Allelopathy--a natural alternative for weed control

Antimicrobial, Herbicidal and pesticidal potential of Tunisian eucalyptus species: Chemoprofiling and biological evaluation

The Eucalyptus genus, characterized by its imposing stature and fragrant foliage, has been a source of fascination for humanity over the centuries. The focus of the present investigation was directed towards the essentials oils (EOs) of five Eucalyptus trees cultivated in Tunisia. The GC-MS analysis unveiled unique compositional profiles, a finding substantiated by both Hierarchical Clustering Analysis (HCA) and Principal Component Analysis (PCA) conducted on the leaves EOs. These analyses resulted in the formation of discrete HCA clades, delineating 23 significant components. Notably, the percentage of eucalyptol emerged as the pivotal factor demarcating the separation between three distinct groups. The statistical analysis revealed a dose-dependent relationship in both phytotoxicity evaluation and antibacterial activity. The EOs from Eucalyptus loxophleba and E. salubris exhibited the highest phytotoxicity, inhibiting radical elongation and germination of various seeds, especially Sinapis arvensis and Raphanus sativus. The antimicrobial assessment demonstrated significant inhibitory effects of the EOs on bacterial strains, with MIC values spanning from 14 to exceeding 50 mg/ml. The EOs also affected biofilm formation and cellular metabolism, displaying varied efficacy among different Eucalyptus species against some bacterial strains. The EOs exhibited selective inhibition against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), α-amylase, and α-glucosidase. E. campaspe EO showed the highest AChE activity, while E. loxophleba and E. salubris EOs were most potent toward α-amylase. E. loxophleba EO demonstrated notable activity against α-glucosidase. Overall, these findings provide important data about the diverse biological activities of Eucalyptus EOs, suggesting potential applications in agriculture, medicine, and pharmacy.

Root uptake of cereal benzoxazinoids grants resistance to root-knot nematode invasion in white clover

Plants synthesize a plethora of chemical defence compounds, which vary between evolutionary lineages. We hypothesize that plants evolved the ability to utilize defence compounds synthesized and released by neighbouring heterospecific plants. In two experiments, we incubated clover (Trifolium repens L.) seedlings with individual benzoxazinoid (BX) compounds (2,4-dihydroxy-1,4-benzoxazin-3-one, 2-hydroxy-1,4-benzoxazin-3-one, benzoxazolinone, and 6-methoxy- benzoxazolin-2-one), a group of bioactive compounds produced by cereals, to allow clover BX uptake. Subsequently, we transplanted the seedlings into soil and quantified BX root and shoot content and invasion of root-knot nematodes in clover roots up to 8 weeks after transplantation. We show that clover root uptake of BXs substantially enhanced clover's resistance against the root-knot nematode Meloidogyne incognita. This effect lasted up to 6 weeks after the clover roots were exposed to the BXs. BXs were absorbed by clover roots, and then translocated to the shoots. As a result of clover metabolization, we detected the parent BXs and a range of their transformation products in the roots and shoots. Based on these novel findings, we envisage that co-cultivation of crop species with complementary and transferable chemical defence systems can add to plant protection.

Deciphering the Genetic Basis of Allelopathy in japonica Rice Cultivated in Temperate Regions Using a Genome-Wide Association Study

Allelopathy has been considered as a natural method of weed control. Despite the nature of allelochemical compounds has been studied, little is known about the genetic basis underlying allelopathy. However, it is known that rice exhibits diverse allelopathic potentials across varieties, and breeding for rice plants exhibiting allelopathic potential conferring an advantage against weeds in paddy fields would be highly desirable. Knowledge of the gene factors and the identification of the genomic regions responsible for allelopathy would facilitate breeding programs. Taking advantage of the existing genetic diversity in rice, particularly in temperate japonica rice, we conducted a comprehensive investigation into the genetic determinants that contribute to rice allelopathy. Employing Genome-Wide Association Study, we identified four Quantitative Trait Loci, with the most promising loci situated on chromosome 2 and 5. Subsequent inspection of the genes located within these QTLs revealed genes associated with the biosynthesis of secondary metabolites such as Phenylalanine Ammonia Lyase (PAL), a key enzyme in the synthesis of phenolic compounds, and two genes coding for R2R3-type MYB transcription factors. The identification of these two QTLs associated to allelopathy in rice provides a useful tool for further exploration and targeted breeding strategies.

(4Z)-Lachnophyllum Lactone, a Metabolite with Phytotoxic and Antifungal Activity against Pests Affecting Mediterranean Agriculture: A New Versatile and Easy Scalable Parallel Synthesis

A methodology for the total and modulable synthesis of (4Z)-lachnophyllum lactone (1), on a gram scale, is reported for the first time. The present work started with the design of a retrosynthetic pathway for the target compound, with the key step identified in Pd-Cu bimetallic cascade cross-coupling cyclization. (4Z)-Lachnophyllum lactone (1) is an acetylenic furanone previously isolated, in a low amount, from the organic extract of the autotrophic weedConyza bonariensis. Tested against the stem parasitic weed Cuscuta campestris in a seedling growth bioassay, (4Z)-lachnophyllum lactone (1) showed almost 85% of inhibitory activity up to 0.3 mM in comparison with the control. At the same concentration, the compound displayed radicle growth inhibitory activity of the root parasitic weeds Orobanche minor and Phelipanche ramosa higher than 70 and 40%, respectively. Surprisingly, the compound showed a high percentage of inhibition, up to 0.1 mM, on C. bonariensis seed germination too. This versatile synthetic strategy was also used to obtain two further natural analogues, namely, (4E)-lachnophyllum lactone (8) and (4Z,8Z)-matricaria lactone (9), that showed, in most cases, the same inhibitory trend with slight differences, highlighting the importance of the stereochemistry and unsaturation of the side chain. Furthermore, all of the compounds showed antifungal activity at 1 mM reducing the mycelial growth of the olive pathogen Verticillium dahliae. The design and implementation of scalable and modulable total synthesis on a gram scale of acetylenic furanones allow the production of a large amount of these natural products, overcoming the limit imposed by isolation from natural sources. The results of the present study pave the way for the development of ecofriendly bioinspired pesticides with potential application in agrochemical practices as alternative to synthetic pesticides.

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.

Allelopathy and Identification of Five Allelochemicals in the Leaves of the Aromatic Medicinal Tree Aegle marmelos (L.) Correa

Aegle marmelos (L.) Correa is an economically and therapeutically valuable tree. It is cultivated as a fruit plant in southeast Asian countries. In this research, we investigated the allelopathy and possible allelochemicals in the leaves of A. marmelos. Aqueous methanol extracts of A. marmelos exhibited significant inhibitory effects against the growth of Lepidium sativum, Lactuca sativa, Medicago sativa, Echinochloa crusgalli, Lolium multiflorum, and Phleum pratense. Bioassay-directed chromatographic purification of the A. marmelos extracts resulted in identifying five active compounds: umbelliferone (1), trans-ferulic acid (2), (E)-4-hydroxycinnamic acid methyl ester (3), trans-cinnamic acid (4), and methyl (E)-3'-hydroxyl-4'-methoxycinnamate (5). The hypocotyl and root growth of L. sativum were considerably suppressed by these compounds. Methyl (E)-3'-hydroxyl-4'-methoxycinnamate also suppressed the coleoptile and root growth of E. crusgalli. The concentrations of these compounds, causing 50% growth reduction (I50) of L. sativum, were in the range of 74.19-785.4 μM. The findings suggest that these isolated compounds might function in the allelopathy of A. marmelos.

