Allelopathic Potential Of Extracts Research Articles

Phytotoxicity and allelopathic potential of extracts from rhizomes and leaves of Arundo donax, an invasive grass in neotropical savannas

The perennial rhizomatous grass Arundo donax L. (Poaceae), the giant reed, is an exotic invasive species in several countries of Europe that is rapidly spreading in the savannas of Central Brazil, locally known as Cerrado. Allelopathy could facilitate the successful invasion of this species by hampering or suppressing the regeneration of the native vegetation. However, information on the phytotoxicity of A. donax extracts is limited. We investigated the allelopathic potential of A. donax leaf and rhizome extracts, screened them for phytochemicals by thin-layer chromatography (TLC) and nuclear magnetic resonance (1H-NMR), and tested the extracts for antioxidant activity, antimicrobial activity, and cytotoxicity against Artemia salina. Aqueous and methanolic extracts were initially tested in germination and seedling growth bioassays using Lactuca sativa L. (Asteraceae). The aqueous extracts were then tested on five Cerrado tree species and on Megathyrsus maximus, an invasive, alien grass in the Cerrado. Extracts negatively affected germination and seedling growth of the target species. Leaf extracts were more inhibitory. Extracts did not show antioxidant and cytotoxic activity and had very low antimicrobial activity. Flavonoids, and other phenolics were detected mostly in leaves. Terpenes, which were also present in the leaves, were the main secondary metabolites in rhizomes. Alkaloids were detected by TLC in leaf methanolic extracts. However, 1H-NMR revealed the presence of indole alkaloids in methanolic extracts from rhizomes and leaves. We confirmed the allelopathic potential of this species and caution against weed control methods relying on cutting the plant back to soil level for favouring release of allelochemicals.

ALLELOPATHIC ACTIVITY OF PLANT SPECIES FROM ASTERACEAE AND POLYGONACEAE FAMILY ON LETTUCE

The allelopathic potential of extracts from nine plants species belonging to Asteraceae and Polygonaceae family was evaluated on germination and early growth of lettuce. Water extracts from dry biomass of different plant parts in concentration of 5% were examined under laboratory bioassay in Petri dishes. Among species of Asteraceae family, the highest germination and seedlings growth inhibition was observed with annual fleabane (Erigeron annuus) leaf extract which reduced all parameters for 100%. Similarly, common sow thistle (Sonchus oleraceus) and common tansy (Tanacetum vulgare) also exhibited considerable negative effect. Germination of lettuce was not greatly affected when extracts from Polygonaceae plant species were applied, however significant inhibition of root and shoot length as well as fresh seedling biomass was recorded, especially in treatments with black bindweed (Fallopia convolvulus).

Allelopathic potential of extracts the from marine macroalga Plocamium brasiliense and their effects on pasture weed

Four extracts from the marine red alga Plocamium brasiliense (Greville) M.A.Howe & W.R.Taylor were prepared to identify and characterize their potential allelopathic effects on seed germination, radicle elongation and hypocotyl development of the weeds Mimosa pudica L. and Senna obtusifolia (L.) Irwin & Barneby. The four extracts were prepared in a sequence of solvents of increasing polarity: n-hexane, dichloromethane, ethyl acetate and ethanol/water (7:3). The germination bioassay was carried out at 25 °C with a 12 h photoperiod and the radicle elongation and hypocotyl development at 25 °C with a 24 h photoperiod. The dichloromethane extract showed inhibitory effects on seed germination of both plants (35 and 14%, respectively, in M. pudica and S. obtusifolia), radical germination (52 and 41.7%, respectively) and hypocotyl development (17.1 and 25.5%, respectively). Given the high sensitivity of this parameter to the potential allelopathic effects and the insufficient number of references found in the literature, these results are expected to stimulate new tests with other species of marine algae. Given the high sensitivity of the method for the detection of allelopathic potential, the species P. brasiliense emerges as a possible source of allelopathic substances against weed species. The results are attributed to the chemical composition, especially in relation to the presence of halogenated monoterpenes.

Study of Bioassay the Allelopathical Effect of Neem (Azadirachta indica) n-hexane, Acetone and Water-soluble Extracts on Six Weeds

Azadirachta indica, or Neem Tree, is an evergreen tree native to Southeast Asia. All parts of the tree have been used medicinally for centuries. The allelopathic potential of extracts of Azadirachta indica L., which is one of the most dominant weeds in tropical regions of South-west Asia, was investigated under laboratory conditions. The n-hexanesoluble, acetone-soluble and water-soluble fractions obtained from the acetone extract of A. indica shoots inhibited the germination and the growth of roots and shoots of six test plant species. The inhibitory activity of the water-soluble fraction was greatest, followed by that of the n-hexane-soluble and acetone-soluble fractions in all bioassays. Significant reductions in the germination and growth of the roots and hypocotyls were observed as the extract concentration increased. The concentration-dependent responses of the test plants to the fractions suggested that all three fractions might contain allelochemicals, but that the greatest potential was in the water-soluble fraction. These

Allelopathic Activity of the Essential Oils of Nigerian Medicinal Plants

AbstractSince many plant-derived substances which possess antibiotic activity also often possess additional bioactivities, we have investigated the allelopathic potential of extracts and essential oils of three plants commonly used in Nigerian folk medicine. Examined were Eugenia uniflora. Piper guineense, and Chromolaena odorata. Of these, C. odorata appears to be allelopathically inactive as measured by lettuce seedling bioassay, E. uniflora appears to be growth stimulatory, and P. guineense is growth inhibitory at concentrations above 400 ppm according to this same bioassay.