Isolation and identification of allelochemicals and their activities and functions.

Allelopathy is the interaction between donor plants and receiver plants through allelochemicals. According to a great number of publications, allelopathy may be involved in several ecological aspects such as the formation of monospecific stands and sparse understory vegetation for certain plant species. Allelopathy also contributes to the naturalization of invasive plant species in introduced ranges. Autotoxicity is a particular type of allelopathy involving certain compounds. Many medicinal plants have been reported to show relatively high allelopathic activity. We selected plant species that show high allelopathic activity and isolated allelochemicals through the bioassay-guided purification process. More than 100 allelochemicals, including novel compounds have been identified in some medicinal and invasive plants, plants forming monospecific stands, plants with sparse understory vegetation, and plants showing autotoxicity. The allelopathic activity of benzoxazinones and related compounds was also determined.

Isolation and Identification of Allelopathic Substances from Forsythia suspensa Leaves, and Their Metabolism and Activity.

The fruit of Forsythia suspensa (Thunb.) Vahl has been used in traditional Chinese medicine as "Forsythiae fructus". The species is also grown in parks and gardens, and on streets and building lots, as an ornamental plant, but it requires pruning. In this study, the allelopathic activity and allelopathic substances in the leaves of pruned branches of F. suspensa were investigated to determine any potential application. The leaf extracts of F. suspensa showed growth inhibitory activity against three weed species; Echinochloa crus-galli, Lolium multiflorum, and Vulpia myuros. Two allelopathic substances in the extracts were isolated through the bioassay-guided purification process, and identified as (-)-matairesinol and (-)-arctigenin. (-)-Matairesinol and (-)-arctigenin, which showed significant growth inhibitory activity at concentrations greater than 0.3 mM in vitro. The inhibitory activity of (-)-arctigenin was greater than that of (-)-matairesinol. However, both compounds were more active than (+)-pinolesinol which is their precursor in the biosynthetic pathway. The investigation suggests that F. suspensa leaves are allelopathic, and (-)-matairesinol and (-)-arctigenin may contribute to the growth inhibitory activities. Therefore, the leaves of the pruned branches can be applied as a weed management strategy in some agricultural practices such as using the leaf extracts in a foliar spray and the leaves in a soil mixture, thereby reducing the dependency on synthetic herbicides in the crop cultivation and contributing to developing eco-friendly agriculture.

Phytotoxicity and Phytotoxic Substances in Calamus tenuis Roxb.

Calamus tenuis is a shrub species distributed across South Asia. It grows well in diversified habitats and tends to dominate plants in the surrounding environment. The phytotoxicity of C. tenuis and the action of its phytochemicals against other plant species could explain its dominant behavior. Compounds with phytotoxic activity are in high demand as prospective sources of ecofriendly bioherbicides. Therefore, we investigated the phytotoxicity of C. tenuis. Aqueous methanol extracts of this plant species significantly limited the growth of four test plant species, two monocots (barnyard grass and timothy), and two dicots (alfalfa and cress), in a dose- and species-dependent manner. Bio-directed chromatographic isolation of the C. tenuis extracts yielded two major active substances: a novel compound, calamulactone {(S)-methyl 8-(5-oxo-2,5-dihydrofuran-2-yl) octanoate}, and 3-oxo-α-ionone. Both of the identified compounds exerted strong growth inhibitory effects on cress and timothy seedlings. The concentrations of 3-oxo-α-ionone and calamulactone required to limit the growth of the cress seedlings by 50% (I50) were 281.6-199.5 and 141.1-105.5 µM, respectively, indicating that the effect of calamulactone was stronger with lower I50 values. Similarly, the seedlings of timothy also showed a considerably higher sensitivity to calamulactone (I50: 40.5-84.4 µM) than to 3-oxo-α-ionone (I50: 107.8-144.7 µM). The findings indicated that the leaves of C. tenuis have marked growth-inhibitory potential, and could affect surrounding plants to exert dominance over the surrounding plant community. Moreover, the two identified phytotoxic substances might play a key role in the phytotoxicity of C. tenuis, and could be a template for bioherbicide development. This paper was the first to report calamulactone and its phytotoxicity.

Isolation and Identification of Plant-Growth Inhibitory Constituents from Polygonum chinense Linn and Evaluation of Their Bioherbicidal Potential.

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-ß-ionone and (-)-3-hydroxy-7,8-dihydro-ß-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-ß-ionone, respectively, and 0.42 and 1.29 mM for (-)-3-hydroxy-7,8-ß-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.

The Allelopathic Effects of Trewia nudiflora Leaf Extracts and Its Identified Substances.

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.

Evolution of the Secondary Metabolites in Invasive Plant Species Chromolaena odorata for the Defense and Allelopathic Functions.

