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Allelopathy studies in weed science in Turkey – a review
Summary
Allelopathy involves both inhibitory and stimulatory biochemical interactions between plants. The phenomenon has received great attention since the 1980’s all over the world; however, in Turkey, research on allelopathy just started in the late 1980’s. Studies have been done with many crops, trees, shrubs and weeds under both laboratory and field conditions to determine their allelopathic potential and its use for weed control. Crops belonging to the Brassica family are the most studied species for allelopathic potential to control weeds. Among the Brassica species, garden radish (Raphanus sativus) has been most studied to control johnsongrass (Sorghum halepense). Allelopathic activity of alfalfa (Medicago sativa) also received some attention. The role of allelopathy in weed interference on crop production was also studied. In conclusion, allelopathy studies should parallel with contemporary studies such as ecological and chemical studies, and an integrated approach should be adopted to fully utilize the applicability of allelopathic plant species to control problem weeds.
Production dynamics of the allelochemical parthenin in leaves of Parthenium hysterophorus L.
Summary
Parthenium hysterophorus L. is regarded as a noxious alien invader in many parts of the world, including southern Africa. There are indications that the invasiveness of the plant may be partly connected with allelopathy, mainly based upon the sesquiterpene lactone parthenin. The aim of the present study was to track parthenin levels in leaves over the life cycle of the plant, in order to get an insight into the production dynamics of parthenin.
Plants were grown in a greenhouse from seeds originally taken from a population in Kruger National Park, South Africa. Leaves were sampled at various growth stages over the life cycle and were chemically analysed for parthenin levels.
Parthenin levels in leaves sampled at 12 different growth stages were determined through HPLC analysis. Results showed that the parthenin content of leaves increased with plant age, reaching a peak at the beginning of flowering. At senescence, the total number of leaves on a single plant yielded about 270 mg parthenin. Considering that P. hysterophorus usually builds up dense stands and other plant parts, notably flower parts and achenes, also contain appreciable amounts of parthenin, a considerable amount of this compound could be released from a P. hysterophorus population into the environment.
Although parthenin is not the only allelochemical produced by P. hysterophorus, findings of this study confirm that it is a major constituent of the leaves of P. hysterophorus. At the high levels of parthenin produced, this phytotoxin could conceivably play a central role in shaping the invaded vegetation.
Allelopathy of middle European agricultural weeds – an overview
Summary
The complete article is written in German
In a narrow sense allelopathy describes interactions between higher plants by release of metabolic chemicals (allelochemicals). The phenomenon is common in nature and also known from weeds and crop plants. At present allelopathic effects are described of at least 66 middle European annual or perennial weeds. Investigations focus on allelopathy of weeds against crop plants, however, sometimes also against other weeds. Inhibitory effects on crop plants dominated over stimulative ones. Sometimes allelopathic weeds can also modify plant successions. If allelopathic effects of weeds occur within the agrobiocenosis they mostly act in the first step on other weeds and crop plants. In addition many allelochemicals, however, can directly affect epigaeic or soil microorganisms and the fauna and successively induce further interactions. In addition many indirect effects occur. Weed allelopathy may be used for stimulating crop plants or for reduction of other weeds, e.g. by use as cover crops or as mulch with weeds. Furthermore allelochemicals may be used as 'biological' herbicides. In future allelopathy of weeds needs more investigations to understand its mode of action and to use it in agriculture.
Allelopathic potential of tea ( Camellia sinensis (L.) Kuntze) on germination and growth of Amaranthus retroflexus L. and Setaria glauca (L.) P.Beauv.
Summary
Laboratory and greenhouse experiments were conducted to determine the effects of tea (Camellia sinensis (L.) Kuntze) extracts (leaf, flower and fruit) at different concentrations on germination and growth of garden cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), redroot pigweed (Amaranthus retroflexus L.) and golden foxtail (Setaria glauca (L.) P.Beauv.). Furthermore, the effects of dried residues of tea on leaf area and dry weight of redroot pigweed and golden foxtail were investigated. Concentrations ranged from 0, 2.5, 5 to 10 % for organ extracts and dried residues were tested in mixtures with perlite at rates of 0, 8, 16, 24 and 32 g kg-1. Polyethylene glycole (PEG) was used in order to distinguish between the inhibitory effect of possible allelopathic substances and effects caused by the osmotic potential of the extracts. Results showed that garden cress and redroot pigweed germination was reduced by all extracts of tea organs with the exception of the leaf extract at the lowest concentration. The same was observed for lettuce and golden foxtail where germination was inhibited with the exception of leaf and fruit extracts at a concentration of 2.5 %. Radicle growth was affected at all test plants used and at all extract concentrations. Lettuce hypocotyl growth was reduced by all extracts of tea organs with the exception of the flower extract at the 2.5 % concentration. Hypocotyl growth of the other test plant species was significantly reduced by all extracts of tea organs as compared with the untreated control. Radicle growth was more sensitive in comparison to hypocotyl growth. Leaf area and dry weight of root, shoot and leaf were significantly lower with tea organ residues incorporated in the growing medium especially at rates of 24 and 32 g kg-1. Low PEG concentrations (1.06 and 2.13 %) had no significant effects on garden cress and lettuce.
