Abstract: Antifeedant and growth inhibitory effects of crude plant extracts (Melia volkensii and Origanum vulgare) and pure allelochemicals (digitoxin, cymarin, xanthotoxin, toosendanin, thymol and trans-anethole) were investigated in the cabbage looper (Trichoplusia ni), and in the armyworm (Pseudaletia unipuncta) using different bioassays. Antifeedant effects of M. volkensii, O. vulgare and thymol were investigated in larvae of the diamondback moth (Plutella xylostella), and of O. vulgare and thymol in the Mexican bean beetle (Epilachna varivestis), using leaf disc choice bioassays. M. volkensii was the most potent growth inhibitor for T. ni and P. unipuncta (dietary EC 50 = 7.6 and 12.5 p.p.m., respectively) of all the test substances. Cymarin was the second most potent growth inhibitor (EC 50 = 132.0 p.p.m.) for T. ni. The most effective feeding deterrents for third instar T. ni larvae were xanthotoxin and M. volkensii (DC 50 = 0.9 and 8.3 μg/cm 2 , respectively). M. volkensii was also the most potent feeding deterrent for third instar P. unipuncta, P. xylostella and adult E. varivestis (DC 50 = 10.5, 20.7 and 2.3 μg/cm 2 , respectively). Because of interspecific differences in response to feeding deterrents and the lack of a strong relationship between EC 50 and DC 50 values, we recommend testing a battery of bioassay species with candidate compounds and the use of more than one bioassay. Based on their growth inhibitory and feeding deterrent properties, some of these plant extracts and pure allelochemicals have potential for use as alternative crop protectants against a number of pest species.

Abstract: 3-Isopropyl-5-acetoxycyclohexene-2-one-1 (1), momilactone B (2), and 5,7,4'-trihydroxy-3',5'-dimethoxyflavone (3) were isolated and identified from an allelopathic rice accession PI312777. These three compounds at low concentrations could inhibit the growth of weeds Echinochloa crusgalli and Cyperus difformis associated with rice, especially mixtures of the compounds had stronger inhibitory activity than did individual compounds. Studies with hydroponic culture, continuous root exudates trapping system (CRETS), and direct resin adsorption methods showed that a total of 7.6 n moles 1, 2, and 3 were exuded from living roots of each seedling into the environment at 10 days after seedlings were transplanted. Furthermore, 1, 2, and 3 were found in the soil growing PI312777 seedlings at day 15 after seedlings emergence and reached a total of 39.5 microg/g soil at day 30. The results indicated that PI 312777 seedlings could release sufficient quantities of 1, 2, and 3 into the environment to act as allelochemicals inhibiting the growth of associated weeds. Investigations on the distribution of 1, 2, and 3 in PI 312777 plant, and its root exudates showed that the levels of 1, 2, and 3 were significantly higher in the shoots and root exudates than in the roots, and only trace 1 was observed in the roots. The results suggest that the roots of rice seedlings are not major site of synthesis or accumulation 1, 2, and 3, but a pathway for their release into the environment. The levels of 1, 2, and 3 in the root exudates were over 2-folds higher under direct resin adsorption than under hydroponic culture and CRETS, and hence, it is the preferred method to collect and identify active allelochemicals in rice exudates in future studies on rice allelopathy.

Abstract: Benzoxazinoids have been described as important allelochemicals from Gramineae as well as Acanthaceae, Rannunculaceae, and Scrophulariaceae plants. Several bioactivities have been described and evaluated for these compounds, including fungistatic, antifeedant, and phytotoxic. In ongoing studies about allelochemicals as natural herbicide models, the description of soil dynamics in phytotoxic agents has high importance, because the possible biotransformations developed by soil microorganisms could yield compounds with modified biological properties, affecting the overall allelopathic capability of the producer plant in a direct manner. Thus, a complete degradation study has been carried out for 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA) and 6-methoxybenzoxazolin-2(3H)-one (MBOA) in two soils cultivated with Triticum aestivum L. varieties (cv. Astron and cv. Ritmo). The main purpose was to identify degradation products and to elucidate biotransformation dynamics. Results show DIMBOA to degrade rapidly, yielding MBOA in both studied soils at different doses (t(1/2) = 31 +/- 1 h, n = 12) and reaching high conversions (80 +/- 4 h, n = 42). MBOA, an intermediate in the degradation pathway from DIMBOA to 2-amino-7-methoxy-3H-phenoxazin-3-one (AMPO), was more resistant toward biodegradation (t(1/2) = 5 +/- 1 days, n = 6). MBOA showed maximum conversions at a dose of 250 mg/kg of soil (36 +/- 3 days, n = 6). Soil belonging to T. aestivum cv. Ritmo crops showed higher degradation capacity than cv. Astron soil. AMPO was the final degradation product observed for DIMBOA in the soils and experimental conditions selected. Consequences for activity and stability of these compounds in relation to allelopathy are discussed.

