Allelopathic activity of Litchi chinensis Sonn.

Couroupita guianensis Aubl. has been traditionally used for medicinal as well as ornamental purposes, but the allelopathic potential of this species has not yet been reported. Hence, the aim of this study is to explore the allelopathic activity of C. guianensis leaves. We examined the effect of aqueous methanol extracts of the leaves of this species at five different concentrations (1, 3, 10, 30, and 100 mg dry weight (DW) equivalent extract mL) on the germination of lettuce (Lactuca sativa L.) and barnyard grass (Echinochloa crus-galli (L.) Beauv.), and on the growth of cress (Lepidium sativum L.), lettuce, alfalfa (Medicago sativa L.), barnyard grass, timothy (Phleum pretense L.), and Italian ryegrass (Lolium multiflorum Lam.) seedlings. The germination of lettuce and barnyard grass, as well as the growth of all test plants, was inhibited by leaf extracts of C. guianensis at concentrations ≥ 1 mg DW equivalent extract mL. The extract obtained from 100 mg C. guianensis leaves completely inhibited germination of lettuce or significantly delayed germination of barnyard grass. The hypocotyl/coleoptile and root growth of all test plants were inhibited by the leaf extracts to less than 10% of control hypocotyl/coleoptile and root growth at the concentration of 100 mg DW equivalent extract mL, except for the hypocotyl/coleoptile growth of alfalfa and barnyard grass. The ranges of I50 values of hypocotyl/coleoptile and root growth of all test plants were 1.22–10.24 and 0.76–3.97 mg DW equivalent extract mL, respectively. The inhibitory activities increased with increasing extract concentrations. The present results suggest that C. guianensis may have allelopathic potential and thus possesses allelopathic substances. Therefore, the leaves of this species could potentially be used as mulch and/or soil additive to control weeds in sustainable crop production.

Ochna integerrima (Lour.) Merr, a deciduous shrub in the family Ochnaceae, is a great source of active compounds and is used as a medicinal plant in tropical Asia, Africa, and America. Previous studies have focused on the pharmacological properties of O. integerrima; however, the allelopathic potential of this plant has not yet been identified. Therefore, this study was carried out with completely randomized design to determine the allelopathic potential of O. integerrima leaf extracts in six concentrations against the seedlings growth of dicots plants [garden cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), and alfalfa (Medicago sativa L.)] and monocot plants [Italian ryegrass (Lolium multiflorum Lam.), timothy (Phleum pratense L.), and barnyard grass (Echinochloa crusgalli (L.) Beauv.)]. The results showed that the leaf extracts inhibited the seedling growth of all the test plants at concentrations ≥10 mg dry weight (D.W.) equivalent extract mL−1, except for the barnyard grass shoots. The concentrations needed for 50% inhibition (I50 values) of the shoot and root growth of the test plants were in the ranges 1.97–48.01 and 1.18–9.64 mg D.W. equivalent extract mL−1, respectively. The I50 values showed the roots of all the tested plants were more susceptible to the extracts than their shoots, except alfalfa. These findings suggested that the leaf extracts of O. integerrima may possess allelopathic substances which could be used as a source of bio-herbicide for reducing the weed burden in crop fields. Thus, more research is needed to isolate and identify the allelopathic substances in O. integerrima in order to produce bio-herbicide for weed management

Acacia pennata (L.) Willd (Mimosaceae), a woody climbing plant, is used as a traditional medicinal plant in the South and Southeast Asia regions and has been documented to have various pharmacological effects. However, the allelopathy of this plant still remains unclear. Thus, the allelopathic potential of A. pennata leaf extracts was examined against the seedling growth of dicot plants [alfalfa (Medicago sativa L.), cress (Lepidium sativum L.), and lettuce (Lactuca sativa L.)] and monocot plants [barnyard grass (Echinochloa crus-galli (L.) Beauv.), Italian ryegrass (Lolium multiflorum Lam.), and timothy (Phleum pratense L.)] at six different concentrations. The results showed that the A. pennata leaf extracts inhibited the seedling growth of all the test plant species at concentrations ≥3 mg dry weight (D.W.) equivalent extract mL-1. The inhibitory activity of the extracts against both shoot and root growth varied with concentration and tested plants. The concentrations required for 50% inhibition of the test plant shoots and roots were 1.5-16.1 and 1.4-8.6 mg D.W. equivalent extract mL-1, respectively. The root growth of all the test plant species was more sensitive to the extracts than their shoot growth, except alfalfa. The results of the present study indicate that the A. pennata leaf extracts may have allelopathic potential and may contain allelopathic substances. Therefore, further studies are required for isolation and identification of the growth inhibitory substances which are responsible for the allelopathic effect of A. pennata.

