Showing papers on "Allelopathy published in 2000"

Search for a Standard Phytotoxic Bioassay for Allelochemicals. Selection of Standard Target Species

Abstract: In the search for a standard bioassay of phytotoxicity for allelochemicals, 22 commercial varieties of eight plant species [four dicotyledons: lettuce (Compositae), carrot (Umbelliferae), cress (Cruciferae), tomato (Solanaceae); and four monocotyledons: onion (Liliaceae), barley, wheat, and corn (Gramineae)] proposed as models for the most common weed families have been tested at different pH and solution volumes per set conditions. Nine commercial varieties selected as standard target species (STS) were tested with standard commercial herbicides to ensure their sensitivity to phytotoxic compounds. Results are discussed to establish the proper growth requirements, and sensitivity of commercial seeds of STS and to find the most suitable commercial herbicides that allow comparison with an internal standard to validate the response of potential allelochemicals.

Effect of chemical environment on seed germination

Abstract: Seeds receive information about the succession of seasons through fluctuations in temperature. In arid and semi-arid zones, the timing of precipitation adds important information. Seeds receive information about their depth in the soil and neighbouring vegetation through the dependency of the germination process on light and fluctuating diurnal temperatures. Therefore, germination of many seed species often only occurs at or close to the surface of the soil and in vegetation gaps. The chemical environment provides seeds with information about the quality of their environment with respect to suitability for growth. In general, chemical factors that promote germination are also beneficial for emergence and seedling growth. The dependence of many species on nitrate for germination is a clear example of this rule. The presence of high soil nitrate levels may even stimulate the germination of the next generation of seeds, via the accumulation of nitrate during seed formation. The dependence of parasitic seeds on chemical promoters excreted by the host plant illustrates the parallelism between the stimulation of germination and seedling growth. Seedlings of the parasite also depend fully on host factors. Similarly, allelopathic substances in the soil, which inhibit germination, are generally deleterious to seedling growth.

Laboratory screening for allelopathic potential of wheat (Triticum aestivum) accessions against annual ryegrass (Lolium rigidum)

Abstract: A new screening bioassay, the ‘equal-compartment-agar-method (ECAM)’, was developed and employed to evaluate 92 wheat cultivars for their allelopathic activity on the inhibition of root growth of annual ryegrass (L. rigidum). Results showed that the allelopathic activity of wheat was associated with the sowing time of ryegrass seeds, the number of wheat seedlings, agar quantities, and agar concentrations. The addition of activated charcoal into the agar medium significantly alleviated wheat allelopathic inhibition on the root growth of ryegrass, indicating that wheat allelopathic activity is chemically driven. There were significant differences between wheat cultivars in their allelopathic potential at the seedling stage on the inhibition of root elongation of annual ryegrass, varying from 23.98% to 90.91%. Re-screening of 22 selected wheat accessions showed that the allelopathic potential of wheat cultivars is consistent between different years under the same experimental conditions. This newly developed screening bioassay successfully separated the allelopathic effect from the competitive effect between wheat and ryegrass plants, and enabled the constant release and accumulation of allelochemicals from living wheat seedlings into the growth medium to affect the growth of ryegrass. The influence of microorganisms was also avoided because of the sterile conditions. The present study describes this new bioassay suitable for the efficient screening of a large number of wheat cultivars under laboratory conditions.

Allelopathic potential of rice hulls on germination and seedling growth of barnyardgrass

Abstract: Hull extracts from 91 cultivated rice cultivars (Oryza saliva L.) were used to determine their allelopathic potential on seed germination and seedling growth of barnyardgrass (Echinochloa crusgalli P. Beauv. var. oryzicola Ohwi). The allelopathic effects of various concentrations of hot and warm water hull extracts from selected cultivars were also investigated. In the initial screening the SR31' extract inhibited germination 59%. The length and dry weight of roots were more affected by hull extract than the shoots. The greatest total seedling length and dry weight inhibition was from the Janganbyeo' warm extracts and was 75 and 96%, respectively. Rice cultivars demonstrating significant allelopathic potential were compared using varying concentrations with a hot or warm extraction procedure. The two extraction procedures displayed different ultra violet (UV) absorption, pH, electrical conductivity (EC), and osmotic potential. Warm extracts exhibited a lower percentage absorbance in the UV range, higher percentage absorbance in the visible range, higher EC (S m 1 ) and osmotic potential (kPa), and showed lower pH than those of hot extracts. As concentration increased, the warm extracts had a greater inhibitory effect on barnyardgrass germination, seedling growth, weight, and caloric content than the hot extracts. The greatest inhibition occurred when the highest concentration (8 g L 1 ) warm water extract was applied. These results suggest that rice hull extracts may be a source of natural herbicide, and warm water may extract more allelochemicals than hot water. There may be genetic differences among rice cultivars for allelopathic potential on barnyardgrass. The breeding of rice cultivars with greater allelopathic potential may be possible.