Abstract: In order to elucidate the allelopathic effect of leaf litter leachates under laboratory conditions, a modified ‘sandwich method’, which places leaves between two layers of agar, was used. Fifty mg of leaves was used per 10 cm2 cell. Agar concentrations at 0.5–1.0% were the best for gel support in determining radicle and hypocotyl elongation of lettuce. The optimum incubation time for bioassay was three days after imbibition onset. Among 20 typical tree species in Asia, Cymbopogon citratus and Derris scandens showed the strongest inhibitory activity determined by the sandwich method, followed by Piper betle, Tamarindus indica, and Gliricidia sepium. This bioassay seems to be a reliable method for screening allelopathic activity from leaf litter leachates.

Abstract: Unknown compounds in crop plants are inhibitory to seed germination and early seedling growth of weed plants. A Petri dish assay showed that barley (Hordeum vulgare L.), oats (Avena sativa L.), rice (Oryza saliva L.) and wheat (Triticum aestivum L.) extracts significantly reduced root growth of alfalfa (Medicago sativa L.), barnyard grass (Echinochloa crus-galli, Beauv. var. oryzicola Ohwi.) and eclipta (Eclipta prostrata L.). As the concentration of crop extracts increased, root growth of the test plants were significantly reduced. A high-performance liquid chromatography analysis with nine standard phenolic compounds showed that the concentrations and compositions of allelopathic compounds depend on the extracted plant extracts. Caffeic acid, hydro-cinnamic acid, ferulic acid, m-coumaric acid, p-coumaric acid and coumarin were present in all the crop plant species, and hydro-cinnamic acid were detected as the highest amount. Coumarin at 10 -3 M significantly inhibited root growth of alfalfa and barnyard grass more than that of eclipta. The research suggests that extracts of barley, oats, rice and wheat have an allelopathic effect on alfalfa, barnyard grass and eclipta and that the findings of bioassay were considerably correlated with the type and amount of causative allelochemicals, indicating that the allelopathic effects on three test plants were ranked in order of wheat (highest), barley, rice and oats (lowest). The results may have value in enabling weed control based on natural plant extracts or crop residues in the fields.

Abstract: Crops that control weeds by root exudation of allelochemicals are receiving increased attention, and there are efforts to breed allelopathic cultivars in several crops. The genetic improvement of allelopathic traits is based upon parental germ plasm with high allelopathic activity. Identification of allelopathic germplasm is done in laboratory screening bioassays, but experimental protocols are limited. We developed a fast and reliable laboratory screening bioassay for grain crops that includes dose-response considerations as an integral part of the experimental design. The bioassay was conducted in hydroponic culture, and a range of experiments with 2-(3H)-benzoxazolinone (BOA), an allelochemical of several grain crops, was carried out to define the basic protocol. Because of its sensitivity to BOA, Sinapis alba L. was selected as the receiver species. BOA affected growth (fresh weight and length of shoot and root), enzyme activities (ascorbate peroxidase, catalase, glutathione S-transferase, peroxidase, phenylalanine ammonia-lyase), and chlorophyll fluorescence, whereby root length was the most reliable response parameter. BOA sensitivity was dependent on nutrients for all parameters measured, and, thus, no nutrients were added. A set of experiments with Secale cereale L. and Triticum aestivum L. as donor species was carried out to optimize the protocol. Light and pH were eliminated as primary causes for the observed inhibition. The proposed bioassay has several methodological advantages over current bioassays.

