Crop allelopathy has seldom been used effectively by farmers in weed management. Traditional breeding methods have not been successful in producing highly allelopathic crops with good yields. Genetic engineering may have the potential for overcoming this impasse. Crops have been made resistant to insects, pathogens, and herbicides with transgenes, but biotechnology has not produced crops that control weeds with allelochemicals. The strategies for producing allelopathic crops by biotechnology are relatively complex, usually involving multiple genes. One can choose to enhance production of allelochemicals already present in a crop or to impart the production of new compounds. The first strategy involves identification of the allelochemical(s), determination of the enzymes and genes encoding them, and the use of genetic engineering to enhance their production. The latter strategy employs altering existing biochemical pathways by insertions of transgenes to produce new allelochemicals. With either strategy, there are potential problems with tissue-specific promoters, autotoxicity, metabolic imbalances, and proper movement of the allelopathic compound to the rhizosphere.
Nomenclature: Glufosinate; barley, Hordeum vulgare L.; celery, Apium graveoens L. var. Dulce (Miller) Pers.; cucumber, Cucumis sativa L.; diffuse knapweed, Centaurea diffusa Lam #3 CENDI.; maize, Zea mays L.; potato, Solanum tuberosum L.; rice, Oryza sativa L.: sorghum, Sorghum bicolor (L.) Moench # SORVU; sudangrass, Sorghum sudanese (Piper) Stapf; tomato, Lypersicon esculentum L.; wheat, Triticum aestivum L.
Additional index words: Allelochemical, genetic engineering, phytotoxin, transgene.
Abbreviations: DIMBOA, 2,4-dihydroxy-7-methoxy-1, 4-benzoxazin-3-one; PCR, polymerase chain reaction.