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Plant parts and extracts that are rich in bioactive substances with allelopathic potential can be explored as a possible alternative to herbicides for natural weed control in sustainable agriculture. In the present study, we investigated the allelopathic potential of Marsdenia tenacissima leaves and its active substances. Aqueous methanol extracts of M. tenacissima showed significant inhibitory activities against the growth of lettuce (Lactuca sativa L.), alfalfa (Medicago sativa L.), timothy (Phleum pratense L.), and barnyard grass (Echinochloa crusgalli (L.) Beauv.). The extracts were purified through various chromatography steps, and one active substance was isolated and determined by spectral data to be a novel compound, assigned as steroidal glycoside 3 (8-dehydroxy-11β-O-acetyl-12β-O-tigloyl-17β-marsdenin). Steroidal glycoside 3 significantly inhibited the seedling growth of cress at a concentration of 0.03 mM. The concentrations needed for 50% growth inhibition of the cress shoots and roots were 0.25 and 0.03 mM, respectively. These results suggest that steroidal glycoside 3 may be responsible for the allelopathy of M. tenacissima leaves.

Polygonum chinense Linn. is a medicinal and invasive plant that belongs to the family Polygonaceae. The pharmacological activities and phytochemical constituents of Polygonum chinense are well reported, but the allelopathic effects and potent allelopathic substances of P. chinense remain to be investigated. Hence, this experiment was conducted to separate and characterize potentially allelopathic substances from an extract of the Polygonum chinense plant. The Polygonum chinense plant extracts highly suppressed the growth of cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), barnyard grass (Echinochloa crusgalli (L.) P. Beauv.), and timothy grass (Phleum pratense L.) seedlings in a species- and concentration-dependent way. Two active substances were separated using a series of purification procedures and determined through spectral analysis as (−)-3-hydroxy-β-ionone and (−)-3-hydroxy-7,8-dihydro-β-ionone. These two compounds significantly suppressed the seedling growth of Lepidium sativum (cress) at concentrations of 0.01 and 1 mM, respectively. The extract concentrations necessary for 50% growth inhibition (I50 values) of the cress hypocotyls and roots were 0.05 and 0.07 mM for (−)-3-hydroxy-β-ionone, respectively, and 0.42 and 1.29 mM for (−)-3-hydroxy-7,8-β-ionone, respectively. These findings suggest that these two compounds are in charge of the inhibitory effects of the Polygonum chinense extract and may serve as weed control agents.

Trewia nudiflora Linn. is a woody plant of the Euphorbiaceae family. It is well known for its use as a folk remedy, but its potential for phytotoxicity has not been explored. Therefore, this study investigated the allelopathic potential and the allelopathic substances in T. nudiflora leaves. The aqueous methanol extract of T. nudiflora was found to have a toxic effect on the plants used in the experiment. The shoot and root development of lettuce (Lactuca sativa L.) and foxtail fescue (Vulpia myuros L.) were significantly (p ≤ 0.05) reduced by the T. nudiflora extracts. The growth inhibition by the T. nudiflora extracts was proportional to the extract concentration and varied with the test plant species. The chromatographic separation of the extracts resulted in the isolation of two substances, identified as loliolide and 6,7,8-trimethoxycoumarin based on their respective spectral analyses. Both substances significantly inhibited lettuce growth at a concentration of 0.01 mM. To inhibit 50% of the growth of the lettuce, the required concentration of loliolide was 0.043 to 0.128 mM, while that of 6,7,8-trimethoxycoumarin was 0.028 to 0.032 mM. Comparing these values, the lettuce growth was more sensitive to 6,7,8-trimethoxycoumarin than loliolide, suggesting that 6,7,8-trimethoxycoumarin was more effective than loliolide. Therefore, the inhibition of the growth of the lettuce and foxtail fescue suggests that loliolide and 6,7,8-trimethoxycoumarin are responsible for the phytotoxicity of the T. nudiflora leaf extracts. Thus, the growth-inhibitory effectiveness of the T. nudiflora extracts and the identified loliolide and 6,7,8-trimethoxycoumarin may be used to develop bioherbicides that restrict the growth of weeds.