The inhibitory potential of green manure return on the germination and seedling growth of Eleusine indica L

Trifolium repens L. (white clover) and Lolium perenne L. (ryegrass) are green manures widely used in conservation tillage systems worldwide. Eleusine indica L. (goosegrass) is a globally recognized noxious weed. Herein, we investigated the effects of aqueous extracts, decomposed liquids, and different straw-to-soil ratios on the germination and growth of goosegrass. The results showed that high concentrations (≥ 30%) of aqueous extracts or decomposed liquids of both green manures significantly inhibited germination-related parameters of goosegrass. The strongest inhibitory effect was observed for the 7-day decomposition treatment, and white clover's inhibitory effect was greater than ryegrass's. A pot experiment showed that non-photochemical quenching, catalase, and peroxidase activity levels of goosegrass leaves were significantly increased. At the same time, the net photosynthetic rate significantly decreased. Seedling growth was inhibited when the straw-to-soil ratio was greater than 3:100. The ryegrass treatments inhibited goosegrass seedlings more than the white clover treatments. This study demonstrated the inhibitory potential of white clover and ryegrass straw return on seed germination and seedling growth of goosegrass. The study has also helped to identify weed-resistant substances in these green manures so that their weed-control properties can be used more effectively and herbicide usage can be reduced.

The Invasive Mechanisms of the Noxious Alien Plant Species Bidens pilosa

Bidens pilosa L. is native to tropical America and has widely naturized from tropical to warm temperate regions in Europe, Africa, Asia, Australia, and North and South America. The species has infested a wide range of habitats such as grasslands, forests, wetlands, streamlines, coastal areas, pasture, plantations, agricultural fields, roadsides, and railway sides and has become a noxious invasive weed species. B. pilosa forms thick monospecific stands, quickly expands, and threatens the indigenous plant species and crop production. It is also involved in pathogen transmission as a vector. The species was reported to have (1) a high growth ability, producing several generations in a year; (2) a high achene production rate; (3) different biotypes of cypselae, differently germinating given the time and condition; (4) a high adaptative ability to various environmental conditions; (5) an ability to alter the microbial community, including mutualism with arbuscular mycorrhizal fungi; and (6) defense functions against natural enemies and allelopathy. The species produces several potential allelochemicals such as palmitic acid, p-coumaric acid, caffeic acid, ferulic acid, p-hydroxybenzoic acid, vanillic acid, salycilic acid, quercetin, α-pinene, and limonene and compounds involved in the defense functions such as 1-phenylhepta-1,3,5-trine, 5-phenyl-2-(1-propynyl)-thiophene, 5-actoxy-2-phenylethinyl-thiophene, and icthyothereol acetate. These characteristics of B. pilosa may contribute to the naturalization and invasiveness of the species in the introduced ranges. This is the first review article focusing on the invasive mechanisms of the species.

Allelopathic studies with furanocoumarins isolated from Ducrosia anethifolia. In vitro and in silico investigations to protect legumes, rice and grain crops

Six different furanocoumarins were isolated from the aerial parts of Ducrosia anethifolia and tested in vitro for plant cell elongation in etiolated wheat coleoptile. They were also tested for their ability to control three different weeds: ribwort plantain, annual ryegrass, and common purslane. These compounds exhibited strong inhibition of plant cell elongation. In the case of (+)-heraclenin, the IC50 was lower than 20 μM, indicating a better inhibition than the positive control Logran®. Computational experiments for docking and molecular dynamics revealed for the investigated furanocoumarins bearing an epoxide moiety an improved fitting and stronger interaction with the auxin-like TIR1 ubiquitin ligase. Furthermore, the formed inhibition complex remained also stable during dynamic evaluation. Bidental interaction at the active site, along with an extended hydrogen-bond lifetime, explained the enhanced activity of the epoxides. The in vitro weed bioassay results showed that Plantago lanceolata was the most affected weed for germination, root, and shoot development. In addition, (+)-heraclenin displayed better inhibition values than positive control even at 300 μM concentration.

Aquatic plant allelochemicals inhibit the growth of microalgae and cyanobacteria in aquatic environments

Excess nitrogen and phosphorus nutrients in the aquatic environment result in the growth of algal cells and water eutrophication, which adversely affect the aquatic environment and human health. Therefore, discovering a safe and efficient algae suppression method is necessary to ensure the ecological safety of water. Recently, the allelopathic effects of aquatic plants on algae have attracted extensive attention from researchers. This review demonstrates the current research hotspot of allelopathic algal inhibition in aquatic plants and lists the common aquatic plant species and allelochemicals. In addition, the inhibition mechanism of allelochemicals from aquatic plants on algae is systematically discussed. Moreover, the key factors affecting the inhibition of allelopathy in algae, such as pH, temperature, algal cell density, and concentration of allelochemicals, are summarized. The present utilization modes of allelochemicals on algae are also presented. Finally, the problems existing in the study of allelopathic algal inhibition of aquatic plants are highlighted, and suggestions for further research are proposed.

Caccinia macranthera Brand var. macranthera: Phytochemical analysis, phytotoxicity and antimicrobial investigations of essential oils with concomitant in silico molecular docking based on OPLS force-field

This study was conducted to extract the essential oils (EOs) of Caccinia macranthera identify their phytochemicals, evaluate their phytotoxicity, antimicrobial activity and enzyme inhibition effects using in silico molecular docking technique. EOs of aerial parts, seeds, and roots of C. macranthera were extracted and analyzed via Gas chromatography-Mass Spectrometry. The antibacterial activity of EOs were determined on nine microorganisms via disk diffusion and microbroth dilution assays. In addition, the allelopathic properties of EOs were investigated by calculating the IC50s for inhibition of germination, seedling length and seedling weight growth of Cuscuta campestris seeds. In order to assess the possible inhibitory effect of major components of C. macranthera EOs on enzymes inhibiting germination and plant growth, molecular docking was employed against the glutamine synthetase (GS), acetohydroxyacid synthetase (AHAS), and 4-hydroxyphenyl pyruvate dioxygenase (HPPD) enzymes. The main compounds of EOs from aerial parts, seeds, and roots EOs were dihydrocarveol (29.5%), Trimethyl-2-Pentadecanone (13.6%), and Palmitic acid (16.8%), respectively. The maximum antibacterial effect was related to the aerial parts EO against Staphylococcus epidermidis. Phytotoxicity analysis exhibited a concentration-dependent increase (p ≤ 0.05) activity. The aerial parts EO demonstrated a substantial allelopathy effect, with IC50 values of 0.22 ± 0.026, 0.39 ± 0.021, and 0.20 ± 0.025 mg/mL, respectively, on inhibitory germination, seedling length and seedling weight growth of Cuscuta campestris seeds. Molecular docking analyzes showed that Oleic acid was suitable for dynamic stabilization of HPPD (-6.552 kJ/mol) and GS (-7.265 kJ/mol) and Eupatoriochromene had the inhibitory potential against AHAS, with docking score of -4.189 kJ/mol. The current research demonstrated that C. macranthera EOs from its aerial parts have an acceptable phytotoxic activity against Cuscuta campestris weed. The major components of EOs, Oleic acid and Eupatoriochromene, presented the strongest binding with HPPD, GS, and AHAS active sites causing disturbance in germination, photosynthesis and weed growth suggesting it as a natural herbicide for controlling the weeds.

