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Biological invasions by alien and range-expanding native plant species can suppress native plants through allelopathy. However, the homeland security hypothesis suggests that some native plants can resist invasion by producing allelopathic compounds that inhibit the growth of invasive plants. Most research has focused on allelopathic interactions between individual native and invasive plant species, with less emphasis on how allelopathy helps entire native communities resist invasions. Additionally, limited knowledge exists about allelopathic interactions between range-expanding native species and recipient native communities, and their influence on invasion success. To bridge this knowledge gap, we conducted two greenhouse competition experiments to test reciprocal allelopathic effects between a native woody range-expanding species, Betula fruticosa , and a community of four native herbaceous species (Sanguisorba officinalis , Gentiana manshurica , Sium suave and Deyeuxia angustifolia) in China. We assessed whether B. fruticosa and the native community differed in their competitive effects and responses, and whether these were influenced by activated carbon, which neutralizes allelochemicals in the soil. Activated carbon reduced the suppressive effects of the native community on the above-ground biomass of B. fruticosa , which indicates that the native community exerted a strong allelopathic effect on B. fruticosa. In contrast, activated carbon only marginally enhanced the suppressive effects of B. fruticosa on the native community, which indicates that allelopathy is not the primary mechanism by which B. fruticosa exerts its suppression. Overall, these findings support the homeland security hypothesis and suggest that biotic resistance from the native herbaceous community may limit the invasion success of the woody range-expander B. fruticosa. [ABSTRACT FROM AUTHOR]

Simple Summary: The spread of large green algae in oceans causes green tides, particularly in the South Yellow Sea of China, where Ulva prolifera has led to the world's largest green tide events. This review looks at how allelopathy, a process where plants release chemicals to affect the growth and development of other plants, influences green tide dynamics. We focus on four main types of these allelochemicals—fatty acids, aldehydes, phenols, and terpenes—explaining how they influence the algae's growth and behavior. We also discuss new methods for quickly detecting these allelochemicals and how these methods can help monitor green tides. By combining allelochemical detection with advanced technologies like satellite observations and environmental DNA analysis, we can better understand and manage green tides. The proliferation of large green macroalgae in marine environments has led to the occurrence of green tides, particularly in the South Yellow Sea region of China, where Ulva prolifera has been identified as the primary species responsible for the world's largest green tide events. Allelopathy among plants is a critical factor influencing the dynamics of green tides. This review synthesizes previous research on allelopathic interactions within green tides, categorizing four extensively studied allelochemicals: fatty acids, aldehydes, phenols, and terpenes. The mechanisms by which these compounds regulate the physiological processes of green tide algae are examined in depth. Additionally, recent advancements in the rapid detection of allelochemicals are summarized, and their potential applications in monitoring green tide events are discussed. The integration of advanced monitoring technologies, such as satellite observation and environmental DNA (eDNA) analysis, with allelopathic substance detection is also explored. This combined approach addresses gaps in understanding the dynamic processes of green tide formation and provides a more comprehensive insight into the mechanisms driving these phenomena. The findings and new perspectives presented in this review aim to offer valuable insights and inspiration for researchers and policymakers. [ABSTRACT FROM AUTHOR]

Iris pallida Lam., also known as Sweetie Iris, is a perennial ornamental and medicinal plant that produces a wide range of secondary metabolites. The Sweetie Iris was recently reported to have high allelopathic properties with the potential to be explored in sustainable weed management. This study aimed to identify and evaluate the contributions of compounds involved in the inhibitory effects of the rhizome of Sweetie Iris. High-performance liquid chromatography (HPLC) analysis was used to determine the content of β-ionone in the rhizome of Sweetie Iris. The phytotoxicity of β-ionone was evaluated on lettuce (Lactuca sativa L.) and other test plants. The content of β-ionone in the crude extract of Sweetie Iris rhizome was found to be 20.0 mg g−1 by HPLC analysis. The phytotoxicity bioassay showed that β-ionone had strong inhibitory activity on the growth of lettuce (Lactuca sativa L.) and the other test plants, including Taraxacum officinale, Stellaria media, Eleusine indica, Amaranthus hybridus, Vicia villosa, and Brassica napus. At a concentration of 23.0 µg mL−1, β-ionone inhibited the growth of all test plant species treated. Therefore, β-ionone is an active compound among the other allelopathic substances contained in the rhizome of Sweetie Iris. [ABSTRACT FROM AUTHOR]

The present study was conducted in Department of Botany, Institute of Science, Nagpur, to investigate the allelopathic effects of Mexican poppy (Argemone mexicana L.) on wheat. Wheat is the most important edible cereal crop. Wheat can grow in a wide variety of soils and temperatures, but thrives in humid regions with 30-90 cm of precipitation. Argemone mexicana L. is a rapidly expanding weed and an important competitor of wheat (in terms of allelochemicals). Weed is one of major cause of crop production loss. The entire plants of Argemone mexicana L. were harvested, rinse with tap water to remove soil debris, roots are dried in shade which kept at 25 degrees celcius (±2) for 72 hours. To demonstrate the germination of seeds of two locally grown wheat varieties (Sharabati and Lokwan), five concentrations of different ratios of root aqueous extract were obtained. A bioassay of a petri dish was carried out to assess the allelopathic potential of Argemone mexicana L. on the germination of Triticum aestivum L. seeds. The water based root extracts of weeds were used for treatment. The differential inhibitory effect of Argemone mexicana L. on Sharbati and Lokwan variety of wheat was observed. [ABSTRACT FROM AUTHOR]

The secondary metabolites of indigenous plants have significant allelopathic inhibitory effects on the growth and development of invasive alien plants. Methyl palmitate (MP) and methyl linolenate (ML) were used as exogenous allelopathic substances. The research investigated the differences of inhibitory effects of MP and ML on the growth of seedlings of Alternantheraphiloxeroides, and calculated their morphological characteristics, biomass, physiological indicators and the response index (RI). The synthetical allelopathic index (SE) of 1 mmol/L MP was the smallest (− 0.26) and the allelopathic inhibition was the strongest; therefore, it was selected as a 13C-labeled allelochemical. The distribution of 1 mmol/L MP in different parts of A.philoxeroides and the correlation between the biomass ratios of roots, stems and leaves and the 13C content were studied by 13C stable isotope tracing experiments. Atom percent excess (APE) between roots, stems and leaves of A.philoxeroides treated with 1 mmol/L MP were significantly different in terms of magnitude, with leaves (0.17%) > roots (0.12%) > stems (0.07%). The root, stem and leaf biomass ratios of invasive weeds had great significant positive correlation with 13C content (p < 0.01, R2 between 0.96 and 0.99). This current research provides a new idea and method for the control of A.philoxeroides, but large-scale popularization remains to be studied. [ABSTRACT FROM AUTHOR]

The sustainable management of the environment and crop production in modern agriculture involves dealing with challenges from climate change, environmental pollution, depletion of natural resources, as well as pressure to cope with dependence on agricultural inputs. Balancing crop productivity with environmental sustainability is one of the main challenges for agriculture worldwide. The emergence of weeds resistant to synthetic herbicides generates huge economic losses, so unconventional weed control strategies, especially those based on ecological principles, are very much needed in modern agriculture. Incorporating a natural eco-friendly approach—allelopathy—as a tool in an integrated weed control plan by growing specific crops or spraying fields with extracts containing allelopathic compounds can significantly reduce the use of herbicides. Allelopathy is considered a multi-dimensional phenomenon occurring constantly in natural and anthropogenic ecosystems, by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of other organisms. The objective of this systematic literature review is to present a comprehensive overview of allelopathy, define this phenomenon, and classify allelochemicals. This paper also discusses and highlights recent advances, ongoing research, and prospects on plant allelopathy management practices applied in agriculture, and the underlying allelopathic mechanisms. The review suggested the holistic view of some allelochemicals as an ecological approach to integrated weed control and is an important contribution to future research directions of multidisciplinary programs, chemoinformatic tools, and novel biotechnology methods to plant breeding. [ABSTRACT FROM AUTHOR]

