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Homegarden, traditional agroforestry system in tropical and subtropical regions, sustains the availability of daily necessities. Mango (Mangifera indica L.) is an essential tree in the homegardens and is used for multiple purposes such as food, folk medicine, fuel, timber, and apiculture. The interaction between mango and weeds or crops has been evaluated in terms of allelopathy and the evidence of the allelopathy accumulated in the literature over two decades. The leaf extracts and leachate of mango inhibited the germination and growth of several other plants species. Soil collected from mango orchard shows growth inhibitory activity. Residues of mango leaves also suppressed the growth of other plant species. Phytotoxic substances such as coumaric, vanillic, caffeic, cinnamic, gallic and protocatechuic acids, and methyl gallate and quercetin‐3‐O‐α‐glucopyranosyl‐(1 → 2)‐β‐D‐glucopyranoside were identified in mango leaves. Those compounds may be released into the soil through the leaf leachate and the decomposition of plant residues and they can inhibit the germination and the growth of neighboring plants as allelopathic substances. Therefore, the allelopathy of mango is potentially useful for the weed management options in homegardens and other agriculture settings to reduce commercial herbicide dependency.

Plants possessing allelopathic potential could be used as a source of bio-herbicide to help decrease the use of synthetic herbicides. Acacia catechu (L.f.) Willd., a deciduous tree from the Mimosaceae family, has been reported to have medicinal properties. However, there have been no reports on the allelopathy of this tree. Therefore, the leaf extracts of A. catechu were examined for allelopathic potential using six concentrations: 0.001, 0.003, 0.01, 0.03, 0.1, and 0.3 g dry weight equivalent extract mL-1. The aqueous methanol extracts of A. catechu significantly suppressed the seedling growth of six test plants such as alfalfa, cress, lettuce, barnyard grass, Italian ryegrass, and timothy. The extracts inhibited the six test plants in a concentration-dependent manner. The shoot and root growth of all the test plant species were completely inhibited from the concentration of 0.3 g of dry weight equivalent extract mL-1, except the shoot growth of barnyard grass. Concentrations needed for 50% growth inhibition (I50 values) ranged from 0.004 to 0.043 g dry weight equivalent extract mL-1 for shoot growth, and 0.003 to 0.019 g dry weight equivalent extract mL-1 for root growth. Moreover, the I50 values indicated that the root growth of all the test plants was more susceptible to the A. catechu extracts than the shoot growth. The inhibitory effects of the extracts of A. catechu suggest that the extracts may contain allelopathic potential and, therefore, may be a potential candidate for the isolation and characterization of allelochemicals to develop an ecofriendly bio-herbicide.

The phytotoxic potential of the leaves and twigs of Schumannianthus dichotomus, discarded in the mat-making industry against four test plants (lettuce (Lactuca sativa L.), rapeseed (Brassica napus L.), foxtail fescue (Vulpia myuros (L.) C.C. Gmel.) and timothy (Phleum pratense L.)) was investigated and found strong phytotoxic activity. An assay-guided fractionation of S. dichotomus extarcts against cress (Lepidium sativum L.) through a series of column chromatography steps yielded two compounds, 8-(5-oxo-2,5-dihydrofuran-2-yl) octanoic acid (ODFO) and (E)-6-hydroxy-2,6-dimethylocta-2,7-dienoic acid (8-carboxylinalool). ODFO and 8-carboxylinalool showed strong phytotoxic activity against cress and timothy. The concentrations required for 50% growth inhibition (I50 value) of the seedlings of cress and timothy were 111.94-128.01 and 36.30-91.75 µM, respectively, for ODFO, but the values were much higher at 315.98-379.13 and 107.92-148.41 µM, respectively, for 8-carboxylinalool, indicating the stronger phytotoxic activity of ODFO. This study is the first to isolate ODFO and 8-carboxylinalool from S. dichotomus and their phytotoxic potential while ODFO is firstly encountered from any natural source. The growth inhibitory activity of the identified compounds may explain their role in the phytotoxic activity of S. dichotomus, which suggests the possible use of its leaves and twigs or its active constituents as natural bioherbicides.

Eleocharis atropurpurea is an annual weed and distributed widely in pantropical and subtropical regions. Yet, there have been no studies on the allelopathy of E. atropurpurea. Therefore, we investi...

The present study was aimed at investigating the allelopathic effects of a crude extract from Chromolaena odorata (L.) R.M.King and H.Rob. (Siam weed). The effects of 70% crude ethanol extract from the whole plant, leaf, stem, and root on the germination and growth of Echinochloa crus-galli and Amaranthus viridis seedlings were evaluated using Petri-dish tests under laboratory conditions. Crude extracts from the leaf showed the highest inhibitory activity. The leaf extract (OR) was further separated by sequential solvent extraction to provide hexane (HX), ethyl acetate (ET), and butanol (BU) fractions, which were also evaluated using Petri-dish tests. The hexane fraction was significantly the most active, therefore, it was selected for formulation in a concentrated suspension and tested for its herbicidal characteristics. The formulation showed greater early post-emergence than post- and pre-emergence activities, respectively. The physiological mechanism of the formulation was tested against E. crus-galli and showed that chlorophyll a and b and the carotenoid contents of the leaf dramatically decreased when the concentration was increased, suggesting its ability to disrupt the process of photosynthesis. As thiobarbituric acid reactive substances also occurred in the leaf of E. crus-galli, this suggests lipid peroxidation and cell disruption. These results represent the possibility that C. odorata extract contains inhibitory compounds with herbicidal activity and could be used as an early post-emergence herbicide for weed control.

