The involvement of allelopathy in various crop–weed competition studies has been suggested by several authors, but its significance has been demonstrated with varying success. It is extremely difficult to unambiguously demonstrate allelopathy in nature because of the complexity of plant interference and its relationship to soil chemistry. However, with an increased understanding of the chemical processes occurring in the agroecosystem, genetic mapping of quantitative traits, and the ability to identify allelochemicals, an effort should now be directed toward understanding the mechanisms for allelopathy, as well as trying to optimize an allelopathic effect to produce more competitive crops. The approach used for rice allelopathy research can be used as a general framework for understanding how genetically encoded traits affect the competitive ability of plants. This framework requires the involvement of a range of scientists from multidisciplinary research areas with the overall objective of optimizing competitive ability in crops. Such research efforts could reduce dependency on herbicides and thus increase the sustainability of weed management practices. This paper aims to illustrate the importance of allelopathy for crop competitive ability and to identify a framework suitable for result-oriented collaborative research toward breeding for competitive ability in crops.

Nomenclature: DNA, deoxyribonucleic acid; IRRI, International Rice Research Institute; QTL, quantitative trait loci; rice, Oryza sativa L.

Additional index words: Competition, plant interference, allelopathic cultivar, weeds.