Improvements in agricultural productivity are required to meet the demand of a growing world population. Phytopathogens, weeds, and insects are challenges to agricultural production. The toxicity and widespread application of persistent synthetic pesticides poses a major threat to human and ecosystem health. Therefore, sustainable strategies to control pests are essential for agricultural systems to enhance productivity within a green paradigm. Allelochemicals are a less persistent, safer, and friendly alternative to efficient pest management, as they tend to be less toxic to non-target organisms and more easily degradable. Microalgae produce a great variety of allelopathic substances whose biocontrol potential against weeds, insects, and phytopathogenic fungi and bacteria has received much attention. This review provides up-to-date information and a critical perspective on allelochemicals from microalgae and their potential as biopesticides. [ABSTRACT FROM AUTHOR]

Alternanthera philoxeroides (Mart.) Griseb is a well-known invasive plant species worldwide. Cinnamomum camphora (L.) Presl. is a plant species that is rich in allelopathic substances which can impede the growth of many other plants. In this study, the allelopathic effects of C. camphora on the growth and development, and physiological-biochemical characteristics of A. philoxeroides were investigated. The findings revealed that the leaves of C. camphora exhibited the capability to suppress the asexual reproduction of A. philoxeroides. The addition of C. camphora leaves resulted in inhibition of the fresh weight, stem length, and stem node number of A. philoxeroides new stems, with the strength of inhibition increasing in proportion to the quantity of C. camphora leaves added. Furthermore, the inhibitory effect of C. camphora leaves on A. philoxeroides was significantly amplified under high temperatures (≥ 30°C). Two allelochemicals had strong inhibitory effects on the vegetative reproduction of A. philoxeroides. The inhibition intensities were all up to 100 % on stem vegetative propagation, were 90.40 % and 100 % on root vegetative propagation from camphor and linalool, respectively. Physiological-biochemical analyses of roots indicated that the two allelochemicals promoted the accumulation of hydrogen peroxide and MDA, disrupting the balance of antioxidant enzyme systems. The two allelochemicals had a strong inhibitory effect on CAT activity and a strong promoting effect on POD activity. The effect on SOD activity was greatly affected by the type and concentration of allelochemicals. Moreover, the two allelochemicals significantly inhibited the accumulation of osmotic regulating substance. The contents of soluble sugar, soluble protein, and proline were significantly down-regulated. In summary, the allelochemicals from C. camphora induced damage to biological membranes, disrupting antioxidant enzyme systems and inhibiting osmoregulation. This resulted in the retardation of growth, development, and potential mortality of A. philoxeroides. These findings would contribute to the knowledge base for A. philoxeroides prevention and control, and enrich the understanding of C. camphora allelopathic substances. [Display omitted] • The mixed treatment with C. camphora leaves effectively inhibited the vegetative propagation of A. philoxeroides. • Two allelochemicals exhibited potent inhibitory effects on the vegetative propagation of A. philoxeroides. • Two allelochemicals enhanced the accumulation of H 2 O 2 and MDA, disrupting the balance of antioxidant enzyme systems. • The allelochemicals significantly impeded the accumulation of osmotic regulating substances. [ABSTRACT FROM AUTHOR]

Recently, field crops with allelopathic activity have gained overwhelming importance in overcoming the adverse effects of chemical herbicides on the environment and the increasing weed resistance to herbicides. Among the many cover crops studied for their allelopathic activity, wheat has exhibited strong allelopathic activity against a wide range of weed species, as reported in the previous literature. Several previous studies have focused on identifying wheat allelochemicals responsible for the weed suppression effect. The current review represents details about the most critical and influential chemical groups, including benzoxazinoids and phenolic compounds. In addition, several methods have been reported to exploit wheat's ability to combat weeds, including growing wheat in a crop rotation, applying wheat residues as soil mulch, or exposing weeds to wheat aqueous extract. A general background is also provided about allelopathy and allelochemicals; their concept, importance, chemical groups, mode of action and environmental impacts. [ABSTRACT FROM AUTHOR]

In the present study, we aimed to demonstrate that allelopathic compounds from the cyanobacterium Phormidium sp. can induce the collapse of large populations of the cyanobacteria Microcystis aeruginosa Kützing Kützing. We employed several strains of this toxic cyanobacteria, from six different locations, in order to test for adaptive variation in resistance to allelochemicals. As a preliminary test to detect allelopathic effect, we performed bioassays with Phormidium allelochemicals against the different strains of M. aeruginosa at low population abundances. Then, we combined long-term competition experiments and mechanistic modelling with two purposes: (a) demonstrate that the inhibitory effect of Phormidium sp. against M. aeruginosa was due to allelopathy and not resource competition; (b) test the effectiveness of these allelochemicals at inducing the collapse of large populations of M. aeruginosa. Our results showed a strong allelopathic effect of Phormidium, which induced the collapse of large populations of M. aeruginosa, without evidence of differences in sensitivity between strains. We demonstrated that allelopathy (interference competition) can reverse the outcome predicted by resource competition (exploitation competition). These results are encouraging in order to take further steps in the development of a bioremediation method, based in Phormidium allelopathy, against blooms of toxic cyanobacteria. [ABSTRACT FROM AUTHOR]

Allelopathy is the releasing of allelopathic compounds by one plant species that inhibit the growth and development of neighboring plants of another species. Weed management in crops is challenging. Besides, weeds remove moisture, nutrients and harbor insects and diseases. Adopting manual weed management is in practice, but it is laborious and expensive. Further, availability of labour at crucial time remains unanswerable. Though, herbicides being effective in increasing yield, indiscriminate use of herbicides have resulted in serious ecological implications such as development of herbicide resistant weeds and weed shift. Recently, research attention has been focused to find out alternative strategies for chemical weed control in several crops. Reduction in herbicide use is one of major goals of modern agriculture and there is much emphasis on search for alternative weed management strategies that are cheap, safe and sustainable. Allelopathy is considered as an effective, economical and environment friendly weed management approach. The release of allelochemicals from leaves, flowers, seeds, stems and roots of living and decomposing plant materials can influence weed density and growth. Keeping this in view, the literature on various allelopathy concepts in weed management is reviewed in this paper [ABSTRACT FROM AUTHOR]

It is now essential to reduce the negative impacts of weed management and especially herbicide use. Weed-suppressive crop species/varieties hold promise for integrated and sustainable weed regulation. Competition for resources and allelopathy are the two main underlying mechanisms. Unlike competition, which is well studied and established, allelopathy by living crops remains a contentious mechanism. A major difficulty to demonstrate the effects of allelopathy in the field is to dissociate them from those of competition. Here, we systematically and quantitatively review the literature, searching for field-based evidence of the role of allelopathy (by root exudation of living crops) in weed regulation, independently of competition, focusing on studies comparing different varieties of a given crop species. Our critical literature analysis also aims to identify weaknesses and strengths in methodology, providing insights on optimal experimental designs and avenues for future research. Our main conclusions are: (1) in most articles, the role of crop competition is disregarded or not exhaustively studied. Consequently, contrary to authors' conclusions, it cannot be determined whether weed regulation is due to allelopathy and/or to competition. (2) Few articles provided convincing evidence of the presence/absence of allelopathy in the field. (3) To further investigate allelopathy in the field we recommend to (i) finely characterize crop competition by measuring traits in the field, (ii) assess crop allelopathic potential with complementary experiments in controlled conditions or by quantifying allelochemicals in the field, and (iii) quantify the contribution of each studied trait/mechanism in explaining weed regulation in the field with multiple regression models. In conclusion, the consistent use of the suggested guidelines, as well as alternative approaches (e.g., creation of varieties with deactivated allelopathic functions, development of process-based simulation models), may provide a basis for quantifying the role of allelopathy in the field and, subsequently, for designing weed management strategies promoting weed biological regulation. [ABSTRACT FROM AUTHOR]