Evaluation of seedling allelopathy in 453 wheat (Triticum aestivum) accessions against annual ryegrass (Lolium rigidum) by the equal-compartment-agar method

Abstract: Allelopathy has been receiving world-wide attention for its potential in integrated weed management. A newly developed screening bioassay, the ‘equal-compartment-agar method’ (ECAM), was used to evaluate seedling allelopathy against annual ryegrass in a collection of 453 wheat accessions originating from 50 countries. Significant differences in allelopathic potential were found in this worldwide collection, inhibiting root growth of ryegrass from 9.7% to 90.9%. Wheat seedling allelopathy also varied significantly with accessions from different countries. Wheat allelopathic activity was normally distributed within the collection, indicating the involvement of multiple genes conferring the allelopathic trait. Of the 453 wheat accessions screened, 2 distinct groups were identified. Condor-derivatives were more allelopathic than Pavon-derivatives, with an average inhibition of root growth of ryegrass by 76% and 46%, respectively. Research was further extended to investigate the near isogenic lines derived from Hartog (Pavon-derivative) and Janz (Condor-derivative). Hartog and its backcrossed lines were less allelopathic than Janz and its backcrossed lines, inhibiting root length of ryegrass by 45% and 81%, respectively. These results strongly indicate that wheat allelopathic activity might also be controlled by major genes, depending on the particular populations. The present study demonstrates that there is a considerable genetic variation of allelopathic activity in wheat germplasm. It is possible to breed for cultivars with enhanced allelopathic activity for weed suppression.

Distribution and Exudation of Allelochemicals in Wheat Triticum aestivum

Abstract: Wheat allelopathy has potential for weed suppression. Allelochemicals were identified in wheat seedlings, and they were exuded from seedlings into agar growth medium. p-Hydroxybenzoic, trans-p-coumaric, cis-p-coumaric, syringic, vanillic, trans-ferulic, and cis-ferulic acids and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) were identified in both the shoots and roots of 17-day-old wheat seedlings and their associated agar growth medium. Wheat accessions with previously identified allelopathic activity tended to contain higher levels of allelochemicals than poorly allelopathic ones. The allelopathic compounds present in the shoots generally also were identified in the roots and in the agar medium. Allelochemicals were distributed differentially in wheat, with roots normally containing higher levels of allelochemicals than the shoots. When the eight allelochemicals were grouped into benzoic acid and cinnamic acid derivatives, DIMBOA, total coumaric, and total ferulic acids, the amount of each group of allelochemicals was correlated between the roots and the shoots. Most of the allelochemicals identified in the shoots and roots could be exuded by the living roots of wheat seedling into the agar growth medium. However, the amounts of allelochemicals in the agar growth medium were not proportional to those in the roots. Results suggest that wheat plants may retain allelochemicals once synthesized. The presence of allelochemicals in the agar growth medium demonstrated that wheat seedlings were able to synthesize and to exude phytotoxic compounds through their root system that could inhibit the root growth of annual ryegrass.

Differential activity of allelochemicals from Secale cereale in seedling bioassays

Abstract: Differential activities of BOA, DIBOA, and crude water extract of Secale cereale ‘Elbon’ were studied in culture dish bioassays using several vegetable and weed species. On average, DIBOA was about seven times more inhibitory to root growth and four times more inhibitory to shoot growth than BOA. Allelochemicals from S. cereale inhibited shoot more than root elongation of cucurbits Cucumis melo, Cucumis sativus, and Cucurbita pepo. Small-seeded crops Lycopersicon esculentum and Lactuca sativa were sensitive to S. cereale. Large-seeded crops, including the cucurbits and Zea mays var. rogusa, were tolerant. Among the small-seeded weeds Amaranthus palmeri, Digitaria sanguinalis, Echinochloa crus-galli, and Eleusine indica, E. crus-galli was least susceptible. Inhibition of germination by BOA or DIBOA occurred only in small- to medium-seeded species, including A. palmeri, D. sanguinalis, E. indica, L. sativa, L. esculentum, and Sida spinosa. Large-seeded species C. melo, C. sativus, C. melopepo, Z. m...