Allelopathic Activity of a Novel Compound, Two Known Sesquiterpenes, and a C13Nor-Isopenoid from the Leave of Croton oblongifolius Roxb. for Weed Control

Investigation of allelopathic substances from herbal plants may lead to the development of allelochemical-based natural herbicides. Croton oblongifolius (Roxb.) is a well-known herbal plant with a long history of being used for traditional medicines and for being the source of a diverse range of bioactive compounds. This plant has been reported to have allelopathic potential; however, its allelopathic-related substances have not yet been described. Therefore, we conducted this investigation to explore the allelopathic substances from the leaves of C. oblongifolius. Aqueous methanol extracts of C. oblongifolius leaves exhibited significant growth inhibitory potential against four test plants (monocot barnyard grass and timothy, and dicot cress and lettuce). The leaf extracts were purified in various chromatographic steps and yielded four active compounds identified as (3R,6R,7E)-3-hydroxy-4-7-megastigmadien-9-one (I), 2-hydroxy alpinolide (a novel compound) (II), alpinolide (III), and epialpinolide (IV) via an analysis of the spectral data. These identified compounds significantly restricted the seedling growth of cress. The concentration necessary for 50% growth reduction of the cress seedlings varied from 0.15 to 0.24 mM for (3R,6R,7E)-3-hydroxy-4-7-megastigmadien-9-one, 0.04 to 0.11 mM for 2-hydroxy alpinolide, 0.07 to 0.12 mM for alpinolide, and 0.09 to 0.16 mM for epialpinolide. Therefore, the leaf extracts of C. oblongifolius and the characterized compounds have the potential to be used as weed-suppressive resources for natural weed control.

The Impact and Invasive Mechanisms of Pueraria montana var. lobata, One of the World's Worst Alien Species

Pueraria montana var. lobata is native to East Asia, and was introduced to many countries due to its potential for multiple uses. This species escaped under the management conditions soon after its introduction, and became a harmful weed species. This species has been listed in the top 100 of the world's worst invasive alien species. P. montana stands expand quickly and threaten the native flora and fauna including microbiota. This species affects the concentration of carbon and nitrogen in soil and aquatic environments, and increases the amount of pollutants in the local atmosphere. Its infestation also causes serious economic losses on forestry and agriculture. Its characteristics of fast growth, thick canopy structure, enormous vegetative reproduction, and adaptative ability to the various environmental conditions may contribute to the invasiveness and naturalization of this species. The characteristics of P. montana regarding their defense functions against their natural enemies and pathogens, and allelopathy may also contribute to the invasiveness of this species. Potential allelochemicals such as xanthoxins, p-coumaric acid, caffeic acid, methyl caffeate and daidzein, and two isoflavones with anti-virus activity were identified in this species. In addition, fewer herbivore insects were found in the introduced ranges. These characteristics of P. montana may be involved in the invasive mechanisms of the species. This is the first review article focusing on the invasive mechanisms of this species.

Invasive Alien Species as a Potential Source of Phytopharmaceuticals: Phenolic Composition and Antimicrobial and Cytotoxic Activity of Robinia pseudoacacia L. Leaf and Flower Extracts

Black locust (Robinia pseudoacacia L.), an invasive tree in Europe, commonly known for its negative impact on biodiversity, is a rich source of phenolic compounds recognized in traditional medicine. Since the metabolite profile depends on the environment and climate, this study aimed to provide the first LC-MS phytochemical screening of the black locust from the Istria region (Croatia). The compounds were extracted from leaves and flowers with 70% ethanol and 80% methanol. Total phenolics (TP) and flavonoids (TF), as well as antioxidant capacity (AC) measured by ABTS (17.49-146.41 mg TE/g DW), DPPH (24.67-118.49 mg TE/g DW), and FRAP (7.38-77.53 mg TE/g DW) assays, were higher in leaf than in flower extracts. Higher TP and total non-flavonoid (TNF) values were displayed in ethanolic than in methanolic extracts. In total, 64 compounds were identified, of which flavonols (20) and hydroxycinnamic acid derivatives (15) were the most represented. Flavanols such as catechin dominated in leaf extracts, followed by flavonols, with kaempferol glucuronyl rhamnosyl hexosides as the main compound, respectively. Flower extracts had the highest share of flavones, followed by ellagitannins, with luteolin dirhamnosyl hexosides and vescalagin, respectively, being predominant. The extracts had good quorum sensing, biofilm formation prevention, and eradicating capacity. The results provided new insights into the phytochemical properties of R. pseudoacacia as the first step toward its potential pharmaceutical use.

Advances in the Biosynthesis of Terpenoids and Their Ecological Functions in Plant Resistance

Secondary metabolism plays an important role in the adaptation of plants to their environments, particularly by mediating bio-interactions and protecting plants from herbivores, insects, and pathogens. Terpenoids form the largest group of plant secondary metabolites, and their biosynthesis and regulation are extremely complicated. Terpenoids are key players in the interactions and defense reactions between plants, microorganisms, and animals. Terpene compounds are of great significance both to plants themselves and the ecological environment. On the one hand, while protecting plants themselves, they can also have an impact on the environment, thereby affecting the evolution of plant communities and even ecosystems. On the other hand, their economic value is gradually becoming clear in various aspects of human life; their potential is enormous, and they have broad application prospects. Therefore, research on terpenoids is crucial for plants, especially crops. This review paper is mainly focused on the following six aspects: plant terpenes (especially terpene volatiles and plant defense); their ecological functions; their biosynthesis and transport; related synthesis genes and their regulation; terpene homologues; and research and application prospects. We will provide readers with a systematic introduction to terpenoids covering the above aspects.

Two different anti-algal control mechanisms in Microcystis aeruginosa induced by robinin or tannin rich plants

Phytochemical is considered an alternative method for cyanobacterial bloom control in aquatic environments. When cyanobacteria are treated with anti-algal materials produced from plant tissues, they tend to exhibit growth inhibition or necrosis of cells. These different anti-algal responses have not been well discussed, and thus, the modes of anti-algal action in cyanobacteria remain obscure. In this study, transcriptomic and biochemical researches were conducted to understand the mechanisms of cyanobacterial growth inhibition and necrosis in harmful cyanobacterial cells exposed to allelopathic materials. The cyanobacteria Microcystis aeruginosa was treated with aqueous extracts of walnut husk, rose leaf, and kudzu leaf. Walnut husk and rose leaf extracts induced mortality of cyanobacterial population with cell necrosis, whereas kudzu leaf extract exhibited poorly grown cells with shrunk size. Through RNA sequencing, it was revealed that the necrotic extracts significantly downregulated critical genes in enzymatic chain reactions for carbohydrate assembly in the carbon fixation cycle and peptidoglycan synthesis. Compared to the necrotic extract treatment, expression of several genes related to DNA repair, carbon fixation, and cell reproduction was less interrupted by the kudzu leaf extract. Biochemical analysis of cyanobacterial regrowth was performed using gallotannin and robinin. Gallotannin was identified as the major anti-algal compound in walnut husk and rose leaf affecting cyanobacterial necrosis, whereas robinin, which is the typical chemical in kudzu leaf, was associated with growth inhibition of cyanobacterial cells. These combinational studies using RNA sequencing and regrowth assays provided evidence supporting the allelopathic effects of plant-derived materials on cyanobacterial control. Furthermore, our findings suggest novel algicidal scenarios with different responses in the cyanobacterial cells depending on the type of anti-algal compounds.

How to build a lichen: from metabolite release to symbiotic interplay

Exposing their vegetative bodies to the light, lichens are outstanding amongst other fungal symbioses. Not requiring a pre-established host, 'lichenized fungi' build an entirely new structure together with microbial photosynthetic partners that neither can form alone. The signals involved in the transition of a fungus and a compatible photosynthetic partner from a free-living to a symbiotic state culminating in thallus formation, termed 'lichenization', and in the maintenance of the symbiosis, are poorly understood. Here, we synthesise the puzzle pieces of the scarce knowledge available into an updated concept of signalling involved in lichenization, comprising five main stages: (1) the 'pre-contact stage', (2) the 'contact stage', (3) 'envelopment' of algal cells by the fungus, (4) their 'incorporation' into a pre-thallus and (5) 'differentiation' into a complex thallus. Considering the involvement of extracellularly released metabolites in each phase, we propose that compounds such as fungal lectins and algal cyclic peptides elicit early contact between the symbionts-to-be, whereas phytohormone signalling, antioxidant protection and carbon exchange through sugars and sugar alcohols are of continued importance throughout all stages. In the fully formed lichen thallus, secondary lichen metabolites and mineral nutrition are suggested to stabilize the functionalities of the thallus, including the associated microbiota.