Abstract: In previous studies, 15 putative allelopathic compounds detected in rice root exudates were quantified by GC/MS/MS. In this study, multiple regression analysis on these compounds determined that five selected phenolics, namely caffeic, p-hydroxybenzoic, vanillic, syringic, and p-coumaric acids, from rice exudates were best correlated with the observed allelopathic effect on arrowhead (Sagittaria montevidensis) root growth. Despite this positive association, determination of the phenolic acid dose-response curve established that the amount quantified in the exudates was much lower than the required threshold concentration for arrowhead inhibition. A similar dose-response curve resulted from a combination of all 15 quantified compounds. Significant differences between the amounts of trans-ferulic acid, abietic acid, and an indole also existed between allelopathic and non-allelopathic rice cultivars. The potential roles of these three compounds in rice allelopathy were examined by chemoassay. Overall, neither the addition of trans-ferulic acid nor 5-hydroxyindole-3-acetic acid to the phenolic mix significantly contributed to phytotoxicity, although at higher concentrations, trans-ferulic acid appeared to act antagonistically to the phytotoxic effects of the phenolic mix. The addition of abietic acid also decreased the inhibitory effect of the phenolic mix. These studies indicate that the compounds quantified are not directly responsible for the observed allelopathic response. It is possible that the amount of phenolic acids may be indirectly related to the chemicals finally responsible for the observed allelopathic effect.

Abstract: . 1. Recent studies have shown that plant–plant interaction via chemicals (allelopathy) can affect insects. Here the effects on aphid acceptance of barley after exposure to volatiles and root exudates from two common weeds, the thistles Cirsium arvense and Cirsium vulgare, were investigated. 2. Settling by bird cherry-oat aphid, Rhopalosiphum padi, was significantly reduced on barley plants that had been exposed to volatiles from Cirsium species for 5 days. Settling by Sitobion avenae was also reduced on Cirsium-exposed plants, whereas settling by Metopolophium dirhodum was not. 3. In olfactometer tests, Cirsium-exposed barley was significantly less attractive to R. padi than was unexposed barley, indicating that exposure causes a change in the volatile profile of barley. 4. Exposure of barley to root exudates from Cirsium species had no effect on R. padi settling. 5. The results lend weight to the theory that the effects of plant–plant allelopathy can extend to higher trophic levels.

Abstract: This article summarizes allelochemicals' active variety, its potential causes and function mechanisms. Allelochemicals' activity varies with temperature, photoperiod, water and soils during natural processes, with its initial concentration, compound structure and mixed degree during functional processes,with plant accessions, tissues and maturity within-species, and with research techniques and operation processes. The prospective developmental aspects of allelopathy studies in the future are discussed.Future research should focus on: (1) to identify and purify allelochemicals more effectively, especially for agriculture, (2) the functions of allelopathy at the molecular structure level, (3) using allelopathy to explain plant species interactions, (4) allelopathy as a driving force of succession, and (5) the significance of allelopathy in the evolutionary processes.

Abstract: The fate of allelochemicals in the soil environment largely determines the expression of allelopathy in the natural environment. In allelopathy research, the sorption of allelochemicals onto soil particles has been less well studied than their degradation. A study was carried out to evaluate the growth of cucumber (Cucumis sativus var Marketmore 76) and radish (Raphanus sativus var Crimson giant) in soil amended with 1, 5, 10 and 20 mg l−1 benzoic acid as model allelopathic substance. Growth of both cucumber and radish was not inhibited in soil amended with benzoic acid. A labeled study indicates that sorption of benzoic acid onto soil particles increases with concentration. Benzoic acid isotherms of both soils were non-linear, with an N value of 0.875 for a garden soil and 0.891 for a garden soil + sand, and they may explain the reason for the limited allelopathic effect of benzoic acid at concentrations often recorded in natural soil.

