Showing papers on "Allelopathy published in 1995"

Mechanism of action of allelochemicals in allelopathy.

Abstract: The primary mode of action has not been established for any allelopathic compound, albeit some physiological actions are known. The array of compounds cuts across many chemical classes, and it is unlikely they have a common mechanism of action. Allelochemicals active against higher plants are typically characterized as suppressing seed germination, causing injury to root growth and other meristems, or inhibiting seedling growth. A primary action on ATP production is indicated for the two quinones, juglone and sorgoleone, since they inhibit chloroplast oxygen evolution (I50 = 0.2 and 2.0 micromolar respectively) and strongly affect mitochondrial functions. The chloroplast block by sorgoleone is in the photosystem II complex. Cinnamic and benzoic acid derivatives alter membrane potential and have several physiological effects that suggest membrane perturbations are their initial site of action. Their thresholds (100 to 1000 micromolar) for inhibition of seedling growth, singly or in combinations, correlate with impairment of plant-water relationships. These phenolic compounds also alter mineral uptake, chlorophyll content, photosynthesis, carbon flow, and phytohormone activity. Phytotoxicity of many allelopathic chemicals may be from a generalized cellular disruption rather than a specific mechanism. A case study of Sorghum allelopathy suggests that inhibition of a receiving species results from the joint action of a number of allelochemicals with different cellular sites of action.

On laboratory bioassays in allelopathy

Abstract: Allelopathy involves the complex chain of chemical communications among plants, including microbes. Laboratory bioassays constitute a significant part of allelopathic research, and various bioassays have been proposed to demonstrate allelopathy under controlled lab conditions. However, many lab bioassays have little or no correspondence to field interaction, which may be due to dissimilarity of the conditions of lab bioassay to natural conditions, lack of standardized techniques, or absence of critical controls. Here we discuss several lab bioassays presently used in allelopathic research for their suitability to demonstrate allelopathy of ecological relevance. We recommend avoiding certain practices, such as grinding plant material to evaluate allelopathic potential and isolation of allelochemicals, using seed germination as the only criterion of growth response, using sand, agar, or autoclaved soil, using organic solvents as extractants in allelopathic bioassays, and eliminating microbial involvement. Care should be taken in the lab to simulate natural conditions and attention should be given to habit, habitat, and life cycle pattern of the allelopathic plants during designing of lab bioassays.

Natural Herbicide Potential of Alfalfa Residue on Selected Weed Species

Abstract: Alfalfa (Medicago sativa L.) contains water-soluble substances that are toxic to itself (autotoxicity) and to other species (allelopathy). Experiments were conducted to determine the potential of using alfalfa residue as a natural herbicide for inhibition of weed seed germination, seedling growth, and development. Various weed species were germinated in aqueous extracts from dried alfalfa using cold (5°C), warm (24°C), and hot (80°C) treatments. Results indicated that inhibition of weed seed germination was dependent on the aqueous extraction method, residue application rate (w/v or w/w), and weed species. The greatest inhibition of germination was 44%, when 60% (w/v) warm aqueous extract was applied to lambsquarters (Chenopodium album L.). Seedling growth was also inhibited by residue application at various rates. Root length was more inhibited than increase in shoot length. In terms of total seedling length, giant foxtail (Setaria faberii Herrm.) was the most resistant species and lambsquarters was the most susceptible among the weed species studied to alfalfa aqueous extracts. Weed seed germination percentage decreased as incubation time increased from 8, 16, 24, and 48 h. An alfalfa aqueous extract incubated for 48 h caused the greatest inhibition of velvetleaf (Abutilon theophrasti Medic.) seed germination (25%). When alfalfa residue was incorporated with silica sand, the growth and development of lambsquarters, pigweed (Amaranthus retroflexus L.), velvetleaf, and crabgrass [Digitaria sanguinalis (L.) Scop.], as measured by plant height, leaf area, and total, shoot, leaf, and root dry weight, were significantly inhibited as the rate increased from 0.0 to 2.0 g kg -1 . Dried alfalfa residue significantly stimulated plant height, leaf area, and total dry weight including shoot, leaf, and root of giant foxtail and cheatgrass (Bromus secalinus L.). Results suggest that alfalfa residue has a contrasting effect on weed growth and development due to water-soluble allelochemicals present in the residue.