Novel and holistic approaches are required to realize allelopathic potential for weed management

Allelopathy, that is, plant-plant inhibition via the release of secondary metabolites into the environment, has potential for the management of weeds by circumventing herbicide resistance. However, mechanisms underpinning allelopathy are notoriously difficult to elucidate, hindering real-world application either in the form of commercial bioherbicides or allelopathic crops. Such limited application is exemplified by evidence of limited knowledge of the potential benefits of allelopathy among end users. Here, we examine potential applications of this phenomenon, paying attention to novel approaches and influential factors requiring greater consideration, with the intention of improving the reputation and uptake of allelopathy. Avenues to facilitate more effective allelochemical discovery are also considered, with a view to stimulating the identification of new compounds and allelopathic species. Synthesis and Applications: We conclude that tackling increasing weed pressure on agricultural productivity would benefit from greater integration of the phenomenon of allelopathy, which in turn would be greatly served by a multi-disciplinary and exhaustive approach, not just through more effective isolation of the interactions involved, but also through greater consideration of factors which may influence them in the field, facilitating optimization of their benefits for weed management.

Allelopathy: an alternative tool for sustainable agriculture

Population increase, poverty, environmental degradation, and the use of synthetic herbicides are interdependent and closely linked and hence influence global food safety and stability of world agriculture. On the one hand, varied weeds, insects, and other pests have caused a tremendous loss in agricultural crop productivity annually. On the other hand, the use of synthetic insecticides, herbicides, fungicides, and other pesticides significantly disturbed the ecology of biotic communities in agricultural and natural ecosystems. Eventually, it destroyed the ecological balance in food chains. Interestingly, natural products released by the plants (allelochemicals) are secondary metabolites involved in ecological interactions and could be an important source of alternative agrochemicals. Mainly released by the plants as an outcome of acquaintances with other plants in their vicinity, these allelochemicals can also be used as eco-friendly substitutes for synthetic herbicides and other pesticides. Despite these facts, agrochemicals are either preferred over allelochemicals or the latter are not known in the direction of their use in achieving sustainability in agriculture. Given this, considering recent reports, this paper aims to: (1) emphasize allelochemicals; (2) overview the major biochemistry of allelochemicals; (3) critically discuss the role of allelopathy (and underlying major mechanisms) in the management of noxious weeds, insect pests, and major plant pathogens; and (4) enlighten the significant aspects so far not or least explored in the current context.

Antibacterial and Antibiofilm Effects of Allelopathic Compounds Identified in Medicago sativa L. Seedling Exudate against Escherichia coli

In this study, the allelopathic properties of Medicago sativa L. (alfalfa) seedling exudates on the germination of seeds of various species were investigated. The compounds responsible for the allelopathic effects of alfalfa were identified and characterized by employing liquid chromatography ion mobility high-resolution mass spectrometry. Crude exudates inhibited the germination of seeds of all various plant species tested. Overall, nine compounds in alfalfa were identified and quantified. The most predominant compounds were a hyperoside representing a flavonoid glucoside, the non-proteinogenic amino acid canavanine, and two dipeptides, identified as H-Glu-Tyr-OH and H-Phe-Glu-OH. The latter corresponds to the first finding that dipeptides are exuded from alfalfa seedlings. In addition, the antibacterial and antibiofilm activities of alfalfa exudate and its identified compounds were elucidated. Both hyperoside and canavanine revealed the best antibacterial activity with minimum inhibitory concentration (MIC) values that ranged from 8 to 32 and 32 to 256 µg/mL, respectively. Regarding the antibiofilm action, hyperoside and canavanine caused a decline in the percentage of E. coli isolates that possessed a strong and moderate biofilm-forming potential from 68.42% to 21.05% and 31.58%, respectively. Studies on their inhibiting effects exhibit that these major substances are predominantly responsible for the allelopathic and antimicrobial effects of the crude exudates.

Bioherbicidal Activity and Metabolic Profiling of Allelopathic Metabolites of Three Cassia species using UPLC-qTOF-MS/MS and Molecular Networking

INTRODUCTION

Compared to synthetic herbicides, natural products with allelochemical properties can inhibit weed germination, aiding agricultural output with less phytotoxic residue in water and soil.

OBJECTIVES

To identify natural product extracts of three Cassia species; C. javanica, C. roxburghii, and C. fistula and to investigate the possible phytotoxic and allelopathic potential.

METHODS

Allelopathic activity of three Cassia species extracts was evaluated. To further investigate the active constituents, untergated metabolomics using UPLC-qTOF-MS/MS and ion-identity molecular networking (IIMN) approach was performed to identify and determine the distribution of metabolites in different Cassia species and plant parts.

RESULTS

We observed in our study that the plant extracts showed consistent allelopathic activity against seed germination (P < 0.05) and the inhibition of shoot and root development of Chenopodium murale in a dose-dependent manner. Our comprehensive study identified at least 127 compounds comprising flavonoids, coumarins, anthraquinones, phenolic acids, lipids, and fatty acid derivatives. We also report the inhibition of seed germination, shoot growth, and root growth when treated with enriched leaf and flower extracts of C. fistula, and C. javanica, and the leaf extract of C. roxburghii.

CONCLUSION

The present study recommends further evaluation of Cassia extracts as a potential source of allelopathic compounds in agricultural systems.

Is the Phytotoxic Effect of Digestive Fluid of Nepenthes x ventrata on Tomato Related to Reactive Oxygen Species?

The digestive fluid of pitcher plants is a rich source of enzymes and secondary metabolites, but its impact on higher plant growth and development remains unknown. The aim of the study was to determine the phytotoxicity of the digestive fluid of the pitcher plant (Nepenthes x ventrata) on the germination of tomato (Solanum lycopersicum L.) seeds, elongation growth and cell viability of roots of tomato seedlings. The digestive fluid was collected from pitchers before feeding and four days after feeding; the pH and electrical conductivity of the fluid were determined. Undiluted and 50% fluids were used in the study. An inhibition of germination of tomato seeds, by around 30% and 55%, was respectively observed in 50% and 100% digestive fluids collected before and after feeding. Digestive fluid did not affect the root growth of tomato seedlings; a slight (6%) inhibition was only observed after the application of 100% digestive fluid from an unfed trap. The roots of the tomato seedlings treated with undiluted fluid were characterized by reduced cell viability. Reactive oxygen species (H₂O₂ and O₂^•-) were mainly localized in the root apex regardless of the used phytotoxic cocktail, and did not differ in comparison to control plants.

Sustainable agricultural practices for food security and ecosystem services

The notion of food security is a global phenomenon that impinges on every human. Efforts to increase productivity and yields have historically degraded the environment and reduced biodiversity and ecosystem services, with the significant impact on the poor. Sustainable agriculture-farming in sustainable ways based on an understanding of ecosystem services-is a practical option for achieving global food security while minimizing further environmental degradation. Sustainable agricultural systems offer ecosystem services, such as pollination, biological pest control, regulation of soil and water quality, maintenance of soil structure and fertility, carbon sequestration and mitigation of greenhouse gas emissions, nutrient cycling, hydrological services, and biodiversity conservation. In this review, we discuss the potential of sustainable agriculture for achieving global food security alongside healthy ecosystems that provide other valuable services to humankind. Too often, agricultural production systems are considered separate from other natural ecosystems, and insufficient attention has been paid to how services can flow to and from agricultural production systems to surrounding ecosystems. This review also details the trade-offs and synergies between ecosystem services, highlights current knowledge gaps, and proposes areas for future research.

