ALLELOPATHIC POTENTIAL IN RICE (ORYZA-SATIVA L) GERMPLASM

Allelopathy is the direct influence of a chemical released from one li ving plant on the development and growth of another plant. The use of allelopathy to control weeds of food crops could contribute towards in creasing yields in sustainable agricultural systems. Various research teams have identified several hundred rice accessions which show indic ations of allelopathic potential, 60 of them showing promising allelop athic activity against one or more weeds. These accessions have differ ent origin and stage of improvement. This, combined with the involveme nt of several allelochemicals and the ability to release these chemica ls, indicates that allelopathic potential is a polygenic characteristi c weakly correlated with yield or other important agronomic features. Successful allelopathy research, however, must be focused both on the discovery and subsequent validation of allelopathic potential. Experim ental factors such as choice of test plants, collection of allelochemi cals, concentration, osmotic pressure and bioassay methodology need co nsiderable attention together with validation through assays with know n chemicals of known concentrations. Without validation using known ch emicals, the contribution of allelopathic research remains obscure. Se veral putative allelochemicals are found in extracts of rice leaf and straw, decomposing straw, and in rice soil. Evidence that these chemic als are being released from living plants is still lacking, but as it is a prerequisite for allelopathic activity in nature, it must be prov ed. Methods of collecting test solutions from living plants need furth er description. Allelopathic activity is believed to be a joint action of several secondary metabolites, and this must be confirmed for rice . Dilution assays with mixtures of putative rice allelochemicals need to be conducted to evaluate possible synergistic effects. In validatio n, these mixture-dose response curves must be compared with assays usi ng collected test solutions. A joint, coordinated and focused research effort on rice allelopathy is necessary before the full potential of allelopathic cultivars can be realised.