Chromolaena odorata (L.) R.M. King & H. Robinson is native to tropical America, and has naturalized in many other countries in tropical Asia, Austria, and West Africa. The species often forms dense thickets and reduces the native species diversity and population in the invasive ranges. The species is also considered as a noxious weed in agriculture fields, and listed in the 100 of the world's worst invasive alien species. The characteristics of its life-history such as the seed production rate, growth pattern, and adaptative ability to the environmental conditions may contribute to the invasiveness of the species. Possible evidence of the defense capacity against the natural enemy, and the allelopathic potential against the competitive plant species for C. odorata has been accumulated in the literature over three decades. The extracts, residues, and/or rhizosphere soil of C. odorata increased the mortality of various insects and parasitic nematodes, and decreased their population. The extracts, residues, and/or rhizosphere soil of C. odorata also inhibited the germination and growth of several plant species including the indigenous plant species in the invasive ranges of C. odorata. Toxic substances, pyrrolizidine alkaloids were found in the leaves and flowers of C. odorata. These pyrrolizidine alkaloids may work as the defense agents against the natural enemies. Several potential allelochemicals such as flavonoids, phenolic acids, and terpenoids were also found in the plant extracts of C. odorata. Some of these compounds may work as allelopathic agents of C. odorata and inhibit the germination and growth of the competitive plant species. These characteristics of C. odorata for the defense function against their natural enemies such as insects and parasitic nematodes, and allelopathic potential against the competitive native plant species may contribute to the invasiveness and naturalization of C. odorata in the new habitats as invasive plant species. However, it is necessary to determine the concentration of these allelochemicals in the neighboring environment of C. odorata such as the rhizosphere soil since allelochemicals are able to work only when they are released into the neighboring environment. It is the first review article focusing on the defense function and allelopathy of C. odorata.

Allelopathic Substances of Osmanthus spp. for Developing Sustainable Agriculture.

Osmanthus fragrans Lour. has been cultivated for more than 2500 years because of the fragrance and color of the flowers. The flowers and roots have been used in tea, liquors, foods, and traditional Chinese medicine. The species contains more than 180 compounds including terpenoids, phenylpropanoids, polyphenols, flavonoids, and sterols. However, there has been limited information available on the allelopathic properties and allelopathic substances of O. fragrans. We investigated the allelopathy and allelopathic substances of O. fragrans and Osmanthus heterophyllus (G.Don) P.S. Green, as well as Osmanthus × fortunei Carrière, which is the hybrid species between O. fragrans and O. heterophyllus. The leaf extracts of O. fragrans, O. heterophyllus, and O. × fortunei suppressed the growth of cress (Lepidium sativum L.), alfalfa (Medicago sativa L.), Lolium multiflorum Lam., and Vulpia myuros (L.) C.C.Gmel with the extract concentration dependently. The extract of the hybrid species O. × fortune was the most active among the extracts. The main allelopathic substances of O. × fortunei and O. fragrans were isolated and identified as (+)-pinoresinol and 10-acetoxyligustroside, respectively. (+)-Pinoresinol was also found in the fallen leaves of O. × fortunei. Both compounds showed an allelopathic activity on the growth of cress and L. multiflorum. On the other hand, several allelopathic substances including (+)-pinoresinol may be involved in the allelopathy of O. heterophyllus. O. fragrans, O. heterophyllus, and O. × fortunei are evergreen trees. but their senescent leaves fall and cover the soil under the trees. It is possible that those allelopathic substances are liberated through the decomposition process of the leaves into their rhizosphere soil, and that they accumulate in the soil and provide a competitive advantage to the species through the inhibition of the growth of the neighboring competing plants. Therefore, the leaves of these Osmanthus species are allelopathic and potentially useful for weed management options in some agriculture settings to reduce commercial herbicide dependency for the developing sustainable agriculture systems.

Identification of four allelopathic compounds including a novel compound from Elaeocarpus floribundus Blume and determination of their allelopathic activity.

Allelopathic compounds can play a vital role in protecting the environment from pollution by synthetic herbicides. Compounds isolated from plant species with allelopathic potential can be used as natural herbicides to control weeds and help reduce environmental pollution. Elaeocarpus floribundus has been reported to contain allelopathic compounds. Aqueous methanolic extracts of the leaves of this plant showed strong growth inhibitory potential against two test species (monocotyledonous Italian ryegrass and dicotyledonous alfalfa) in plants- and dose-dependent technique. Several extensive chromatographic separations of the E. floribundus leaf extracts yielded four active compounds 1, 2, 3, and 4 (novel compound). All the identified compounds showed strong growth inhibitory potential against cress. The concentrations caused for 50% growth limitation (I50 values) of the cress seedlings were in the range 500.4-1913.1 µM. The findings indicate that the identified compounds might play a pivotal function in the allelopathic potential of E. floribundus tree. This report is the first on elaeocarpunone and its allelopathic potential.