Dischidia imbricata (Blume) Steud. is a herbaceous plant belonging to the Apocynaceae family. This plant has been reported to possess various pharmacological properties, however, there has been no report related to its allelopathic properties. Therefore, the aqueous methanol extracts of D. imbricata were examined for possible allelopathic activity against the seedling growth of dicotyledonous plants; lettuce (Lactuca sativa L.), cress (Lepidium sativum L.), and alfalfa (Medicago sativa L.), and monocotyledonous plants; barnyard grass (Echinochloa crus-galli (L.) P. Beauv.), Italian ryegrass (Lolium multiflorum Lam.), and timothy (Phleum pratense L.). D. imbricata extracts exhibited a significant inhibition on the seedling growth of all the test plant species at the concentration ≥ 0.01 g dry weight equivalent extract mL-1. The seedling growth of lettuce showed the highest inhibition with D. imbricata extracts followed by alfalfa and cress, whereas the least inhibition was found on the seedling growth of timothy. Concentrations required for 50% inhibition (I50 values) of all the test plant species were in the range of 0.003 to 0.067 g D.W. equivalent extract mL-1 for shoot growth, and 0.018 to 0.026 g D.W. equivalent extract mL-1 for root growth. In addition considering the I50 values, the root growth of the test plant species was more sensitive to D. imbricata extracts than their shoot growth, except cress seedling. These results indicated that D. imbricata may possess allelopathic activity and may contain allelopathic substances.
 
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 In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue.
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Exploration of allelochemicals with phytotoxic effects is intended to minimize a current dependency on synthetic herbicides in weed management. Several allelochemicals from the tropical tree <em>Cerbera manghas</em> (sea mango) have been reported as termiticides and bactericides. The present study investigated possible phytotoxic effects of <em>C. manghas</em> leaf extracts under laboratory conditions. Four monocots: barnyard grass (<em>Echinochloa crus-galli</em>), foxtail fescue (<em>Vulpia myuros</em>), Italian ryegrass (<em>Lolium multiflorum</em>), and timothy (<em>Phleum pratense</em>) and four dicots: alfalfa (<em>Medicago sativa</em>), garden cress (<em>Lepidium sativum</em>), lettuce (<em>Lactuca sativa</em>), and rapeseed (<em>Brassica napus</em>) were used as test species. Elongation of both shoots and roots of seedlings was measured to assess any phytotoxic effects. The results showed that the sensitivities of shoots and roots were different between the test species, and the inhibition of seedling elongation significantly increased with increasing concentration of leaf extracts of <em>C. manghas</em> for all the test species. The IC<sub>50</sub> (50% inhibitory concentration) values showed that 8.50–32.30 and 4.26–34.67 mg dry weight equivalent extract mL<sup>−1</sup> of <em>C. manghas</em> inhibited seedling elongation by 50%, for shoots and roots respectively. Isolation and identification of the phytotoxic substances from <em>C. manghas</em> are suggested for future investigation.

Allelopathy is involved in the formation of pure colonies of the fern Gleichenia japonica

In this study, leaves, stalks and roots of Cymbopogon nardus were separately evaluated to determine the most active parts that contained the strong growth inhibitory activity. Each aqueous methanol extracts of Cymbopogon nardus were determined their allelopathic activity by using six test plant species; alfalfa (Medicago sativa L.), cress (Lepidum sativum L.), lettuce (Lactuca sativa L.), barnyard grass (Echinochloa crus-galli L.), Italian ryegrass (Lolium moltiflorum Lam.) and jungle rice (Echinochloa colonum (L.) P. Beauv.). Four extract concentrations (0.01, 0.03, 0.1 and 0.3 g dry weight equivalent extract/mL) were used for the bioassay. The results showed that these three extracts have inhibitory activity and the percent inhibition increased concentration dependently. However, the inhibitory activity of leaf and root extracts was more effective than stalk extract at 95% level of significance. Barnyard grass, Italian ryegrass and jungle rice were the most sensitive to the leaf, stalk and root extracts, respectively. The concentrations required for 50% growth inhibition of C. nardus leaf, stalk and root extracts on all test plants were 0.000-0.025, 0.009-0.077 and 0.003- 0.023 g dry weight equivalent extract/mL, respectively. In addition, separation of these extracts through silica gel column indicated that root extract contained the most active fractions with strong growth inhibition. The present results suggest that C. nardus may have allelopathic compounds and the root extracts have the greatest inhibitory activity. Studies are in progress for the isolation and identification of allelopathic compounds in aqueous methanol extracts of C. nardus roots for the development of natural herbicides.

