Assessment of Allelopathic Potential in Rice - Exploration of Two Promising Allelochemicals.

Allelopathy is the direct influence of an organic chemical (allelochemical) released from one living plant on the growth and development of other plants.  Allelochemicals produced by certain rice cultivars have potential for the development of an environmentally friendly weed-control strategy to biologically control barnyardgrass (Echinochloa crus-galli L.), a major yield-limiting factor for rice (Oryza sativa L.) production in Asia and North America.  In this study, a bioassay-guided approach was used to identify allelopathic fractions from a Vietnamese rice cultivar (OM 5930) and was coupled with reverse-phase chromatography to isolate several allelopathic compounds.  The concentrations of the aqueous methanol extract of rice tissue required for 50% inhibition (defined as E50) of root and shoot growth of cress, lettuce, canola and barnyardgrass as determined by a logistic regression analysis, averaged 0.066 g ml-1 per roots and 0.062 g ml-1 per shoots, respectively.  The E50 of barnyardgrass roots and shoots were 0.052 and 0.114 g ml-1, respectively.  Two allelopathic substances in the aqueous methanol extract of OM 5930 were isolated (5930-A and 5930-B), and their inhibitory activities on cress seedlings were determined.  At a concentration of 100 ppm, 5930-A and 5930-B inhibited cress root growth by 91.7 and 80.2%, respectively, compared to control plants.  These findings encourage further investigations into the suppression of barnyardgrass in the field by Vietnamese rice cultivar OM 5930.