Allelopathic effects ofPolygonum aviculare L. II. Isolation,characterization, and biological activities of phytotoxins

In earlier work, we found thatPolygonum aviculare had pronounced allelopathic effects against several test species. Four inhibitors were isolated from livingPolygonum plants, three of which were glucosides. Four different inhibitors were isolated fromPolygonum residues and soil underPolygonum stands, and none of these occurred in soil fromCynodon dactylon (L.) Pers. stands. Three of these were glycosides containing both fructose and cellobiose as the sugars. Color reactions of all the inhibitors indicated that they are phenolic in nature. All the inhibitors reduced seed germination and/or seedling growth ofChenopodium album L. Moreover some of them inhibited growth of different strains ofRhizobium andAzotobacter.     

Allelopathic effects ofPolygonum aviculare L. I. Vegetational patterning

Polygonum aviculare was observed to spread rapidly into heavy stands ofCynodon dactylon (L.) Pers. resulting in death of the latter. This indicated a strong interference againstCynodon dactylon. Measurements of selected soil minerals and physical factors indicated that competition was probably not the chief cause of that interference. Soil collected under deadPolygonum was very inhibitory to all test species exceptSporobolus pyramidatus (Lam.) Hitchc., suggesting the presence of inhibitory compounds. Tops and roots ofPolygonum, root exudates, and leachate of the tops inhibited seed germination and seedling growth of most test species. Therefore, allelopathy apeared to be the dominant component of the interference, with competition probably accentuating its effects.Polygonum aviculare was inhibitory toGossypium barbadense L. andSorghum bicolor (L.) Moench, indicating that allelopathy is an important component of the interference byPolygonum against crop yields.     

Allelopathic inhibition ofCynodon dactylon (L.) pers. and other plant species byEuphorbia prostrata L.

Field observations indicated thatEuphorbia prostrata strongly interferes withCynodon dactylon (L.) Pers. Analysis of some physical and chemical soil factors indicated that competition was not the dominant factor of that interference. Soil collected from underE. prostrata stands was very inhibitory to seed germination and seeding growth of some of the test species including C.Dactylon. This suggests the presence of inhibitory compounds in soil ofE. prostrata stands. Subsequent experiments showed that aqueous extract, decaying residues, and root exudates ofE. prostrata were inhibitory to most of the test species including C.Dactylon. Thus, it appears that allelopathy is the major component of the interference, with competition probably accentuating its effect. It also was found that allelopathy is an important component of the interference byE. prostrata againstAmaranthus retroflexus, Medicago sativa, andGossypium hirsutum.     

Allelopathic and autotoxic effects ofAnastatica hierochuntica L.

Laboratory experiments were undertaken to investigate the autotoxic effects ofAnastatica hierochuntica and possible effects on five other desert plants:Rumex cyprius, Trigonella stellata, Diplotaxis harra, Cleome droserifolia, andFarsetia aegyptia. Seed germination, seedling growth, and cell division of all species tested were inhibited by the shoot aqueous extract ofA. hierochuntica. A gradual increase in the percentage of prophase and decrease in the other mitotic stages as well as the mitotic index were observed with increasing extract concentration. At an extract concentration of 8% the mitotic index was reduced from the control by 55% inC. droserifolia, 54% inT. stellata, 45% inF. aegyptia, 43% inA. hierochuntica, and 35% inR. cyprius. The inhibitory substances are apparently released onto soil by repeated washing of the standing plants by rain and dew interception.     

Allelopathic potential ofnuphar lutea (L.) Sibth. & Sm. (Nymphaeaceae)

Aqueous extracts ofNuphar lutea (L.) Sibth. & Sm. leaves (blades plus petioles) and roots plus rhizomes were tested for allelopathic activity using lettuce seedling andLemna minor L. assay systems. The 12.5, 25, 125, and 250 parts per thousand (ppt) treatments of both extracts killed the lettuce seedlings. At 2.5 ppt of extract, radicle growth of lettuce was 29% of the control for leaves and 31% of the control for roots plus rhizomes.Lemna minor frond number was reduced to 34% of the control by the 25 ppt leaf extract and to 43% of the control by the 25 ppt roots plus rhizomes extract.L. minor was killed by concentrations of 125 ppt and above of both plant part extracts. As expected, the frond number and total chlorophyll content measured by theL. minor assay were highly correlated. Osmotic potentials below 143 mOsmol/kg had no influence onL. minor growth. Neither the osmotic potential nor the pH of the undiluted extracts ofN. lutea were in the range known to influence the growth of either lettuce seedlings orL. minor. Nuphar lutea extracts were many times more inhibitory than 16 other hydrophytes we previously examined.     