Phytotoxic activity of Ocimum tenuiflorum (Lamiaceae) plant extracts was investigated against the germination and seedling growth of cress (Lepidium sativum), lettuce (Lactuca sativa), alfalfa (Medicago sativa), Italian ryegrass (Lolium multiflorum), barnyard grass (Echinochloa crus-galli), and timothy (Phleum pratense) at four different concentrations. The plant extracts at concentrations greater than 30 mg dry weight equivalent extract mL−1 reduced significantly the total germination percent (GP), germination index (GI), germination energy (GE), speed of emergence (SE), seedling vigour index (SVI), and coefficient of the rate of germination (CRG) of all test species except barnyard grass and GP of lettuce. In contrast, time required for 50% germination (T 50) and mean germination time (MGT) were increased at the same or higher than this concentration. The increasing trend of T 50 and MGT and the decreasing trend of other indices indicated a significant inhibition or delay of germination of the test species by O. tenuiflorum plant extracts and vice versa. In addition, the shoot and root growth of all test species were significantly inhibited by the extracts at concentrations greater than 10 mg dry weight equivalent extract mL−1. The I 50 values for shoot and root growth were ranged from 26 to 104 mg dry weight equivalent extract mL−1. Seedling growth was more sensitive to the extracts compared to seed germination. Results of this study suggest that O. tenuiflorum plant extracts have phytotoxic properties and thus contain phytotoxic substances. Isolation and characterization of those substances from this plant may act as a tool for new natural, biodegradable herbicide development to control weeds.

The inhibitory effects of aqueous methanol extract of Cymbopogon nardus (L.) Rendle were determined on seedling growth of eight test plant species: alfalfa ( Medicago sativa L.), cress ( Lepidum sativum L.), lettuce ( Lactuca sativa L.), rapeseed ( Brassica napus L.), barnyard grass ( Echinochloa crus-galli L.), Italian ryegrass ( Lolium moltiflorum Lam.), jungle rice ( Echinochloa colonum (L.) P. Beauv.) and timothy ( Phleum pratense L.). The bioassay was conducted with four extract concentrations (0.01, 0.03, 0.1 and 0.3 g dry weight equivalent extract/mL). The extracts inhibited significantly shoot and root growth of four test plants such as cress, lettuce, rapeseed and Italian ryegrass at the concentration ? 0.03 g dry weight equivalent extract/mL. The inhibitions of shoots and roots increased with increasing extract concentrations. The concentrations required for 50% growth inhibition of all test plants ranged 0.007-0.090 g dry weight equivalent extract/mL. Roots of all test plants were more sensitive to the extract than their shoots. Lettuce was most sensitive, follows by cress and timothy. The results suggest that C. nardus may have allelopathic compounds and may be a candidate for isolation and identification of allelopathic compounds to develop an alternative weed management option.

Weed plants having strong allelopathic potential provide themselves with a competitive advantage in crop fields through the release of allelochemicals. Fimbristylis dichotoma, a well-known weed, was taken in the present study to evaluate its allelopathic potentiality under laboratory condition. Aqueous methanol extracts of dried F. dichotoma were applied on the seedling growth of four dicotyledonous [cress (Lepidum sativum L.), lettuce (Lactuca sativa L.), alfalfa (Medicago sativa L.) and rapeseed (Brassica napus L.)], and four monocotyledonous [Italian ryegrass (Lolium multiflorum Lam.), barnyard grass (Echinochloa crus-galli L.), timothy (Phleum pratense L.) and sand fescue (Festuca megalura Nutt.)] at four concentrations 0.01, 0.03, 0.1 and 0.3 g dry weight (DW) equivalent extract/ml. The seedling growth of all test plant species experienced an inhibition in all concentrations by the extracts of F. dichotoma and the inhibition was concentration-dependent. A complete inhibition of lettuce seedling was found at 0.1 g DW equivalent extract/ml and also the seedling growth of cress, lettuce, alfalfa and sand fescue was inhibited completely at the concentration of 0.3 g DW equivalent extract/ml. Considering concentrations required for 50% growth inhibition shoot of alfalfa and root of lettuce showed most sensitivity to the extract of F. dichotoma. These results imply that Fimbristylis dichotoma may have allelopathic properties and may contain allelochemicals which may exert deleterious effect to its surrounding environment.