Allelopathic potential of Alliaria petiolata and Lepidium perfoliatum , two weeds of the Cruciferae family
Summary
Allelopathic potential of two weeds of the cruciferae family, namely garlic mustard ( Alliaria petiolata (M. Bieb.) Cavara & Grande) and clasping pepperweed ( Lepidium perfoliatum L.), on lettuce ( Lactuca sativa L.) and garden cress ( Lepidium sativum L.) was studied in germination assays applying donor plant extracts. Weed plant parts were dried individually at 60 °C and then ground. Each plant's powder was used to produce aqueous extracts of 10 % (w/v) concentration. After centrifugation and filtration, the extracts were diluted with double distilled water to concentrations of 2.5 and 5 %, whereby double distilled water was used as control. The experiment was carried out in a factorial design with two levels of weed, two levels of test plant and four levels of extract concentration. Results showed that weed extracts had a similar and significant inhibitory effect on germination percentage of each of test plant with increasing extract concentration. Radicle growth of both of test plants and hypocotyle growth of lettuce also were decreased with increasing extract concentration. However, garden cress hypocotyl growth was decreased only in response to garlic mustard extracts while extracts of the second weed at first caused an increase in hypocotyl growth at concentrations of 2.5 and 5 % and a decrease only at a concentration of 10 %. Overall negative allelopathic effects on lettuce growth parameters were greater than on garden cress.
Allelopathic effects of Rumex obtusifolius leaf extracts against native grassland species
Summary
In perennial grasslands Rumex obtusifolius (broad-leaved dock) is often surrounded by certain plant species. Thus, it is hypothesized for the current study that Rumex can affect their neighbouring plant species by allelopathic interactions. To test this hypothesis, in a series of laboratory and field experiments aqueous extracts of green R. obtusifolius leaves were sprayed on seeds of 14 herbaceous plant species (graminoids, non-leguminous forbs and leguminous forbs) commonly native to perennial grasslands and its effects on seed germination compared with those with tap water spraying. An allelopathic effect was defined as inhibitory influence of Rumex extracts on seed germination relative to tap water. Generally, results of the laboratory experiments showed a species-specific susceptibility of grassland species to Rumex extracts; no species was promoted by Rumex extracts. All grasses tested were heavily inhibited by Rumex extracts, herbs and legumes varied from not affected until heavily inhibited. Spraying of Rumex extracts in the field had no effect on germination of these species. The results could be considered in designing seeding mixtures for resowing sward damages to especially contain species not susceptible to Rumex allelopathy (e.g. Trifolium pratense, T. repens, Plantago lanceolata) that would thus be assumed to be more competitive against R. obtusifolius regrowing in these grasslands.
The allelopathic potential of common dandelion ( Taraxacum officinale WEB.)
Summary
The common dandelion (Taraxacum officinale WEB.) is one of the most troublesome weeds in meadows, pastures, grasses, turf grasses, orchards and vineyards.
The aim of this study was to establish the allelopathic effect of the perennial dicotyledonous weed and to ascertain to what degree is it able to influence the germination of grass species widespread in turfs. Seed of selected Gramineae and Fabaceae species(Lolium perenne L., Arrhenatherum elatior L., Festuca rubra L., Dactylis glomerata L., Poa pratensis L., Lotus corniculatus L., Trifolium repens L., Trifolium fragiferum L., Bromus inermis L., Bromus erectus L.),which are regarded as important components of turfs, were treated with acetonic, ethanolic and aqueous extracts of T. officinale roots and leaves. The effect of treatments was evaluated by determining seed germination of the test species.
The acetone and ethanol extracts of dandelion roots generally inhibited seed germination the most. Aqueous, acetone and ethanol extracts of leaves were generally less inhibitive. Germination of test species’ seed decreased as extract concentrations increased.
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