The plant Plumbago rosea Linn., belonging to the Plumbaginaceae family, is an important medicinal herb distributed in part of Southeast Asia, and there are many reports of its pharmacological properties. However, the allelopathic activities of P. rosea have not been examined. Thus, the present study was conducted to assess the allelopathic activity of P. rosea and to identify its allelopathic substances. The aqueous methanol stem extract of P. rosea significantly suppressed the seedling growth of barnyard grass (Echinochloa crus-galli L. P. Beauv.), Italian ryegrass (Lolium multiflorum Lam.), timothy (Phleum pretense L.), cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), and alfalfa (Medicago sativa L.). The extract of P. rosea was then purified through chromatographic steps, and two active substances were isolated and determined as 7,4′,5′-tri-O-methyl dihydroquercetin and 7,4′,5′-tri-O-methylampelopsin. The two compounds significantly inhibited the seedling growth of cress, with 7,4′,5′-tri-O-methylampelopsin showing a greater inhibitory effect than 7,4′,5′-tri-O-methyl dihydroquercetin. This result may be due to the 3′-OH group in 7,4′,5′-tri-O-methylampelopsin. The effective concentrations of both compounds required for 50% growth inhibition (EC50 values) of cress seedlings were 0.24 mM and 0.59 mM for root and shoot, and 0.07 mM and 0.21 mM, respectively. These findings suggest that the two compounds may contribute to the allelopathic effect of P. rosea and could be used as a natural source of allelopathic substances.

Resumen Introducción. El extracto de pino puede presentar actividad herbicida. Objetivo. Evaluar el efecto preemergente de un extracto de Pinus sp. en invernadero. Materiales y métodos. Se realizaron dos experimentos en el invernadero K de la Estación Experimental Agrícola Fabio Baudrit Moreno (EEAFBM), Universidad de Costa Rica, el primero en el mes de julio y el segundo entre setiembre y octubre del 2018. En el primero se evaluó el efecto preemergente del pino, con y sin adherente añadido al caldo de aspersión, sobre Arthraxon quartinianus (A. Rich.) y un banco de semillas que contenía diferentes especies; en el segundo experimento se evaluó el efecto preemergente del pino sobre Amaranthus sp., Ischaemum rugosum Salisb., arroz (Oryza sativa), pepino (Cucumis sativus) y un banco de semillas. En ambos experimentos se asperjó una formulación de extracto de pino al 15 % (3,75 kg i.a. ha-1). En ambos experimentos se contó el número de plántulas emergidas, en el primero se anotó a los nueve días después de la aspersión (dda) y en el segundo a los 17 dda. Resultados. El efecto preemergente sobre especies de hoja ancha no fue significativo, pero si lo fue para A. quartinianus (A. Rich.) (p=0,0009). El adherente redujo el efecto del extracto de pino sobre A. quartinianus (A. Rich.) (p=0,0116) y sobre otras especies de hojas angostas (p=0,0398). Se produjo un aumento de la germinación de las malezas procedentes del banco de semillas, 121 % para las especies de hoja ancha en general y 92 % para el Amaranthus sp. (p=0,013); además, el adherente aumentó la germinación de las semillas de arroz en un 34 % (p

Introduction.The pine extract may have herbicidal activity to other plants, affecting seed emergence.Objective.To evaluate the pre-emergent effect of aPinussp. extract in a greenhouse.Materials and methods.Two experiments were carried out in the K greenhouse of the Fabio Baudrit Moreno Agricultural Experimental Station (EEAFBM), Universidad de Costa Rica, the first in July and the second between September and October 2018. In the first one, the pre-emergent effect of pine extract, with and without added adherent to the spraying broth, onArthraxon quartinianus (A. Rich.) and a seed bank containing different species were evaluated; in the second experiment the pre-emergent effect of pine onAmaranthussp.,Ischaemum rugosumSalisb., rice (Oryza sativa), cucumber (Cucumis sativus), and a seed bank was evaluated. For both experiments, a 15 % formulation of pine extract (3.75 kg a.i. ha-1) was sprayed. In both experiments, the number of seedlings emerged was counted, in the first experiment it was recorded at nine days after spraying (das) and in the second at 17 das.Results.The pre-emergent effect on broad-leaved species was not significant, but it was forA. quartinianus(A. Rich.) (p=0,0009). The adherent reduced the effect of the pine extract onA. quartinianus(A. Rich.) (p=0,0116) and other species (p=0,0398). There was an increase in the germination of weeds coming from the seed bank, 121 % for broad-leaved species in general, 92 % forAmaranthussp. (p=0,013). Besides, the adherent increased the germination of rice seeds by 34 % (p