Abstract: In Mediterranean areas, the establishment of multi-species pastures for extensive livestock use is an alternative to the growing of traditional cereal crops. Lolium rigidum Gaud. is one of the most valuable forage grasses adapted to semiarid environments but its performance in mixtures is not fully understood. Field observations suggest that the species exerts allelopathic effects, although there is no evidence in the literature to support this assumption. The objective of the study was to determine whether L. rigidum affects the germination and seedling growth of common forage species by allelopathic means. Two bioassays were conducted to test for the allelopathic potential of seeds and adult (shoot and root) tissues of L. rigidum on two grasses, Lolium multiflorum Lam. and Dactylis glomerata L., and a legume, Medicago sativa L. The three species showed different degrees of sensitivity to L. rigidum with L. multiflorum being particularly sensitive to allelopathy. Positive and negative effects of L. rigidum on seedling development were noted. Shoot extracts of L. rigidum displayed the most consistent negative effects by inhibiting elongation of the radicle of the three target species. The significance of the results is that in drought-prone environments and where water resources are scarce poor root development decreases the ability of the plants to grow and survive.

Abstract: Soil infested with Chenopodium murale and amended with it were investigated to verify their allelopathic effects on seedling emergence and some growth and physiological parameters of five test species, Trifolium alexandrinum, Triticum aestivum, Melilotus indicus, lycopersicum esculentum and Cucumus sativus. The two types of soil exhibited phytotoxic effects on the seedling emergence of the test species. Growth and physiological parameters were significantly inhibited when the soil was amended with a high concentration of C. murale tissues. Soil amended with shoot tissue had more inhibitory effects than soil amended with root tissue, at the same concentration. M. indicus was more inhibited than the other species in relation to leaf area, dry matter, pigment, carbohydrates and protein contents.

Abstract: Allelopathic performance of the bark and seed of Tamarindus indica L tree was evaluated through bioassay-guided studies using seven common agronomic crops (asparagus, cucumber, lettuce, radish, sesame, tomato and welsh onion) and seven weed species (barnyard grass, Chinese milk vetch, perennial ryegrass, phacelia, timothy grass, white clover and wild ginger) under laboratory conditions As demonstrated by a sandwich method, the bark of the tamarind tree caused strong growth inhibition (compared to the corresponding controls) in both radicles and hypocotyls of the species tested, and the inhibitory effect was highest in barnyard grass (52–65%) and lowest in welsh onion (19–13%) The crude-water soluble extracts of bark at different concentrations (1, 5 and 10%) (w/v) exhibited a strong growth inhibition in all the plant species tested, and a proportional increase in the percentage of growth inhibition was observed with an increase in the concentrations of the extracts The magnitude of inhibition in weed species was higher (5–60%) than those of agronomic crop species (3–40%) The growth of all the weed species tested was strongly inhibited (17–56%), while the agronomic crop species showed both inhibited (5–21%) and stimulated (5–27%) growth due to the effect of crude-water soluble exudates of tamarind seed Among the agronomic crop species tested, lettuce (22–27%) followed by radish (20–25%) and sesame (5–8%) showed stimulatory growth with the crude-water soluble exudates of seed In the pot culture experiments using four agronomic crops (lettuce, radish, tomato and cucumber) and two weed species (barnyard grass and white clover), spraying of crude-water soluble extracts of tamarind seed-coat at three different concentrations (1, 5 and 10%) (w/v) showed that the growth of lettuce (35–62%) and radish (32–56%) was stimulated, while all other species tested showed growth inhibition (29–61%) When the spraying of crude extracts of seed-coat was turned off, the growth of both lettuce and radish continued to be stimulated (4–7%) and all other previously inhibited species recovered well, the recovery percentage ranging between 78 and 82% However, when spraying of crude extracts of seed-coat was continued, growth increased (10–14%) in lettuce and radish, and reduced (37–76%) in four other species tested The inhibitory or stimulatory effects of the crude extracts on agronomic crop and weed species were higher in the radicle than the hypocotyl and reached a peak with 10% (w/v) concentrations These results clearly demonstrated the differential allelopathic effects (inhibitory and excitatory) of bark and seed of tamarind tree in the species tested Thus, it is evident that these two organs contain certain biologically active true growth regulator(s) and are either additively or synergistically involved in the plant-specific expression, particularly by the seed-coat

Abstract: Twenty-eight rice varieties with different countries of origin, maturity and stage of improvement were screened in the laboratory for allelopathic potential against arrowhead. Initial rice-density experiments established appropriate bioassay parameters and demonstrated that arrowhead response to rice root exudates follows a typical dose-response curve. Results from the equal compartment agar method (ECAM) bioassay showed that a range of allelopathic potential exists in rice germplasm. This work, together with other published studies suggests such potential to be species specific. In this study, the degree of root inhibition ranged from 26.6 to 99.7%. The potential allelopathic effect of arrowhead on rice seedlings was determined to be negligible.

