Potential Allelopathic Effect of Six Phaseolus Vulgaris Recombinant Inbred Lines for Weed Control

Abstract: The phytotoxicity of aqueous foliar extracts and ground dried residues of six common bean (Phaseolus vulgaris) Recombinant Inbred Lines (RILs 147, 83, 104, 115, 34 and 75), recently introduced from France for possible cultivation and improvement under Egyptian conditions, against certain weed and crop species was investigated as a possible source for natural herbicides. Aqueous extracts at 10% were prepared and evaluated on seedling root and shoot growth of perennial ryegrass (Lolium perenne), slender amaranth (Amaranthus viridis), wheat (Triticum aestivum) and lettuce (Lactuca sativa) as bioassay. Root and shoot growth were significantly inhibited by the different extracts, with a superior activity against root growth rather than on shoot growth. No great differences were observed between the extracts obtained at flowering stage and those obtained at harvesting stage in affecting assayed species, and crop seedlings were generally more sensitive than weed seedlings. The suppressions by the RILs 34 and 147 were comparatively the greatest, especially with the RIL-34 where it displayed remarkable inhibitory effect against weeds growth (in particular ryegrass). The stability of the RIL-34 extract (along eight days of lab experimentation) against soil conditions was measured on the same test species. The recovered extracts showed good activity with decline in toxicity with time. Ryegrass and lettuce were the most sensitive (root growth in particular). Wheat was, to some extent, the most tolerant followed by slender amaranth. No clear toxicity was observed on shoot growth after the day two of incubation in most cases. Analysis (using paper chromatography) for the existence of the phenolics that might have a role in the observed allopathic effect in the RIL-34 (at flowering stage), revealed two phenolics (e.g., caffeic acid and p-coumaric acid) could be involved in this. This study demonstrates that the potential exists for P. vulgaris plants to be used as natural source for herbicides, but this shackled by many considerations that should be taken into account