Phytotoxic substances released from plants are considered eco-friendly alternatives for controlling weeds in agricultural production. In this study, the leaves of Afzelia xylocarpa (Kurz) Craib. were investigated for biological activity, and their active substances were determined. Extracts of A. xylocarpa leaf exhibited concentration-dependent phytotoxic activity against the seedling length of Lepidium sativum L., Medicago sativa L., Phleum pratense L., and Echinochloa crus-galli (L.) P. Beauv. Bioassay-guided fractionation of the A. xylocarpa leaf extracts led to isolating and identifying two compounds: vanillic acid and trans-ferulic acid. Both compounds were applied to four model plants using different concentrations. The results showed both compounds significantly inhibited the model plants’ seedling length in a species-dependent manner (p &lt, 0.05). The phytotoxic effects of trans-ferulic acid (IC50 = 0.42 to 2.43 mM) on the model plants were much greater than that of vanillic acid (IC50 = 0.73 to 3.17 mM) and P. pratense was the most sensitive to both compounds. In addition, the application of an equimolar (0.3 mM) mixture of vanillic acid and trans-ferulic acid showed the synergistic effects of the phytotoxic activity against the root length of P. pratense and L. sativum. These results suggest that the leaves of A. xylocarpa and its phytotoxic compounds could be used as a natural source of herbicides.

We conducted an investigation to search for the possibility of phytotoxic compounds and then identify them in C. aciculatus. The aqueous methanol extracts of C. aciculatus imposed a strong suppressive effect on the shoots and roots growth of Medicago sativa and Echinochloa crus-galli. The C. aciculatus extracts were subsequently purified through chromatography and three growth-inhibitory compounds were identified by spectral data as methyl cis-p-coumarate, methyl trans-p-coumarate, and trans-ferulaldehyde. The seedlings growth of Lepidium sativum was suppressed by methyl cis-p-coumarate, methyl trans-p-coumarate, and trans-ferulaldehyde. The I50 values (concentration required for 50% growth inhibition) for the seedling growth of L. sativum ranged from 1.25 to 1.73 mM for methyl cis-p-coumarate, 0.74 to 1.23 mM for methyl trans-p-coumarate, and 1.05 to 1.84 mM for trans-ferulaldehyde. Our finding indicates that methyl cis-p-coumarate, methyl trans-p-coumarate, and trans-ferulaldehyde may contribute to the phytotoxic effects of C. aciculatus.

Wedelia chinensis (Asteraceae) is a wetland herb native to India, China, and Japan. It is a valuable medicinal plant recorded to have pharmaceutical properties. However, the phytotoxic potential of Wedelia chinensis has not yet been examined. Thus, we carried out this study to establish the allelopathic effects of Wedelia chinensis and to identify its phytotoxic substances. Extracts of Wedelia chinensis exhibited high inhibitory activity against the root and shoot growth of cress, alfalfa, rapeseed, lettuce, foxtail fescue, Italian ryegrass, timothy, and barnyard grass. The inhibition was varied with species and was dependent on concentrations. The extracts were separated through several purification steps, and the two effective substances were isolated and characterized as vanillic acid and gallic acid using spectral analysis. Vanillic acid and gallic acid significantly arrested the growth of cress and Italian ryegrass seedlings. The concentrations of vanillic acid and gallic acid needed for 50% inhibition (I50 values) of the seedling growth of the cress and Italian ryegrass were 0.04&ndash, 15.4 and 0.45&ndash, 6.6 mM, respectively. The findings suggest that vanillic acid and gallic acid may be required for the growth inhibitory activities of Wedelia chinensis.

Momilactone B was released into the neighboring environment from rice throughout its life cycle. The rate of momilactone B release from rice increased until flowering initiation, and then decreased. The release rate of momilactone B at the day of flowering started was 2.1 μg plant–1 d–1. On average, a single rice plant released about 100 μg of momilactone B into the neighboring environment over its life cycle. Since momilactone B is a growth inhibitor, these results suggest that momilactone B released from rice plants may serve as an allelochemical to inhibit the germination and growth of neighboring plants.

The phytotoxic potential of plants and their constituents against other plants is being increasingly investigated as a possible alternative to synthetic herbicides to control weeds in crop fields. In this study, we explored the phytotoxicity and phytotoxic substances of Schumannianthus dichotomus, a perennial wetland shrub native to Bangladesh, India, and Myanmar. Leaf extracts of S. dichotomus exerted strong phytotoxicity against two dicot species, alfalfa and cress, and two monocot species, barnyard grass and Italian ryegrass. A bioassay-driven purification process yielded two phenolic derivatives, syringic acid and methyl syringate. Both constituents significantly inhibited the growth of cress and Italian ryegrass in a concentration-dependent manner. The concentrations required for 50% growth inhibition (I50 value) of the shoot and root growth of cress were 75.8 and 61.3 &mu, M, respectively, for syringic acid, compared with 43.2 and 31.5 &mu, M, respectively, for methyl syringate. Similarly, to suppress the shoot and root growth of Italian rye grass, a greater amount of syringic acid (I50 = 213.7 and 175.9 &mu, M) was needed than methyl syringate (I50 = 140.4 to 130.8 &mu, M). Methyl syringate showed higher phytotoxic potential than syringic acid, and cress showed higher sensitivity to both substances. This study is the first to report on the phytotoxic potential of S. dichotomus and to identify phytotoxic substances from this plant material.

The yield of kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson] often decreases after 20 years of cultivation. Replanted young kiwifruit plants cannot grow well in fields where aged trees were previously cultivated. Phytotoxicity is considered one possible reason for this problem. However, allelopathic or phytotoxic substances from kiwifruit have not been reported. This study aimed to isolate and identify potentially allelopathic active substances in kiwifruit leaves. Extracts from kiwifruit leaves inhibited the growth of cress, suggesting that kiwifruit leaf extracts may contain growth-inhibitory substances. The extracts were then purified using a silica-gel column, Sephadex LH-20 column, ODS cartridge, and HPLC. The inhibitory activity of all fractions obtained in each purification step was determined by the cress bioassay. Quercitrin was finally isolated and identified as a growth-inhibitory substance. This substance inhibited cress root growth by more than 50% of control at 3 mM. The aglycone of quercitrin, quercetin, did not significantly inhibit cress growth. Quercitrin may work as an allelopathic substance and cause the kiwifruit replant problem. Further study is in progress to investigate the influence of kiwifruit leaf extracts and these flavonoids on kiwifruit seedlings.