Green tides have been increasing in frequency and severity in coastal areas in recent years, and thus, the adverse effects of green tides on the environment have attracted much research attention. Allelopathy is one of the most significant effects of green tide algae on the surrounding organisms. In this study, a series of experiments were developed to fully investigate the allelopathic effects of the green tide alga Ulva linza on two common coastal phytoplankton species and to isolate and identify the chemical compositions of the allelochemicals. Our results indicated that the fresh tissue, dry powder, and aqueous extracts all inhibited the population growth of the two experimental phytoplankton species, indicating the occurrence of allelopathy; further analysis of the allelochemicals identified multiple kinds of fatty acids as allelopathic compounds, in which the most abundant ones were hexadecanoic acid; 9Z, 12Z, 15Z-octadecatetrienoic acid; and 9E-octadecenoic acid. Our findings enrich the database for research on allelopathy between marine green tide algae and phytoplankton. Both algae and phytoplankton could increase their own competitive abilities during bloom formation, thereby changing the phytoplankton community structure. [ABSTRACT FROM AUTHOR]

Background and objectives: Integrated weed management in commercial wheat production is urgently needed due to increasing herbicide resistance and production costs. Benzoxazinoids (BXs), which include benzoxazinones and benzoxazolinones, are unique bioactive metabolites produced by certain members of the Poaceae including maize, wheat, rye and some dicots. BXs play important roles in plant defence and are causal agents of allelopathic interference. We investigated the role of genetics, environment and crop growth stage on BX abundance in the roots and rhizoplane of selected commercial wheat cultivars, and quantified their microbial transformation products (aminophenoxazinones) in roots and rhizosphere soils. Methods: Cultivar trials of competitive wheat (Triticum aestivum L.) genotypes were conducted in two moderate to low rainfall (449–572 mm) locations in southeastern Australia in 2015 and 2016. Replicated shoot, root, rhizoplane, and rhizosphere soil samples were collected for metabolic profiling at selected crop phenological stages, extracted and further analysed for known benzoxazinoid metabolites by liquid chromatography coupled with high resolution mass spectrometry. Results: Fifteen BXs and related microbially derived aminophenoxazinones were detected in wheat shoots, roots, rhizoplanes and rhizosphere soils in both years and locations. MBOA, HMBOA and HMBOA-Glc were the three most abundant BX metabolites in wheat tissues, with the heritage cultivar Federation producing the highest levels of MBOA. The phytotoxic aminophenoxazinones APO and AMPO were the most abundant BX microbial transformation products and were detected in wheat roots, rhizoplanes and rhizospheres. Abundance varied with cultivar, growth stage, location and year. Conclusions: Microbially-produced aminophenoxazinones generated from both heritage and modern wheat root exudates were detected and quantified in rhizosphere soils, with abundance dependent on cultivar, growth stage, and season. Concentrations of microbial metabolites APO, AMPO, and AAPO were higher in the rhizosphere of young wheat seedlings in contrast to that of mature plants suggesting that phenoxazinone production was upregulated early in the season. Our findings demonstrate that BX metabolites at all life stages of wheat potentially undergo rapid biotransformation to aminophenoxazinones under field conditions, resulting in ecologically relevant concentrations sufficient for weed suppression by certain wheat cultivars. [ABSTRACT FROM AUTHOR]

Microwave‐assisted extraction (MAE) of allelochemicals from germinated wheat (Triticum aestivum L.) seeds was optimized by using response surface methodology. Under the optimal conditions (temperature 70 °C, power 283 W, liquid/solid ratio 17 L kg–1 and time 20.0 min), the inhibitory rate of allelochemicals on cucumber (Cucumis sativus L.) seeds germination was 64.21±1.99%. Three main allelochemicals including p‐Hydroxybenzoic acid, 3‐methoxy‐4‐hydroxycinnamic acid, and 3,5‐dimethoxy‐4‐hydroxybenzoic acid were identified by liquid chromatography–tandem mass spectrometry (LC‐MS/MS) analysis. These allelochemicals significantly inhibited the growth of cucumber seeding and root. Furthermore, malondialdehyde (MDA) content increased and root vitality and amylase activity decreased after the treatment of allelochemicals. Glutathione (GSH) content, glutathione peroxidase (GSH‐Px), and glutathione transferase activities rose first and then fell with the allelochemicals concentration increased. These results suggested that the extract from germinated wheat seeds could inhibit the growth of cucumber by affecting the physiological and biochemical processes in cucumber. Core Ideas: Allelochemicals inhibited the growth of cucumber and induced its physiological stress.Main allelopathic compounds extracted by microwave‐assisted extraction were identified as three acids.Microwave‐assisted extraction exhibited the higher inhibitory activity on cucumber growth than that of ultrasound‐assisted extraction and solvent reflux extraction. [ABSTRACT FROM AUTHOR]

Mikania micrantha and Ipomoea cairica are two invasive plants widely distribute and seriously damage in Hainan island. In this study, the leaves extracts of two weeds were collected and determined for their allelopathic potentials on Chrysanthemum coronarium. The phytotoxicity bioassay showed that when the extract concentration was 50 and 100 mg/ml, the inhibited effects of M. micrantha on growth of C. coronarium were greater than by I. cairica. However, when the extract concertation at 400 mg/ml, the opposite inhibited effects were observed. We speculated this phenomenon was caused by different allelopathic compounds. Therefore, using gas chromatography–mass spectrometry, 19 and 23 compounds were identified respectively, benzoic acid and cinnamic acid were the main components in the two leaves extracts, which were selected to carry out the further bioassays. Subsequent bioassay results showed the effects of two allelochemicals on morphological index and chlorophyll content and POD activity were all negative to C. coronarium, whereas the content of MDA and activity of SOD, CAT represented adverse changes. Moreover, the inhibitions by cinnamic acid were generally greater than those by benzoic acid. Thus, the phenolic acids played the most crucial roles in the allelopathic effccts of M. micrantha and I. cairica leaves extracts. [ABSTRACT FROM AUTHOR]

In West Bengal, India, Desmostachya bipinnata L. Stapf (Poaceae), Parthenium hysterophorus L. (Asteraceae) and Alternanthera sessilis L. R. Br. ex DC. (Amaranthaceae), are three weeds with potential allelochemicals. An investigation therefore was carried out for the determination and evaluation of their allelopathic potential in terms of relative allelopathic potential. Allelochemicals in various concentrations [1:5, 1:10 and 1:20 (w/v)] of leaf extracts and leachates of the three weeds respectively were tested on Allium cepa root tips which is generally a very responsive bioassay material for sensing allelopathic property. Cytological evaluation of allelopathic potential is done by microscopic study of allelochemical induced alterations of cytological characters with particular reference to various anomalies during cell-division and chromosomal structural abnormalities like condensation, pole deviation, anaphase bridge, clumping, bi-nucleation, depurination, fragmentation, stickiness, multinucleate cells, late separation with micronuclei formation. Chromosomal Abnormality Index reveal that Desmostachya bipinnata> Parthenium hysterophorus > Alternanthera sessilis in terms of allelopathic potential inducing chromosomal abnormalities in Allium cepa root tips indicating that the monocotyledonous weed Desmostachya is more allelopathically vigorous than the other two dicotyledonous weeds- Parthenium and Alternanthera. Further research is thus required to know the interaction of other invasive dicotyledonous and monocotyledonous weeds on other weed and crop species giving newer dimensions to allelopathy research. [ABSTRACT FROM AUTHOR]

Both Heterosigma akashiwo and Phaeodactylum tricornutum have been reported to produce allelochemicals capable of inhibiting the growth of co-occurring microalgae. Here, potential allelopathy between H. akashiwo and P. tricornutum was evaluated using bi-algal culture, cell-free culture filtrate and a no-contact co-culturing system in nutrient-replete media. Experiments were also conducted in the no-contact co-culturing system under nutrient-limited conditions. In nutrient-replete bi-algal culture, the growth of P. tricornutum and H. akashiwo each tended to be strongly suppressed when the other species was inoculated at high cell densities. A mathematical model was used to simulate the growth interactions of the two species in bi-algal culture and showed that P. tricornutum outcompeted H. akashiwo over time with different initial cell densities under nutrient-sufficient conditions, indicating that P. tricornutum was more potent in allelopathy. Heterosigma akashiwo growth was inhibited both in the P. tricornutum culture filtrate and no-contact co-culturing system. This confirmed that the extracellular allelopathic compounds released by P. tricornutum were one of the sources of the H. akashiwo growth inhibition. Nutrient deficiency did not increase the extent of allelopathic activity of allelochemicals. [ABSTRACT FROM AUTHOR]