Plants are sources of diversified allelopathic substances that can be investigated for use in eco-friendly and efficient herbicides. An aqueous methanol extract from the leaves of Garcinia xanthochymus exhibited strong inhibitory activity against barnyard grass (Echinochloa crus-galli (L.) P. Beauv.), foxtail fescue (Vulpia myuros (L.) C.C.), alfalfa (Medicago sativa L.), and cress (Lepidium sativum L.), and appears to be a promising source of allelopathic substances. Hence, bio-activity guided purification of the extract through a series of column chromatography steps yielded a novel compound assigned as garcienone ((R, E)-5-hydroxy-5-((6S, 9S)-6-methyl-9-(prop-13-en-10-yl) tetrahydrofuran-6-yl) pent-3-en-2-one). Garcienone significantly inhibited the growth of cress at a concentration of 10 &mu, M. The concentrations resulting in 50% growth inhibition (I50) of cress roots and shoots were 120.5 and 156.3 &mu, M, respectively. This report is the first to isolate and identify garcienone and to determine its allelopathic potential.

Albizia richardiana, a fast-growing, large deciduous tree belonging to the Fabaceae family, grows well in hot and humid areas but mainly grows in the tropics of the Old World. The medicinal and other uses of Albizia richardiana are well documented, but the phytotoxic effects of this tree have not yet been investigated. We conducted this study to investigate the phytotoxic activity of Albizia richardiana leaves and to identify growth inhibitory substances for controlling weeds in a sustainable way. Aqueous methanol extracts of Albizia richardiana leaves greatly suppressed the growth of cress and barnyard grass seedlings in a concentration- and species-dependent manner. Two phytotoxic substances were separated using several purification steps and characterized through spectral analysis as dehydrovomifoliol and loliolide. Dehydrovomifoliol and loliolide significantly arrested the seedling growth of cress in the concentrations of 0.1 and 0.01 mM, respectively. The extract concentrations needed for 50% growth inhibition (I50 values) of cress seedlings were 3.16–3.01 mM for dehydrovomifoliol and 0.03–0.02 mM for loliolide. The results suggest that these two allelopathic substances might play a vital role in the phytotoxicity of Albizia richardiana leaves.

La berce du Caucase (Heracleum mantegazzianum) est une espèce envahissante provoquant des photodermatites lors d’un contact avec la sève. Son éradication laisse le sol à nu, facilitant ainsi sa réinfestation. L’objectif de mon projet est d’évaluer l’effet de l’ensemencement d’un couvert végétal pour empêcher l’établissement de la berce par phénomène de compétition. J’ai d’abord effectué une expérience en mésocosme utilisant cinq mélanges d’espèces herbacées afin de tester l’effet de la composition sur la germination, la croissance et la survie de la berce du Caucase. Trois mélanges, incluant ceux contenant Solidago canadensis, ont réduit le nombre de semences ayant germé. Tous les mélanges ont réduit la croissance et la survie des semis. Afin de déterminer si l’allélopathie pouvait être le mécanisme responsable de ce phénomène, j’ai testé l’effet de substances allélopathiques, extraites des feuilles et des racines du S. canadensis, sur la germination des semences de la berce. Bien qu’elle montre un effet allélopathique sur une espèce modèle (le radis), mon expérience n’a pas permis de détecter d’effet négatif sur la germination de la berce. Étant donné que celle-ci peut se faire dans l’obscurité, un mécanisme autre que la lumière ou l’allélopathie serait la cause de la réduction du taux de germination chez certains mélanges. Par contre, la réduction de la lumière par le couvert végétal serait la cause probable de la diminution de croissance et de la survie des semis. En définitive, un mélange composé majoritairement de graminées et produisant rapidement un couvert végétal dense aurait un meilleur potentiel pour la restauration suite à des travaux de lutte., Giant Hogweed (Heracleum mantegazzianum) is an invasive species that causes human skin photodermatitis after contact with the sap. Control techniques of the plant often produced a soil devoid of vegetation cover, which facilitates reinvasion. The objective of my project was to evaluate the effect (competition) of plant seeding on the establishment of Giant Hogweed. First, I conducted a mesocosm experiment using five herbaceous plant mixtures in order to test the effect of composition and associated cover on germination, growth and survival of Giant Hogweed. Three mixtures, especially those with Solidago canadensis, reduced germination rate. Every mixture reduced growth and survival of Giant Hogweed seedlings. In order to identify the mechanism responsible for this phenomenon, I tested the effect of allelopathic substances, extracted from leaves and roots of S. canadensis, on germination of Giant Hogweed seeds. Although an allelopathic effect on a model species (radish) was detected, the substances did not impede Giant Hogweed germination. Considering germination occurs in darkness, a mechanism other than light or allelopathy would be responsible for the reduction of germination rate in certain plant mixtures. However, the reduction of light through plant cover would likely be the cause for the decrease of growth and survival of Giant Hogweed seedlings. A seed mixture mostly composed of grasses and rapidly producing a dense plant cover has a good potential for restoration following weeding.