Caesalpinia mimosoides (Fabaceae) has been used as a folk medicine and reported to have pharmacological properties. However, the phytotoxicity of C. mimosoides has not yet been studied. Therefore, the phytotoxic activity of C. mimosoides leaf and stem extracts was evaluated against the growth of dicotyledonous and monocotyledonous plants. Aqueous methanol extracts of C. mimosoides leaves and stems exhibited inhibitory effects on the growth of all the test plants. The growth of the test plants decreased with the increase of concentrations of the extracts. Comparison of the concentrations required for 50% growth inhibition (I50 values) indicates that the leaf extracts had more inhibitory effects than the stem extracts. Thus, the active substances in the leaf extracts were purified using column chromatographic separations and a growth inhibitory substance was isolated and identified as methyl gallate by using spectral analysis. This study reports the first isolation of methyl gallate in C. mimosoides leaves. Methyl gallate at 10 mM completely inhibited the growth of cress shoots and inhibited its roots by 4.7% of control growth. At the same concentration, the shoots and roots of barnyard grass were inhibited by 84.2 and 1.7% of control growth, respectively. I50 values of methyl gallate for the growth of cress and barnyard grass ranged from 2.3 to 2.9 and 0.3 to 30.5 mM, respectively. The results suggest that methyl gallate may be responsible for the phytotoxic effects of C. mimosoides.

The leaves of Ginkgo biloba contain abundant active compounds, including flavonoids and terpene lactones. Leaves of 1–5-year-old seedlings are typically harvested for ginkgo leaf extract, which is used for treatment of cardiovascular diseases, dementia, and dizziness. However, the effects of planting densities on leaf yield and leaf active compound accumulation in ginkgo are largely unknown. Here, we conducted field experiments at four planting densities (control, moderate density [MD], medium-high density [MHD] and high density [HD]) of ginkgo seedlings to investigate their leaf production and quality. As planting density increased, stem elongation was enhanced whereas root growth was inhibited. In addition, soluble sugar and starch contents were decreased in leaves with density increasing. Although the fresh and dry weights of leaves per plant were reduced, the leaf yield per unit area increased by 60.5–138.8 % in two successive years at MD-HD. Interestingly, compared with other densities, MD resulted in a higher accumulation of various bioactive secondary metabolites, including 13 flavonoids (such as homoeriodictyol, baimaside, and ladanein), ginkgolides, and bilobalide. Correspondingly, the genes encoding chalcone synthase (CHS), chalcone isomerase (CHI), and flavonol synthase (FLS), which are involved in flavonoid biosynthesis, were upregulated. However, when exceeding MD, the contents of bioactive secondary metabolites and the expression of related genes decreased dramatically. These results suggest that the MD as the optimal density could not only enhance leaf yield, but also improve active-compound accumulation in G. biloba seedling leaves, providing a practical and theoretical reference for leaf-use ginkgo plantation.

The global population is increasing day by day. To meet the food demand for such a huge number of people, crop production must increase without damaging the environment, and to prevent synthetic chemical herbicides from polluting the environment, controlling weeds using bioherbicides is essential. Accordingly, using phytotoxic substances obtained from plants for biological weed management has attracted attention. The plant Albizia richardiana possesses phytotoxic compounds that have been previously recorded. Hence, we have conducted this research to characterize more phytotoxic compounds in Albizia richardiana. Aqueous methanolic extracts of Albizia richardiana plant significantly restricted the growth of the examined plants lettuce and Italian ryegrass in a species- and concentration-dependent manner. Three active phytotoxic compounds were isolated through various chromatographic methods and identified as compound 1, 2, and 3. Compound 3 exhibited stronger phytotoxic potentials than the other two compounds and significantly suppressed the growth of Lepidium sativum (cress). The concentration of the compounds required for 50% growth reduction (I50 value) of the Lepidium sativum seedlings ranged between 0.0827 to 0.4133 mg/mL. The results suggest that these three phytotoxic compounds might contribute to the allelopathic potential of Albizia richardiana.

To protect our environment from the toxic effect of herbicides, it is necessary to reduce the application of synthetic herbicides for controlling weeds in crop fields as well as to increase the use of natural herbicides produced from plant sources. Phytotoxic compounds obtained from plant species have gained attention as an alternate biological method for managing weeds. Albizia richardiana was previously reported to contain a number of phytotoxic substances. Therefore, we carried out this study to investigate more allelopathic substances in Albizia richardiana leaves. Aqueous methanol extracts of Albizia richardiana leaves were significantly inhabited the seedling growth of the two test species (alfalfa and timothy) in a concentration-dependent manner. The two most active substances were separated through different chromatographic steps and characterized as a novel compound 3-hydroxy-4-oxo- β -dehydroionol [(E)-6-hydroxy-3-(3-hydroxybut-1-en-1-yl)-2,4,4-trimethylcyclohexa-2,5-dien-1-one], and compound 3-oxo- α -ionone [3,5,5-trimethyl-4-(3-oxo-1-butenyl)-2-cyclohexen-1-one]. The novel compound 3-hydroxy-4-oxo- β -dehydroionol showed relatively stronger growth inhibitory potential compare to the compound 3-oxo- α -ionone and significantly restricted the seedling growth of crees and timothy. The required concentration for 50% reduction in the growth ( I 50 values) of the cress and timothy seedlings varied from 63.78 to 141.61 μ M for 3-hydroxy-4-oxo- β -dehydroionol and 1059.60 to 1616.10 μ M for 3-oxo- α -ionone. The results indicate that these two allelopathic compounds may be responsible for the phytotoxicity of Albizia richardiana leaves.

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.