Effects of Vaccinium myrtillus on Spruce Regeneration: Testing the Notion of Coevolutionary Significance of Allelopathy

Abstract: Failure of natural regeneration of conifers, such as subalpine spruce (Picea abies) and black spruce (Picea mariana), has been reported in the presence of dominant ericaceous understory plants of boreal forests of North America, Fino-Scandinavia, and northern Europe. Among other factors such as competition for light and nutrients, conifer regeneration failure has been attributed to allelopathic effects of the understory ericaceous plants. Rabotnov theorized that (the manifestation of) allelopathy is a result of long-term coevolution within established plant communities and that it may have maximum inhibitory effects on introduced species. Our objectives were to determine what components of the understory ericaceous plant, Vaccinium myrtillus, affect spruce regeneration and to test Rabotnov's hypothesis. Field experiments were complemented with laboratory studies in which seed germination and primary growth of the two spruces were used as response variables. We found that P. mariana was generally more affected than P. abies by V. myrtillus allelochemicals, both in field and in vitro experiments. Field germination of P. abies was only 2% and 3% in the undisturbed sowed plots and in Vaccinium-removed sowed plots, respectively, but P. marana did not germinate at all in these treatments. In humus-removed sowed plots, P. abies had 27% germination, while P. marian had only 15%. In a controlled experiment, P. mariana had the highest decrease in dry weight of primary root in the fresh leaf treatment of V. myrtillus (77%), followed by its leaf leachate (71%), humus (29%), and humus leachate (13%). The decreases in root dry weights of P. abies due to these treatments were 67, 47, 30, and 10%, respectively. Our results provide support for Rabotnov's hypothesis. It is possible that both V. myrtillus and Kalmia angustifolia, involved in the growth inhibition process of P. abies and P. mariana, respectively adopted similar "strategies" of allelopathic inhibition of conifers, by allocating a large part of their carbon pool to the production of secondary metabolites.

Effects of plant phenology, nutrients and herbivory on growth and defensive chemistry of plantain, Plantago lanceolata.

Abstract: To assess the combined effect of herbivory, nutrient availability and plant phenology on plant mass and defensive chemistry, we conducted a field experiment with plantain (Plantago lanceolata: Plantaginaceae) using three levels of herbivory, three levels of fertilizer and two harvest dates. Shoot mass of the no-herbivory plants showed a nonlinear response to increased fertilizer such that mass with high fertilizer was no greater than that with low fertilizer. In contrast, shoot mass of the low-herbivory plants (12% damage) was not influenced by fertilizer, but for high-herbivory plants (23% damage), there was a positive linear response to increased fertilizer. Increasing nutrient levels caused a decrease in iridoid glycoside concentration. Herbivory did not induce higher iridoid glycoside concentration in leaves of any age. But increasing herbivory resulted in a decrease in the concentration of catalpol in new leaves. Another experiment assessed how leaf age and plant age affected plant defensive chemistry. Total iridoid glycosides increased over 5 weeks, but catalpol only increased in new leaves. Overall, the order of importance in determining variation in iridoid glycoside concentration was plant phenology, nutrient availability and, to a much lesser extent, herbivory.

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

Abstract: 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

Field testing for pollen allelopathy. A review.

Abstract: Field testing for pollen allelopathy comprises several approaches. In vitro tests must be done first to establish the existence of a pollen allelopathic effect. The number of pollen grains required to elicit an in vitro pollen allelopathic effect then is compared to observations of the number of pollen grains of pollen allelopathic species adhering to stigmas of heterospecifics. In animal-pollinated species, the amount of potential heterospecifics may first be assessed by observing pollinator behavior, but actual enumeration of grains is necessary. In all species, enumeration of the amount of heterospecific pollen transfer requires that stigmas be clipped before they senescence, carefully preserved in small test tubes, and assessed immediately thereafter with aid of a compound microscope. Stigmas may be examined for relative amounts of allelopathic and conspecific pollen to determine if the number of conspecific pollen tubes declines hyperbolically with increasing amounts of allelopathic pollen. Enumerating the number of heterospecific pollen grains on stigmas is used to support testing of the ecological impact of pollen allelopathy by direct manipulation. In habitats (e.g., old fields surrounded by forest tracts) where atmospheric conditions prevent export or import of other pollen from surrounding areas, the influorescences of a pollen allelopathic species can be clipped within a large area and the subsequent effect on seed set of target species can be assessed. The hypothesis that pollen allelopathy causes an ecological impact (reduced sexual reproductive success) is not rejected under two conditions. An absence of pollen from the allelopathic species must result in an increase in seed set in target species and the amount of pollen transferred from allelopathic species to heterospecifics is similar to that causing in vitro reductions in sexual reproduction in the targets. This experimental approach must be repeated over several sites and years in order to provide an unequivocal test for ecological effects of pollen allelopathy. This methodological approach has allowed me to demonstrate that pollen allelopathy is an important ecological interaction between Hieracium pratense and five sympatric Asteraceae species and between Phleum pratense and three sympatric Poaceae species.

