Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/1/2001
Publication Date: 4/9/2003
Citation: Rimando, A.M., Duke, S.O. 2003. Studies on rice allelochemicals. In: Smith, C.W., Dilday, R.H., editors. Rice: Origin, History, Technology, and Production. Hoboken, NJ: John Wiley & Sons, Inc. P. 221-244. Interpretive Summary: Research activities related to rice allelopathy was reviewed. Allelopathic rice cultivars identified over the last decade was listed. Rice phytotoxins that have been reported were largely ubiquitous compounds, mainly long- chain fatty acids and their derivatives. A group of phytotoxic ticyclic diterpenes known as momilactones and oryzalexins, which may be unique in rice, were identified from rice straw following a bioassay-guided isolatio process. These compounds, however, were also reported as phytoalexins, and were also isolated from rice cultivars that are not known to be allelopathic. Further research work has to be done in order to identify the true allelochemical(s) in rice. Mechanisms of action of potential rice allelochemicals were discussed. The utilization and application of genetic engineering technology to increase production of rice allelochemicals, as a natural means of controlling paddy weeds, was presented.
Technical Abstract: The worldwide focus on allelopathy research during the past decade is unprecedented. Although rice varieties with clear allelopathic activity have been identified, this trait has not been used as a selling point. A few studies have been conducted in order to isolate allelochemicals in rice. Most of the compounds isolated are common secondary metabolites that are ubiquitous in plants. A group of trycyclic diterpenes known as momilactones and oryzalexins, some of which have been reported as highly phytotoxic, may be compounds that are unique to rice. These compounds have also been reported as phytoalexins, and that they are induced by both biotic and abiotic stress factors. They have also been reported in rice cultivars that are not known to be allelopathic. Therefore, it is doubtful that these are the true allelochemicals in rice. A bioassay-guided method of isolation can facilitate the discovery of rice allelochemicals. This process can now be more conveniently carried out wit availability of modern instrumentation. After allelochemicals have been identified, it will be possible to use the information to synthesize the compound, or to enhance its natural synthesis and have a variety with enhanced natural chemical defense. Genetically engineering highly allelopathic rice varieties may eventually lead to varieties that will consistently provide good yields and improved weed management.