Allelopathic potential in rice (Oryza sativa L.) germplasm

Abstract: Summary Allelopathy is the direct influence of a chemical released from one living plant on the development and growth of another plant. The use of allelopathy to control weeds of food crops could contribute towards increasing yields in sustainable agricultural systems. Various research teams have identified several hundred rice accessions which show indications of allelopathic potential, 60 of them showing promising allelopathic activity against one or more weeds. These accessions have different origin and stage of improvement. This, combined with the involvement of several allelochemicals and the ability to release these chemicals, indicates that allelopathic potential is a polygenic characteristic weakly correlated with yield or other important agronomic features. Successful allelopathy research, however, must be focused both on the discovery and subsequent validation of allelopathic potential. Experimental factors such as choice of test plants, collection of allelochemicals, concentration, osmotic pressure and bioassay methodology need considerable attention together with validation through assays with known chemicals of known concentrations. Without validation using known chemicals, the contribution of allelopathic research remains obscure. Several putative allelochemicals are found in extracts of rice leaf and straw, decomposing straw, and in rice soil. Evidence that these chemicals are being released from living plants is still lacking, but as it is a prerequisite for allelopathic activity in nature, it must be proved. Methods of collecting test solutions from living plants need further description. Allelopathic activity is believed to be a joint action of several secondary metabolites, and this must be confirmed for rice. Dilution assays with mixtures of putative rice allelochemicals need to be conducted to evaluate possible synergistic effects. In validation, these mixture-dose response curves must be compared with assays using collected test solutions. A joint, coordinated and focused research effort on rice allelopathy is necessary before the full potential of allelopathic cultivars can be realised.

A chemical basis for differential allelopathic potential of sorghum hybrids on wheat

Abstract: The basis for differential allelopathic potentials among sorghum (Sorghum bicolor L. Moench) hybrids was investigated by conducting quantitative and qualitative studies of their phenolic contents. Total phenolic content in sorghum plant parts varied within hybrids, among hybrids, and between growing seasons. Inhibition of wheat (Triticum aestivum L.) radicle growth was positively associated (r=0.66) with concentrations of total phenolics contained in plant parts. Extracts from culms contributed the higherst proportion of toxicity from sorghum plants, inhibiting radicle growth up to 74.7%. Concentrations of five phenolic acids,p-hydroxybenzoic (POH), vanillic (VAN), syringic (SYR),p-coumaric (PCO), and ferulic (FER), differed in all plant parts of the three sorghum hybrids. Concentrations of POH, VAN, and SYR were consistently higher than PCO and FER. PCO and FER wer absent from some plant parts, with FER being the most frequently missing. Inhibition of wheat radicle growth was found to be positively associated with the concentration of each phenolic acid. Vanillic acid was most highly associated (r=0.44) with inhition. Thus, above-ground sorghum tissues contained phenolic acids that contributed to allelopathic potential. Additionally, sorghum roots exuded POH, VAN, and SYR that may enhance the overall allelopathic potential of sorghum during growth and after harvest when residues remain on the soil surface or are incorporated prior to planting a subsquent crop.

Inhibition of growth, and effects on nutrient uptake of arctic graminoids by leaf extracts - allelopathy or resource competition between plants and microbes?