Chemical Composition, Phytotoxic and Antibiofilm Activity of Seven Eucalyptus Species from Tunisia

This study was carried out to characterize the chemical composition of the essential oils from seven Eucalyptus species (E. griffithsii, E. hemiphloia, E. lesouefii, E. longicornis, E. pyriformis, E. viminalis, and E. wandoo), as well as their phytotoxic and antibacterial activities. The essential oils were analyzed by GC/MS and the potential in vitro phytotoxicity was evaluated against germination and radical elongation of Raphanus sativus, Lolium multiflorum, and Sinapis arvensis seeds. The antibiofilm activity was studied against both Gram-negative (Pseudomonas aeruginosa, Escherichia coli and Acinetobacter baumannii) and Gram-positive (Staphylococcus aureus and Listeria monocytogenes) bacteria. The inhibition of biofilm formation and its metabolism was determined at different times. Eucalyptol was the most abundant component in all essential oils studied (ranging from 40.8% for E. lesouefii EO to 73.6% for E. wandoo) except for that of E. pyriformis where it was present but at 15.1%. E. pyriformis was the most active against both germination and radical elongation of S. arvensis. The action of all essential oils proved to be highly effective in inhibiting the bacterial adhesion process of the five strains considered. In light of these results, these essential oils could have potential applications both in the agricultural and health fields.

Clover Root Uptake of Cereal Benzoxazinoids (BXs) Caused Accumulation of BXs and BX Transformation Products Concurrently with Substantial Increments in Clover Flavonoids and Abscisic Acid

Metabolomic studies on root uptake and transformation of bioactive compounds, like cereal benzoxazinoids (BXs) in non-BX producing plants, are very limited. Therefore, a targeted mass-spectrometry-based metabolomics study was performed to elucidate the root uptake of BXs in white clover (Trifolium repens L.) and the impact of absorbed BXs on intrinsic clover secondary metabolites. Clover plants grew in a medium containing 100 μM of individual BXs (five aglycone and one glycoside BXs) for 3 weeks. Subsequently, plant tissues were analyzed by liquid chromatography-tandem mass spectrometry to quantify the BXs and clover secondary metabolite concentrations. All BXs were taken up by clover roots and translocated to the shoots. Upon uptake of 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), 2-hydroxy-1,4-benzoxazin-3-one (HBOA), and 2-β-d-glucopyranosyloxy-1,4-benzoxazin-3-one (HBOA-glc), the parent compounds and a range of transformation products were seen in the roots and shoots. The individual BX concentrations ranged from not detected (nd) to 469 μg/g of dry weight (dw) and from nd to 170 μg/g of dw in the roots and shoots, respectively. The root uptake of BXs altered the composition of intrinsic clover secondary metabolites. In particular, the concentration of flavonoids and the hormone abscisic acid increased substantially in comparison to control plants.

Phytotoxic Metabolites Isolated from Aspergillus sp., an Endophytic Fungus of Crassula arborescens

Aspergillus sp., an endophytic fungus isolated from Crassula arborescens, displayed potent inhibitory activity against the seed germination of Arabidopsis thaliana. The bioactivity-guided fractionation of the culture extract of Aspergillus sp. MJ01 led to the isolation of nine compounds, including one previously undescribed furanone, namely aspertamarinoic acid (1), and eight known compounds, (-)-dihydrocanadensolide (2), kojic acid (3), citreoisocoumarin (4), astellolide A (5), astellolide B (6), astellolide G (7), cyclo-N-methylphenylalanyltryptophenyl (8) and (-)-ditryptophenaline (9). In the evaluation of the phytotoxic activities of compounds 1-9, the results suggested that 1 and 5 showed significant inhibitory activity on the seed germination of A. thaliana. This is the first report to disclose the phytotoxic activity of these compounds.

Cloning and functional characterization of three sesquiterpene synthase genes from Chamaecyparis formosensis Matsumura

Terpene synthase (TPS) analysis may contribute to a better understanding of terpenoids biosynthesis and the evolution of phylogenetic taxonomy. Chamaecyparis formosensis Matsumura is an endemic and valuable conifer of Taiwan. Its excellent wood quality, fragrance, and durability make it become the five precious conifers in Taiwan. In this study, three sesquiterpene synthase genes that belong to the TPS-d2 clade were isolated and characterized through in vitro reaction of recombinant protein and in vivo reaction of Escherichia coli heterologous expression system. The main product of Cf-GerA was germacrene A using GC/MS analysis, while the product of Cf-Aco and Cf-Gor were identified as acora-4(14),8-diene and (5R,6R,10S)-α-gorgonene by using NMR analysis. These are the first reported enzymes that biosynthesize acora-4(14),8-diene and (5 R,6 R,10 S)-α-gorgonene. Both sesquiterpene synthases may isomerize the farnesyl pyrophosphate substrate to nerolidyl pyrophosphate for further cyclization. Cf-Aco may catalyze 1,6-cyclization of nerolidyl cation while Cf-Gor may catalyze through an uncharged intermediate, isogermacrene A.

Inuloxin A Inhibits Seedling Growth and Affects Redox System of Lycopersicon esculentum Mill. and Lepidium sativum L

Allelochemicals are considered an environment-friendly and promising alternative for weed management, although much effort is still needed for understanding their mode of action and then promoting their use in plant allelopathy management practices. Here, we report that Inuloxin A (InA), an allelochemical isolated from Dittrichia viscosa, inhibited root elongation and growth of seedlings of Lycopersicon esculentum and Lepidium sativum at the highest concentrations tested. InA-induced antioxidant responses in the seedlings were investigated by analysing the contents of glutathione (GSH) and ascorbate (ASC), and their oxidized forms, dehydroascorbate (DHA), and glutathione disulphide (GSSG), as well as the redox state of thiol-containing proteins. An increase in ASC, DHA, and GSH levels at high concentrations of InA, after 3 and 6 days, were observed. Moreover, the ASC/DHA + ASC and GSH/GSSG + GSH ratios showed a shift towards the oxidized form. Our study provides the first insight into how the cell redox system responds and adapts to InA phytotoxicity, providing a framework for further molecular studies.

Evaluation of the phytotoxic effect of the essential oil from Artemisia absinthium

The chemical profile and the phytotoxicity of Artemisia absinthium essential oil (EO) were investigated to evaluate its potential value as a biopesticide for food safety purposes. A total of 54 compounds were identified in A. absinthium EO, with the most abundant constituents being eucalyptol (25.59%), linalool (11.99%), and β-myrcene (10.05%). The EO, linalool, and a mixture of three major components exhibited potent suppressive activity against four receiver species; however, eucalyptol and β-myrcene showed a much weaker effect. Bioassay-guided fractionation led to the isolation of linalool as the major active compound responsible for the EO's phytotoxicity. Subsequent scanning electron microscopy (SEM) analysis revealed that linalool significantly inhibited root-hair formation and metaxylem development. This is the first report on the determination of linalool as the major active phytotoxic compound in A. absinthium EO, as well as the elucidation of its mechanism of phytotoxicity from the perspective of root structure changes in the receiver species. Our results suggest that both the EO and its major constituents have potential value as environmentally friendly herbicides.

