Production Of Allelochemicals Research Articles

Endophytic bacteria with allelopathic potential regulate gene expression and metabolite production in host Casuarina equisetifolia.

Casuarina equisetifolia is a common protective forest in coastal areas. However, artificial C. equisetifolia forests cannot self-renew, mainly due to the accumulation of allelochemicals. Endophytic bacteria may alleviate the root growth inhibition caused by allelochemicals in C. equisetifolia seedlings. B. amyloliquefaciens and B. aryabhattai were endophytic bacteria with strong allelopathy in C. equisetifolia root. The allelopathy mechanism of these two endophytes and their interaction with C. equisetifolia remains to be studied. Whole-genome sequencing of B. amyloliquefaciens and B. aryabhattai isolated from the roots of allelochemical-accumulating C. equisetifolia was performed using Illumina Hiseq and PacBio single-molecule sequencing platforms. Sterile seedlings of C. equisetifolia were treated with either individual or mixed bacterial cultures through root drenching. Transcriptional and metabolomics analyses were conducted after 3 days of infection. Whole-genome sequencing of Bacillus aryabhattai and Bacillus amyloliquefaciens showed that the two strains contained various horizontal gene transfer elements such as insertion sequence, prophage and transposon. In addition, these two strains also contain numerous genes related to the synthesis and catabolism of allelochemicals. After these two strains of bacteria were individually or mixed infected with C. equisetifolia, metabolomics and transcriptomic analysis of C. equisetifolia showed the 11 important secondary metabolite biosynthesis among them alkaloids biosynthesis, phenylpropanoid and terpenes biosynthesis and related genes were putatively regulated. Correlation analysis revealed that 48 differentially expressed genes had strong positive correlations with 42 differential metabolites, and 48 differentially expressed genes had strong negative correlations with 36 differential metabolites. For example, CMBL gene showed positive correlations with the allelochemical (-)-Catechin gallate, while Bp10 gene showed negative correlations with (-)-Catechin gallate. The intergenerational accumulation of allelochemicals may induce horizontal gene transfer in endogenic bacteria of Casuarina equisetifolia root. Endophytic Bacillus plays an allelopathic role by assisting the host in regulating gene expression and the production and/or variety of allelochemicals. This comprehensive study sheds light on the intricate genetic and metabolic interactions between Bacillus endophytes and C. equisetifolia. These findings provide insights into endophyte-mediated allelopathy and its potential uses in plant biology and forest sustainability.

Allelochemicals determine competition and grazing control in Alexandrium catenella

The production of allelochemicals by the toxigenic dinoflagellate Alexandrium catenella is one of the suggested mechanisms to facilitate its bloom formation and persistence by outcompeting other phototrophic protists and reducing grazing pressure. In Southern California, toxic events caused by A. catenella and paralytic shellfish toxins (PSTs) regularly impact coastal ecosystems; however, the trophic interactions and mechanisms promoting this species in a food web context are still not fully understood. In the present study, we combined a dynamical mathematical model with laboratory experiments to investigate potential toxic and allelochemical effects of an A. catenella strain isolated off the coast of Los Angeles, Southern California, on competitors and a common zooplankton consumer. Experiments were conducted using three toxigenic strains of A. catenella, comparing the new Californian isolate (Alex Cal) to two strains previously described from the North Sea, a lytic (Alex2) and non-lytic (Alex5) strain, testing for donor density-dependent effects on two phytoplankton species (Rhodomonas salina, Tetraselmis sp.) and on the rotifer Brachionus plicatilis. Bioassays revealed a steep decline in competitor and consumer populations with increasing Alex Cal concentrations, indicating an intermediate lytic activity compared to the North Sea strains (lytic Alex2 and non-lytic Alex5). The rotifer fed and grew well on the PST- toxic, but non-lytic Alex5 strain, while its survival significantly decreased with increasing concentrations of the two lytic strains Alex Cal and Alex 2, indicating that negative effects on the rotifer were mediated by allelochemicals rather than PST-toxins. Mixed culture experiments including both competitors and consumers demonstrated that the intensity of allelochemical effects not only depended on the A. catenella density but also on the target density. Negative effects on grazers were alleviated by co-occurring competitors with a lower sensitivity to allelochemicals, thus reducing harmful compounds and allowing grazing control on the dinoflagellate to come into effect again. Results from mixed culture experiments were supported by the mathematical approach used in this study which was calibrated with data from simple monoculture growth, pairwise competition and predator-prey experiments, demonstrating the applicability of this model approach to predict the outcome of more complex food web dynamics at the community level.

