Showing papers on "Allelopathy published in 1988"

Allelochemicals from Plants as Herbicides

Abstract: Allelochemicals representing numerous chemical groups have been isolated from over 30 families of terrestrial and aquatic plants. Some of the compounds also have been isolated from soil in quantities sufficient to reduce plant growth. Although selected allelochemicals are believed to influence plant densities and distributions, none isolated from higher plants have been considered active enough for development as commercial herbicidal products. Almost all herbicidal allelochemicals exist in plants in nontoxic, conjugated forms. The toxic moiety may be released upon exposure to stress or upon death of the tissue. The most successful use of allelochemicals in weed control has been management of selectively toxic plant residues. For example, rye residues have controlled weeds effectively in a variety of cropping systems. Several weed species may interfere with crop growth through chemicals released from their residues. A number of noxious perennial species appear to exploit allelochemicals in their interference processes. This review focuses on the more recent chemical discoveries and how they might be exploited for weed control.

Potentials for exploiting allelopathy to enhance crop production.

Abstract: Strategies for utilizing allelopathy as an aid in crop production include both avoidance and application protocols. There are immediate opportunities for management of weed and crop residues, tillage practices, and crop sequences to minimize crop losses from allelopathy and also to use allelopathic crops for weed control. Varieties of grain and forage sorghums (Sorghum Spp.), sunflower (Helianthus annuus L.), oats (Avena sativa L.), wheat (Triticum sativum L.),rye (Secale cereale L.), and others may provide weed control and in some instances crop stimulation from their residues. Our four-year field study with cultivated sunflower resulted in no differences in weed biomass between plots with and without herbicide (EPTC) applications. Strip cropping that included sorghum showed that in the subsequent year weed density and biomass were significantly lower in the previous-year sorghum than in soybean strips. Possibilities exist for modification of crop plant metabolism to alter production of allelochemicals. Allelochemical-environmental interactions must be considered in efforts to benefit from allelopathy. Under greenhouse conditions, joint application of low levels of atrazine, trifluralin, alachlor, or cinmethylin with a phenolic allelochemical showed that these two categories of inhibitors acted in concert to reduce plant growth. Allelochemicals may also be adapted as yield stimulants or environmentally sound herbicides, such as cinmethylin and methoxyphenone. Isolation of bialophos, tentoxin, and others shows that bacteria and fungi are good sources of biologically active compounds.

Bioassay of naturally occurring allelochemicals for phytotoxicity.

Abstract: The bioassay has been one of the most widely used tests to demonstrate allelopathic activity. Often, claims that a particular plant species inhibits the growth of another are based entirely on the seed germination response to solvent extracts of the suspected allelopathic plant; few of these tests are of value in demonstrating allelopathy under natural conditions. The veracity of the bioassay for evaluating naturally occurring compounds for phytotoxicity depends upon the physiological and biochemical response capacity of the bioassay organism and the mechanism(s) of action of the allelochemicals. The possibility that more than one allelochemical, acting in concert at very low concentrations, may be responsible for an observed allelopathic effect makes it imperative that bioassays be extremely sensitive to chemical growth perturbation agents. Among the many measures of phytotoxicity of allelochemicals, the inhibition (or stimulation) of seed germination, radicle elongation, and/or seedling growth have been the parameters of choice for most investigations. Few of these assays have been selected with the view towards the possible mechanism of the allelopathic effect.

Degradation of juglone by soil bacteria.

Abstract: Bacteria that can degrade juglone (5-hydroxy-1,4-naphthoquinone) were isolated from soil beneath black walnut trees. Autecological studies with one of these bacteria (Pseudomonas J1), demonstrated that it could grow rapidly using juglone as its sole source of carbon and energy. Using nonlinear regression analysis and the Monod equation, it was determined that this bacterium had a high affinity for juglone (Ks = 0.95 μg/ml).Pseudomonas J1 can also utilize other aromatic compounds from plants as its sole source of carbon and energy. Compounds such as chlorogenic acid, ferulic acid, gallic acid, and 2-hydroxy-1,4-naphthoquinone (Lawson) were rapidly degraded byPseudomonas J1. The rapid degradation of juglone and other suspected allelochemicals by soil bacteria make it unlikely that these compounds are important mediators of plant-plant interactions under natural conditions.