Research Advances in Allelopathy of Volatile Organic Compounds (VOCs) of Plants

Allelopathy is an ecological phenomenon in which organisms interfere with each other. As a management strategy in agricultural systems, allelopathy can be mainly used to control weeds, resist pests, and disease and improve the interaction of soil nutrition and microorganisms. Volatile organic compounds (VOCs) are allelochemicals volatilized from plants and have been widely demonstrated to have different ecological functions. This review provides the recent advance in the allelopathic effects of VOCs on plants, such as growth, competition, dormancy, resistance of diseases and insect pests, content of reactive oxygen species (ROS), enzyme activity, respiration, and photosynthesis. VOCs also participate in plant-to-plant communication as a signaling substance. The main methods of collection and identification of VOCs are briefly summarized in this article. It also points out the disadvantages of VOCs and suggests potential directions to enhance research and solve mysteries in this emerging area. It is necessary to study the allelopathic mechanisms of plant VOCs so as to provide a theoretical basis for VOC applications. In conclusion, allelopathy of VOCs released by plants is a more economical, environmentally friendly, and effective measure to develop substantial agricultural industry by using the allelopathic effects of plant natural products.

Determination of the Effect of Co-cultivation on the Production and Root Exudation of Flavonoids in Four Legume Species Using LC-MS/MS Analysis

Flavonoids play a key role in the regulation of plant-plant and plant-microbe interactions, and factors determining their release have been investigated in most of the common forage legumes. However, little is known about the response of flavonoid production and release to co-cultivation with other crop species. This study investigated alterations in the concentration of flavonoids in plant tissues and root exudates in four legumes [alfalfa (Medicago sativa L.), black medic (Medicago polymorpha L.), crimson clover (Trifolium incarnatum L.), and subterranean clover (Trifolium subterraneum L.)] co-cultivated with durum wheat [Triticum turgidum subsp. durum (Desf.) Husn.]. For this purpose, we carried out two experiments in a greenhouse, one with glass beads as growth media for root exudate extraction and one with soil as growth media for flavonoid detection in shoot and root biomass, using LC-MS/MS analysis. This study revealed that interspecific competition with wheat negatively affected legume growth and led to a significant reduction in shoot and root biomass compared with the same legume species grown in monoculture. In contrast, the concentration of flavonoids significantly increased both in legume biomass and in root exudates. Changes in flavonoid concentration involved daidzein, genistein, medicarpin, and formononetin, which have been found to be involved in legume nodulation and regulation of plant-plant interaction. We hypothesize that legumes responded to the co-cultivation with wheat by promoting nodulation and increasing exudation of allelopathic compounds, respectively, to compensate for the lack of nutrients caused by the presence of wheat in the cultivation system and to reduce the competitiveness of neighboring plants. Future studies should elucidate the bioactivity of flavonoid compounds in cereal-legume co-cultivation systems and their specific role in the nodulation process and inter-specific plant interactions such as potential effects on weeds.

Exploratory and discriminant analysis of plant phenolic profiles obtained by UV-vis scanning spectroscopy

Some species of cover crops produce phenolic compounds with allelopathic potential. The use of math, statistical and computational tools to analyze data obtained with spectrophotometry can assist in the chemical profile discrimination to choose which species and cultivation are the best for weed management purposes. The aim of this study was to perform exploratory and discriminant analysis using R package specmine on the phenolic profile of Secale cereale L., Avena strigosa L. and Raphanus sativus L. shoots obtained by UV-vis scanning spectrophotometry. Plants were collected at 60, 80 and 100 days after sowing and at 15 and 30 days after rolling in experiment in Brazil. Exploratory and discriminant analysis, namely principal component analysis, hierarchical clustering analysis, t-test, fold-change, analysis of variance and supervised machine learning analysis were performed. Results showed a stronger tendency to cluster phenolic profiles according to plant species rather than crop management system, period of sampling or plant phenologic stage. PCA analysis showed a strong distinction of S. cereale L. and A. strigosa L. 30 days after rolling. Due to the fast analysis and friendly use, the R package specmine can be recommended as a supporting tool to exploratory and discriminatory analysis of multivariate data.

Phytotoxic Activity of p-Cresol, 2-Phenylethanol and 3-Phenyl-1-Propanol, Phenolic Compounds Present in Cistus ladanifer L

Numerous studies about the leaf exudate of Cistus ladanifer highlight this Mediterranean shrub as an allelopathic species. Despite the very high diversity of secondary metabolites identified in its labdanum, only a few components have been evaluated. p-Cresol, 2-phenylethanol and 3-phenyl-1-propanol are three phenolic components present in the labdanum of C. ladanifer whose role has not been specified to date. The present study, through a static acute toxicity test, analyzed their activity, with respect to Allium cepa and Lactuca sativa. These three separate compounds and the mixture of all of them have a more or less phytotoxic activity depending on the medium, species and concentration tested. When the test is carried out on paper, the three pure allelochemicals and their mixture at 1 mM significantly inhibited the total germination, the germination rate and the development of the Allium cepa and Lactuca sativa seedlings to a lesser extent, but when the test performed in soil, the effects on the size of roots and cotyledons are attenuated. Furthermore, in the two species tested on paper, the joint action of the three compounds at 1 mM shows a significantly greater inhibition of the measured indices than each of the compounds separately.

Seed Priming with Sorghum Water Extract Improves the Performance of Camelina (Camelina sativa (L.) Crantz.) under Salt Stress

Seed priming with sorghum water extract (SWE) enhances crop tolerance to salinity stress; however, the application of SWE under salinity for camelina crop has not been documented so far. This study evaluated the potential role of seed priming with SWE in improving salt stress tolerance in camelina. Primed (with 5% SWE and distilled water-hydropriming) and nonprimed seeds were sown under control (no salt) and salt stress (10 dS m-1) conditions. Salinity reduced camelina's emergence and growth, while seed priming with SWE improved growth under control and stress conditions. Under salt stress, seed priming with SWE enhanced emergence percentage (96.98%), increased root length (82%), shoot length (32%), root dry weight (75%), shoot dry weight (33%), α-amylase activity (66.43%), chlorophyll content (60-92%), antioxidant enzymes activity (38-171%) and shoot K+ ion (60%) compared with nontreated plants. Similarly, under stress conditions, hydrogen peroxide, malondialdehyde (MDA) content, and shoot Na+ ion were reduced by 60, 31, and 40% by seed priming with SWE, respectively, over the nonprimed seeds. Therefore, seed priming with SWE may be used to enhance the tolerance against salt stress in camelina.

Essential Oil of Deverra tortuosa Aerial Parts: Detailed Chemical Profile, Allelopathic, Antimicrobial, and Antioxidant Activities

Essential oils (EOs) are a promising group of natural products of the aromatic plants due to their various biological effects such as allelopathic, antioxidant, antimicrobial activities. The present study aimed to construct the detailed chemical profile of the EO derived from Deverra tortuosa aerial parts along with assessing its allelopathic, antimicrobial, and antioxidant potentialities. The EO was extracted by hydrodistillation and analyzed via gas chromatography-mass spectrometry (GC/MS). The allelopathic activity of the EO was assessed against the germination and seedling growth of the weed Chenopodium murale. Also, the EO was tested against five microbes. The antioxidant activity was determined using the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The GC/MS analysis of EO revealed the presence of 86 compounds with a preponderance of oxygenated sesquiterpenes and monoterpene hydrocarbons. Widdrol, β-phellandrene, piperitol, cubedol, α-terpinene, (E)-10-heptadecen-8-ynoic acid methyl ester, citronellyl tiglate, and m-cymene were the major compounds. A comparative profile was established between the EOs constituents of our study with the documented EOs of D. tortuosa and the other Deverra species around the world via agglomerative hierarchical clustering (AHC) and principal components analysis (PCA). The EO showed a substantial allelopathic activity against C. murale, as well as it showed considerable antimicrobial and antioxidant activities. Thereby, the EO of D. tortuosa could be considered as a promising environmental-friendly bioherbicide against weeds. Also, it could be integrated into food preservation due to its potent antimicrobial and antioxidant activities. However, further study is recommended for more characterization of the major compounds and evaluation of their activities, either singular or synergistic, and assess their efficiency and biosafety.

