Allelopathic potential of wild oat (Avena fatua) on spring wheat (Triticum aestivum) growth.

Wild oat plants may produce toxic substances that suppress the growth and development of desirable species, thus accounting for severe yield loss in infested fields. The purpose of this study was to determine the allelopathic potential of wild oat (Avena fatua) on the growth of spring wheat (Triticum aestivum var. Fieldwin) in the absence of plant competition. Wild oat and spring wheat plants were grown separately in 250-ml beakers in a sand medium. Root exudates were extracted from wild oat medium at the 1-, 2-, 3-, and 4-leaf stages of wild oat development and added to beakers containing spring wheat in temporally corresponding stages of development. Spring wheat root and leaf dry weights were measured to determine if one or more allelochemical agents were released from wild oat roots. Spring wheat leaf and root dry weights were significantly reduced by exudates from wild oat plants at the 2- and 4-leaf stages of development, respectively. Allelochemicals were isolated from wild oat root exudates at various stages of plant development. Paper chromatography analysis indicated that at least two unknown compounds were present.R f values in benzene-acetic acid-water of the two unknown compounds (0.825 and 0.930) were similar to scopoletin (7-hydroxy-6-methoxycoumarin) and vanillic acid (4-hydroxy-3-methoxybenzoic acid), respectively. Additional tests using diazotizedp-nitraniline, ultraviolet absorption spectra, and gas chromatography analysis also indicated that the unknowns were coumarin-related compounds such as scopoletin and vanillic acid.