The effects of cover crops on weeds and the underlying mechanisms of competition, physical control and allelopathy are not fully understood. Current knowledge reveals great potential for using cover crops as a preventive method in integrated weed management. Cover crops are able to suppress 70–95% of weeds and volunteer crops in the fall‐to‐spring period between two main crops. In addition, cover crop residues can reduce weed emergence during early development of the following cash crop by presenting a physical barrier and releasing allelopathic compounds into the soil solution. Therefore, cover crops can partly replace the weed suppressive function of stubble‐tillage operations and non‐selective chemical weed control in the fall‐to‐spring season. This review describes methods to quantify the competitive and allelopathic effects of cover crops. Insight obtained through such analysis is useful for mixing competitive and allelopathic cover crop species with maximal total weed suppression ability. It seems that cover crops produce and release more allelochemicals when plants are exposed to stress or physical damage. Avena strigose, for example, showed stronger weed suppression under dry conditions than during a moist autumn. These findings raise the question of whether allelopathy can be induced artificially. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Some plants use allelopathy to compete against neighbouring plants, and the ability to induce allelopathic compound production in response to competition is hypothesized to be adaptive, as plants can save costs of metabolite production in the absence of competitors. However, whether plants induce allelopathy has rarely been explored so far. We studied the inducibility of polyacetylenes – putative allelopathic compounds in Solidago altissima – in response to competition. Polyacetylenes were found in natural soil surrounding S. altissima patches within the range of concentration known to inhibit competitor growth. Individual S. altissima plants with higher polyacetylene concentration in roots suppressed the growth of the competitor plants more, suggesting that root polyacetylene levels proximate plants' allelopathic capacity. Competition induced polyacetylenes in a context‐dependent manner: Whereas introduced Japanese and Australian populations of S. altissima had higher constitutive concentration of polyacetylenes than the native North American populations, inducibility was observed only in Australian plants, where the population is still at an early stage of invasion. Also, induction became more prominent under nutrient depletion, where enhanced allelopathy may be particularly beneficial for suppressing a competitor's exploitative capacity. Finally, we found weak evidence for a tradeoff between constitutive and induced polyacetylenes. The observed patterns suggest that allelopathic plants could respond to competition by inducing allelochemical production, but the benefit of such plasticity may vary across time and space. Shifts in competitor communities in introduced range over time may shape plant's plastic responses to competition, while variation in resource availability may alter competitive environment to influence the degree to which plants induce allelopathy. [ABSTRACT FROM AUTHOR]

Plants generate various secondary metabolites named as allelochemicals that can be release into the environment and influence the growth and development of other plants or the same plant. The potential allelopathic effect of maize (Zea mays L.) on seed germination, seedling growth and physiology was investigated with three medicinal plants (Platycodon grandiflorum A.DC, Scutellaria baicalensis Georgi and Salvia miltiorrhiza Bge) with different concentrations (0, 0.5%, 1.0%, 2.5%, 5.0%, 10.0%). Low concentrations (0.5%, 1.0%) of maize leaf aqueous extract stimulated the germination and seedling growth (root length, shoot height, fresh weight) of all receptor plants significantly. With the concentration of the aqueous extract increased, the stimulating effects gradually decreased, and even changed into inhibited. The aqueous leachate of maize leaves exerted different allelopathic effects on physiology of different test medicinal plants. For Platycodon grandiflorum A.DC, there was no significant difference in photosynthesis rate at all the tested concentration compared with control. In Scutellaria baicalensis Georgi the lower concentration (0.5%, 1.0%, 2.5%) of leachates stimulated the net photosynthesis rate, yet the higher concentration (5.0%, 10.0%) decreased the net photosynthesis rate, and all the tested concentration have inhibited effects on Salvia miltiorrhiza Bge and decreased its net photosynthesis rate. However, the content of soluble sugar and soluble protein of all receptor plants were stimulated by low concentrations (0.5%, 1.0%, 2.5%) of maize leaf aqueous extract. Allelopathy can affect the seed germination, early seedling growth and physiology of three medicinal plants. [ABSTRACT FROM AUTHOR]

Cyperus alternifolius (C. alternifolius) and Canna generalis (C. generalis) are widely used as artificial floating-bed (AFB) plants for water pollution control. This study evaluated the release of anti-cyanobacterial allelochemicals from both plants in AFB systems. A series of cyanobacterial assays using pure culture solutions and extracts of culture solutions of C. alternifolius and C. generalis demonstrated allelopathic growth inhibition of a cyanobacterium M. aeruginosa. After 45 days of incubation by the culture solutions, both final inhibitory rates of M. aeruginosa were more than 99.6% compared with that of the control groups. GC/MS analyses indicated the presence of a total of 15 kinds of compounds, including fatty acids and phenolic compounds, in both plants' culture solutions, which are are anti-cyanobacterial. These findings provide a basis to apply artificial floating-bed plants for cyanobacterial inhibition using allelopathic effects. [ABSTRACT FROM AUTHOR]

Allelopathy is very important for the scientific disposition of garden plants. To understand the allelopathic potential of Koelreuteria bipinnata Franch. var. integrifoliola, the germination of Agrostis tenuis Sibth., Festuca arundinacea Schreb. and Lolium perenne L. were determined under laboratory conditions. The results showed that root, stem and leaf aqueous extracts of K. bipinnata var. integrifoliola had allelopathic effects on all three turf grasses, and the allelopathic activity varied according to extract concentrations, test species, and extract sources. Lower extract concentrations did not affect or promoted the germination and initial seedling growth of turf grasses, but the highest concentrations almost had inhibitory effect. The order of allelopathic potentials of the three organs on germination of these receptors was root < stem < leaf. And at the highest concentration of leaf extract, the most strongly inhibition was found in A. tenuis, followed by F. arundinaces and then L. perenne. In addition, according to gas chromatography-mass spectrometry (GC-MS) analysis, the allelopathic potential compounds and their abundance in root, stem and leaf were obviously different. Therefore, the allelopathic compounds may responsible for allelopathy of K. bipinnata var. integrifoliola. These findings suggested that more attention should be paid to the leaf of K. bipinnata var. integrifoliola for the relative higher allelopathic effects. [ABSTRACT FROM AUTHOR]

Abstract: Invasive plant species such as Ludwigia hexapetala might have a competitive advantage if they produce allelopathically active compounds against primary producers. Both phytoplankton and plant community structure may be affected due to different, species‐specific sensitivity to allelochemicals. Moreover, such allelopathic interactions could vary over the year depending on (i) the plant's phenological stage and (ii) the abilities of the native macrophytes to suppress—or the non‐native macrophytes to stimulate—the non‐native macrophyte population. We tested the allelopathic effects of aqueous leaf extracts of L. hexapetala on the photosynthetic activity of three target phytoplankton strains (Scenedesmus communis, a toxic Microcystis aeruginosa strain and a non‐toxic Microcystis aeruginosa strain) over three seasons of development (spring, summer and autumn). We also tested seasonal allelopathic effects of aqueous leaf extracts of both L. hexapetala (i.e. the non‐native invasive species) and the native Mentha aquatica on L. hexapetala seed germination. Finally, we identified three main secondary compounds present in the aqueous leaf extracts of L. hexapetala and we tested each individual compound on the phytoplankton's photosynthetic activity and on L. hexapetala seed germination. We observed marked seasonal and species‐specific patterns of L. hexapetala allelopathy on phytoplankton. The photosynthetic activities of S. communis and the toxic M. aeruginosa strain were stimulated by L. hexapetala aqueous leaf extracts in autumn and spring, respectively, whereas the non‐toxic M. aeruginosa strain was strongly inhibited in these two seasons. In summer, photosynthesis of all phytoplankton strains was inhibited. The germination rate of L. hexapetala seeds was stimulated by both L. hexapetala and M. aquatica aqueous leaf extracts, especially in summer, concomitant with the strong negative effects observed on the three phytoplankton strains. Three flavonoid glycosides (myricitrin, prunin and quercitrin) were identified as the main secondary compounds present in the L. hexapetala aqueous leaf extracts. The photosynthetic activity of S. communis was slightly stimulated by the three compounds. The photosynthetic activity of the toxic M. aeruginosa strain was stimulated by myricitrin and quercitrin, whereas that of the non‐toxic M. aeruginosa strain was inhibited by prunin. Finally, the germination rate and the germination velocity of L. hexapetala seeds were stimulated by myricitrin and prunin. These findings suggest that L. hexapetala could favour the photosynthetic activity of toxic cyanobacteria in spring and reduce their photosynthetic activity in summer, potentially leading to drastic changes in the phytoplankton communities and therewith ecological functioning of invaded ponds. Moreover, the stimulation of its seed germination could give a strong competitive advantage to L. hexapetala, thus promoting its invasiveness. [ABSTRACT FROM AUTHOR]