Autotoxic Compounds from Fresh Alfalfa Leaf Extracts: Identification and Biological Activity

Abstract: Many investigators have attempted to identify the allelochemicals in alfalfa (Medicago sativa), that cause autotoxicity. The autotoxic compounds from fresh alfalfa leaves were separated and quantified, and their biological activity was determined. Chemical separation procedures involved an 80% methanol extract of fresh alfalfa leaves, treatment with activated charcoal, microcrystalline cellulose thin-layer chromatography (MCTLC), and finally separation by Sephadex LH-20 column chromatography. The various fractions were examined further by high-performance liquid chromatography (HPLC). Preliminary identification by HPLC analysis resulted in peaks with retention times close to those of chlorogenic (m/z = 354) and salicylic acid (m/z = 138) standards, and these compounds were confirmed with GC-MS. Several other peaks remain unidentified. Chlorogenic acid occurs in relatively large amounts (0.39 mg/g) in alfalfa aqueous extracts as compared to salicylic acid (0.03 mg/g), and bioassays suggest that chlorogenic acid is involved in alfalfa autotoxicity.

Efeito alelopatico de Ilex paraguariensis A. St.-Hil. na germinacao e crescimento inicial de Lactuca sativa L

Abstract: This study aimed at evaluating the allelopathic activity of Ilex paraguariensis A.St.-Hil (erva mate) to advise the potential of co-cultivation of this species with other crops. Bioassays were carried out with lettuce asthe test species. Aqueous extracts were prepared from various parts of the plant: young and mature leaves (the latter taken from different positions in the tree), branches, and fruits in three stages of ripening. All pans were processed right after harvest or after being dried in an oven at 68°C. The extracts were prepared with hot distilled water and were used immediately or after a 50 days storage period at 5°C. Extracts were analyzed for pH, osmotic potential and yield. Results showed differences in yield of the various extracts and that pH and osmotic potential did not affect the responses of lettuce to the extracts. Mature leaves and ripe fruit extracts were effective in germination inhibition. All extracts reduced growth and caused abnormalities in seedlings. Extracts prepared with dried parts were less inhibitory to germination and growth. The evaluation of stored extract showed that allelopathic activity remained for up to 50 days. As the inhibition of growth and change in the morphology of the plantlets (without participation ofpH and osmotical potential) are considered "bona fide" indicators of allelopathic activity, the results strongly suggest that I. paraguariensis is an allelopathic species.

Effect of soil type, salinity, and allelochemicals on germination and seedling growth of a medicinal plant Lepidium sativum L.

Abstract: Summary The present work was conducted to elucidate the effect of soil type, salinity stress and allelochemicals from alfalfa on the germination efficiency, seedling growth and photosynthetic pigments of Medicago sativa L. The highest germination rate (69.9%) was recorded for seeds cultivated in sandy soil followed by that of clay soil (42%) and then loamy soil (19%). The maximum germination rate was attained at 50 mM NaCl concentration level, after that the values were decreased as the salinity levels increased. The maximum lengths (cm) of plumule and radicle and their growth rates (cm/day) were obtained at control level and found to decline significantly as the salinity increased. Aqueous extracts of alfalfa reduced the germination rate, radicle and plumule growth and seedling dry weight of L. sativum. However, chlorophyll and carotenoid content was increased, their maxima were recorded at 50% concentration level. The chlorophyll a/b ratio attained its maximum at the full strength concentration level.

Allelopathy in forest ecosystems

Abstract: In forest plantations, many types of plant spp. grow together for long periods and hence, are ideal location for allelopathic research. The high yielding exotic spp. introduced to increase productivity of forests are most allelopathic than indigenous spp. These reduce the vegetation diversity and understorey flora due to inhibitory allelopathic efforts. The information about transformation and degradation processes of allelochemicals in soil is little known, hence, needs further studies. Various types of stresses (biotic/abiotic) greatly influence the production and release of allelochemicals in environment. Eucalyptus globulus is most allelopathic tree spp. in forest plantations and its leachates contain large number of allelochemicals. Allelopathic interactions are mediated by a mixture of many allelochemicals. Under field conditions, the concentrations of individual allelochemicals is too low to cause allelopathic effects.