Assessment of Glyphosate Impact on the Agrofood Ecosystem

Agro-industries should adopt effective strategies to use agrochemicals such as glyphosate herbicides cautiously in order to protect public health. This entails careful testing and risk assessment of available choices, and also educating farmers and users with mitigation strategies in ecosystem protection and sustainable development. The key to success in this endeavour is using scientific research on biological pest control, organic farming and regulatory control, etc., for new developments in food production and safety, and for environmental protection. Education and research is of paramount importance for food and nutrition security in the shadow of climate change, and their consequences in food production and consumption safety and sustainability. This review, therefore, diagnoses on the use of glyphosate and the associated development of glyphosate-resistant weeds. It also deals with the risk assessment on human health of glyphosate formulations through environment and dietary exposures based on the impact of glyphosate and its metabolite AMPA-(aminomethyl)phosphonic acid-on water and food. All this to setup further conclusions and recommendations on the regulated use of glyphosate and how to mitigate the adverse effects.

Transcriptome Profiling of the Potato Exposed to French Marigold Essential Oil with a Special Emphasis on Leaf Starch Metabolism and Defense against Colorado Potato Beetle

Flower strips of French Marigold are commonly used pest repellents in potato fields. However, the effect of French Marigold volatiles on potato metabolism, physiology and induced defense is unknown. Thus, a microarray transcriptome analysis was performed to study the effects of French Marigold essential oil (EO) on laboratory-grown potato. After 8 h of exposure to EO, with gas chromatography/mass spectrometry (GC/MS)-detected terpinolene and limonene as dominant compounds, 2796 transcripts were differentially expressed with fold change >2 compared to expression in controls. A slightly higher number of transcripts had suppressed expression (1493 down- vs. 1303 up-regulated). Since transcripts, annotated to different photosynthesis-related processes, were mostly down-regulated, we selected a set of 10 genes involved in the leaf starch metabolism pathway, and validated microarray patterns using quantitative reverse transcription polymerase chain reaction (RT-qPCR). Except for decreased synthesis and induced decomposition of starch granule in leaves, 8 h long EO exposure slightly elevated the accumulation of sucrose compared to glucose and fructose in subjected potato plants. An in vitro feeding bioassay with Colorado potato beetle showed that EO-induced alternations on transcriptional level and in the sugars’ metabolism caused the enhancement of feeding behavior and overall development of the tested larvae. Results of comprehensive analysis of transcriptional responses in potato exposed to French Marigold EO provide a basis for further elucidation of molecular mechanisms underlying eco-physiological interactions in companion planting cropping systems.

Evaluation of Dittrichia viscosa (L.) Greuter Dried Biomass for Weed Management

Dittrichia viscosa (L.) Greuter, a plant species common in the Mediterranean basin, produces several bioactive compounds, some of which have herbicidal effects. A number of greenhouse and field experiments were carried out in order to evaluate if these effects could be obtained also by using the whole plant biomass, to identify the efficacious doses, determine their effects on seed germination and weed emergence, and to evaluate influence of soil characteristics on biomass efficacy. The experiments carried out evidenced that: (i) the dried biomass completely hampers plant emergence when high doses (30–40 kg biomass m⁻³ of soil) are mixed into the soil, or delays it at a lower dose (10 kg m⁻³); (ii) the detrimental effects are not affected by soil type. The exploitation of the D. viscosa dried biomass appears to be a feasible option in weed management practices and its potential is discussed.

Asteraceae family: a review of its allelopathic potential and the case of Acmella oleracea and Sphagneticola trilobata

Abstract Asteraceae family is as an interesting target for researching natural alternatives for crop protection. Many species from this family grow as weeds, and some of them can influence the development of other species by the allelopathy phenomenon. This paper aimed to review the literature for the main genera and species of the Asteraceae family with allelopathic or phytotoxic potential, as well as the classes of secondary metabolites present in this family and responsible for such activity. Artemisia, Ambrosia, Bellis, Bidens, Helianthus and Tagetes were identified as the main genera with phytotoxic or allelopathic activity. Among the secondary metabolites from this family, terpenes, polyacetylenes, saponins, sesquiterpene lactones, phenolic acids and flavonoids were described as responsible for inhibiting the development of other species. In addition, the phytotoxic potential of Acmella oleracea and Sphagneticola trilobata against the weeds Calopogonium mucunoides. and Ipomoea purpurea was described for the first time. At 0.2 mg/mL, crude extract and fractions of A. oleracea inhibited above 60% of C. mucunoides root growth. Hydroalcoholic extract and fractions of S. trilobata, except hexane, significantly affected I. purpurea root growth, ranging from 38 ± 14% to 59 ± 8% of inhibitory effect at different concentrations (0.19 mg/mL to 1.13 mg/mL).

Allelopathy: The Chemical Language of Plants

In Nature, the oldest method of communication between living systems is the chemical language. Plants, due to their lack of mobility, have developed the most sophisticated way of chemical communication. Despite that many examples involve this chemical communication process-allelopathy, there is still a lack of information about specific allelochemicals released into the environment, their purpose, as well as in-depth studies on the chemistry underground. These findings are critical to gain a better understanding of the role of these compounds and open up a wide range of possibilities and applications, especially in agriculture and phytomedicine. The most relevant aspects regarding the chemical language of plants, namely kind of allelochemicals, have been investigated, as well as their releasing mechanisms and their purpose will be described in this chapter.

Recent Advances in Saffron Soil Remediation: Activated Carbon and Zeolites Effects on Allelopathic Potential

Saffron (Crocus sativus L.) is a highly valuable plant. Iran provides nearly 90% of the world’s total saffron and is the biggest global producer. The allelopathic effects of saffron corm (SC) and saffron field soil (SFS) have been hypothesized to play an important role in replanting. Recently, adsorbent materials have been used to neutralize the effects of allelochemicals. These materials, including activated carbon and zeolite, have large surface areas, pore volumes, as well as tremendous adsorptive capacity and complex chemical and physical properties. In this study, three independent experiments were conducted. In the first test, the allelopathic effects of aqueous and methanolic extracts of SC remnant and 9-year-old SFS as well as filtered aqueous extract of soil were investigated. In the second assay, the effects of SC remnants and SFS with different ages (i.e., 4, 6, and 9 years old) in combination with adsorbents were examined on the germination and growth of lettuce (Lactuca sativa L.) seedlings by the sandwich method. In the third experiment, we examined the effects of SC remnants combined with adsorbents on lettuce growth parameters. Our results showed that the allelopathic effects of aqueous and methanolic extracts of SC remnant were significantly superior to those of 9-year-old SFS. The aqueous extract of SC remnant reduced the root length of lettuce by 50%. The use of activated carbon and zeolites significantly decreased the observed allelopathic effect. Moreover, lettuce growth in rhizosphere soil was significantly inhibited by SC remnant and SFS extracts. The allelopathic effects of SC remnants caused a growth imbalance between the shoot and roots. Based on biochemical analyses, using the adsorbents increased the carotenoid content and chlorophyll index of lettuce by 23.33% and 5.25%, respectively. Adsorbents may play a role in treating soils contaminated by allelochemicals.