Management of Rumex dentatus L. in Vicia faba L. cultivations via Ononis vaginalis Vahl. As a potential bioherbicide

Biological control of undesirable weeds associated with crop cultivation is a sustainable approach that can reduce chemical herbicide dependence. The current study aimed to assess the bio-herbicidal potential of the donor species Ononis vaginalis Vahl. on germination efficiency as well as various growth and physiological parameters of the recipient species Rumex dentatus L., a major broad bean pest (Vicia faba L.). To assess the greatest inhibitory allelopathic effect on the recipient species in mixed (Rumex dentatus L. and Vicia faba L.) and pure cultures (each one separately), two experiments were conducted under laboratory conditions. A Petri dish experiment using O. vaginalis shoot aqueous extract (5%, 10%, 20%, and 40%) and a pot experiment using O. vaginalis shoot crude powder (1%, 2%, 5%, and 10%) were conducted to investigate its biological activity on some growth and physiological parameters of both crop and weed species. O. vaginalis underwent a general phytochemical screening that revealed a high production of allelochemicals, which are secondary metabolites and may have a function like that of natural herbicides. The result showed that the germination of V. faba seeds in both pure and mixed cultures was not significantly affected by low levels of O. vaginalis shoot aqueous extract treatments in pure and mixed cultures, in contrast, those recorded for R. dentatus gradually dropped as levels of O. vaginalis increased in both cultures. Results recorded a significant increase in total phenolics of V. faba shoots and roots under different treatments, except at the high concentrations of crude powder at the donor species level (5 and10%). A reduction in the total phenolic and flavonoid fractions was observed in R. dentatus roots under varying concentration treatments. Conversely, under high concentration treatments, flavonoids decreased in the roots of the mixed culture of R. dentatus but increased in the shoots. In conclusion, allelopathy can be used to suppress weeds in field crops. The study confirmed the use of O. vaginalis into current weed control techniques. O. vaginalis could be explored further for weed suppression in the field.

Effect of Allelochemicals from Cereal Rye Cultivar and Pythium lutarium on Corn Growth and Disease

Allelopathic chemicals produced by a cereal rye (CR; Secale cereale L.) cover crop have been implicated in the negative effect of CR on corn planted into decomposing CR residue. Production of allelochemicals varies among CR cultivars. In the current study, the allelopathic effect of crude extracts from five CR cultivars (Elbon, Hazlet, Serafino, Tayo, and Yankee) was evaluated on corn seedling growth, mycelial growth of Pythium lutarium, and root rot of corn caused by P. lutarium using a plate assay. In general, crude extracts from all CR cultivars slowed pathogen growth and reduced corn coleoptile and radicle lengths. When corn was grown on media amended with crude extracts from the CR cultivars and colonized with P. lutarium, corn growth was reduced and root rot severity increased compared with the check (no extract with pathogen). Subsequently, a cup assay was used to further investigate the allelopathic effect of Elbon, Hazlet, and Serafino on corn seedling growth and root rot. Corn grown in cups into which each cultivar had been planted had shorter radicles and coleoptiles compared with the check (no CR), regardless of the CR cultivar. Results from this study suggest that allelochemicals released from decomposing CR vary among cultivars, and their interaction with Pythium spp. could affect seedling disease on corn. Consequently, choice of CR cultivar may be an important management decision to reduce the negative effects of CR on corn. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

The role of signaling compounds in enhancing rice allelochemicals for sustainable agriculture: an overview.