Tradescantia spathacea Sw. (Commelinaceae) is widely cultivated as an ornamental and medicinal plant in Southeast Asia, and its pharmacological properties are well known. On the other hand, this plant species is classified as an invasive weed in some countries. As a noxious weed, T. spathacea has been reported to disrupt the growth of native plants. However, no study has reported on its allelopathic activity. Thus, we investigated the allelopathic property and inhibitory substance of T. spathacea. The extracts of T. spathacea significantly inhibited the shoots and roots of alfalfa (Medicago sativa L.), cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), barnyard grass (Echinochloa crus-galli (L.) P. Beauv.), Italian ryegrass (Lolium multiflorum Lam.), and timothy (Phleum pratense L.) at concentrations ≥ 3mg dry weight (D.W.) equivalent extract/mL. As the extract concentration increased, the growth of the shoots and roots decreased. The I50 values of the test plant shoots and roots were 11.6-72.4 and 5.4-19.5mg D.W. equivalent extract/mL, respectively. The extracts were purified by column chromatography, and an inhibitory substance was separated, which inhibited the shoots and roots of cress to 18.8 and 11.6% of control growth, respectively. The results of present findings indicate that T. spathacea extracts possess an allelopathic property, and its inhibitory substance may contribute this activity.

The allelopathic properties of plants can be used as an alternative weed control method to reduce the use of synthetic herbicides. Accordingly, the present study was carried out to determine the allelopathic activity of Garcinia pedunculata. Six different concentrations of aqueous methanol extracts of G. pedunculata fruit were prepared and used to determine their effect on the growth of eight test plants: alfalfa (Medicago sativa L.), cress (Lepidum sativum L.), lettuce (Lactuca sativa L.), rapeseed (Brassica napus L.), barnyard grass (Echinochloa crus-galli (L.) P. Beauv.), foxtail fescue (Vulpia myuros (L.) C.C. Gmel.), Italian ryegrass (Lolium multiflorum Lam.), and timothy (Phleum pratense L.). The test plants were grown in Petri dishes and after 48 h incubation, the length of the roots and shoots of the seedlings was measured and compared with control seedlings. Experiments were carried out in a completely randomized design (CRD). Analysis of variance (ANOVA) of the data was performed using the SPSS statistical package, and the I50 values were measured from a regression equation. The extracts at each concentration significantly inhibited the shoot and root growth of all the test plants, except the concentration of 0.001 g dry weight equivalent extract/mL, compared with control. At a concentration of 0.3 g of dry weight equivalent extract/mL, the shoot and root growth of all the tested plants were completely inhibited, except the shoot growth of barnyard grass. The degree of inhibition increased in line with increased extract concentration. The shoots of alfalfa and the roots of barnyard grass were determined to be the most susceptible to the G. pedunculata extract based on the concentration of extract resulting in 50% (I50) growth inhibition of the test plants. These results suggest that G. pedunculata may have allelopathic potential and may possess allelochemicals. From our study, we can conclude that G. pedunculata could be developed as an eco-friendly weed control option.

Citronella grass (Cymbopogon nardus) is a perennial herb. Many researchers have studied the exploitation of the active compounds in this plant for medicinal purposes, but there have been no studies on its phytotoxic compounds. Therefore, we investigated the phytotoxic active compounds in the roots of C. nardus. A significant inhibition was observed on the germination of cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), barnyard grass (Echinochloa crus-galli L.), and Italian ryegrass (Lolium multiflorum Lam.) by the aqueous methanol extract of C. nardus roots. The extract decreased the total germination percentage (GP) and germination index (GI, progressive total of daily cumulative germination), and extended the time required for 50% germination (T 50) of all test species. A phytotoxic compound of the extract was isolated and identified as N-octanoyl tyramine by spectral analysis. This compound showed the inhibition on the germination of cress and barnyard grass. The decline in GP, GI, and T 50 was observed at concentrations of 30–2000 μM of N-octanoyl tyramine. The compound also showed the significant inhibition on the growth of cress and barnyard grass seedlings at concentrations greater than 100 and 300 μM, respectively. This study suggests that C. nardus could produce phytotoxic compounds, and N-octanoyl tyramine may be responsible for its phytotoxic activity.

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.

A phytotoxic active substance in the decomposing litter of the fern Gleichenia japonica