酸模叶蓼和绵毛酸模叶蓼中脂肪酸的研究

用索氏提取法提取脂溶性成分,GC-MS联用法结合计算机检索,首次对酸模叶蓼及其变种绵毛酸模叶蓼的脂肪酸成分进行了分离和鉴定。从酸模叶蓼和绵毛酸模叶蓼中各分离鉴定出21个和13个化合物,分别占峰面积的63.26%和74.73%,其中,脂肪酸成分占53.53%和35.58%,甾类成分占9.73%和39.15%。用峰面积归一化法测定了各成分的相对质量分数,酸模叶蓼中主要成分为:花生酸(11.82%),亚麻酸(10.36%),棕榈酸(9.79%),亚油酸(8.51%),22,23-二氢豆甾醇(5.88%),γ-谷甾醇(3.85%),山嵛酸(3.15%),木蜡酸(2.6%)。绵毛酸模叶蓼主要成分为:γ-谷甾醇(20.61%),22,23-二氢豆甾醇(18.54%),亚油酸(10.41%),棕榈酸(7.42%),油酸(7.50%),花生酸(3.21%),硬脂酸(2.38%)。该文报道工作的新颖性,已为河南大学图书馆2008年9月9日出具的第CX2008008号《科技查新报告》所证实。     

Allelopathic effects of phenolic mixtures on respiration of two spruce mycorrhizal fungi

Investigations were conducted to determine whether the allelopathic effect (inhibition of oxygen consumption) of mull- and mor-type humic solutions on ectomycorrhizal fungi was due to the solutions' phenolic contents. In the first experiment, two concentrations (10^–3 M and 10^–7 M) of binary equimolar phenolic mixtures were tested on the oxygen consumption ofLaccaria laccata andCenococcum graniforme. The high concentrations of most of the mixtures induced an increase of fungal respiration, whereas the 10^–7 M treatments all reduced the rate of respiration. In the second experiment, the effects on respiration of the phenolic mixture reproducing mull- and mortype humic solutions were compared with the effects of natural humic solutions. The resulting data suggest that allelopathic effect of humic solutions can at least in part be attributed to their phenolic contents.     

Allelopathic polyacetylenes fromCentaurea repens (Russian knapweed)

The allelopathic weed Russian knapweed (Centaurea repens) was found to contain polyacetylenes VIII–XIV in the roots. Dose vs. response of the root length elongation against lettuce, alfalfa, barnyard grass, and red millet showed IX to be active. Closely related isomers were not active. Examination of the soil surrounding the Russian knapweed roots revealed the presence of IX in sufficient concentration to have an appreciable effect on the surrounding plant community.     

Allelopathic effects ofChrysanthemum morifolium on germination and growth of several herbaceous plants

Aqueous extracts obtained from young green tops ofChrysanthemum morifolium inhibited the germination of six flowering plants, including chrysanthemum itself, provided for experiments. The same phenomenon was also clearly observed when powder made from young green tops and old leaves of chrysanthemum was used. Moreover, the growth of seedlings planted again in garden soil which was once used for the culture of chrysanthemum was greatly interrupted. Chrysanthemum cultured in used garden soil showed far less dry weight than that cultured in fresh garden soil. The weight of chrysanthemum cultured using its root exudates was also less than that cultured with water leachate of fresh garden soil, and therefore these results may be considered to indicate allelopathic effects. In order to find the allelochemicals related to this phenomenon, benzoic acid and phenolic acids such as salicylic,p-hydroxybenzoic, vanillic, gentisic, protocatechuic, syringic, gallic, ferulic, and caffeic acids were identified by gas chromatography.     