Natural and Synthetic Podolactones with Potential Use as Natural Herbicide Models

Abstract: A collection of 11 natural and synthetic podolactones have been tested as allelochemicals in a range between 10(-4) and 10(-9) M, and their potential use as natural herbicide models is discussed. Their effects on the germination and growth of the dicots Lactuca sativa (cv. Nigra and cv. Roman), Lepidium sativum, and Lycopersicon esculentum and the monocots Allium cepa, Hordeum vulgare, and Triticum aestivum as standard target species have been studied. An important inhibitory effect on the germination and growth of all tested species (average = 90%) was produced by compounds 9-11 at 10(-4) M. The specific structural requirements related to their activities are studied. On the basis of these results, their use as potential natural herbicide models is proposed.

Allelopathic potential of eupatorium adenophorum

Abstract: Eupatorium adenophorum, a weed with strong invasibility and exotic to the Lancang River watershed, has an allelopathic effect on other plants. Its petroleum, ethanol and water extracts showed inhibitory effects on the germination and seedling growth of the garden pea (Pisum sativum). At the relative concentration of 2%, the petroleum, ethanol and water extracts showed 100%, 40% and 50% inhibition on pea germination respectively. Its allelochemicals are mainly located in petroleum extract and the methanol eluent of the petroleum extract absorbed in activated charcoal. The major active fractions of the petroleum extract are FR2 (identified as 9 Oxo Ageraphorone), FR3 and FR4. At the relative concentration of 1%, the FR2, FR3 and FR4 showed 100%, 90% and 90% inhibition on the germination of pea respectively. Moreover, germinated peas treated with 1% FR3 and FR4 did not show any shoot and root growth. It is suggested that the allelopathic effect of this plant occurs through the release of volatile allelochemicals from aerial part tissues and the leaching of water soluble allelochemicals from both aerial tissues and litter.

Allelopathy in Maize. II. Allelopathic potential of a new benzoxazolinone, 5-chloro-6-methoxy-2-benzoxazolinone and its analogues.

Abstract: To characterize the allelopathic activity of a new benzoxazolinone, 5-chloro-6-methoxy-2-benzoxazolinone (Cl-MBOA), seeds or seedling of monocotyledonous and dicotyledonous plants were exposed to Cl-MBOA for two or three days in a Petri dish, and effects of Cl-MBOA on the seed germination and the plant growth were determined and compared to those of its analogues, 6-methoxy-2-benzoxazolinone (MBOA) and benzoxa-zolinone (BOA). Cl-MBOA, MBOA and BOA dose-dependently inhibited the seed germination and growth of roots and shoots of cockscomb (Amaranthus caudatus L.), cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), crabgrass (Digitaria sanguinalis L.), timothy (Phleum pratense L.) and ryegrass (Lolium multiflorum Lam.). A new benzoxazolinone, Cl-MBOA was the most active in all bioassays followed in order by MBOA and BOA. The results that the attachment of CI at C-5 position on MBOA leads to an increase in the activity.

Allelopathic effects of sunflower (Helianthus annuus L.) on germination and seedling growth of wheat (Triticum aestivum L.)

Abstract: The allelopathic influence of water extracts of sunflower on wheat’s germination and seedlings growth have been evaluated. It was observed that sunflower water extracts at a concentration of 25, 50, 75 and 100% showed inhibitory effect on wheat germination and the effect differed significantly in all the treatments. The growth of wheat seedlings was found significant in terms of root and shoot lengths and non-significant for fresh and dry weights in comparison to the control. Chemical composition of wheat seedlings influenced by four sunflower water extracts indicated a significant change in the starch contents in all the treatments in comparison to the control. A similar trend was also found in the protein and phosphorus contents. Potassium contents of wheat seedlings were decrease gradually except at 75% concentration. Whereas ash contents increased in 25 and 75% concentration and decreased in 50% and 100% concentrations suggesting the stimulatory and inhibitory potencies of sunflower water extracts at different concentrations. It is concluded that the degree of inhibition was dependent upon the concentration of the extract. The chemical parameters like starch, protein, phosphorus, potassium and ash were also reduced confirming the influence of water extracts of sunflower at various concentrations.

