Isolation and purification of growth‐inhibitors from Vietnamese rice cultivars

Abstract

Bioactive compounds that are produced by select rice cultivars have the potential to control barnyardgrass, a major rice yield‐limiting factor. In this study, the Vietnamese rice cultivars, OM 3536, OM 4498 and OM 5930, were selected and their inhibitory activity on cress, lettuce, canola and barnyardgrass was evaluated by using donor–receiver bioassays. These bioassays revealed that OM 3536 and OM 5930 exerted the greatest inhibitory activity, with an average growth inhibition of 57.2% on the roots and shoots of barnyardgrass. A bioassay‐guided approach was used to identify the allelopathic fractions from OM 5930 and was coupled with reverse‐phase chromatography in order to isolate several growth‐inhibitory fractions. The effective dose of the aqueous methanol extract of the rice plants that was required for 50% inhibition (ID50) of the shoot and root growth of the four test plant species, as determined by a logistic regression analysis, averaged 0.091 and 0.062 g mL−1 for OM 5930 and 0.112 and 0.072 g mL−1 for OM 3536, respectively. The ID50 of the barnyardgrass roots and shoots in the assays, as determined by a logistic regression analysis, was 0.044 and 0.149 g mL−1 for OM 3536 and 0.052 and 0.114 g mL−1 for OM 5930, respectively. A growth‐inhibitory fraction in the aqueous methanol extract of OM 5930 was isolated and the inhibitory activity on lettuce seedlings was determined. At a concentration of 100 p.p.m., this growth‐inhibitor inhibited lettuce root growth by up to 80.2%, compared to the control plants. These findings demonstrate that the dried plant tissues of Vietnamese rice cultivars could contain bioactive compounds that strongly inhibit plant growth.