The fruits of Piper retrofractum Vahl. contain a variety of compounds, but no phytotoxic compound with plant growth inhibitory activity has been reported. Therefore, the phytotoxic activity of P. retrofractum fruit extracts was investigated and found the reduction of seedling growth of cress, lettuce, alfalfa, barnyard grass, Italian ryegrass, and jungle rice. Seven bioactive compounds were isolated from the fruit extracts and identified as 3-phenylpropanoic acid (1), (2E,4E)-methyl piperate (2), (2E,4Z)-methyl piperate (3), piperlonguminine (4), dihydropiperine (5), isochavicine (6), and piperine (7). There have been no reports for their phytotoxic activity. The activity of these compounds was determined against the germination and seedling growth of cress and barnyard grass. The total germination percentage (GP) of cress was significantly inhibited by 1, 2, and 6 (40–100% inhibition), while its germination index or progressive total of cumulative germination (GI) was the most sensitive to 1, leading to the longest time required for 50% germination (T50) at 57 h behind control. However, the seedling growth of cress was highly inhibited by 6 with I50 values of 11 µM. The compounds 1 and 5–7 showed significant inhibition on GP of barnyard grass by 55–47%, while 5 and 1 effectively reduced GI and extended T50 to 42–48 h behind control, and 7 showed the most growth inhibition with I50 values of 37 µM. The inhibitory effects of the seven compounds indicate the phytotoxic property of P. retrofractum fruits, which 1, 5–7 may be the main compounds responsible for the phytotoxicity.

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.

The present study was aimed to determine the allelopathic potential of mango (Mangifera indica L.) leaves and to identify allelopathic substances in the leaves. The aqueous methanol extracts of mango leaves inhibited seedling growth of garden cress, radish, rapeseed, foxtail fescue and crabgrass, and the inhibitory effects increased with the increasing extract concentration, suggesting that mango leaves may contain allelopathic substances. The extract was then purified by several chromatographic runs through a bioassay-directed fractionation, and an growth inhibitory substance was isolated and identified by spectral data as methyl-3,4,5-trihydroxybenzoate (methyl gallate). Methyl gallate at the concentration of 10 mM inhibited 98.6% and 99.8% of root and shoot growth of garden cress relative to the control, respectively, and 94.4% and 49.3% of those of foxtail fescue, respectively. The concentrations of methyl gallate required for 50% growth inhibition (I50) on garden cress roots and shoots were 3...

Aglaia odorata Lour. (Meliaceae) was found to have very strong allelopathic activity and a bioherbicide PORGANIC(™) was developed from its leaf extracts. However, the phytotoxic substances causing the strong allelopathic activity of the plants have not yet been determined. Therefore, we investigated allelopathic properties and phytotoxic substances in A. odorata. Aqueous EtOH extracts of A. odorata leaves inhibited root and shoot growth of garden cress (Lepidum sativum), lettuce (Lactuca sativa), alfalfa (Medicago sativa), timothy (Phleum pratense), ryegrass (Lolium multiflorum), and Echinochloa crus-galli with the extract concentration-dependent manner. The extracts were then purified and a major phytotoxic substance with allelopathic activity was isolated and identified by spectral data as rocaglaol. Rocaglaol inhibited the growth of garden cress and E. crus-galli at concentrations > 0.3 and 0.03 μm, respectively. The concentrations required for 50% inhibition ranged from 0.09 to 2.5 μm. The inhibitory activity of rocaglaol on the weed species, E. crus-galli, was much greater than that of abscisic acid. These results suggest that rocaglaol may be a major contributor to the allelopathic effect of A. odorata and bioherbicide PORGANIC(™) .

Flavonoids are the main secondary metabolites in Ginkgo biloba leaves. Most previous studies focused on the molecular mechanisms of structural genes and transcription factors regulating flavonoid synthesis. Few reports have examined the long non-coding RNAs (lncRNAs) regulating flavonoid synthesis in G. biloba. Here, we performed high-throughput sequencing of three stages of G. biloba leaves with significant differences in flavonoid contents. We identified 2124 lncRNAs, including 1032 intergenic lncRNAs and 1092 antisense lncRNAs. Enrichment analysis revealed that cis-regulated target genes of upregulated lncRNAs were significantly enriched in the flavonoid biosynthesis pathway. Among these, 28 differentially expressed structural genes in this pathway and 14 key transcription factors may be regulated by multiple lncRNAs. In addition, we found that lncRNAs may act as precursors and endogenous target mimics of miRNAs to indirectly regulate protein-coding genes (PCgenes). More importantly, we found that multiple lncRNAs may serve as the targets of miR156a, miR172a, miR396a, miR828a, and miR858a and participate in the synthesis of ginkgo flavonoids by forming lncRNA (target)–miRNA–PCgene networks. Taken together, our results characterize the differences in the structure and expression levels of G. biloba lncRNAs and protein-coding genes, and demonstrating that lncRNAs may participate in the regulation of biosynthesis of G. biloba flavonoids in several ways.

In forestry systems, many types of forest trees possess allelopathic properties and release a wide variety of allelochemicals that influence the growth and development of surrounding species. Dalbergia cochinchinensis, a forest tree distributed in Southeast Asia, is reputed to possess several biological properties and contain several secondary compounds. However, there have been no studies on the allelopathy of D. cochinchinensis. Therefore, D. cochinchinensis leaf extracts were examined for allelopathic potential. The present study showed that D. cochinchinensis extracts significantly inhibited the seedling growth of six test plant species: timothy, Italian ryegrass, barnyard grass, cress, alfalfa, and lettuce. Concentrations of the D. cochinchinensis extracts negatively correlated with the shoot length (r = −0.50 to −0.89) and root length (r = −0.65 to −0.89) of all the test plant species. The extracts were then purified using several chromatographic steps and the growth inhibitory substance was isolated. The chemical structure of the substance was identified through spectroscopic analysis as 3,4-dihydroxybenzoic acid (protocatechuic acid). Protocatechuic acid at a concentration higher than 3 mM significantly inhibited the growth of cress seedlings, whereas barnyard grass seedlings were inhibited at concentrations higher than 0.3 mM. As the protocatechuic acid concentration increased, the seedling growth of cress and barnyard grass was significantly reduced. I50 values showed the effectiveness of protocatechuic acid against both test plant species was apparently greater on root growth than shoot growth. Results of this study suggest that protocatechuic acid isolated from D. cochinchinensis might be responsible for its inhibitory effects.