Three trophic level interactions: allelochemicals, Manduca sexta (L.) , and Bacillus thuringiensis var. kurstaki Berliner

Abstract: The role of plant allelochemicals in reducing the ability of Bacillus thuringiensis var. kurstaki Berliner to kill larvae of Manduca sexta (L.) was studied by comparing the effects of the alkaloid nicotine and the flavonoid rutin on the toxicity of B. thuringiensis. Concentrations of nicotine and rutin reflecting levels found in tobacco and tomato plants (0, 0.2, 0.4, 0.6, 0.8, 1.0% wet weight) were incorporated into synthetic diet containing 0.001% B. thuringiensis and B. thuringiensis -free diet. Survivorship of M. sexta larvae increased at higher levels of nicotine (0.6, 0.8, 1.0% wet weight), but higher concentrations of rutin did not increase larval survivorship. Experiments on colony growth of B. thuringiensis on nutrient agar containing nicotine or rutin (0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9% wet weight) demonstrated that nicotine reduced colony growth to a greater extent than rutin. Consequently, plant allelochemicals potentially are an important factor in reducing larval mortality caused by B. thuringiensis on certain crops. Specialist herbivores that can tolerate high concentrations of allelochemicals may gain protection from pathogens by feeding on plants or plant parts with higher levels of toxins.

Allelopathic effects of palmer amaranth (Amaranthus palmeri) on seedling growth.

Abstract: Palmer amaranth (Amaranthus palmeri S. Wats. #3 AMAPA) residue was incorporated into soil to deter- mine its allelopathic effects on the seedling growth of grain sorghum (Sorghum bicolor L. Moench.), cabbage (Brassica oleracea, var. capitata L.), carrot (Daucus carota L.), and onion (Allium cepa L.). Root and shoot growths were equally sensitive to the toxic effects of soil-incorporated Palmer amaranth. Growth of 'Grand Slam' cultivar of cabbage was 17 to 30% more sensitive than the growth of 'Sanibel' cabbage. Growth of onion and carrot seedlings was less inhibited than either cabbage or grain sorghum. Growth of grain sorghum root was severely inhibited by 8000 and 16 000 ppm of Palmer amaranth in soil and was not affected by oven dryings other than lyophilization. Seedling growth was more severely inhibited by thyrsus and leaf tissues than by stem and root tissues of Palmer amaranth. Additional index words. Allelopathy, seedling growth, Amaranthus palmeri, Allium cepa, Sorghum bicolor L., Brassica oleracea var. capitata L., AMAPA.

Allelopathic potential of raspberry foliar leachates on growth of ectomycorrhizal fungi associated with black spruce

Abstract: In vitro bioassays on seven species of ectomycorrhizal fungi associated with black spruce (Picea mariana (Mill.) BSP) were tested under allelopathic action of raspberry (Rubus idaeus L.). Radial growth inhibitions were observed when fungi were confronted with increasing concentrations (0%/0.I %0.5%/o2.5%) of foliar leachates made from May, July, and September material (1986). For the 2.5% treatment, species Paxillus involutus, Laccaria proxima, Laccaria bicolor, Thelephora terrestris, and Cortinarius pseudonapus grew only 6, 8, 32, 42, and 46% of their control, whereas Hebeloma cylindrosporum and Cenococcum geophilum were stimulated. Tree seedlings from raspberry invaded plantation showed mycorrhizal infection rate over 75%, with fine roots mainly colonized by C. geophilum. In combination with efforts of tree improvement and based on the results of this study, it seems important to select a well-adapted mycorrhizae, when interference by raspberry is involved.

Biological activity and tentative identification of flavonoid components in velvetleaf ( Abutilon theophrasti Medik.) seed coats

Abstract: The biological activity of aqueous extracts of velvetleaf (Abutilon theophrasti Medik.) seed coats and their flavonoid components against three plant species and five soil fungi was investigated. Aqueous extracts slightly inhibited germination and significantly inhibited radicle growth of all plant species tested. Fungal growth was inhibited or not affected, depending on species, by aqueous extracts. The aqueous extracts were extracted into methanol and separated using paper chromatography for identification of compounds responsible for inhibition of seedling and fungal growth. Six flavonoid compounds were isolated and tentatively identified as delphinidin, cyanidin, quercetin, myricetin, (+)-catechin, and (−)-epicatechin. Bioassays revealed that the flavonoid compounds significantly inhibited germination and radicle growth of all test species at a concentration of 1.0 mM. Individual flavonoids had variable effects on fungi but appeared to inhibit growth and sporulation of potential seed-decomposing fungi rather than “beneficial” fungi. These results indicate that the flavonoid complement of velvetleaf seed coats may function in a dual defensive role against competing seedlings and seed-attacking fungi.