Abstract: Summary Allelopathy denotes biochemical interactions among all types of plants and microorganisms. Allelochemicals occur in the majority of secondary plant products and belong to terpenoids, phenolic compounds, phenylpropane derivatives, flavonoids, organic cyanides, long-chain fatty acids. In fields, allelopathy involves a complex of compounds, which complicates investigations of underlying mechanisms of its appearance. There is no single physiological function controlled by allelochemicals. The action of allelochemicals is diverse and affects a large number of physiological functions and biochemical reactions eg.: seed germination, cell division, cell elongation, membrane permeability and ion uptake. Significant effects of allelochemicals on photosynthesis and respiration have been also observed. The reduction of crop yields by weed competition is aggravated by the allelopathic effect of weeds on crop. Crop plants may inhibit their owngrowth and reduce the yield of subsequent crops due to the so called soil sickness. Crop rotation helps to cures soil sickness only when the subsequent crop is not affected by the accumulated allelochemicals of the previous crop or when they have been detoxified by soil microorganisms. Allelopatic weed control with crop plants has long been practised by farmers and horticulturists. The challenge is twofold: tominimize the negative impact of allelochemicals on crop growth and yield and to exploit allelopathic mechanisms for pest control and crop growth regulation strategies. Allelochemicals in new crop cultivars may provide naturally occurring pesticides that can limit or suppress weeds as well as prevent insect and nematode attack and damage. Biotechnology resources for the production of herbicide-resistant crops could then be channeled into the engineering of other desired crops qualities. Allelochemicals may furnish an entirely new generation of naturally produced weed-controlling compounds, replacing synthetic herbicides and other pesticides with nonacumulatting easy-degradable substances.

Abstract: A series of experiments was conducted to examine the effects of competition on allometry and defense using tomato plants (Lycopersicon esculentum). No mortality occurred over the 4-wk test period, even with a plant density of 30 plants per 10-cm2. However, allometric patterns for log canopy diameter vs. log height indicated that competition occurred as early as 8 d after transplant and for pots with as few as two young plants (density of about 2 plants per 10-cm2). There was a change towards less root mass for greater height as competition increased. Leaf concentration of the allelochemicals chlorogenic acid, rutin and tomatine increased with decreasing competition, with the sum of these exhibiting a sigmoid-like pattern for allelochemical concentration. But competition did not affect leaf proteinase inhibitor activity, or petiole glandular trichomes or total trichomes. While the results are compatible with the growth-differentiation balance (GDB) hypothesis, they also indicate some of the difficulties that will be encountered in testing the GDB hypothesis rigorously.

Abstract: Dwarf lilyturf (Ophiopogon japonicus K.), used as a weed-suppressing cover crop and a medicinal plant, was suggested to be a promising natural herbicide to control weeds in the rice field through its allelopathic potential. Allelopathic chemicals from the dwarf lilyturf were identified and their growth-inhibiting effects on two major weeds in the rice field in Japan were examined. High pressure liquid chromatograph (HPLC) analysis showed the existence of at least six allelopathic chemicals, viz., salicylic acid, syringic acid, syringaldehyde, vanillic acid, ρ-hydroxybenzoic acid and sinapic acid in dwarf lilyturf plant. The chemical detected at the highest concentration was salicylic acid (251.04 ¼g g-1), which occupied more than half of total allelopathic chemicals detected (317.16 ¼g g-1), followed by syringic acid (37.30 ¼g g-1), syringaldehyde(13.30 ¼g g-1) and sinapic acid (11.03 ¼g g-1). The chemicals detected at the lowest concentration was vanillic acid (1.69 ¼g g-1). Salicylic acid displa...