Allelopathic potential of menthofuran monoterpenes fromCalamintha ashei

A reversed-phase HPLC analysis was used to separate and quantify five menthofuran monoterpenes inCalamintha ashei leaf soaks and washes. (+)-Evodone and desacetylcalaminthone were the major constituents of both soaks and washes. Concentrations of (+)-evodone and desacetylcalaminthone were as high as 0.66 and 0.74 mM, respectively, in leaf soaks. The highest concentration of monoterpenes in leaf washes obtained by misting was 0.021 mM. Aqueous solubilities of the menthofurans were determined to exceed concentrations required for growth inhibition. Bioassays of individualCalamintha monoterpenes demonstrated effects on germination as low as 0.05 mM for (+)-evodone. An equimolar mixture of desacetylcalaminthone and (+)-evodone reducedRudbeckia hirta germination by 17% at a combined concentration of 0.025 mM forLeptochloa dubia. Confirmation of allelopathic effects byCalamintha ashei will require long-term bioassays ofCalamintha menthofurans on the growth of native sandhill species under conditions comparable to the harsh environment of the Florida scrub.     

Allelopathic potential ofSalsola kali L. and its possible role in rapid disappearance of weedy stage during revegetation

Salsola kali L. is one of the species that invades during early successional stages on mine-spoil material, but tend to disappear rapidly from the weedy stage. What controls its rapid disappearance from the weedy stage becomes a logical question.Salsola was found to be an allelopathically active species, which also decreased the growth of selected associated species during its decaying process. However, leaf leachate did not play an important role in depressing the growth of associated species.Salsola was autotoxic, but its germinatoin was not inhibited by any of the isolated phytotoxins applied. The phytotoxins identified fromSalsola leaves were caffeic, ferulic, chlorogenic, isochlorogenic, and neochlorogenic acids, and quercetin. Allelopathy may play an important role in the rapid disappearance of the weedy stage, similar to what is established for old farm lands. However, further studies are desirable.Contribution No. R780402 from Project Reclamation, University of North Dakota supported by Grant No. 0264001 from Bureau of Mines, Department of the interior to Dr. M.K. Wali.The work was partially completed when the author was a visiting research associate professor at the University of North Dakota.     

Allelopathic Potential of <Emphasis Type="Italic">Robinia pseudo-acacia</Emphasis> L.

Robinia pseudo-acacia L. (black locust) is a nonindigenous species currently invading the central part of Japanese grasslands. Several allelochemicals were identified and characterized from the leaf tissue. The growth of both radicle and hypocotyl in the tested species (barnyard grass, white clover, lettuce, and Chinese cabbage) was reduced when grown in soil mixed with the leaves of R. pseudo-acacia at various concentrations. Aqueous leaf extracts, when bioassayed, exhibited a significant suppression of radicle growth. Chromatographic separation of an ethanolic extract of R. pseudo-acacia leaves resulted in isolation of three compounds, identified as robinetin (1), myricetin (2), and quercetin (3) by nuclear magnetic resonance and mass spectroscopy. All inhibited root and shoot growth of lettuce. Robinetin, found in a large amount, caused 50% suppression of the root and shoot growth of lettuce at 100 ppm. The presence of these bioactive substances in leaf tissue suggests a potential role for flavonoids in R. pseudo-acacia invasion in introduced habitats.     

Allelopathic potential ofErica vagans,calluna vulgaris,andDaboecia cantabrica

In laboratory tests the allelopathic potential ofErica vagans, Calluna vulgaris, andDaboecia cantabrica was determined. Aqueous extracts of flowers ofD. cantabrica and leaves ofC. vulgaris inhibit root and hypocotyl growth of red clover, the former causing 51% inhibition of germination. Intact aerial parts of the Ericaceae here studied drastically reduced the growth of red clover and 100% inhibition of germination was caused by flowers ofD. cantabrica. Inhibition of aqueous extracts remains after Chromatographic separation, and two well-defined inhibition zones may be observed. Hydrosoluble organic compounds (phenol-like compounds) could probably be responsible for the inhibitions detected.     

Allelopathic Effects of Humus Phenolics on Growth and Respiration of Mycorrhizal Fungi

Allelopathy due to humus phenolics is a cause of natural regeneration deficiency in subalpine Norway spruce (Picea abies) forests. If inhibition of spruce germination and seedling growth due to allelochemicals is generally accepted, in contrast there is a lack of knowledge about phenolic effects on mycorrhizal fungi. Thus, this work tested effects of a humic solution and its naturally occurring phenolics on the growth and respiration of two mycorrhizal fungi: Hymenoscyphus ericae (symbiont of Vaccinium myrtillus, the main allelochemical-producing plant) and Hebeloma crustuliniforme (symbiont of P. abies, the target plant). Growth and respiration of H. crustuliniforme were inhibited by growth medium with the original humic solution (–6% and –30%), respectively, whereas the same humic solution did not affect growth but decreased respiration of H. ericae (–55%). When naturally occurring phenolics (same chemicals and concentrations in the original humic solution) were added to the growth medium, growth of H. crustuliniforme was not affected, whereas that of H. ericae significantly increased (+10%). We conclude that H. ericae is better adapted to the allelopathic constraints of this forest soil than H. crustuliniforme and that the dominance of V. myrtillus among understory species could be explained in this way.     