[ES] Para la identificación de compuestos hidrosolubles que se consideran potencialmente alelopáticos en los extractos acuosos de Artemisia absinthium L se procedió a la recolección de material vegetal procedente de dos zonas geográficas distintas, España y Hungría, respectivamente. Los extractos acuosos se obtuvieron de las partes aéreas de A. absinthium. Tras la obtención de los extractos acuosos, se liofilizaron y se concentraron con metanol para la identificación, mediante cromatografía en capa fina (CCF), de principios amargos (lactonas sesquiterpénicas), cumarinas, flavonoides y antraquinonas. Paralelamente, a partir de los extractos acuosos liofilizados y los extractos metanólicos de las hojas, se realizaron ensayos cualitativos para una rápida identificación de flavonoides, fitoesteroles y taninos. Los ensayos cualitativos resultaron positivos para los cuatro extractos, la presencia de flavonoides resultó más notoria en los extractos metanólicos de las hojas de ambas zonas, la presencia de fitoesteroles resultó más intensa en el extracto metanólico del ajenjo español, en cambio, la presencia de taninos fue más notoria en los extractos metanólicos húngaros. La caracterización de los extractos metanólicos mediante CCF se llevó a cabo mediante las indicaciones especificadas en la bibliografía. Se identificaron dos cumarinas (escopoletina y umbeliferona) en ambos extractos acuosos liofilizados; por otro lado, la presencia de flavonoides resultó más significativa en ambos extractos metanólicos de las hojas. La presencia de saponinas se manifestó en los cuatro extractos metanólicos. En cuanto a la identificación de lactonas sesquiterpénicas, se identificó artabsina en el extracto metanólico de las hojas del ajenjo húngaro. Por último, la presencia de compuestos antracénicos fue notoria en ambos extractos metanólicos de las hojas. Una vez identificada la presencia de sustancias potencialmente alelopáticas en los extractos acuosos de A. absinthium se procedió a evaluar su actividad fitotóxica in vitro frente a Amaranthus retroflexus y Lolium perenne utilizando también extracto acuoso emulsionado con aceite esencial de A. absinthium Tras los resultados de estos ensayos se afirmó que la actividad fitotóxica de los extractos acuosos depende tanto de la especie sobre la que actúa como de la dosis empleada. De los resultados de este trabajo se confirma el interés de seguir investigando en rangos maores de dosis tanto los extractos acuosos como las emulsiones de estos con el aceite esencial., [EN] For the identification of water-soluble compounds, which are considered potentially allelopathic, in aqueous extracts of Artemisia absinthium L, plant material from two different geographical areas, Spain and Hungary, respectively, was harvested. The aqueous extracts were obtained from the aerial parts of A. absinthium. After obtaining aqueous extracts, they were lyophilized and concentrated with methanol for identification by thin layer chromatography (TLC) of bitter principles (sesquiterpene lactones), coumarins, flavonoids and anthraquinones. In parallel, from the lyophilized aqueous extracts and methanol extracts of the leaves, qualitative tests for rapid identification of flavonoids, phytosterols and tannins were performed. Qualitative tests were positive for the four extracts. The presence of flavonoids was more noticeable in the methanol extracts of the leaves from both areas. The presence of phytosterols was more intense in the methanol extract of Spanish absinthe. However, the presence of tannins was more noticeable in the Hungarian methanol extracts. The characterization of the methanol extracts by TLC was carried out using the information specified in the literature. Two