Schumannione, a new butenolide derivative, was isolated from the leaves of Schumannianthus dichotomus through phytotoxic assay-guided fractionation. The structure of the compound was elucidated by detailed spectroscopic analysis including ECD spectra. Schumannione displayed significant phytotoxicity against timothy and cress with a minimum 10 µM concentration having IC50 values ranging from 109.8 to 160.9 µM, indicating it might play a role in the phytotoxic potential of S. dichotomus.

Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae) is native to Mexico and Central America. The species is spreading quickly and has naturalized in more than 70 countries. It has often been recorded as a harmful invasive plant that disturbs native plant communities. Phytotoxic chemical interactions such as allelopathy between invasive plants and native plants have been reported to play an important role in the invasion. Evidence for allelopathy of T. diversifolia has accumulated in the literature over 30 years. Thus, the objective of this review was to discuss the possible involvement of allelopathy in the invasive potential of T. diversifolia. The extracts, root exudates, and plant residues of T. diversifolia inhibited the germination and growth of other plant species. The soil water and soil collected from T. diversifolia fields also showed inhibitory growth effects. The decomposition rate of T. diversifolia residues in soil was reported to be high. Phytotoxic substances such as sesquiterpene lactones were isolated and identified in the extracts of T. diversifolia. Some phytotoxic substances in T. diversifolia may be released into the soil through the decomposition of the plant residues and the exudation from living tissues of T. diversifolia, including its root exudates, which act as allelopathic substances. Those allelopathic substances can inhibit the germination and growth of neighboring plants and may enhance the competitive ability of the plants, make them invasive.

Wedelia chinensis has been widely used as a traditional medicine and several bioactive compounds have been isolated. We investigated phytotoxic property and phytotoxic substances in the species. An aqueous methanol extract of W. chinensis inhibited the growth of roots and shoots of cress. The extracts were then purified by several chromatographic runs with monitoring the inhibitory activity and a phytotoxic substance was isolated. The substance was determined by spectral data to be a novel kaurene-type compound, wedelienone. Wedelienone inhibited the growth of cress and timothy (Phleum pratense L) at concentrations greater than 10–30 μM. These results suggest that wedelienone may contribute to the phytotoxic effects caused by the extracts.

Heliotropium indicum L. belongs to the family Boraginaceae. The plant has been used as a folk medicine because it contains substances of various biological activities. It is also identified as a common weed which grows wildly in crop fields in tropical and subtropical regions of the world. However, there is little information on the allelopathic effect in this plant. Therefore, this study was undertaken to investigate the growth inhibitory effect and to identify the growth inhibitory substances in H. indicum. An aqueous methanol extract of H. indicum inhibited shoot and root growth of barnyard grass, foxtail fescue, timothy, cress, lettuce and rapeseed at concentrations higher than 10 mg dry weight equivalent extract/mL. The concentrations required for 50% growth inhibition (I50) of those test plants ranged from 3-282 mg dry weight equivalent extract/mL. The extract was then separated using a sequence of chromatographic fractionations and a growth inhibitory substance was isolated and identified by spectral analysis as methyl caffeate. Methyl caffeate inhibited the growth of lettuce and foxtail fescue at concentrations higher than 1.0 mM. The results suggest that methyl caffeate may contribute to the growth inhibitory effect of H. indicum and may play an important role in the allelopathic effect of H. indicum.

Leucas aspera (Lamiaceae), an aromatic herbaceous plant, is well known for many medicinal properties and a number of bioactive compounds against animal cells have been isolated. However, phytotoxic substances from L. aspera have not yet been documented in the literature. Therefore, current research was conducted to explore the phytotoxic properties and substances in L. aspera. Aqueous methanol extracts of L. aspera inhibited the germination and growth of garden cress (Lepidum sativum) and barnyard grass (Echinochloa crus-galli), and the inhibitory activities were concentration dependent. These results suggest that the plant may have phytotoxic substances. The extracts were then purified by several chromatographic runs. The final purification was achieved by reversed-phase HPLC to give an equilibrium (or inseparable) 3:2 mixture of two labdane type diterpenes (compounds 1 and 2). These compounds were characterized as (rel 5S,6R,8R,9R,10S,13S,15S,16R)-6-acetoxy-9,13;15,16-diepoxy-15-hydroxy-16-methoxylabdane (1) and (rel 5S,6R,8R,9R,10S,13S,15R,16R)-6-acetoxy-9,13;15,16-diepoxy-15-hydroxy-16-methoxylabdane (2) by spectroscopic analyses. A mixture of the two compounds inhibits the germination and seedling growth of garden cress and barnyard grass at concentrations greater than 30 and 3 μM, respectively. The concentration required for 50% growth inhibition (I50) of the test species ranges from 31 to 80 μM, which suggests that the mixture of these compounds, are responsible for the phytotoxic activity of L. aspera plant extract.

Tinospora tuberculata Beumee has been used widely as a folk medicine and several bioactive compounds have been isolated. However, no herbicidal compound has been reported in this species. Therefore, we investigated the presence of phytotoxins in T. tuberculata. The aqueous methanol extracts of T. tuberculata inhibited the growth of roots and shoots of cress (Lepidum sativum L.), lettuce (Lactuca sativa L.), timothy (Phleum pratense L.) and barnyard grass (Echinochloa crus-galli (L.) Beauv.). The extract was then purified by several chromatographic runs with monitoring the inhibitory activity and the main phytotoxic substance was isolated. The chemical structure of the compound was determined by spectral data as syringin (4-[(1E)-3-Hydroxyprop-1-en-1-yl]-2,6-dimethoxyphenyl β-d-glucopyranoside). It inhibited the root and shoot growth of all test plant species at concentrations >10 µM. The concentrations required for 50 % inhibition of root and shoot growth of cress and lettuce ranged from 78.2 to 412 μM, and that of timothy and barnyard grass renged from 9.8 to 73.2 µM. Effectiveness of syringin on monocotyledonous (timothy and barnyard grass) plants was greater than that on dicotyledonous (cress and lettuce) plants. These results suggest that syringin may contribute to the allelopathic effect caused by the T. tuberculata extract.