Allelopathic effect of parthenium (Parthenium hysterophorus L.) extract and residue on some agronomic crops and weeds

Allelopathic effects of entire shoot extract, plant part extracts, and shoot residue of parthenium (Parthenium hysterophorus L.) on corn (Zea mays L.), ryegrass (Lolium multiflorum Lam.), wheat (Triticum aestivum L.), velvetleaf (Abutilon theophrasti Medik.), and soybean [Glycine max (L) Merr.] growth were examined. Parthenium shoot contained water-soluble materials that were toxic to root growth of velvetleaf and wheat. At 4% (w/ v) concentration, root growth of velvetleaf and wheat were reduced by 60 and 75%, respectively. The order of increasing sensitivity to parthenium was ryegrass, corn, wheat, and velvetleaf. There was a strong correlation between extract concentration and increased toxicity to test species. The toxicity of plant part extracts was also concentration dependent. At 1 and 2% (w/v), the inflorescence and leaves caused more root inhibition than stem extract. Parthenium shoot incorporated in soil at 1% (w/w) caused significantly more root inhibition of wheat than soybean, corn, and ryegrass. At 4% (w/w), root growth of all the test species was inhibited compared to the control. Toxicity of parthenium residue to wheat diminished with increasing periods of decomposition. Residue decomposed for four weeks was less toxic than the undecomposed residue.Florida Agricultural Experiment Stations Journal Series No. 7506.     

Allelopathic potential of compounds isolated fromIpomoea tricolor cav. (Convolvulaceae)

The allelopathic potential ofI. tricolor, used in traditional agriculture as a weed controller, has been demonstrated by measuring the inhibitory activity of aqueous lixiviates and organic extracts of the plant material on seedling growth ofAmaranthus leucocarpus andEchinochloa crusgalli. Bioactivity-guided fractionation of the most active organic extract led to the isolation of the allelopathic principles, which turned out to be a mixture of glycosides, having jalapinolic acid as the aglycone portion glycosidically linked in the 11 position to an oligosaccharide composed of glucose, rhamnose, and fucose, which also combines with the carboxyl group of the aglycone to form a macrocyclic ester.This study was sponsored by Project PCECCNA-050954 of Consejo Nacional de Ciencia y Tecnología.     

Allelopathic research of subtropical vegetation in Taiwan II. Comparative exclusion of understory byPhyllostachys edulis andCryptomeria japonica

On many hillsides of Taiwan there is a unique pattern of weed exclusion byPhyllostachys edulis (bamboo) andCryptomeria japonica (conifer) in which the density, diversity, and dominance of understory species are very different. Although the physical conditions of light, soil moisture, and soil nutrients strongly favor the growth of understory in a bamboo community, the biomass of its undergrowth is significantly low, indicating that physical competition among the understory species in the bamboo and conifer communities does not cause the observed differences. However, the biochemical inhibition revealed by these two plants appeared to be an important factor. The growth ofPellionia scabra seedlings, transplanted from the study site into greenhouse pots, was evidently suppressed by the aqueous leachate of bamboo leaves but was stimulated by that of conifer leaves. The radicle growth of lettuce, rye grass, and rice plants was also clearly inhibited by the leachate and aqueous extracts of bamboo leaves but not by those of conifer leaves. Six phytotoxins,o-hydroxyphenylacetic,p-hydroxybenzoic,p-coumaric, vanillic, ferulic, and syringic acids were found in the aqueous leachate and extracts of leaves and alcoholic soil extracts ofP. edulis, while the first three compounds were absent in the extracts ofC. japonica. The phytotoxicities of extracts were correlated with the phytotoxins present in both leaves and soils. The understory species might be variously tolerant to the allelopathic compounds produced by the two plants, resulting in a differential selection of species underneath. Therefore, comparative allelopathic effects ofPhyllostachys edulis andCryptomeria japonica may play significant roles in regulating the populations of the understories.Paper No. 253 of the Scientific Journal Series of the Institute of Botany, Academia Sinica, Taipei, Taiwan. This study was supported by the National Science Council of the Republic of China.     