The Protective Action of a Higher Plant Toxic ProductBiochemical studies reveal how the allelochemical L-canavanine disrupts insect development

Abstract: mong the thousands of secondary metabolites that underlie the characteristic properties of higher plants are a diverse assemblage of potentially toxic allelochemicals Allelochemicals are those natural products that affect the growth, health, behavior, or population biology of members of other species (Whittaker and Feeny 1971) There is convincing evidence that these toxic natural products constitute the chemical defense arsenal of higher plants (Feeny 1975, 1976; Rosenthal and Janzen 1979, and Whittaker and Feeny 1971) They render protection against herbivores, particularly insects, molluscs, and many small rodents; pathogenic fungi, bacteria, and viruses; and even other plants with which they compete (Bell 1978, Harborne 1977, Rice 1974) That allelochemicals may impart a selective advantage to plants is suggested by such evidence as their potent toxicity to specific herbivores These substances can inhibit, repulse, and even kill nonadapted organisms that may otherwise feed upon or compete with the producing plant Plants or plant parts containing toxic compounds are attacked by a limited number of herbivores; thus, these compounds have demonstrable effectiveness and survival value in limiting herbivore attack on plants Some her-

Evaluation of some weed extracts against field dodder on alfalfa (Medicago sativa).

Abstract: Experiments were conducted to evaluate the effectiveness of some weed extracts against field dodderCuscuta campestris Yunck. on alfalfa (Medicago stiva L.) and to identify and quantify the phytotoxic agents of these extracts. All concentrations of aqueous extract of every weed showed significant effectiveness on dodder when compared to the untreated plant under lath house and field conditions. Control percentages of the (0.5 g) of Bermuda grass (Cynodon dactylon) and wall goosefoot (Chenopodium murale) ranged between 83 and 96, and the same concentration caused injury to alfalfa foliage up to 43% when applied in the field. Phytotoxic agents were identified as phenolic compounds such as chlorogenic, isochlorogenic,p-coumaric acids, and scopoletin. Their quantities varied with species; Bermuda grass had the highest content (32.2 μg/g dry weight) followed by Johnson grass (Sorghum halepense), well goosefoot, and tumble pigweed (Amaranthus albus). These results might aid in screening for effective alternate approaches for controlling dodder on alfalfa planted for seeds.

Asymmetric small-scale distribution and allelopathy: interaction between Rumex obtusifolius L. and meadow species.

Abstract: Analysis of small-scale distribution may allow allelopathic interaction among plant species to be distinguished from competitive interaction. If all environmental factors except slope are uniform, allelopathy produces spatial asymmetry in the association with a hypothetical receptor species and the corresponding hypothetical emitter species in the neighborhood of the latter. The interaction betweenRumex obtusifolius and the meadow speciesLolium perenne, Poa pratensis, Dactylis glomerata, andTrifolium repens is analyzed by way of example.

Biological suppression of nitrification by selected cultivars ofHelianthus annum L.

Abstract: The allelopathic potential of different cultivars ofHelianthus annuus against nitrification was studied using the soil incubation method. The results indicated that aqueous extracts and residues of roots and shoots of all test cultivars significantly reduced the nitrification rate in soil. However, cultivars Local and Citosol were found to be more inhibitory to nitrification than others.

ALLELOPATHIC ACTIVITY OF QUACKGRASS (Agropyron repens) EXTRACTS AND RESIDUES ON ALFALFA (Medicago sativa)

Abstract: Experiments were conducted to characterize the allelopathic activity of quackgrass on alfalfa. Both percent germination and seedling length of alfalfa were recorded to evaluate the toxicity of aqueous extracts from rhizomes or shoots of field-grown quackgrass harvested at three stages of growth in 1984 and 1985. The length of alfalfa seedlings was more sensitive to extracts than was percentage of germination. Aqueous solutions simulating levels of salinity, cyanide content and osmotic pressure equivalent to those found in quackgrass extracts did not affect the growth of alfalfa seedlings. Only quackgrass extracts were phytotoxic to alfalfa. Similar results with hot and cold extraction procedures demonstrated that temperature did not influence the release of water-soluble toxins. Shoot extracts were generally more toxic than were rhizome extracts. Shoot extracts were more inhibitory to alfalfa seedlings when quackgrass was harvested at the vegetative stage than at later stages. Rhizome extracts did not inf...