The weedy annual grass Lamium amplexicaule (L.) originated from the Mediterranean region, spreads quickly, and becomes naturalized in areas it invades. It was assumed that volatile phytotoxic substances are one of the invasive characteristics of L. amplexicaule. However, no volatile compound has been found. Therefore, we re-evaluated the allelopathic potential of L. amplexicaule and investigated the phytotoxic substances with allelopathic activity. An extract of L. amplexicaule inhibited the root and shoot growth of Lepidium sativum, Lactuca sativa, Arctium lappa, Lolium multiflorum Lam., Echinochloa crus-galli, and Vulpia myuros, which indicates that the extract has an allelopathic effect. The extract was purified using bioassay-guided chromatographic separations, and a phytotoxic substance with allelopathic activity was isolated and characterized as methyl caffeate. The compound significantly inhibited the root and shoot growth of L. sativum and L. multiflorum. The present results suggest that methyl caffeate may contribute to the allelopathic effect of the L. amplexicaule extracts and consequently, may be partly responsible for the invasive characteristics of the species.

Sugars are not only important energy sources and structural components, but they also act as signaling molecules that are involved in specific signal sensing. Among all ketohexose analogs (d-fructose, d-psicose, d-tagatose, d-sorbose, l-fructose, l-psicose, l-tagatose and l-sorbose), only d-psicose inhibited the growth of Arabidopsis roots. Phosphorylation by fructokinase occurred in d-fructose and d-psicose. d-Psicose-induced inhibition was relieved by adding d-fructose. Thus, the inhibition could not be attributed to the toxicity of phosphorylated d-psicose. The phosphorylation process requires ATP. After phosphorylation, d-fructose is metabolized in glycolysis and becomes energy sources and structural components, whereas d-psicose cannot contribute to the energy sources and structural components because it does not get metabolized further. However, d-psicose did not affect ATP level in the Arabidopsis roots, suggesting that the d-psicose-induced growth inhibition may not be related to the starvation of ATP. The phosphorylation of ketohexoses by fructokinase is known to a trigger signal-sensing resulting in growth inhibition. Therefore, d-psicose can be phosphorylated by fructokinase and this process may play a possible role in signal-sensing. This is probably one of the useful model systems for the study of the hexokinase-independent sugar-sensing function and for developing new types of weed-control agents.

Although momilactone is known to play an important role in the allelopathy of rice (Oryza sativa L.), there is no information available about the mode of action of momilactone on the allelopathy of Arabidopsis. The present research describes the allelopathic activity of momilactone A and B on the germination of Arabidopsis thaliana and the effects of momilactone A and B on protein expression during germination. Momilactone A and B inhibited the germination of Arabidopsis at concentrations >30 and 10 μmol L−1, respectively. The protein bands of 18, 19 and 21 kDa on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) were abundant in the momilactone A- and B-treated Arabidopsis compared with the control. The protein bands of 18, 19 and 21 kDa were identified by the N-terminal amino acid sequencing as cruciferin 2, cruciferina and cruciferin 3, respectively. Cruciferins and cruciferina are important storage proteins and play an important role as the initial source of nitrogen for seed germination. These results suggest that momilactone A and B may inhibit the germination of Arabidopsis seeds by inhibiting the degradation process of cruciferin and cruciferina.

Orthosiphon stamineus (Java tea) has been widely used as traditional herb and several bioactive compounds against animal cells have been isolated. However, no bioactive compound against plants has been reported. Therefore, we investigated possible allelopathic properties and substances in O. stamineus. Aqueous methanol extracts of O. stamineus inhibited root and hypocotyl growth of cress (Lepidium sativum) and lettuce (Lactuca sativa) seedlings. Increasing the extract concentration increased the inhibition, which suggests that O. stamineus may have allelopathic properties. When the extract was divided into an ethyl acetate and an aqueous fraction, the ethyl acetate fraction showed the stronger inhibitory effect. Thus, the ethyl acetate phase was further purified, and the main allelopathic substance was isolated and identified as 13-epi-orthosiphol N, a novel compound, by spectral data. 13-epi-Orthosiphol N inhibited root and hypocotyl growth of cress and lettuce at concentrations greater than 10 μmol/L. The concentrations required for 50% inhibition ranged from 41 to 102 μmol/L. These results suggest that 13-epi-orthosiphol N may be an allelochemical and main contributor to the growth inhibitory effect of O. stamineus and may have potential as a template for the development of new plant control substances.

The possible involvement of the chemical-mediated interaction in allelopathy between rice and barnyard grass was investigated. Effcts of rice seedlings and rice root exudate on the alleloapthic activity of barnyard grass were determined and a key compound invovled in the allelopathic interaction between rice and barnyard grass was isolated. Allelopathic activity of barnyard grass was increased by the presence of rice seedlings. Rice root exudates also elevated the allelopahtic activity of barnyard grass. A key compound, which increased the allelopathic activity of barnyard grass, in the rice root exudates was isolated and determined as momilactone B. Momilactone B increased the allelopathic activity of barnyard grass at concentrations greater than 3 μM, and increasing the momilactone B concentration increased the activity. Momilactone B is known to act as a potent rice allelochemical and to possess strong growth inhibitory activity against barnyard grass. The present research suggests that barnyard grass may response to the presence of neighboring rice by sensing momilactone B in rice root exudates and increase allelopathic activity. Thus, momilactone B may not only act as a rice allelochemical but also play an important role in rice-induced allelopathy of barnyard grass. The induced-allelopathy may provide a competitive advantage for barnyard grass through the growth inhibition of competing plant species including rice. Barnyard grass allelopathy may be one of the inducible defense mechanisms by chemical-mediated plant interaction between rice and barnyard grass. Rice allelopathy was also reported to be increased by the presence of barnyard grass through increasing production and secretion of momilactone B into surrounding environments. During the evolutional process, rice and barnyard grass may have developed the chemical cross talk to activate the defense mechanisms against some biotic stress conditions by detection of certain key compounds.