Abstract: Previous research has shown that plant extracts, e.g. from boreal dwarf shrubs and trees, can cause reduced growth of neighbouring plants: an effect known as allelopathy. To examine whether arctic and subarctic plants could also be affected by leaching of phytochemicals, we added extracts from the commonly occurring arctic dwarf shrubs Cassiope tetragona and Empetrum hermaphroditum, and from mountain birch, Betula pubescens ssp. tortuosa to three graminoid species, Carex bigelowii, Festuca vivipara and Luzula arcuata, grown in previously sterilized or non-sterilized arctic soils. The graminoids in non-sterilized soil grew more slowly than those in sterilized soil. Excised roots of the plants in non-sterilized soil had higher uptake rate of labelled P than those in sterilized soil, demonstrating larger nutrient deficiency. The difference in growth rate was probably caused by higher nutrient availability for plants in soils in which the microbial biomass was killed after soil sterilization. The dwarf shrub extracts contained low amounts of inorganic N and P and medium high amounts of carbohydrates. Betula extracts contained somewhat higher levels of N and much higher levels of P and carbohydrates. Addition of leaf extracts to the strongly nutrient limited graminoids in non-sterilized soil tended to reduce growth, whereas in the less nutrient limited sterilized soil it caused strong growth decline. Furthermore, the N and P uptake by excised roots of plants grown in both types of soil was high if extracts from the dwarf shrubs (with low P and N concentrations) had been added, whereas the P uptake declined but the N uptake increased after addition of the P-rich Betula extract. In contrast to the adverse extract effects on plants, soil microbial respiration and soil fungal biomass (ergosterol) was generally stimulated, most strongly after addition of the Betula extract. Although we cannot exclude the possibility that the reduced plant growth and the concomitant stimulation of microbial activity were caused by phytochemicals, we believe that this was more likely due to labile carbon in the extracts which stimulated microbial biomass and activity. As a result microbial uptake increased, thereby depleting the plant available pool of N and P, or, for the P-rich Betula extract, depleting soil inorganic N alone, to the extent of reducing plant growth. This chain of events is supported by the negative correlation between plant growth and sugar content in the three added extracts, and the positive correlation between microbial activity, fungal biomass production and sugar content, and are known reactions when labile carbon is added to nutrient deficient soils.

Effect of Alfalfa Plant and Soil Extracts on Germination and Growth of Alfalfa

Abstract: Alfalfa (Medicago sativa L.) plants contain water-soluble substances that inhibit the germination and seedling growth of alfalfa. Determining where allelochemicals may be found in alfalfa in the greatest concentration would aid in trying to isolate the compound or compounds responsible for autotoxicity. This study investigated the allelopathic effects of various alfalfa plant parts, and the soil in which alfalfa had been grown, on alfalfa germination and seedling growth. Aqueous extracts of alfalfa leaf, stem, flower, seed, and root plant parts were made to determine their effects on germination and dry weights of hypocotyl, radicle and total length of 5-d-old alfalfa seedlings over a range of extract concentrations. Soil samples (Flanagan series: fine, montmorillonitic, mesic Aquic Argiudolls) from around alfalfa plants at the vegetative and reproductive stages were compared with sterilized and nonsterilized soil formerly seeded with alfalfa, hairy vetch (Vicia villosa Roth), and winter rye (Secale cereate L.). Increasing the aqueous extracts concentrations of separated alfalfa plant parts significantly inhibited alfalfa germination, seedling length and weight. Radicle length was more sensitive to extract source than seed germination or hypocotyl length. Based on 5-d-old alfalfa radicle length growth, and averaged across all extract concentrations, the degree of toxicity of different alfalfa plant parts and soil from around alfalfa can be classified in order of decreasing inhibition as follows: leaf, seed, complete plant mixture, soil, root, flower, and stem. Leaf extracts (12 g kg⁻¹) caused a 48% decrease in water up take by alfalfa seed. Soil in which alfalfa had previously grown was the most inhibitory to alfalfa growth after 25 d of growth compared with soil where winter rye or hairy vetch had previously grown. Inhibitory effects were greater for soil collected around alfalfa grown at the reproductive than the vegetative growth stage. These data indicate that alfalfa autotoxicity may mult from a release of one or more water-soluble compounds from alfalfa leaf tissue. Exp. Stn. Project 1-6-55179.