Phytotoxic Effect of Macerates and Mulches from Cupressus leylandii Leaves on Clover and Cress: Role of Chemical Composition

The use of plant secondary metabolites is an attractive strategy to control weeds. In this work, cypress (Cupressus leylandii) leaves were collected and tested as aqueous macerates or mulches for their ability to control seed germination and seedling growth of Trifolium repens and Lepidium sativum. Leaves were collected on trees facing the north (S) or facing the sun (L). The rate of seed germination measured on sand was drastically slowed down by the cypress leaves after 8 d of maceration, reaching inhibition of >85% compared to the control at 7 d post-imbibition (dpi). Analysis of macerates by UHPLC-MS revealed the presence of organic acids, phenols, and sugars in amounts increasing with maceration time and the phytotoxic effect. A 5 cm layer of cypress leaf mulch also significantly reduced (p < 0.001) the rate of seedling appearance of Lepidium sativum measured on potting soil compared to the control. Mulches prepared using L leaves were more efficient than those prepared with S leaves (p = 0.0029). Analysis of ethanolic extracts of leaves by mass spectrometry (MS) coupled to liquid (UHPLC) or gas chromatography (GC) showed the presence of a variety of monoterpenes, monoterpenoids, and diterpenoids with a labdane backbone. They were all more concentrated in mulches prepared with L leaves than those prepared with S leaves, in particular diterpenoids, which were about 10-fold more concentrated. However, the identification of phytotoxic components needs further research. It is concluded that due to their phytotoxic properties, Cupressus leylandii leaves could be used as mulch or macerate for target treatment of weedy areas.

Root-Exuded Benzoxazinoids: Uptake and Translocation in Neighboring Plants

Plants have evolved advanced chemical defense mechanisms, including root exudation, which enable them to respond to changes occurring in their surroundings rapidly. Yet, it remains unresolved how root exudation affects belowground plant-plant interactions. The objective of this study was to elucidate the fate of benzoxazinoids (BXs) exuded from the roots of rye (Secale cereale L.) plants grown with hairy vetch (Vicia villosa). A rapid method that allows nondestructive and reproducible chemical profiling of the root exudates was developed. Targeted chemical analysis with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was performed to investigate the changes in the composition and concentration of BXs in the rye plant, and its root exudate in response to cocultivation with hairy vetch. Furthermore, hairy vetch plants were screened for the possible uptake of BXs from the rhizosphere and their translocation to the shoot. Rye significantly increased the production and root exudation of BXs, in particular 2-β-d-glucopyranosyloxy-4-hydroxy-1,4-benzoxazin-3-one (DIBOA-glc) and 2-β-d-glucopyranosyloxy-4-hydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA-glc), in response to cocultivation with hairy vetch. DIBOA-glc and DIMBOA-glc were absorbed by the roots of the cocultivated hairy vetch plants and translocated to the shoots. These findings will strongly improve our understanding of the exudation of BXs from the rye plant and their role in interaction with other plant species.

Chemical Characterization and Phytotoxic Effects of the Aerial Parts of Ruzigrass (Urochloa ruziziensis)

Studies of the phytotoxic effects between plants can be a crucial tool in the discovery of innovative compounds with herbicide potential. In this sense, we can highlight ruzigrass (Urochloa ruziziensis), which is traditionally used in the crop rotation system in order to reduce weed emergence. The aim of this work was to characterize the secondary metabolites of ruzigrass and to evaluate its phytotoxic effects. In total, eight compounds were isolated: friedelin, oleanolic acid, α-amyrin, 1-dehydrodiosgenone, sitosterol and stigmasterol glycosides, tricin and p-coumaric acid. Phytotoxic effects of the crude methanolic extract and fractions of ruzigrass were assessed using germination rate, initial seedling growth, and biomass of Bidens pilosa, Euphorbia heterophylla and Ipomoea grandifolia. Chemometric analysis discriminated the weed species into three groups, and B. pilosa was the most affected by fractions of ruzigrass. The phytotoxic activities of 1-dehydrodiosgenone, tricin, and p-coumaric acid are also reported, and p-coumaric acid and 1-dehydrodiosgenone were active against B. pilosa.

Cellular Base of Mint Allelopathy: Menthone Affects Plant Microtubules

Plants can use volatiles for remote suppression of competitors. Mints produce essential oils, which are known to affect the growth of other plants. We used a comparative approach to identify allelopathic compounds from different Mints (genus Mentha, but also including Cat Mint, Nepeta cataria, and Corean Mint, Agastache rugosa, belonging to sisters clades within the Mentheae) using the standard cress germination assay as readout. To understand the mechanism behind this allelopathic effect, we investigated the response of tobacco BY-2 cell lines, expressing GFP-tagged markers for microtubules and actin filaments to these essential oils. Based on the comparison between bioactivity and chemical components, we identified menthone as prime candidate for the allelopathic effect, and confirmed this bioactivity targeted to microtubules experimentally in both, plant cells (tobaccoBY-2), and seedlings (Arabidopsis thaliana). We could show that menthone disrupted microtubules and induced mortality linked with a rapid permeabilization (less than 15 min) of the plasma membrane. This mortality was elevated in a tubulin marker line, where microtubules are mildly stabilized. Our study paves the way for the development of novel bioherbicides that would be environmentally friendly.

Insights into physiological responses of mosses Physcomitrella patens and Pohlia drummondii to lichen secondary metabolites

It is widely accepted that allelopathy among mosses and lichens do exist due to its similar ecological needs, though it is rarely documented. With an aim to test whether there is an effect of allelochemicals to mosses, we grow axenically two moss species (namely Physcomitrella patens and Pohlia drummondii) in controlled conditions and use them to test the effect of lichen Pseudevernia furfuracea acetone extracts containing active compounds: atranorin, chloratranorin, and physodic acid. The photosynthesis value and the biochemical parameters were measured to detect changes in moss organisms upon application of different concentration of lichen extract. The results obtained clearly showed that both moss species reacted to allelochemicals applied in test but to different extent. This suggests that tested moss species have various patterns on reaction to allelochemicals, and that the process of allelopathy is rather a recently coevolving one, than pre-defined. The lichen secondary metabolites are allelochemicals effective also to moss species that are not selected lichen cohabitants.

Phytochemical analysis and effect of the essential oil of Psidium L. species on the initial development and mitotic activity of plants

The use of allelopathic compounds is an alternative for weeds control, since they present low toxicity when compared with the synthetic herbicides, that may cause several damages, as the contamination of the environment. Our objective was to determine the chemical composition and allelopathic properties of the essential oils of Psidium cattleianum, P. myrtoides, P. friedrichsthalianum, and P. gaudichaudianum on the germination and root growth of Lactuca sativa and Sorghum bicolor, and to evaluate their action on the cell cycle of root meristematic cells of L. sativa. The main compound found in all the studied species was (E)-caryophyllene (P. cattleianum-23.4 %; P. myrtoides-19.3%; P. friedrichsthalianum-24.6% and P. gaudichaudianum-17.0%). The different essential oils were tested at different concentrations on L. sativa and S. bicolor, reducing germination, germination speed index, and root and shoot growth of lettuce and sorghum seedlings. The cytotoxicity and aneugenic potential of these oils were evidenced by the reduction of the mitotic index and increase of the frequency of chromosomal alterations in L. sativa. The essential oils of the species of Psidium studied have potential to be used in weeds control.

Recent advances in allelopathy for weed control: from knowledge to applications

Allelopathy is the biological phenomenon of chemical interactions between living organisms in the ecosystem, and must be taken into account in addressing pest and weed problems in future sustainable agriculture. Allelopathy is a multidisciplinary science, but in some cases, aspects of its chemistry are overlooked, despite the need for a deep knowledge of the chemical structural characteristics of allelochemicals to facilitate the design of new herbicides. This review is focused on the most important advances in allelopathy, paying particular attention to the design and development of phenolic compounds, terpenoids and alkaloids as herbicides. The isolation of allelochemicals is mainly addressed, but other aspects such as the analysis and activities of derivatives or analogs are also covered. Furthermore, the use of allelopathy in the fight against parasitic plants is included. The past 12 years have been a prolific period for publications on allelopathy. This critical review discusses future research areas in this field and the state of the art is analyzed from the chemist's perspective. © 2019 Society of Chemical Industry.