An organ-specific-growth inhibitory substance was isolated from an aqueous methanol extract of red pine needles and determined by spectral data as 1-mono(16-hydroxyhexadecanoyl)glycerol. This substance inhibited root growth of cress (Lepidium sativum L.) and barnyard grass (Echinochloa crus-galli (L.) Beauv) seedlings at concentrations greater than 0.01 and 0.03 μM, respectively. The concentrations required for 50 % growth inhibition on roots of cress and barnyard grass were 0.16 and 3.4 μM, respectively. However, the inhibitory activity of the substance on shoots of cress and barnyard grass was very weak. The endogenous concentration of 1-mono(16-hydroxyhexadecanoyl)glycerol in the pine needles was 4.6 μmol kg−1. Two related compounds, 1-monohexadecanoylglycerol and 16-hydroxyhexadecanlic acid had no activity up to 1,000 μM on cress roots and shoots. The effectiveness of 1-mono(16-hydroxyhexadecanoyl)glycerol on root growth inhibition and the occurrence of 1-mono(16-hydroxyhexadecanoyl)glycerol in pine needles suggest the substance may play an important role in the allelopathy of red pine. Root-specific-growth-inhibition by the substance may be one of the strategies for red pine to compete with neighboring plants for nutrients and space because root growth of competitive plants may be very important for their whole plant development.

A potent growth inhibitory substance was isolated from an aqueous methanol extract of cucumber (Cucumis sativus L. cv. Phung Tuong) plants and determined as (2S)-2,3-dihydro-2α-(4-hydroxy-3-methoxyphenyl)-7-methoxy-5-(1,2,3-trihydroxypropyl)benzofuran-3β-methanol (sisymbrifolin) by spectral data. Sisymbrifolin inhibited the growth of cress (Lepidium sativum) and Echinochloa crus-galli seedlings at concentrations greater than 3 μM. Concentration of sisymbrifolin in the cucumber plants was the greatest among four growth inhibitory substances, (S)-2-benzoyloxy-3-phenyl-1-propanol, 9-hydroxy-4,7-megastigmadien-9-one, (6S,7E,9S)-6,9,10-trihydroxy-4,7-megastigmadien-3-one, and sisymbrifolin found in the cucumber, whereas growth inhibitory activity of 9-hydroxy-4,7-megastigmadien-9-one against cress and E. crus-galli was the greatest. Total activities of these substances (concentration of the substance/concentration required 50 % growth inhibition) were 14.4, 13.2, 8.5 and 10.7 for (S)-2-benzoyloxy-3-phenyl-1-propanol, 9-hydroxy-4,7-megastigmadien-9-one, (6S,7E,9S)-6,9,10-trihydroxy-4,7-megastigmadien-3-one and sisymbrifolin, respectively. These total activities were about 100-fold greater than those of phenolic acids, which are often mentioned as putative allelochemicals of plants. Thus, these substances may play important roles in the allelopathy of cucumber plants through the growth inhibition of neighboring plant species.

Since red pine (Pinus densiflora Sieb. et Zucc.) often forms sparse forest floors where herbaceous plants do not grow well, allelopathy of red pine was investigated. A growth inhibitory substance was isolated from an aqueous methanol extract of red pine needles and determined by spectral data as abscisic acid-β-d-glucopyranosyl ester (ABA-GE). This substance inhibited root and shoot growth of cress and E. crus-galli seedlings at concentrations greater than 0.1 μM. The concentrations required for 50% growth inhibition on roots and shoots of cress were 0.23 and 0.61 μM, respectively, and those of E. crus-galli were 1.1 and 2.8 μM, respectively. The activity of ABA-β-d-glucosidase, which liberates free ABA from ABA-GE, in cress and E. crus-galli seedlings was 13–29 nmol mg−1 protein min−1. Endogenous concentration of ABA-GE in the pine needles was 4.1–21.5 μmol kg−1 and the concentration in soil water of the pine forest was 2.5 μM. The effectiveness of ABA-GE on growth inhibition and the occurrence of ABA-GE in pine needles and soil water suggest ABA-GE may play an important role in the allelopathy of red pine resulting in the formation of sparse forest floors.

Although d-glucose increased the root growth of Arabidopsis seedlings, d-allose (a d-glucose epimer at the third carbon atom) inhibited the root growth at concentrations >0.1 mmol L−1 and the inhibition increased with increasing d-allose concentrations. Allitol (a reduction product of d-allose) did not show any significant effect on the growth. The addition of d-glucose into the growth medium of Arabidopsis reversed the d-allose-induced growth inhibition, which suggests that the inhibition is not caused by the toxicity of the accumulation of d-allose and/or its metabolites in the seedlings. d-Allose is phosphorylated by hexokinase, using ATP and phosphate, to allose-6-phosphate, with no known capacity for further metabolism. The addition of phosphate into the growth medium did not affect the d-allose-induced growth inhibition and d-allose did not reduce the ATP level in the roots. These results suggest that the inhibition is not due to phosphate starvation and ATP depletion. d-Mannoheptulose, a specific competitive inhibitor of hexokinase, defeated the d-allose-induced growth inhibition. Hexokinase is known to have a sugar-sensing function and possibly triggers a signal cascade, resulting in the change of several gene expressions. Therefore, the phosphorylation of d-allose by hexokinase might trigger a signal cascade, resulting in the inhibition of Arabidopsis root growth. This is probably a useful model system for studies of the hexokinase-mediated sugar-sensing function and for developing new types of weed-control agents.