Allelopathy in Maize I. : Isolation and identification of allelochemicals in maize seedlings

Abstract: Allelochemicals were isolated from the germinating maize (zea mays L.) seeds in order to know the allelopathic constituents in the plants at the early developmental stage. Three allelochemicals were found in the acetone extract obtained from the mesocotyls and coleoptiles of the 5-day-old seedlings. By spectral analysis, they were identified as 5-chloro-6-methoxy-2-benzoxazolinone (Cl-MBOA) which is a naturally occurring new benzoxazolinone, 6-methoxy-2-benzoxazolinone (MBOA) and 2,4-dihydroxy-l,4-benzoxazin-3-one (DIBOA). At concentrations greater than 0.03 mM for Cl-MBOA and DIBOA and 0.1 mM for MBOA, respectively, were inhibited the growth of the roots of cress (Lepidium sativum L.) seedlings. Activity of a new benzoxazolinone, Cl-MBOA, was greater than that of its analogue, MBOA. These results suggest that germinating maize seeds have at least three allelochemicals which may affect the growth or germination of other plant species.

Allelopathic Effects of Artemisia lavandulaefolia

Abstract: The allelopathic effects of Artemisia lavandulaefolia were studied using several test plants and microbes. Aqueous extracts and volatile compounds of A. lavandulaefolia inhibited seed germination, seedling and root growth of the test species such as Achyranthes japonica. Lactuca sativa, Artemisia princeps var. orientalis. Oenothera odorata, Plantago asiatica. Aster yomena, Elsholtzia ciliata, and Raphanus sativus var. hortensis for. acanthiformis. The root growth of test species was more affected than shoot growth by allelochemicals of A. lavandulaefolia. Essential oil of A. lavandulaefolia had antibacterial and antifungal effects. However, the antimicrobial activity of the essential oil was dependent upon the microbial species and concentrations. Callus growth of Oryza sativa, Brassica campestris subsp. napus var. pekinensis and Achyranthes japonica was sensitive by the essential oil of A. lavandulaefolia. Twenty three chemicals were identified from A. lavandulaefolia essential oil by gas chromatography. Primary allelochemicals among them were 1, 8-cineole, 1--terpineol, -terpinene. camphor, 2-buten-1-ol and azulene. We concluded that aqueous extract and essential oil of A. lavandulaefolia were responsible for allelopathic effects.

Assessment of Allelopathic Potentiality and Identification of Allelopathic Compounds on Korean Local Rice Varieties

Abstract: This study was conducted to assess the allelopathic potentiality of Korea traditional seventy-nine rice (Oryza sativa L.) cultivars on barnyardgrass (Echinochloa crus-galli P. Beauv. var. oryzicola Ohwi) and to identify possible allelopathic compounds from selected rice cultivars, such as Seogandodobyeo, Huadobyeo and Heugbalbyeo. In the straw mixture, Seogandodobyeo showed the greatest inhibition (67.07%) on total emergence percentage. The greatest inhibition on total seedling length and dry weight of barnyardgrass occurred in Huadobyeo (58.32 %) and Heugbalbyeo (81.20%), respectively. An HPLC analysis with nine standard compounds showed that the concentrations and compositions of allelopathic compound depend upon the cultivars. Four compounds including Ο-coumaric acid in Seogandodobyeo extracts, four compounds including p-coumaric acid in Huadobyeo extracts, and seven compounds including Ο-coumaric acid in Heugbalbyeo were detected, respectively. Ο-coumaric acid (0.97 mg/g) in Seogandodobyeo, p-coumaric acid (0.92mg/g) in Huadobyeo and Ο-coumaric acid (1.02 mg/g) in Heugbalbyeo was detected as the highest amounts, respectively. The preliminary identification by HPLC analysis resulted in peaks with retention times close to those of standards which were confirmed with EI/MS. The mass spectra of p-coumaric, and Ο-coumaric acids showed molecular ions (m/z) at 164 and 164, and their base peaks (m/z) at 164 and 118, respectively.

Assessment of the allelopathic potential of extracts of evolvulus alsinoides

Abstract: The allelopathic potential of extracts of Evolvulus alsinoides L., which is one of the most dominant weeds in tropical regions of South-east Asia, was investigated under laboratory conditions. The n-hexane-soluble, acetone-soluble and water-soluble fractions obtained from the acetone extract of E. alsinoides 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 results indicate that E. alsinoides may produce potent allelochemicals, which should be investigated further in the laboratory and the field.