Allelopathic Properties of Lamiaceae Species: Prospects and Challenges to Use in Agriculture.

Herbicide resistance due to the increasing reliance on herbicides is a near-term challenge for the world's agriculture. This has led to a desire to develop new herbicides with a novel mode of action, to address resistance in weed species. Lamiaceae, a large dicotyledonous plant family, is very well known for the multitudinous pharmacological and toxicological properties of its member species. Moreover, many species of this family are significant for their allelopathic activity in natural and laboratory settings. Thus, plants in Lamiaceae have the potential to be sources of alternative herbicides. However, gaps in our knowledge need to be addressed prior to adopting these allelopathic activities in agriculture. Therefore, we review the existing state of knowledge about the Lamiaceae family, the reported allelopathic properties of plant extracts, and their isolated allelochemicals under laboratory, greenhouse, and field conditions. In addition, we offer a perspective on existing challenges and future opportunities for adopting the allelopathic properties of Lamiaceae plant species for green agriculture.

Assessment of allelopathic activity of Tradescantia spathacea Sw. for weed control.

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 ≥ 3 mg 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 5.4-19.5 mg 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.

Three Active Phytotoxic Compounds from the Leaves of Albizia richardiana (Voigt.) King and Prain for the Development of Bioherbicides to Control Weeds.

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.

Allelopathic Potential and Active Substances from Wedelia Chinensis (Osbeck).

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 0.04-15.4 and 0.45-6.6 mM, respectively. The findings suggest that vanillic acid and gallic acid may be required for the growth inhibitory activities of Wedelia chinensis.

Potential use of Schumannianthus dichotomus waste: the phytotoxic activity of the waste and its identified compounds.

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.

Phytotoxic activity of crop residues from Burdock and an active substance.

Problems related to weed management such as outbreaks of herbicide-resistant weeds have recently increased. An interesting approach to such problems is to use plant materials with phytotoxic activity. Burdock (Arctium lappa L.) is a biennial herb belonging to Asteraceae and is cultivated in several countries. The present study investigated the phytotoxic activity of burdock and its active substances. Extracts of both burdock leaves and roots inhibited the shoot and root growth of cress and barnyard grass, where the level of inhibition increased with increasing extract concentration. The leaf extracts had 2.0-2.5 times higher activity than the root extracts. Bioassay-guided separations of the leaf extracts led to isolation of a phytotoxic substance, onopordopicrin. Onopordopicrin significantly inhibited the shoot and root growth of cress and barnyard grass. The concentrations of the substance required for 50% growth inhibition were 0.27 and 0.26 mM for cress shoots and roots, respectively, and 1.86 and 0.35 mM for barnyard grass shoots and roots, respectively. The present results suggest that burdock leaves have high phytotoxic activity and onopordopicrin may play a major role in the activity. Burdock leaves may be a good resource for weed management.

Allelopathic Potency and an Active Substance from Anredera cordifolia (Tenore) Steenis.

Anredera cordifolia (Tenore) Steenis is widely planted as an ornamental and medicinal plant in Indonesia. On the other hand, in some other countries this plant is classified as a noxious weed. As a harmful weed, A. cordifolia is reported to have the ability to smother all native vegetation, collapse canopies of tall trees, cultivate as a ground cover and disrupt native seedling development. There is no available information about the involvement of any allelochemicals from A. cordifolia related to these issues. The present study evaluated the allelopathic effect by isolating and identifying the allelopathic substance from A. cordifolia leaf extract. The allelopathic potency of A. cordifolia was determined by a series of bioassays of shoot and root growth on some selected test plants. Separation and purification of the active substances was achieved through several chromatography processes. Finally, the substances with allelopathic activity were identified through high-resolution electrospray ionization mass spectrometry (HRESIMS) analysis and determined by the specific rotation of compound, proton and carbon NMR spectroscopies. The results show that A. cordifolia possesses allelopathic properties which affect other plant species. The isolated compound from the plant material, 3-hydroxy-alpha-ionone, may contribute to the allelopathic effects of A. cordifolia.

Isolation and identification of a growth inhibitory substance from Heliotropium indicum L.

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.

Involvement of an autotoxic compound in asparagus decline.