Allelopathy offers potential for weed control through the production and release of allelochemicals from leaves, flowers, seeds, stems and roots. In this research, allelopathy potentials of ethanolic and aqueous extracts of Vinca rosea L. leaves were evaluated. Three extract concentrations, including 2.5, 5 and 10% (w/v) of both aqueous and ethanolic were prepared from a 10% w/v stock solution in a completely randomized design with three replications. Distilled water was used as negative control. The inhibitory effects of V. rosea extracts on seed germination, hypocotyl (the part of the stem of an embryo plant) and radicle (the part of a plant embryo that develops into the primary root) length and seedlings growth of five plants were tested. The plants were cucumber (Cucumis sativus), redroot amaranth (Amaranthus retroflexus), garden cress (Lepidium sativum), scale cereal (Secale montanum) and desphia herb (Descurainia sophia). Results showed that the 10% aqueous extracts on the A. retroflexus, D. sophia and L. sativum and 10% ethanolic extracts on the five tested plants inhibited seed germination completely. The 10% aqueous extract inhibited the hypocotyls lenght of L. sativum, A. retroflexus and D. sophia completely. The 10% aqueous and ethanolic extract of V. rosea inhibited the radicle lenght of L. sativum, A. retroflexus and D. sophia completely. The inhibitory effects of the V. rosea extract may be related to the presence of allelochemicals, including alkaloids, flavonoids and phenolic acids. The use of allelopathic materials into agricultural management may reduce the use of pesticides and lessen environmental side effects. [ABSTRACT FROM AUTHOR]

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With the exploration and development of the practical technology for prevention and control of harmful algae blooms (HABs), cyanobacterium Microcystis aeruginosa ( M. aeruginosa ) blooms have been an urgent problem in the area of water resources protection. Allelopathic algicides are regarded as potential natural resources to constrain HABs for their exclusive and efficient characteristics. Previously, the allelopathic effect of rice has received great attention, but most of them are focused on herbicides to inhibit barnyard grass. In the present study, the effect of algal cells treatment with different concentrations of the rice straw aqueous extract were tested. A continuous culture system was established and the results suggested that the doses of rice straw aqueous extract in the range from 4.0 to 10.0 g L −1 observably suppressed the growth of algae cells in a concentration-dependent way. After 9 days of treatment, the algae cells' metabolic activity decayed and the largest inhibition rate could be up to 98%, almost no algae growth was observed. In the case of eliminate the interference of nutrient elements, these results confirmed that rice straw aqueous extract may act as an algistatic agent. [ABSTRACT FROM AUTHOR]

Picocyanobacteria are extremely important organisms in the world's oceans and freshwater ecosystems. They play an essential role in primary production and their domination in phytoplankton biomass is common in both oligotrophic and eutrophic waters. Their role is expected to become even more relevant with the effect of climate change. However, this group of photoautotrophic organisms still remains insufficiently recognized. Only a few works have focused in detail on the occurrence of massive blooms of picocyanobacteria, their toxicity and allelopathic activity. Filling the gap in our knowledge about the mechanisms involved in the proliferation of these organisms could provide a better understanding of aquatic environments. In this review, we gathered and described recent information about allelopathic activity of picocyanobacteria and occurrence of their massive blooms in many aquatic ecosystems. We also examined the relationships between climate change and representative picocyanobacterial genera from freshwater, brackish and marine ecosystems. This work emphasizes the importance of studying the smallest picoplanktonic fractions of cyanobacteria. [ABSTRACT FROM AUTHOR]

Allelopathy determines the dynamics of plant species in different environments. Plants can release chemicals into the environment that suppress the growth and establishment of other plants in their vicinity, a process known as 'allelopathy'. Chemicals with allelopathic functions have other ecological roles, such as plant defence, nutrient chelation and regulation of soil biota in ways that affect decomposition and soil fertility. In this review we explore allelopathy in the context of environmental characteristics that control the production and release of allelochemicals in both natural and agricultural systems. This study highlights the current understanding of how evolution might affect the intensity and importance of allelopathic interactions. Understanding this biological phenomenon could help to understand the environmental changes caused by allelochemicals and summarizes the knowledge about the mechanisms of action of these compounds. [ABSTRACT FROM AUTHOR]

Macrophytes are known to release allelochemicals that have the ability to inhibit the proliferation of their competitors. Here, we investigated the effects of the fresh leaves of two magnoliophytes (Zostera noltei and Cymodocea nodosa) and thalli of the macroalgae Ulva rigida on three HAB-forming benthic dinoflagellates (Ostreopsis cf. ovata, Prorocentrum lima, and Coolia monotis). The effects of C. nodosa and U. rigida were also tested against the neurotoxic planktonic dinoflagellate Alexandrium pacificum Litaker sp. nov (former Alexandrium catenella). Co-culture experiments were conducted under controlled laboratory conditions and potential allelopathic effects of the macrophytes on the growth, photosynthesis and toxin production of the targeted dinoflagellates were evaluated. Results showed that U. rigida had the strongest algicidal effect and that the planktonic A. pacificum was the most vulnerable species. Benthic dinoflagellates seemed more tolerant to potential allelochemicals produced by macrophytes. Depending on the dinoflagellate/macrophyte pairs and the weight of leaves/thalli tested, the studied physiological processes were moderately to heavily altered. Our results suggest that the allelopathic activity of the macrophytes could influence the development of HAB species. [ABSTRACT FROM AUTHOR]

Despite increasing knowledge of the involvement of allelopathy in negative interactions among plants, relatively little is known about its action at the root level. This study aims to enhance understanding of interactions of roots between a crop and associated weeds via allelopathy., Based on a series of experiments with window rhizoboxes and root segregation methods, we examined root placement patterns and root interactions between allelopathic rice and major paddy weeds Cyperus difformis, Echinochloa crus-galli, Eclipta prostrata, Leptochloa chinensis and Oryza sativa (weedy rice)., Allelopathic rice inhibited growth of paddy weed roots more than shoots regardless of species. Furthermore, allelopathic rice significantly reduced total root length, total root area, maximum root width and maximum root depth of paddy weeds, while the weeds adjusted horizontal and vertical placement of their roots in response to the presence of allelopathic rice. With the exception of O. sativa (weedy rice), root growth of weeds avoided expanding towards allelopathic rice. Compared with root contact, root segregation significantly increased inhibition of E. crus-galli, E. prostrata and L. chinensis through an increase in rice allelochemicals. In particular, their root exudates induced production of rice allelochemicals. However, similar results were not observed in C. difformis and O. sativa (weedy rice) with either root segregation or root exudate application., The results demonstrate that allelopathic rice interferes with paddy weeds by altering root placement patterns and root interactions. This is the first case of a root behavioural strategy in crop-weed allelopathic interaction. [ABSTRACT FROM AUTHOR]