Abstract: Water extracts of rice husk (Oryza sativa L.), above ground foliage of barnyard grass (Echinochola crus-galli (L.) Beauv) and sorghum stalk (Sorghum bicolor L.) were used to investigate their allelopathic effects on the germination and seedling growth of barnyard grass in a laboratory study. All the water extracts exhibited suppressive effects on the germination and seedling growth of barnyard grass. The order of suppression was rice > sorghum barnyard grass. Regression analysis showed that better germination had the beneficial effect on the later growth of the seedling.

Abstract: Laboratory and greenhouse experiments were conducted to evaluate the allelopathic potential of dwarf lily turf (Ophiopogon japonicus Ker-Gawler) on lettuce, alfalfa, timothy and mustard plant growth. Dry leaf debris, aqueous extract of fresh leaves and O. japonicus grown soil were investigated. Emergence, dry weight, and root and shoot length of all bioassay species were inhibited when grown in soil incorporated with oven-dried leaves of O. japonicus. The inhibitory effects were often dependent on the concentration. However, the degree of inhibition varied among the test plant species. The aqueous leaf extract was highly phytotoxic and it significantly reduced germination, seedling growth, and the fresh weight of all the test species at all rates. The emergence and growth of all four tested plants were severely inhibited when planted in O. japonicus contaminated soil. These results indicate that O. japonicus incorporated leaf debris, leaf aqueous extract and its rhizosphere soil suppress seed germination, radicle growth, seedling emergence and seeding growth of certain weeds and suggest that these responses were attributed to an allelopathic effect.

Abstract: Four higher plants, namely glory bowers (Clerodendrum trichotomum L.), jimsonweed (Datura stramonium L.), beggarweed (Desmodium triflorum L.) and Chinaberry (Melia azedarach L.), with the strong allelopathic potential among 19 allelopathic species from Southeast Asia, were tested for their effects on weed emergence in paddy soil and field. In a greenhouse experiment, D. stramonium, D. triflorum and M. azedarach exhibited similar inhibitory magnitude at 1 t ha -1 achieving more than 90 % weed control. C. trichotomum achieved about 70 % weed reduction at 2 t ha -1 . In paddy fields, D. triflorum was the most promising material for weed control and attained the highest rice yield among treatments, at the concentration of 2 t ha -1 , whereas the inhibition of D. stramonium and M. azedarach was weakened in the greenhouse. No injury of rice plants was observed. These plants might be used as natural herbicides to reduce the dependence on synthetic herbicides.

Abstract: Dwarf lilyturf (Ophiopogonjaponicus Ker-Gawl), a medicinal plant, hasbeen used for sore throat therapy andinhibition of physiological thirst sinceancient times. Experimental studies wereconducted to determine the allelopathic effectsof dwarf lilyturf plants on germination andgrowth of three main weed species, viz.,barnyardgrass (Echinochloa crusgalli L.),monchoria (Monocharia vaginalis P.) andsmallflower umbrella (Cyperus difformisL.), in rice production and on emergence andgrowth of weeds in rice fields in Japan. Theseresults showed that all aqueous extracts (1, 2,4, 8%, w/v) from the dried powders ofunderground parts of dwarf lilyturf containedwater-soluble substances that significantlyinhibited seed germination and seedling growthfor monchoria and smallflower umbrella. Withrespect to barnyardgrass, all aqueous extractshad less effect on germination, but lowconcentrations ( 4%, w/v) had significantinhibitory effects. In a glasshouse experiment,all treatments (50, 100, 150 g m−2) of thedried powders significantly inhibited theemergence and dry weights of weeds in ricepaddy fields and the inhibition became strongeras the concentration increased, except that50 g m−2 concentration had slightstimulatory effects on the emergence ofbarnyardgrass. The 150 g m−2 concentrationmarkedly inhibited emergence (77.6%) and dryweight (91.1%) of rice field weeds. Inaddition, all treatments had no inhibition oninitial rice plant growth. Dwarf lilyturfplants may have inhibitory potential on weedsas a natural rice field herbicide.