The allelopathic effect of three Amaranthus spp. (pigweeds) on wheat (Triticum durum)

Abstract: Summary The allelopathic effect of Amaranthus retroflexus L., Amaranthus blitoides S. Wats, and Amaranthus gracilis Desf. on wheat Triticum durum L. was investigated under laboratory, glasshouse and field conditions. Laboratory experiments showed that fresh shoot or root extract of the three weed species reduced germination, coleoptile length, root length and root dry weight of wheat seedlings. The inhibitory effects were rate dependent, with low concentrations of shoot extract promoting shoot growth of wheat. Fresh plant extracts were more phytotoxic than dried plant extracts and shoot extracts had higher detrimental effects than root extracts. In pot experiments, dried shoot extract of A. gracilis increased shoot and root dry weights of wheat seedlings. For A retroflexus and A. blitoides the extracts of these and dried shoots (8 g kg−1), which had been added to soil mixtures significantly reduced ger-mination and growth of wheat seedlings. Addition of up to 16 g kg−1 of A. gracilis residues promoted shoot growth of wheat and had no significant harmful effect on root growth. Roots appeared more sensitive to allelopathic effect than shoots. Under field conditions, incorporation of A. retroflexus or A. blitoides residues in the soil reduced height, grain and straw yield of wheat, whereas A. gracilis residues stimulated plant height and increased yield.

Allelopathic influence of nine forage grass extracts on germination and seedling growth of alfalfa

Abstract: Poor establishment of alfalfa (Medicago sativa L.) often results when the alfalfa is sown with cool-season perennial grasses. This study was conducted to screen the inhibitory characteristics of grasses that are often grown in combination with alfalfa in grass swards. Laboratory and greenhouse studies were conducted to determine the allelopathic potential of nine grasses to alfalfa germination and seedling growth. Alfalfa seeds were germinated in aqueous extracts of nine grasses, using distilled water as a control. Measurements were taken to determine the effect of the extracts on germination, seedling length, and weight. Alfalfa germination ranged from 64% for tall fescue (Festuca arundinacea Schreb.) extracts to 91% for the control. Total alfalfa seedling length was reduced by 39% for grain sorghum [Sorghum bicolor (L.) Moench] extracts. Dry weights of alfalfa cotyledons, hypocotyls, and radicles were reduced significantly by several grass extracts. Smooth bromegrass (Bromus inermis Leyss.), orchardgrass (Dactylis glomerata L.), and grain sorghum extracts were more inhibitory than other grass extracts. Alfalfa seedling emergence and survival percentage was affected by various grass root residues. Timothy (Phleum pratense L.) extracts caused the lowest survival percentage of 59% compared to the control of 88%. Redtop [Agrostis gigantea Roth; syn. Agrostis alba L. sensu auct. (American)] and reed canarygrass (Phalaris arundinacea L.) extracts had no effect on alfalfa seedling emergence and survival. Leached and nonleached residues significantly inhibited alfalfa height, leaf area, and dry weights of leaves and stems. The extent of reduction was greater in nonleached than in leached residues. These results suggest that grass residues may affect alfalfa growth and development because of inhibitory effects of allelochemicals present in grass residues.

Phytotoxicity of Extracts from Sorghum Plant Components on Wheat Seedlings

Abstract: Wheat (Triticum aestivum L.) yield is depressed when the crop is grown after grain sorghum [Sorghum bicolor (L.) Moench], a known allelopathic species. Since little is known about the variability of allelopathic potential among sorghum hybrids on wheat, six sorghum hybrids were selected from a 1989-1990 sorghum-wheat sequence for further study. The range in yield depression observed was 16%. The six hybrids were grown in 1991 and separated into plant parts at maturity. A bioassay using wheat seedlings to detect allelopathic potential was developed. Bioassays of water extracts from mature seeds, glumes, leaves, stems, and roots of sorghum were conducted to (i) quantify the allelopathic potential of sorghum on wheat ; (ii) compare allelopathic potential of individual sorghum hybrids ; and (iii) identify the plant parts that are the most important sources of allelopathic substances. Wheat radicle growth response to water extracts revealed a highly allelopathic hybrid and two hybrids with low allelopathic potential. These were retained for study in 1992. All plant parts, regardless of hybrid, contained water-soluble materials inhibitory to wheat seedling growth. Stems, leaves, and roots were the most inhibitory components of a sorghum plant, reducing wheat radicle elongation by 74.7, 68.5, 64.0%, respectively. Within a sorghum hybrid, an individual plant part was not consistently allelopathic at the same level across years. Bioassays can rapidly detect the differences in allelopathic potential that may occur within and among hybrids. These results have implications for using sorghum-wheat rotations where residues of certain sorghum hybrids might negatively influence growth and development of wheat, possibly resulting in decreased wheat yields.