Potential allelopathic interactions betweenSkeletonema costatumandAlexandrium minutumwere investigated using mixed cultures and culture filtrate in nutrient-replete medium.A. minutumgrowth was inhibited when grown inS. costatumfiltrate, with the inhibitory effect directly proportional to the percentage of filtrate added. This demonstrates that the release of allelopathic compounds caused the growth inhibition. In contrast, the filtrate ofA. minutumexerted no allelopathic activity onS. costatum. An autoinhibitory compound (15(S)-HEPE) extracted and purified fromS. costatumculture was added to cultures of bothS. costatumandA. mintum. This substance could depressS. costatumgrowth, but showed no significant inhibitory activity onA. minutum. This documented a second type of allelochemical interaction, termed auto-allelopathy, caused by a different compound from the one or ones that affectedA. minutumin the co-cultures with added crude filtrate. Further studies are needed to explore the relative importance of these two types of allelopathy as factors influencing the competition betweenS. costatumandA. minutumin the field. Furthermore, given the observed decrease in diatom dominance relative to dinoflagellates with increasing eutrophication, one can predict that toxic species likeA. minutummight become more prevalent in the future in the East China Sea if the trend of increasing pollution of coastal waters continues. [ABSTRACT FROM AUTHOR]

β-cembrenediol ((1S,2E,4R,6R,7E,11E)-2,7,11-cembratriene-4,6-diol), shown to be one of the most important allelochemicals of tobacco in previous studies, effectively inhibited the root and stem growth of receptor plants and the inhibitory effects was concentration-dependent. However, its mechanism of action remains unclear. Seedlings of lettuce (Tai Yuan Sun) were treated with β-cembrenediol to clarify its mode of action. Results showed that β-cembrenediol significantly inhibited the seedling growth and reduced fresh weight of L. sativa. The compounds effectively affected cell mitotic index and caused cell death. Exposure to β-cembrenediol induced overproduction of reactive oxygen species (ROS). Moreover, increased content of hydrogen peroxide, malondialdehyde, and proline, and decreased in chlorophyll content indicated lipid peroxidation and induction of oxidative stress. These results suggested that β-cembrenediol caused oxidative damage through enhanced generation of ROS, as indicated by increased lipid peroxidation, disruption of membrane integrity and impacted mitosis, ultimately resulted in growth inhibition of the receptor plant. [ABSTRACT FROM AUTHOR]

Studying the influence of cogongrass (lmperata cylindrica L.) extract on germination and seedling growth of some weeds and crops indicated that the dicotyledonous weeds such as goosefoot and sowthistle were the most affected by the aqueous extract of cogongrass (rhizome and foliage) than the monocotyledonous crops, wheat and onion, based on IC50 values. Delay in germination was more pronounced in weeds than crops. Dry weight of wheat and onion seedlings were not significantly affected meanwhile the dry weight of goosefoot, fieldbind and sowthistle seedlings were significant, by,lower than control. Rhizome extract was generally more effective than foliage extract. Allelochemicals in cogongrass (rhizome and foliage) analyzed by liquid chromatography/mass spectrometry (LC/MS) were identified as phenolic compounds that included 3'-o-methyl-(-)-epicatechin-7-o-sulphate, vanillic, ferulic and coumaric acids in rhizome extract, in addition to (-)epigallocatechin- 3 ,5-digallate, caffeic and gallic in foliage extract. Chlorogenic acid was the principal phenolic compound in both extracts. These results suggest that cogongrass might have an inhibitory effect. Considering that cogongrass is an allelopathic plant might suggest its use as soil additive material for weed control and could also serve as natural herbicide. [ABSTRACT FROM AUTHOR]

In this study, we investigated the allelopathic interactions among five representative allelochemicals at different proportions using bloom-forming Microcystis aeruginosa as the test receptor. Binary or ternary mixtures of allelochemicals obtained three types of allelopathic interactions, i.e., synergistic, antagonistic, and additive effects. However, combinations of four or five allelochemicals only yielded antagonistic effects. Interestingly, the algal inhibition gradually increased with the tested period for all treatments. For instance, the synergistic interaction occurred with the mixture including coumarin + ρ-hydroxybenzoic acid at 80%:20%; the mixture on the 10th day showed 0.80 of algal inhibition. While the mixture comprised protocatechuic acid + stearic acid + ρ-aminobenzene-sulfonic acid at 33.3%:33.3%:33.3%, the additive interactions occurred and then the maximum algal inhibition (0.83) was acquired at the end of tested period. In conclusion, the joint effects of different allelochemicals depend on various factors such as the chemicals used, their respective proportions, the total concentration of the mixture, and the receptor species. Thus, it is necessary to consider the complexity of allelopathic interactions and the field conditions during the control and management of noxious cyanobacteria. [ABSTRACT FROM AUTHOR]

An effective, environmentally friendly, and eco-sustainable approach for removing harmful microalgae is exploiting the allelopathic potential of aquatic macrophytes. In this study, we simulated field pollution conditions in the laboratory to investigate algal inhibition by allelochemicals, thereby providing insights into field practices. We tested five allelochemicals, i.e., coumarin, ρ-hydroxybenzoic acid, protocatechuic acid, stearic acid, and ρ-aminobenzenesulfonic acid, and a typical green alga, Chlorella pyrenoidosa, under two conditions. In the unpolluted treatment, individual allelochemicals had strong algal inhibition effects, where coumarin and ρ-hydroxybenzoic acid had greater potential for algal inhibition than protocatechuic acid, stearic acid, and ρ-aminobenzenesulfonic acid based on the 50 % inhibitory concentration. However, when two or three allelochemicals were mixed in specific proportions, the algal inhibition rate exceeded 80 %, thereby indicating allelopathic synergistic interactions. Mixtures of four or five allelochemicals had weak effects on algal inhibition, which indicated antagonistic interactions. Furthermore, the presence of low lead pollution significantly reduced the antialgal potential of individual allelochemicals, whereas the allelopathic synergistic interactions with mixtures between two or three allelochemicals were changed into antagonistic effects by low pollution. In particular, the allelopathic antagonistic interactions between four or five allelochemicals were increased by pollution. The allelopathic performance of these five allelochemicals may depend on various factors, such as the chemical species, mixture parameters, and algal strain. Thus, we found that low level pollution reduced the allelopathic inhibition of microalgae by allelochemicals. Therefore, the control of algae by the direct addition of allelochemicals should consider various environmental factors. [ABSTRACT FROM AUTHOR]

Allelochemicals released by invasive plants contribute to the successful invasion of new habitats. However, the relationship between allelopathic effects and competitive ability of invasive plants has not been characterized. We quantified the neighbor effects of Wedelia trilobata (family: Asteraceae) and the allelopathic effects of its leaf litter on two Asteraceae competitor species (invasive Eupatorium catarium and non-invasive Lactuca sativa) and on its own ramet growth. The seed germination rate and seedling biomass of the two competitor species decreased following treatment with W. trilobata leaf extracts. When co-cultured with W. trilobata, the total biomass of the two competitor species significantly decreased regardless of whether leaf extracts were present. Under low plant density co-culture conditions, W. trilobata leaf extracts enhanced the inhibitory effects on E. catarium. In contrast, W. trilobata leaf extracts promoted the growth of W. trilobata adventitious roots, resulting in increased competitive ability. Therefore, W. trilobata growth was promoted by its own allelochemicals in leaf extracts, whereas the growth of the invasive and non-invasive competitors was inhibited by the same chemicals. These responses facilitated the invasion by W. trilobata. Our study demonstrates that leaf litter of invasive plants may inhibit the growth of neighboring species to enhance the competitive ability of the invasive plants during the early stages of invasion. [ABSTRACT FROM AUTHOR]

Marine sessile organisms often inhabit rocky substrata, which are crowded by other sessile organisms. They acquire living space via growth interactions and/or by allelopathy. They are known to secrete toxic compounds having multiple roles. These compounds have been explored for their possible applications in cancer chemotherapy, because of their ability to kill rapidly dividing cells of competitor organisms. As compared to the therapeutic applications of these compounds, their possible ecological role in competition for space has received little attention. To select the potential candidate organisms for the isolation of lead cytotoxic molecules, it is important to understand their chemical ecology with special emphasis on their allelopathic interactions with their competitors. Knowledge of the ecological role of allelopathic compounds will contribute significantly to an understanding of their natural variability and help us to plan effective and sustainable wild harvests to obtain novel cytotoxic chemicals. This review highlights the significance of studying allelopathic interactions of marine invertebrates in the discovery of cytotoxic compounds, by selecting sponge as a model organism. [ABSTRACT FROM AUTHOR]