The root and coleoptile growth of aerobically germinated rice (Oryza sativa L.) seedlings was suppressed by anoxic stress, but the suppression was more conspicuous in roots than in coleoptiles. In this study, the physiological and metabolic responses of roots to anoxia were compared with those of coleoptiles in aerobically germinated rice seedlings. ATP concentration in the coleoptiles was higher than that in the roots under anoxia. Alcohol dehydrogenase activity and ethanol concentration in the coleoptiles were also higher than in the roots under anoxia, which suggest that ethanolic fermentation may be more active in the coleoptiles than in the roots where glycolysis and ethanolic fermentation are the main source of ATP production. Activity of α-amylase, which mobilized reserved starch in the seeds, was not detected in the roots and coleoptiles of rice seedlings either under aerobic or anoxic conditions. However, α-amylase activity was found in endosperms of the rice seedlings even under anoxia. The α-amylase activity in anoxic endosperms was 64% of that in aerobic endosperms. Sugar concentration in the anoxic coleoptiles was higher than that in the anoxic roots. ATP and ethanol concentrations in the roots and coleoptiles of rice seedlings were correlated well with sugar concentrations in the roots and coleoptiles, which also showed a good correlation with anoxia tolerance of roots and coleoptiles with respect to elongation. These results suggest that the sugar level may be important for the anoxia tolerance of the roots and coleoptiles since the availability of sugar is essential for the operation of ethanolic fermentation leading to ATP production under anoxia, and it may serve to distinguish the anoxia tolerance of the roots and coleoptiles of the rice seedlings.

Eight cultivars of rice (Oryza sativa L.) inhibited shoot and root growth of Echinochloa crus-galli when co-cultured with rice seedlings in a bioassay medium. Momilactone A and B were found in the bioassay medium of all rice cultivars, and concentrations of momilactone A and B in the medium were 0.21-1.5 and 0.66-3.8 micromol/L, respectively, indicating that all rice cultivars may secrete momilactone A and B into the medium. Exogenously applied momilactone A and B inhibited the growth of shoots and roots of E. crus-galli at concentrations greater than 30 and 1 micromol/L, respectively. The concentrations required for 50% growth inhibition of E. crus-galli shoots and roots, respectively, were 146 and 91 micromol/L for momilactone A and 6.5 and 6.9 micromol/L for momilactone B. Considering the growth inhibitory activity and concentrations found in the bioassay medium, momilactone A may have caused only 0.8-2.2% of the observed growth inhibition of E. crus-galli roots and shoots by rice. However, momilactone B in the medium was estimated to be able to cause 59-82% of the observed growth inhibition of E. crus-galli roots and shoots by the rice seedlings. In addition, the concentrations of momilactone B in the medium reflected the observed differences in the growth inhibition of E. crus-galli by the eight rice cultivars investigated. This suggests that the allelopathic activity of rice may depend primarily on the secretion level of momilactone B. Therefore, momilactone B may play a very important role in rice allelopathy.

The growth inhibitory activity of seven rice (Oryza sativa L.) cultivars and the secretion level of momilactone B from these rice cultivars were determined to understand chemical basis of the interaction of rice with other plant species. All rice cultivars inhibited the growth of hypocotyls and roots of lettuce (Lactuca sativa L.) seedlings when the lettuce was grown together with the rice, and showed different range of the inhibitory activity. These results suggest that all rice cultivars may possess allelopathic activity and the activity may be cultivar dependent. Momilactone B, which is a potent growth inhibitor, was found in root exudates of all rice cultivars, and the momilactone B concentration was also cultivar-dependent. The allelopathic activity of each rice cultivar was closely correlated with momilactone B concentration in the root exudates. The present results suggest that rice cultivars possess various allelopathic activities and their allelopathic activity may depend on the secretio...

Aqueous methanol extracts of rattail fescue (Vulpia myuros) inhibited the growth of roots and shoots of cress (Lepidium sativum), lettuce (Lactuca sativa), alfalfa (Medicago sativa), timothy (Phleum pratense), Digitaria sanguinalis and Lolium multiflorum. Increasing the extract concentration increased the inhibition, suggesting that rattail fescue may have growth inhibitory substances and possess allelopathic potential. The aqueous methanol extract of rattail fescue was purified and two main inhibitory substances were isolated and identified by spectral data as (−)-3-hydroxy-β-ionone and (+)-3-oxo-α-ionol. Both substances inhibited root and shoot growth of cress at concentrations greater than 0.3 μM. The concentrations required for 50% growth inhibition on root and shoot growth of cress, lettuce, alfalfa, timothy, D. sanguinalis and L. multiflorum were 2.7–19.7 μM for (−)-3-hydroxy-β-ionone, and 2.1–34.5 μM for (+)-3-oxo-α-ionol. The concentration of (−)-3-hydroxy-β-ionone and (+)-3-oxo-α-ionol, respectively, in rattail fescue was 7.8 and 3.7 μg g−1 fresh weight. Considering the endogenous level and the inhibitory activity, (−)-3-hydroxy-β-ionone and (+)-3-oxo-α-ionol may work as allelopathic substances in rattail fescue through the growth inhibition of neighboring plant species.

Summary Extract of soil under colonies of Hypnum plumaeforme inhibited the growth of roots and shoots of cress, lettuce, lucerne, ryegrass, timothy, Digitaria sanguinalis and Echinochloa crus-galli. Increasing the extract concentration increased the inhibition, which suggest that the soil may contain growth inhibitory substances and possess allelopathic potential. The extract of the soil under H. plumaeforme was purified and two main inhibitory substances were isolated and determined by MS and 1H- and 13C-NMR spectral data as momilactone A and B. Momilactone A and B inhibited hypocotyls and roots of cress seedlings at concentrations >10 and 1 μm respectively. The endogenous concentration of momilactone A and B in H. plumaeforme was 58.7 and 23.4 μg g−1 dry weight respectively and the concentration of momilactone A and B in MS growth medium of H. plumaeforme was 4.3 and 6.4 μg g−1 dry weight of H. plumaeforme, respectively. These results suggest that momilactone A and B were probably secreted into the medium during the incubation and momilactone A and B found in the soil under H. plumaeforme may have been released by the moss. Therefore, growth inhibitory activity of the soil under H. plumaeforme may be caused by momilactone A and B, which may act as allelopathic agents of H. plumaeforme.