Allelopathic effects of Prosopis juliflora Swartz

Abstract: Allelopathic effects of aqueous extracts from under canopy soil and from different parts of Prosopis juliflora on germination and early seedling growth of various cultivars of Zea mays, Triticum aestivum and Albizia lebbeck were studied. Fruit and seed extracts considerably delayed and reduced germination, root, shoot and seedling growth compared with root, leaf and flower extract. Soil extract showed an inhibitory effect on germination but seedling growth remained unaffected in most of cultivars.

Endophytic bacterial systems governing red clover growth and development

Abstract: SUMMARY Endophytic competent bacteria capable of promoting both beneficial and detrimental growth responses in red clover (Trifolium pratense L.) were recovered from three adjacent areas of farmland each having a different cropping history — continuous red clover, continuous potatoes (Solanum tuberosum L.) or a 2 yr rotation of red clover and potatoes. The population composition of these rhizobacteria was altered by the various crop sequences. The greatest instance of significant growth responses (beneficial or detrimental) occurred with those bacteria derived from the clover-potato soil, suggesting increased interactive ‘competition’ among bacterial populations at the ‘interface’ between different crop rotations. Whether bacterial strains promoted or inhibited growth appeared to depend on the cropping history and prior exposure of pre-bacterised clover plants to the natural microflora in the peat-based growing media. The interaction between bacterial colonists influenced plant trait expression to the degree that some characteristics were completely masked. Improvements in plant growth were interpreted as an allelopathic side-effect of the competition between endophytes for the same ecological niche, from which the plant inadvertently benefits.

Inhibitory effects of Myrica cerifera on Pinus taeda

Abstract: -Pinus taeda naturally invades Myrica cerifera thickets as the shrub community succeeds to a maritime forest on southeastern USA barrier islands. Potential mechanisms supporting the persistence of M. cerifera thickets on barrier islands were examined in an environmental chamber. The inhibitory effects of allelochemicals from M. cerifera leaf litter and the soil in which it grows, and the interaction between allelochemicals and light intensity were quantified for seed germination and seedling growth of P taeda. Germination of P taeda seeds was significantly reduced by treatment with leachate from dead M. cerifera leaves, but light level had no significant effect. In contrast, root, shoot and total seedling growth were significantly lower under low light (44 Rmol m-2 sec-1). Root growth under high light (300 Rmol m-2 sec-1) was significantly lower for P taeda seedlings grown in soil collected from beneath Myrica thickets. Both root and shoot growth of P taeda in Myrica soil were significantly higher in the presence of Myrica leaf litter in high light. Thus, litter accumulation may assist P taeda in invading Myrica thicket gaps, possibly by counteracting allelopathic effects of Myrica root exudate. Low light levels and allelopathic effects may interact and contribute to the persistence of Myrica thickets limiting root growth of invading P taeda seedlings, thereby reducing competition for space, soil moisture and nutrients.

Differences in Autotoxicity among Seven Alfalfa Cultivars

Abstract: There is a need to determine if alfalfa (Medicago sativa L. subsp. sativa) can be selected for low concentrations of allelopathic compounds. The objective of this study was to evaluate alfalfa cultivar differences in autotoxic traits in relation to various concentrations of aqueous extracts. Plant extracts from seven alfalfa cultivars (Apollo-Supreme, Arrow, Vernal, DK-125, Dawn, Pioneer 5472, and Magnum III) were evaluated in the laboratory for autotoxic effects on the same cultivar at four levels of extract solution (10, 20, 30, and 40% w/v). Double-distilled water was used as a control. Germination percentage, seedling length, and seedling dry weight were measured to determine the effect of the same cultivar extracts on alfalfa growth. These parameters were significantly reduced as the extract concentration increased. The highest concentration (40%) caused the greatest reduction in hypocotyl and radicle length, seedling dry weight, germination percentage, and seedling vigor in all cultivars. It also significantly increased the time required for germination. Autotoxicity effects were significantly different among the various cultivars. Cultivars may be classified in the following order of decreasing inhibition : Pioneer 5472, Arrow, Magnum III, Vernal, Apollo-Supreme, DK-125 and Dawn. The results indicate that there may be genetic differences among cultivars for resistance to alfalfa autotoxicity, and that selection for low autotoxicity may be possible.