Allelopathic interactions between macrophytes and zooplankton are important to understand the plankton dynamics in shallow waterbodies. Egeria densa is a native, perennial, submerged macrophyte in the tropical and subtropical zones of South America. It has been introduced to Central and North America and is now common in many Mexican lakes. This macrophyte produces chemical substances that negatively affect some phytoplankton species. However, it is not clear how zooplankton species adapt different life history strategies in the chemical presence of this macrophyte. Here, we tested the direct and indirect effects of allelochemicals released by E. densa on the population growth of Scenedesmus acutus and on the demographic variables of three species of Simocephalus, S. exspinosus, S. serrulatus and S. mixtus (via alga exposed to the macrophyte allelochemicals). To quantify the effect of E. densa on S. acutus we set up four treatments: control, artificial Egeria, natural Egeria and allelochemicals from Egeria. To test the allelochemical effects on Simocephalus species, we compared four treatments: Control, indirect effect (using S. acutus grown on Egeria-allelochemicals), direct effect (using Egeria-conditioned medium) and together with direct and indirect effects. Scenedesmus had the highest cell density in the presence of allelochemicals from Egeria, followed by controls. The specific algal growth rate (µ) between control and allelochemicals treatment was not significant (P<0.05). However, the µ of alga in the presence of artificial or natural Egeria was significantly lower than in controls or in treatments involving allelochemicals. The age-specific survivorship of the three cladoceran species was longer in treatments containing Egeria-conditioned medium. Cladocerans receiving Egeria conditioned-medium and algae cultured on macrophyte-allelochemicals also had a longer survivorship. Daily fecundity of S. serrulatus increased after reaching mid-age while S. expinosus and S. mixtus showed continuous reproduction starting from the first week. In general, Egeria-allelochemicals enhanced the age-specific reproductive output for all the three cladoceran species. The average lifespan of the three Simocephalus varied from 17 to 46 days, depending on the cladoceran species and treatment. S. serrulatus had lower lifespan compared to other two cladoceran species. For the three species, lifespan significantly increased in treatments containing macrophyte-conditioned medium + algae grown on the plant-allelochemicals; also under these conditions, both gross and net reproductive rates were significantly enhanced. This stimulatory effect was also evident in generation time (about 50% higher). The rate of population increase ranged from 0.23 to 0.38 per day for the three tested Simocephalus species but there were no significant differences (P>0.05) among treatments. Our results suggest that the biological activity as well as physical structure of E. densa had negative effects on S. acutus population growth but had stimulatory effects on the demography of Simocephalus. [ABSTRACT FROM AUTHOR]

The methanolic extracts of fresh fruiting bodies ofTuber melanosporum,T. aestivum,T. magnatumandT. borchiiwere evaluated for their free fatty acids (FFAs) content to test their contribution to truffle allelopathic activity. Linoleic acid was the major FFA detected in all truffle species. In addition to linoleic acid, oleic acid and palmitic acid were the other abundant FFAs in theTuberspp. extracts. Looking at the total production,T. melanosporumandT. aestivumsynthesized significantly higher amounts of all identified FFA thanT. magnatumandT. borchii.The allelopathic activity, based on the specific activity (EC50) of the identified compounds, was evaluated in the growth ofArabidopsis thaliana,Lotus corniculatus,Melica ciliataandSilene vulgaris. Linoleic acid had the lowest specific activity and palmitic acid had the highest. The black truffle extracts had a higher inhibitory activity than white truffles, and this could be explained by the high relative amount of FFAs in them. [ABSTRACT FROM PUBLISHER]

The invasion process ofAcacia dealbatais partially mediated by releasing allelochemicals that affect native plants and soil microbes. However, non-volatile chemical compounds responsible for the allelopathic effect remain unknown, even though the allelopathic potential of this species has been studied under Europe conditions. We examined the allelopathic potential of aqueous extracts obtained from different plant materials ofA. dealbata: litter from leaf, flowers, pods and seeds and fresh leaves and also litter extract's phytotoxicity evolution on germination and early seedling growth ofLactuca sativaL. Bioassays based on aqueous extracts and direct effect of plant materials showed that radicle length (RL), degree of root necrosis and germination percentage were the variables that gave the best prediction for assessing the inhibitory allelopathic effect. Chemical compounds present in all types of litter significantly reduced the hypocotyl and RL ofL. sativa. GC–MS analysis reveals the presence predominantly of resorcinol, maculosin and moretenone in leaves; stigmasterol,d-alpha-tocopherol quinone, and lupanin in pods; and methylp-anisate,p-anisyl alcohol, stigmasterol and anisal were identified in flowers. The inhibitory effect induced onL. sativaby the different plant parts supports the hypothesis thatA.dealbataexerts its allelopathic potential throughout its phenological cycle. [ABSTRACT FROM PUBLISHER]

Algae control by using allelochemicals secreted from plants is a safe and novel biological algal inhibiting technology. In this work, Hydrilla verticillata was cultivated with algae in coexisting systems, and its possible inhibitory effect and mechanism on planktonic algae were studied in eutrophic water. The results showed that 12 g L H. verticillata under nutrient sufficient conditions had an allelopathic inhibitory effect on planktonic algae at initial concentrations of 10, 10 and 10 cells mL, with an inhibitory ratio of 25.75, 38.49, and 58.17, respectively. H. verticillata played a role of 'promoting with low biomass while inhibiting with high biomass' on planktonic algae. The optimal biomass of H. verticillata for the growth inhibition of planktonic algae at initial concentration of 10 cells mL was 12 g L. H. verticillata produced possible inhibitory effects on Ankistrodesmus spirali, Closterium sp. , Ankistrodesmus angustus, Dactylococcopsis sp. and Microcystis aeruginosa of planktonic algae. The possible inhibitory effects shown in descending order were as A. spirali > Closterium sp. > A. angustus > Dactylococcopsis sp. > M. aeruginosa. However, little effect could be observed on Ankistrodesmus falcatus and Tetrasporales sp. It is predicted that allelochemicals of H. verticillata with algal inhibiting effect were as follows: compounds of lipid, acid, hexanol, amide and ketone. [ABSTRACT FROM AUTHOR]

Extensive use of synthetic pesticides has negative effects on the environment and on human and animal health. Knowledge of allelopathic interactions could provide powerful tools for a better exploitation of natural resources in the management of weeds and insects without using herbicides and insecticides. Therefore effect of two concentrations (0.1% and 0.2%) of Salvia sclarea L. aqueous extract on lipid peroxidation process, as well as the activity of the antioxidant enzymes (superoxid dismutase, guaiacol peroxidase, pyrogallol peroxidase and catalase) in leaves and roots of pepper (Capsicum annum L.) and black nightshade (Solanum nigrum L.) seedlings were examined. Our results showed that lower concentration of S. sclarea aqueous extract induced lipid peroxidation in black nightshade roots. The second aim was to evaluate effectiveness of aqueous extract as contact toxicant against whitefly (Trialeurodes vaporariorum). It was observed that aqueous extract with concentration of 0.1% showed toxic effect with 56.66% mortality. [ABSTRACT FROM AUTHOR]