coumarins (umbelliferone and scopoletin) in both freeze-dried aqueous extracts were identified; on the other hand, the presence of flavonoids was more significant in both methanol extracts of the leaves. The presence of saponins was manifested in the four methanolic extracts. Regarding the sesquiterpene lactones, artabsina was identified in the methanolic extract from the leaves of Hungarian wormwood. Finally, the presence of anthracene compounds was evident in both methanol extracts of the leaves. Having identified the presence of potentially allelopathic substances in aqueous extracts of A. absinthium, their phytotoxic activity was evaluated in vitro assays against Amaranthus retroflexus and Lolium perenne germination, using aqueous extract and also aqueous extracs emulsified with A. absinthium essential oil. From the results of these experiments it is stated that the phytotoxic activity of aqueous extracts depends on the species against they acts, as on the dose employed. Further research is necessary with wide doses and mixes of both, aqueous extracts and their emulsions with the essential oil in more weeds to comprehend their herbicidal potential., [CA] Per a la identificació de compostos hidrosolubles que es consideren potencialment alelopàtics en els extractes aquosos d'Artemisia absinthium L. es va procedir a la recol·lecció del material vegetal procedent de dos zones geogràfiques distintes, d'Espanya i d'Hongria, respectivament. Els extractes aquosos es van obtindre de les parts aèries de A. absinthium. Després de l'obtenció dels extractes aquosos, es van liofilitzar i es van concentrar amb metanol per a la identificació, per mitjà de cromatografia en capa fina (CCF), de principis amargs (lactones sesquiterpénicas), cumarines, flavonoides i antraquinones. Paral·lelament, a partir dels extractes aquosos liofilitzats i els extractes metanòlics dels fulls, es van realitzar assajos qualitatius per a una ràpida identificació de flavonoides, fitoesterols i tanins. Els assajos qualitatius van resultar positius per als quatre extractes, la presència de flavonoides va resultar més notòria en els extractes metanólicos dels fulls d'ambdós zones, la presència de fitoesteroles va resultar més intensa en l'extracte metanòlic del donzell espanyol, en canvi, la presència de tanins va ser més notòria en els extractes metanólicos hongaresos. La caracterització dels extractes metanólicos per mitjà de CCF es va dur a terme per mitjançant les indicacions especificades en la bibliografia. Es van identificar dos cumarines (escopoletina i umbel·liferassa) en ambdós extractes aquosos liofilitzats; d'altra banda, la presència de flavonoides va resultar més significativa en ambdós extractes metanólicos dels fulls. La presència de saponines es va manifestar en els quatre extractes metanólicos. Quant a la identificació de lactones sesquiterpénicas, es va identificar artabsina en l'extracte metanòlic dels fulls del donzell hongarés. Finalment, la presència de compostos antracènics va estar notòria en ambdós extractes metanólicos dels fulls. Una vegada identificada la presència de substàncies potencialment alelopàtiques en els extractes aquosos de A. absinthium es va procedir a avaluar la seua activitat fitotóxica in vitro enfront d'Amaranthus retroflexus i Lolium perenne utilitzant també extracte aquós emulsionat amb oli essencial de A. absinthium. Després dels resultats d'aquestos assajos, es va afirmar que l'activitat fitotóxica dels extractes aquosos depén tant de l'espècie sobre la qual actua com de la dosi emprada. Dels resultats d'aquest treball es confirma l'interés en continuar investigant en amb majors dosis de tant dels extractes aquosos com de les emulsions amb l’oli essencial.