ALLELOCHEMICALS EFFECTS OF SOME WEEDS ON ASSOCIATED PLANTS AND RHIZOBACTERIA

The present work was carried out to investigate the allelochemical characteristics of common dandelion (Taraxacum officinale), black nightshade (Solanum nigrum L.), mallow (Malva parviflora) in El-Jabel Al-khdar region, Libya. The effects of these plants exudates were examined in associated naturally occurring rhizosphere bacteria communities. Aqueous extracts were bioassayed on wheat (Triticum aestivum L.), faba bean (Vicia faba) and lolium grass (Lolium multiflorum) seed germination and growth parameters. As regard to the effect of water extract, the calculated EC50 values of T. officinale were 17.5, 10.5 and 13.6g 100ml^-1 (T. aestivum), 7.0, 3.20 and 2.80g 100ml^-1 (L. multiflorum) against germination, root length and shoot length, respectively. Meanwhile, M. parviflora had a least EC50 values by 2.5, 1.2 and 5.0 mg ml^-1 (T. aestivum), 2.50, 2.0 and 1.80g 100ml-1 (L. multiflorum) against germination, root length and shoot length, respectively. Finally, the S. nigrum EC50 values were 6.8, 5 and 5.0 g100 ml^-1 (T. aestivum), 5.9, 6.5 and 10.2 g 100 ml^-1 (L. multiflorum) against germination, root length and shoot length, respectively. Organic extracts by ethyl acetate and chloroform of T. officinale, S. nigrum and M. parviflora exhibited prominent herbicidal activity as compared to hexane extract on L. multiflorum weeds and T. aestivum. The highest allelopathic activity against the tested plants achieved from M. parviflora was followed by S. nigrum. However, the lowest phytotoxicity was achieved from T. officinal. Root exudates exhibited marked effects in total counts of rhizosphere bacteria than non rhizosphere soils, while S. nigrum and M. parviflora had a strikingly allelopathy activity against tested plants which colonized with higher number of rhizobacteria as compared with T. officinale which has lower allelopathic activity and rhizobacteria counts. These results offered a great potential of allelopathic weeds towards both the weeds control and crop growth.