With the rapid development of the seaweed industry in China, the scale and production of its commercial seaweed are ranked among the most significant worldwide. Consequently, the control of algal blooms, especially fouling diatoms, during macroalgae industrialisation is an important issue. Many diatom bloom studies have focused on physical and chemical controls, with limited economic and eco-friendly biological controls reported. In our study, Gracilaria bailiniae fresh thalli and aqueous extract profoundly suppressed Nitzschia closterium growth (50% inhibition concentration of the fourth day (IC 50–4 day) was 0.667 × 10−3 g·mL−1 and 3.889 × 10−3 g·mL−1, respectively). The cellular morphology changes of N. closterium exposed to the G. bailiniae aqueous extract were severe atrophies and plasmolysis and dissolution of endocellular structures. To explore more potential allelochemicals to control N. closterium , the intracellular compounds of G. bailiniae were detected and screened. Three organic acids (citrate, hydroxyethanesulfonic acid (HA) and taurine) had allelopathic potential against N. closterium. Our results showed that citrate and HA markedly suppressed N. closterium (IC 50–4 day : 1.035 mM and 1.151 mM, respectively); however, taurine poorly suppressed N. closterium (IC 50–4 day : 2.500 mM). Therefore, HA is one of the main allelopathic compounds in G. bailiniae. Further, the allelopathic mechanism of HA against the N. closterium photosynthetic system broke its photosynthetic apparatus (oxygen-evolving complex, reaction centres, the effective antenna size and the donor side of photosystem II) and hindered electron transport. The experimental results provide a new and eco-friendly strategy to control diatom blooms. • Gracilaria bailiniae fresh thalli and aqueous extract have allelopathic potential against the Nitzschia closterium. • Two organic acids (Citrate and Hydroxyethanesulfonic acid) were the main allelochemicals of the Gracilaria bailiniae intracellular compounds. • Hydroxyethanesulfonic acid could ruin the PSII system of Nitzschia closterium. [ABSTRACT FROM AUTHOR]

Allelopathy is the process whereby an organic chemical (allelochemical) released from one plant influences the growth and development of other plants. Allelochemicals produced by specific rice ( Oryza sativa L.) cultivars have potential to manage barnyard grass ( Echinochloa crus-galli L.), a major yield-limiting weed species in rice production systems in Asia and North America. In this study, isolation and identification of an allelopathic compound, N-trans -cinnamoyltyramine (NTCT), in a Vietnamese rice cultivar ‘OM 5930’ was accomplished through bioassay-guided purification using reversed-phase liquid chromatography coupled with spectroscopic techniques, including tandem mass spectrometry, high resolution mass spectrometry, as well as one-dimensional and two-dimensional 1 H NMR and 13 C NMR spectroscopy. The identified compound, NTCT is considered a β-phenylethylamine. NTCT inhibited root and hypocotyl growth of cress ( Lepidium sativum L.), barnyard grass and red sprangletop ( Leptochloa chinensis L. Nees) at concentrations as low as 0.24 μM. The ED 50 (concentration required for 50% inhibition) of NTCT on barnyard grass root and hypocotyl elongation were 1.35 and 1.85 μM, respectively. Results further demonstrated that mortality of barnyard grass and red sprangletop seedlings was >80% at a concentration of 2.4 μM of NTCT. By 20 days after transplanting, 0.425 nmol of NTCT per OM 5930 rice seedling was released into the culture solution. With concentrations of 42 μg g −1 fresh weight, production of NTCT in intact rice plants can be considered high. These findings suggest that developing plants of Vietnamese rice cultivar OM 5930 release NTCT and may be utilized to suppress barnyard grass in rice fields. The potency of NTCT may encourage development of this compound as a bio-herbicide. [ABSTRACT FROM AUTHOR]

Allelopathy may contribute to the formation of mono-dominant stands of exotic species, but the effects of allelochemicals can be highly conditional. We explored variation in the production of phenolics in leaves, accumulation of phenolics in soils, and the inhibitory effects of soils under an aggressive invader Prosopis juliflora across a range of invaded sites and potential mechanisms by which soils alter the effects of P. juliflora leaf litter. For eight sites in Northwest India we compared the concentration of total phenolics and the seedling growth of Brassica campestris in soils from beneath P. juliflora to that in soils collected away from P. juliflora canopies. We then explored these effects in detail in soils from two sites that differed substantially in texture by germinating seeds of B. campestris in these soils amended with P. juliflora macerated leaf leachate. Finally, we tested the effects of L-tryptophan in soils from these two sites on the seedling growth of B. campestris. Across all sites soil beneath P. juliflora contained higher levels of total phenolics and suppressed the growth of B. campestris than soil that was not under P. juliflora. We observed much variation among P. juliflora-invaded sites in the total phenolic levels of soils and the degree to which they suppressed B. campestris and the concentration of phenolics in soils significantly correlated with the root length of B. campestris when grown in these soils. Soil from two sites amended with P. juliflora macerated leachate suppressed seedling growth of B. campestris, with the effect being higher in sandy soil than sandy loam soil. In soil amended with leachate the strong suppression of B. campestris corresponded with much higher total phenolic and L-tryptophan concentrations. However, in other tests L-tryptophan did not affect B. campestris. Our results indicate that the allelopathic effects of P. juliflora can be highly conditional and that variation in soil texture might contribute to this conditionality. [ABSTRACT FROM AUTHOR]

The paralytic shellfish toxin (PST) producing dinoflagellate Alexandrium ostenfeldii forms dense, recurrent blooms during summer in shallow coastal areas of the Baltic Sea. We studied the intra-population variability of its allelochemical potency and the responses of co-occurring and potentially competing dinoflagellates to the allelochemicals. The lytic activity of 10 northern Baltic A. ostenfeldii strains was evaluated by their EC 50 values (i.e. the cell concentration yielding a 50% decline in cryptophyte density), which were found to vary between 236 and 1726 cells ml −1 . When co-occurring dinoflagellates ( Kryptoperidinium foliaceum , Levanderina fissa and Heterocapsa triquetra ) were exposed to filtrate of A. ostenfeldii , short-term (<1 h) responses of the target species after an initial immobilization were species-specific. Almost all of the K. foliaceum cells formed cysts, L. fissa cells lost their cell shape and lysed, whereas H. triquetra cells shed their thecae. After 24 h, K. foliaceum had returned into vegetative cells and the number of immotile L. fissa and H. triquetra cells had significantly decreased. The results indicate that A. ostenfeldii can disturb the growth of competing dinoflagellates by excreting allelochemicals at bloom concentrations and that co-occurring species may develop efficient means to escape and recover from the allelochemicals, allowing them to coexist with A. ostenfeldii . [ABSTRACT FROM AUTHOR]

Seedling emergence and stand establishment of crops following the allelopathic crops are often affected. When the crops are grown in rotation, they are influenced by allelopathy of preceding crop. In this study, consisting of three independent experiments, allelopathic effect of tobacco, rich in several allelochemicals, on the subsequent maize and mungbean crops was investigated. In first experiment, maize and mungbean were sown in field previously occupied by tobacco or was fallow. In second experiment, maize and mungbean were planted in pots after the harvest of tobacco. Whereas in third experiment, maize and mungbean seeds were soaked in water or 2 and 4 mM nicotine and were then sown in soil-filled pots. Stand establishment, leaf emergence and growth of maize were significantly improved when grown after tobacco, whereas in mungbean these characters were suppressed when grown after tobacco. Likewise external application of nicotine improved the emergence uniformity, seedling dry weight and chlorophyll contents in maize and suppressed these parameters in mungbean. Tobacco allelopathy also increased the total soil nitrogen, zinc, iron, nicotine and total phenolics. Nicotine-induced change in chlorophyll contents and α-amylase activity seems the possible reason of differential response of maize and mungbean to tobacco allelopathy. When grown in rotation with tobacco, stand establishment and growth of maize were improved, whereas mungbean stand and growth were suppressed. In crux, allelopathic nature of the crops must be considered while making the crop rotations. [ABSTRACT FROM AUTHOR]

A simple, effective, and green ion chromatography method with conductivity detection was developed for the determination of benzoic acid, cinnamic acid, syringic acid, and p-hydroxybenzoic acid in the root exudates of allelopathic rice. The analytes were well separated within 25 min in an anion exchange column (150 mm × 4.0 mm i.d., 5 µm particle size) with mixtures of 6.4 m mol L−1Na2CO3and 2.0 m mol L−1NaHCO3as the mobile phase at a flow-rate of 0.7 mL min−1. Detection limits of benzoic acid, cinnamic acid, syringic acid, and p-hydroxybenzoic acid were 0.05, 0.20, 0.50, and 0.05 µg mL−1, respectively. Intra- and inter-day precision was ≤4.0% and 3.2%, respectively, and the intra- and inter-day accuracy, indicated by relative error, ranged from −8.0% to 9.0%. The developed method was successfully used to determine phenolic acids in the root exudates of allelopathic rice. The average recoveries of the analytes were between 90.7% and 103.0%. [ABSTRACT FROM AUTHOR]