Allelopathic effects of sandbur leachate on switchgrass germination: observations

Abstract: Switchgrass (Punicum virgtatum L.) est8blishmeot from seed wu limited by currat-year’s groutb of saadbur [Cmchrus long&pinus (Hack.) Fern.] in tbc Nebraska -. stmd reduction was greater tb8n other w8rm-sason gr8sses seeded 8t the ame time, indk8ting possIbk 8Uelop8thy. Germhutioo studke were conducted to ev8hmte potentkl andbur 8lkloprthy with switchgr8ss. Fresh andbur pknt m8terkl wu cxtr8cted with distilled water for 24 hours. Root, shoot, 8nd whole pknt k8ch8te (2% w/v) from andbur pknts colkcted between the veget8tive 8nd culm eloog8tioo st8p 8nd whok pknt lach8te (2,4% w/v) from vcget8tive or nuture pknts ~8s used. Switchgur germhution ~8s not influenced by root, shoot, or whole pknt lach8te from andbur pknts cornposited over phenolgial st8gen. However, k8ch8te reduced the length of the prim8ry root urd incre8sed shoot length me8sured 8t 11 diys. Generally, the response ‘118s grater with veget8tive andbur compued to mrture 8nd with the higher lachute conceotrcltioo. Whok pknt lach8te (4% w/v) from vept8tive andbur reduced switchgmss germhution compued to m8ture pknt Iach8te. The rehtively rapid development of 8 srodbur cover prior to switchgr8ss seed germirmtion on andy sites mry 8ffect switchgmss germhution 8nd wly root development through 8n 8llelop8thk inter8ctioo. Since tilkge promotea npid andbur development, no-till seedings should be considered for switchon andy soib.

Allelopathic effects of Kentucky bluegrass on northern red oak and yellow-poplar.

Abstract: Allelopathic effects of Kentucky bluegrass (Poa pratensis) on seedling growth of northern red oak (Quercus rubra) and yellow-poplar (Liriodendron tulipifera) were in- vestigated. Foliage extracts and leachates from potted Ken- tucky bluegrass did not reduce the growth of either species in a Hagerstown top soil over a 139-day period from seed ger- mination. Removal of northern red oak cotyledons at the one- flush stage reduced growth of the stem and root, but did not affect susceptibility to bluegrass foliage extractives and pot leachates. The results suggest that previously reported detrimental interference between Kentucky bluegrass and seedlings of northern red oak or yellow-poplar can be at- tributed to competition rather than allelopathy.

Determination of Phenolic Compounds Responsible for Allelopathy in Upland Weeds

Abstract: Phenolic compounds present in upland weeds (Artemisia asiatica Nakai, Capsella bursa-pastoris (L.) Medik, Portulaca orleracea L. and Trifolium repens L.) which have shown allelopathic activity were determined using paper chromatography (PC) and high performance liquid chromatography (HPLC). Effect of the determined phenolic compounds on germination and post-germination growth of test plants was also investigated. Kinds of phenolic compounds determined by PC in the four weed species were greater in the aqueous extract than in the methanol extract. Ferulic acid was found in both extracts of the weeds studied, whereas benzoic acid was that the weeds commonly contained hydroquinone, p-hydroxybenzoic, ferulic and cinnamic acids. Out of the phenolic compounds determined by PC and HPLC p-hydroxybenzoic, cinnamic and ferulic acids inhibited germination and post-germination growth of radish and sesame. Inhibition of the phenolic compounds on the radicle growth was greater than on the germination of the test plants.

Allelopathic I. Fleet of Root Exudates From the Obnoxious Weed, Parthenium Hysterophorus L.