Allelopathic effect of alfalfa (Medicago sativa) on bladygrass (Imperata cylindrica)

Greenhouse and laboratory experiments were conducted at the Agricultural and Water Resources Research Center Station, Baghdad, in 1985 and 1986 to investigate the possible allelopathic potential of alfalfa (Medicago saliva L.) and its decomposed residues on bladygrass (Imperata cylin-drica L. Beauv.), a noxious weed in Iraq, and to isolate, characterize, and quantify possible allelopathic agents in alfalfa residues and root exudates. Results indicated that decomposed alfalfa roots and their associated soil produced a 51–56% reduction in bladygrass seed germination. Root and shoot length of bladygrass seedlings were reduced by an average of 88%. Decayed and undecayed mixtures of alfalfa roots and soil at 0.0151 (w/w) inhibited bladygrass seedlings reproduced from rhizomes by 30 and 42%. It was found that root exudates of alfalfa seedlings caused significant reduction in shoot and root dry weights of bladygrass seedlings when alfalfa and bladygrass were grown together in nutrient culture. Caffeic, chlorogenic, isochloro-genic,p-coumaric,p-OH-benzoic, and ferulic acids were detected in alfalfa root exudates and residues. The highest amount (126 fig phenolic acids/g soil) of these compounds was found in alfalfa root residues after six months of decomposition in soil.     

Phenolic inhibitors inErica australis L. and in associated soil

Fifteen phenolic compounds were identified in methanolic extracts obtained from flowers, leaves, stems, and roots ofErica australis L. and the associated soil. It is possible that the compounds identified may be connected with allelopathic phenomena.     

Allelopathic research of subtropical vegetation in Taiwan

Leucaena leucocephala plantations in Kaoshu, southern Taiwan, exhibit, after several years of growth, a unique pattern of weed exclusion beneathLeucaena canopy. The pattern has been observed in manyLeucaena plantations in Taiwan and is particularly pronounced in the area where a substantial amount ofLeucaena litter has accumulated on the ground. Field data showed that the phenomenon was primarily not due to physical competition involving light, soil moisture, pH, and nutrients. Instead, aqueous extracts ofLeucaena fresh leaves, litter, soil, and seed exudate showed significantly phytotoxic effects on many test species, including rice, lettuce,Acacia confusa, Alnus formosana, Casuarina glauca, Liquidambar formosana, andMimosa pudica. However, the extracts were not toxic to the growth ofLeucaena seedlings. The decomposing leaves ofLeucaena also suppressed the growth of the aforementioned plants grown in pots but did not inhibit that ofLeucaena plants. By means of paper and thin-layer chromatography, UV-visible spectrophotometry, and high-performance liquid chromatography, 10 phytotoxins were identified. They included mimosine, quercetin, and gallic, protocatechuic,p-hydroxybenzoic,p-hydroxyphenylacetic, vanillic, ferulic, caffeic, andp-coumaric acids. The mature leaves ofLeucaena possess about 5% dry weight of mimosine, the amount varying with varieties. The seed germination and radicle growth of lettuce, rice, and rye grass were significantly inhibited by aqueous mimosine solution at a concentration of 20 ppm, while that of the forest species mentioned was suppressed by the mimosine solution at 50 ppm or above. However, the growth ofMiscanthus floridulus andPinus taiwanensis was not suppressed by the mimosine solution at 200 ppm. The seedlings ofAgeratum conzoides died in mimosine solution at 50 ppm within seven days and wilted at 300 ppm within three days. It was concluded that the exclusion of understory plants was evidently due to the allelopathic effect of compounds produced byLeucaena. The allelopathic pattern was clearly shown in the area with a heavy accumulation ofLeucaena leaf litter, which was a result of drought and heavy wind influence.Paper No. 292 of the Scientific Journal Series of the Institute of Botany, Academia Sinica, Taipei, Taiwan. This study was supported in part by a grant to C.H. Chou. Part of this paper was a MS thesis submitted by Y.L. Kuo to the Department of Forestry, National Taiwan University, and presented at the Seminar on Allelochemicals and Pheromones, sponsored by the CCNAA and AIT on June 21–26, 1982.