Abstract: Five parental rice lines with varied levels of allelopathic potential were employed in a partial diallel crossing program to generate 10 F1 hybrids. The allelopathic effects of the aqueous leaf extracts of the five rice parents and 10 F1s grown under two different conditions were assessed at different growth stages using lettuce (Lactuca sativa L.) as a bioassay species. Conditional genetics of rice seedling allelopathy and its genotype × environment effects were analyzed by using additive–dominant developmental genetic models. The results showed that conditional additive and dominant effects expressed alternatively from 3- to 8-leaf stage of rice seedlings. The additive effects were significant in the 5|4, 6|5, and 8|7-leaf phases, whilst the dominance effects appeared to play an important role in the 4|3 and 7|6 leaf phases. The conditional narrow sense heritability was significant in the 5|4, 6|5, and 8|7 leaf phases, the broad sense heritability was pronounced among all the growth periods investigated, suggesting that selection for allelopathic activity should be performed during this three leaf phases in order to improve selection response.

Abstract: Allelopathic potentials of volatiles from Ageratum conyzoides were studied at four growth stages (4-leaf, pre-flowering, peak flowering and mature growth stages) in plants growing in three habitats [cultivated field (no shading), roadside (no shading) and under the citrus canopy in orchard (50% shading)]. The allelopathic potentials of A. conyzoides were stronger on weeds and pathogens at peak flowering than at other growth stages. Its allelopathic potential was very strong on roadside, but very weak under the citrus canopy in orchard. Thus, its allelopathic potential varied significantly at different growth stages and in various habitats. Its volatiles were analyzed and their components were identified, which varied at different growth stages and habitats. Further, the inhibitory effects of volatiles and its major components (precocenes, beta-caryophyllene, (beta-bisabolene and (beta- farnesene) were evaluated on weeds and pathogens. The combined strong effects of these components indicated synergism among the allelochemicals.

Abstract: Allelopathic potential of aqueous extracts of leaves of Prosopis juliflora and Eucalyptus camaldulensis and bark of Acacia nilotica @ 0, 150, 100 and 50 g L. The dry plant materials were ground and soaked for 24 hours in water. Ten seeds each of Triticum aestivum, Avena fatua, and Carthamus oxycantha were used as test species. The data were recorded on germination percentage, seedling length (mm) and biomass (mg) plant. There were two identical runs of the experiment. The inhibition was recorded in all the species tested for all the parameters studied, but it was most pronounced in the germination percentage. Carthamus oxycantha was the most inhibited species. Wheat was the most tolerant. Only 20% seeds as compared to the respective check germinated in this species when exposed to E. camaldulensis @150 g L. All other concentrations of P. juliflora and E. camaldulensis proved severely inhibitory to germination of C. oxycantha. For other parameters the inhibition was observed at the higher concentrations of P. juliflora and E. camaldulensis. Acacia nilotica emerged as the weakest species in inhibiting the growth parameters of the tested species.

Abstract: With an increase in the abundance and cover of Eupatorium adenophorum, there is a concurrent decrease in the abundance and cover of native species; how ever, this decrease varies at different sites and in different forests. The rela tive abundance and cover of E. adenophorum in deciduous broad-leaved forests and a long the roadside were 3-5 times greater than in evergreen broad-leaved forests. T he composition, relative abundance and cover of native plants in deciduous b road-leaved forests and along the roadside decreased by 30%, 50% and 70%, respec tively, as compared to the evergreen broad-leaved forest. By bioassay, we investigated the allelopathy of aquatic extract from E. adenop horum that grew under evergreen broad-leaved forests, deciduous broad-leaved f orests a nd along the roadside. We found that allelopathy of aquatic extract of E. aden ophorum was different among sites, viz. roadside deciduous broad-leaved fore sts e vergreen broad-leaved forests. Correlation analysis showed that allelopathy of E. adenophorum was significantly correlated to the relative abundance of native spec ies at each of the sites. These results showed that differences in invasiveness among sites are due to differences in allelopathy at the different sites. The ca bbage biomass showed that the allelopathy of aquatic extract from E. adenophor um s hoots was greater among sites than its roots. This suggests that the allelopathy o f aquatic extract from E. adenophorum shoots contributes to different levels of invasiveness among sites more than its roots. The growth of E. adenophorum is hearty and the biomass per unit area is grea t al ong roadsides and under deciduous broad-leaved forests, so the allelopathy of E. adenophorum populations per unit area along roadsides and under deciduous bro ad-leaved forests must be much more than in evergreen broad-leaved forests. Henc e, the a ffects of E. adenophorum will be greater on these communities accelerating t heir decline.