Allelopathic Pollen Extract from Phleum pratense L. (Poaceae) Reduces Germination, In vitro, of Pollen of Sympatric Species

Abstract: In vitro studies were performed to quantify the putative allelopathic effect of pollen from Phleum pratense (Aveneae: Poaceae). Extract from ground pollen was partitioned, using ion-exchange chromatography. Acidic, basic, and neutral fractions were isolated. These fractions, along with extract from intact pollen, were applied in increasing concentrations of the equivalent of 0 (control), 0.1, 1, 3, 5, 10, and 25 pollen grains of P. pratense/μL. Pollen from five sympatric, wind-pollinated species of Poaceae and P. pratense was germinated on agar medium that contained different extract concentrations. In response to increasing extract concentrations, from intact pollen or from acidic fractions, mean percentage of germination of pollen of Agropyron repens, Bromus inermis, Danthonia compressa, and Poa compressa decreased in a nonlinear manner. Basic, neutral, and solvent fractions did not show any allelopathic activity; hence, the allelochemicals may be acidic in nature. An extract concentration equivalent to...

The Role of Allelopathy in Legume Decline in Pastures. II.* Comparative Effects of Pasture, Crop and Weed Residues on Germination, Nodulation and Root Growth

Abstract: Sterile cold water extracts of a range of residues from pasture, crop and weed species have been shown to exert allelopathic effects on subterranean clover and other species of pasture legumes, resulting in reduced germination, stunted growth of the radicle and reduced root growth and nodulation. Roots exposed to the extracts became discoloured and shortened with distorted and scant root hair formation which may result in reduced nodulation. Seedlings exposed to these allelopathic compounds were smaller, less robust and slower growing than the control seedlings and hence more susceptible to attack by plant pathogens.

Allelopathic potential of an annual weed, Polypogon monspeliensis, in crops in India

Abstract: The question of whether annual weeds are allelopathic under natural conditions still remains to be critically answered. Investigations were carried out to understand the involvement and mode of operation of allelopathy in an annual weed, Polypogon monspeliensis. Comparative studies of soils associated with and without the weed under field conditions revealed that there was no significant difference in toxicity of the two soils, and thus the possibility of its allelopathic effect on crops grown in the same season could be ruled out. However, soil amended with weed straw had significantly higher total phenolics including higher relative concentrations of phenolic fractions that were not detected in unamended soil. Phenolic fractions significantly affected the seedling growth of radish and cluster bean. It is likely that P. monspeliensis did not interfere chemically with the crops cultivated during the same season, but interfered with the following season crop through incorporated straw. These results indicate how a monocarpic annual such as P. monspeliensis can be allelopathic under field conditions and allelopathic potential can be managed. We suggest that before detailed investigations on allelopathy are performed as per earlier recommended protocols, data on weed life cycle pattern and agricultural practices should be collected.

Soybean nodulation and nitrogen fixation on soil amended with plant residues.