Abstract: A novel system called "Continuous Root Exudate Trapping System" was employed to investigate the allelopathic potentials of the hazardous weed, Parthenium hysterophorus L. The setup allowed the collection of root exudates alone from an undisturbed living plant. The exudates, thus collected were separated into three fractions and each of them was tested against the germination and seedling growth of pearl millet seeds. The greatest inhibition was found in the neutral fraction. Germination was significantly inhibited by all the fractions at all the concentrations. W th the seedling growth, radicle length was inhibited more than the plumule growth. Following the results of thin hyer chromatography, it was concluded that Parthenin or any other major sesquiterpene lactone was not a part of the exudates from the roots of P. hysterophorus.

Search for Allelochemicals in Rice (Oryza Sativa L.) and Structure Determination of External Flavonoids of Calamintha Ashei.

Abstract: The f i r s t p a r t of t h i s work was conducted to search fo r a l l e lo ch em ica l s from the r i c e v a r i e t i e s PI346833 (moderately r e s i s t a n t ) and Mars ( su sc e p t ib le ) t h a t may be re sp o n s ib le f o r r e s i s t a n c e to f a l l armyworm, spodoptera f r u g ip e r d a ■ ( J . E. Smith) feed ing . Mature t i l l e r s and seedl ings were e x t r a c te d with petroleum e t h e r (PE), dichloromethane (DCM), acetone , methanol and water . The search f o r b io lo g ica l a c t i v i t y towards f a l l armyworm (FAW) was d i r e c t e d by growth i n h i b i t i o n bioassay. S ig n i f i c a n t a n t i b i o t i c a c t i v i t y t o FAW was observed with the PE and DCM crude e x t r a c t s . Bioassay of the f r a c t i o n s of the PE and DCM e x t r a c t s in d ica ted t h a t the f r a c t i o n s from PI346833 seed l ings adverse ly a f f e c t e d the development of FAW, mainly by blocking pupation . P u r i f i c a t i o n o f one of the a c t i v e f r a c t i o n s (PE-4) led to the i s o l a t i o n of the s i t o s t e r o l s 6 s i t o s t e r o l , s t igm aste ro l and campesterol and, the t r i t e r p e n e i s o a r b o r in o l . Dose-response b ioassays with a u th en t i c s t ig m as te ro l and a s i t o s t e r o l mixture adverse ly a f fe c ted the development of FAW but did not show a p o s i t i v e c o r r e l a t i o n between dose and a n t i b i o s i s . V o la t i l e compounds of the r i c e seed l ings were c o l l e c t e d by dynamic headspace sampling and t rapp ing on Tenax TA. Thermal desorp t ion and cryogenic focusing were used to in troduce the v o l a t i l e compounds to the column f o r ana lys is by gas chromatography-mass spec t rometry . Among the compounds d e tec te d , tw en ty -e igh t compounds were i d e n t i f i e d . Mars contained numerous and g r e a t e r q u a n t i t i e s of v o l a t i l e compounds compared to PI346833. Twelve compounds were found only in Mars and two were found only in P I346833. The second p a r t o f t h i s re sea rch d e a l t with the i s o l a t i o n and i d e n t i f i c a t i o n o f the major ex terna l f lavono ids from leaves of caiamin tha a she i (Lamiaceae). A new f lavone , 5 , 6 , 4 ' t r ih y d ro x y 7 , 8 ,3 ' t r im ethoxyflavone (1 ) , a new n a tu ra l aglycone, 5 , 6 , 4 ' t r ihydroxy-7 ,3 ' -d im ethoxyf lavone (Z), 5 ,4 ' d i h y d r o x y 6 , 7 , 8 , 3 ‘te tramethoxyflavone (3) and 5 -hydroxy-6 ,7 ,8 ,3* , 4 '-pentamethoxyflavone (4) were i d e n t i f i e d by spec t ro scop ic methods. The NMR method INAPT ( I n s e n s i t i v e Nuclei Assigned by P o l a r i z a t i o n Transfe r ) was used and demonstrated as a new general method of so lv ing problems in flavonoid s t r u c t u r e de te rm ina t ion . INAPT was found to be a s e n s i t i v e and s e l e c t i v e method of d i s t i n g u i s h in g among 5 , 6 , 7 , 5 ,7 ,8 s u b s t i t u t e d f l a v o n o l / f l a v o n e and 5 , 6 , 7 , 8 s u b s t i t u t e d flavone.