Asparagus (Asparagus officinalis L.) is a widely cultivated perennial veritable and can be harvested more than ten years. However, the crop quality and yield decline after a few year's cultivation, which is called "asparagus decline". Even though those asparagus plants were replaced with new young asparagus plants, the productivity and quality of the crop remain relatively low, which is known as a "asparagus replant problem". One of the possible reasons for "asparagus decline" and "asparagus replant problem" is thought to be autotoxicity of asparagus. However, the compounds involved in the autotoxicity is not clear. The objective of this study was therefore to determine the potential role of autotoxicity in the "asparagus decline" and "asparagus replant problem". An aqueous methanol extract of 10-year-asparagus-cultivated soils inhibited the growth of asparagus seedlings and other two test plants with concentration dependent manner. The result confirmed that the asparagus soils have autotoxic activity. The extract was then purified by several chromatographies with monitoring the inhibitory activity and a potent growth inhibitory substance causing the autotoxic effect was isolated. The chemical structures of the compound was determined by spectral data to be trans-cinnamic acid. trans-Cinnamic acid inhibited the growth of asparagus seedlings at concentrations greater than 10 µM. The concentrations required for 50% growth inhibition of asparagus (IC50) were 24.1-41.6 µM. trans-Cinnamic acid accumulated 174 µM in the 10-year-asparagus-cultivated soils, which may be enough levels to cause the growth inhibition on asparagus considering its IC50 value. Therefore, trans-cinnamic acid may contribute to the autotoxic effect of asparagus soils, and may be in part responsible for "asparagus decline" and "asparagus replant problem".

Phytotoxic property of the invasive plant Tithonia diversifolia and a phytotoxic substance.

Tithonia diversifolia (Hermsl.) A. Gray is a perennial invasive plant and spreads quickly in the invasive areas. The extracts of T. diversifolia were found to be toxic to several crop plant species such as rice, maize, sorghum, lettuce and cowpea, and several putative allelopathic substances were identified. However, there is limited information available for the effects of T. diversifolia on wild plants including weed plant species. We investigated the allelopathic potential of T. diversifolia extracts on weed plants, and searched for phytotoxic substances with allelopathic activity. An aqueous methanol extract of T. diversifolia leaves inhibited the growth of weed plants, Lolium multiflorum Lam., Phleum pretense L., Echinochloa crus-galli (L.) Beauv. The extract was then purified by several chromatographic runs and a phytotoxic substance with allelopathic activity was isolated and identified by spectral analysis as tagitinin C. The substance inhibited the growth of Lolium multiflorum, Phleum pratense and Echinochloa crus-galli at concentrations greater than 0.1 - 0.3 mM. The present results suggest that T. diversifolia may possess allelopathic potential on weed plants and tagitinin C may be responsible for the allelopathic effects of T. diversifolia. The allelopathic potential of T. diversifolia may contribute to its invasive characteristics.

Suppression of reproductive characteristics of the invasive plant Mikania micrantha by sweet potato competition.

BACKGROUND: As a means of biologically controlling Mikania micrantha H.B.K. in Yunnan, China, the influence of sweet potato [Ipomoea batatas (L.) Lam.] on its reproductive characteristics was studied. The trial utilized a de Wit replacement series incorporating six ratios of sweet potato and M. micrantha plants in 25 m(2) plots over 2 years. RESULTS: Budding of M. micrantha occurred at the end of September; flowering and fruiting occurred from October to February. Flowering phenology of M. micrantha was delayed (P < 0.05), duration of flowering and fruiting was reduced (P < 0.05) and duration of bud formation was increased (P < 0.05) with increasing proportions of sweet potato. Reproductive allocation, reproductive investment and reproductive index of M. micrantha were significantly reduced (P < 0.05) with increasing sweet potato densities. Apidae bees, and Calliphoridae or Syrphidae flies were the most abundant visitors to M. micrantha flowers. Overall flower visits decreased (P < 0.05) as sweet potato increased. Thus the mechanism by which sweet potato suppressed sexual reproduction in M. micrantha was essentially two-fold: causing a delay in flowering phenology and reducing pollinator visits. The number, biomass, length, set rate, germination rate, and 1000-grain dry weight of M. micrantha seeds were suppressed (P < 0.05) by sweet potato competition. With proportional increases in sweet potato, sexual and asexual seedling populations of M. micrantha were significantly reduced (P < 0.05). The mortality of both seedling types increased (P < 0.05) with proportional increases in sweet potato. CONCLUSIONS: These results suggest that sweet potato significantly suppresses the reproductive ability of the invasive species M. micrantha, and is a promising alternative to traditional biological control and other methods of control. Planting sweet potato in conjunction with other control methods could provide a comprehensive strategy for managing M. micrantha. The scenario of controlling M. micrantha by utilizing a crop with a similar growth form may provide a useful model for similar management strategies in other systems.

A Potent Phytotoxic Substance in Aglaia odorata Lour.

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(™) .