Abstract: Residues from some tree species may contain allelopathic chemicals that have the potential to inhibit plant growth and symbiotic N2-fixing microorganisms. Soybean [Glycine max (L.) Merr] was grown in pots to compare nodulation and N2-fixation responses of the following soil amendments: control soil, leaf compost, red oak (Quercus rubra L.) leaves, sugar maple (Acer saccharum Marsh) leaves, sycamore (Platanus occidentalis L.) leaves, black walnut (Juglans nigra L.) leaves, rye (Secale cereale L.) straw, and corn (Zea mays L.) stover. Freshly fallen leaves were collected from urban shade trees. Soil was amended with 20 g kg-1 air-dried, ground plant materials. Nodulating and nonnodulating isolines of “Clark” soybean were grown to the R2 stage to determine N2-fixation by the difference method. Although nodulation was not adversely affected, soybean grown on leaf-amended soil exhibited temporary N deficiency until nodulation. Nodule number was increased by more than 40% for soybean grown on amended soil, but nodule dry matter per plant generally was not changed compared with control soil. Nonnodulating plants were severely N deficient and stunted as a consequence of N immobilization. Nodulating soybean plants grown on leaf or crop residue amended soil were more dependent on symbiotically fixed N and had lower dry matter yields than the controls. When leaves were composted, the problem of N immobilization was avoided and dry matter yield was not reduced. No indication of an allelopathic inhibition on nodulation or N2-fixation from heavy application of oak, maple, sycamore, or walnut leaves to soil was observed.

Identification of allelochemicals in Eucalyptus citriodora and Polygonum sachalinense

Abstract: The relationship between the allelochemicals, p-menthane-3,8-diols (cis and trans) and the ontogenetic age in Eucalyptus citriodora was elucidated. The diols in the soil from a Eucalyptus grove were analysed by chromatography. On the other hand, the root exudates from Polygonum sachalinense in a recirculating system significantly inhibited lettuce seedling growth. Bioassay of the neutral-acidic fraction on the TLC agar plate showed the inhibitory activity corresponded to the two yellow pigments. Two compounds were isolated and identified as anthraquinone compounds; emodin and physcion. The results indicate that these anthraquinones are responsible for the observed interference in nature and are potent allelochemicals

Allelopathic potential of Ipomoea tricolor (Convolvulaceae) in a greenhouse experiment.

Abstract: The allelopathic potential ofIpomoea tricolor, a plant used in Mexican agriculture to control weeds, and tricolorin A, the major phytogrowth inhibitor present in the so-called "resin glycosides" of this plant, have been evaluated by testing leachates of the plant and the compound on the germination and radicle growth ofAmaranthus hypochondriacus, Echinochloa crusgalli, Senna uniflora, I. tricolor, andI. purpurea. The allelopathic potential ofI. tricolor was evaluated in a greenhouse experiment with dryI. tricolor mixed with sterile and nonsterile soil in pots.A. hypochondriacus was sown in pots containingI. tricolor, 2-chloro-4-(ethylamino)-6-(isopropylamino)-1,3,5 triazine (Gesaprim) or 1-glyphosphate, and the glyphosphate salt of isopropylamine (Faena), two different commercial herbicides used as a comparison toI. tricolor. Number and dry weights of different monocotyledonous and dicotyledonous weeds andA. hypochondriacus growing in the different treatments were measured.Ipomoea and Faena herbicide had a similar inhibitory effect on monocots.

Sweet potato allelopathic substance inhibits growth of purple nutsedge (Cyperus rotundus).

Abstract: The allelopathic influence of sweet potato cultivar 'Regal' on purple nutsedge was compared to the influence on yellow nutsedge under controlled conditions. Purple nutsedge shoot dry weight, total shoot length and tuber numbers were significantly lower than the controls (47, 36, and 19% inhibition, respectively). The influence on the same parameters for yellow nutsedge (35, 21, and 43% inhibition, respectively) were not significantly different from purple nutsedge. Sweet potato shoot dry weight was inhibited by purple and yellow nutsedge by 42% and 45%, respectively. The major allelopathic substance from 'Regal' root periderm tissue was isolated and tested in vitro on the two sedges. The I 50 's for shoot growth, root number, and root length were 118, 62, and 44 μg/ml, respectively, for yellow nutsedge. The I 50 's for root number and root length were 91 and 85 μg/ml, respectively, for purple nutsedge and the I 50 for shoot growth could not be calculated. Nomenclature: Purple nutsedge, Cyperus rotundus L. # 3 CYPRO, yellow nutsedge, Cyperus esculentus L. # CYPES, sweet potato, Ipomoea batatas (Lam.), 'Regal'