Plant phytotoxin synthesis is influenced by intricate signaling networks like jasmonic acid (JA) and salicylic acid (SA). These compounds not only induce allelochemical production but also aid weed suppression and plant immunity. (-)-Loliolide, JA, SA, and their derivatives trigger rice allelochemical synthesis and gene expression. Enhancing allelochemical synthesis in crops offers an alternative, reducing reliance on traditional herbicides for effective weed management. Rice (Oryza sativa L.) serves as a crucial staple food crop, nourishing over half of the global population, particularly in South Asia. Within rice plants, various secondary metabolites are produced, contributing to its nutritional value and providing energy to consumers. Over the last 5 decades, researchers have investigated 276 distinct types of secondary metabolites found in rice plants. These metabolites predominantly include phenolic acids, flavonoids, steroids, alkaloids, terpenoids, and their derivatives. The role of these secondary metabolites is to regulate the growth and development of the rice plant. In this research paper, we have focused on the allelopathic potential of rice, which involves its active defense strategy to suppress other species in its vicinity. This defense mechanism is regulated by plant signaling compounds. These signaling compounds enable rice plants to recognize and detect competitors, pathogens, and herbivores in their environment. As a response, the rice plants elevate the production of defensive secondary metabolites. One crucial aspect of rice allelopathy is the phenomenon of neighbor detection. Rice plants can sense the presence of neighboring plants and respond accordingly to establish their competitive advantage and ensure their survival. This paper specifically highlights the impact of exogenously applied signaling compounds, namely Methyl salicylate (MeSA) and Methyl Jasmonate (MeJA), on paddy rice. The aim is to provide deeper insights into the signaling mechanisms involved in rice allelopathy and how the exogenous application of signaling compounds influence the induction and regulation of defensive secondary metabolites in rice plants. Comprehensive analysis of various researchers' studies clearly reveals that the application of these elicitor compounds noticeably augments the allelopathic potential of rice, resulting in heightened accumulation of phenolic acid compounds. Expansion in more enlistment of phenolics may be because of expansion in the activities of enzymes, such as cinnamate 4-hydroxylase (C4H) and phenylalanine ammonia-lyase (PAL), the two main enzymes of the phenylpropanoid pathway, which are associated with allelopathic crop plants, and along this, they recognize the presence of weeds and react by expanding allelochemical focuses. Consequently, substantial endeavors have been dedicated in recent times to discover and characterize plant-derived signaling molecules. In bioassays conducted by Patni et al. in 2019, both competitive and non-competitive rice genotypes exhibited elevated phytotoxicity against Echino colona following treatment with MeSA. MeSA-treated rice plants displayed accelerated growth, increased yield, and concurrently demonstrated weed-suppressing properties. Published studies from 1976 to 2021 are reviewed in this paper. The study indicates that signaling compounds induce allelochemical concentrations, enhancing allelopathic activity. This insight may lead to development of novel herbicides for effective sustainable weed management.

Inhibitory Effect of Aqueous Extracts from Egeria densa Planch. on Cyanobacteria Microcystis aeruginosa (Kützing) Lemmermann Growth

This study aimed to investigate the allelopathic effect of live Egeria densa Planch. and its aqueous extracts in inhibiting the cyanobacterium Microcystis aeruginosa (Kützing) Lemmermann through a possible growth inhibition pathway. Under coexistence, the presence of live E. densa reduced the growth of M. aeruginosa by 48% compared to when M. aeruginosa was alone. Consequently, we prepared two separate aqueous extracts with distilled water: one from E. densa plants collected from monocultures, and the other from E. densa plants collected from co-cultivation with M. aeruginosa. At a concentration of 0.5 g/L, both extracts successfully suppressed the growth of M. aeruginosa throughout the 5-day exposure period. The extracts obtained from E. densa plants grown in a combined culture with M. aeruginosa showed significant growth-inhibiting capabilities compared to the extracts obtained from E. densa monoculture (p < 0.05). They showed 22% more growth inhibition compared to cultures exposed to monoculture extracts at day 5, indicating that the production of allelochemicals in E. densa was induced during co-existence with cyanobacteria. However, the higher concentrations (2 and 4 g/L) of both extracts did not effectively exhibit a successful inhibitive ability, possibly due to the presence of high nutrient concentrations, specifically PO43−, which may be potentially suppressing the activity of allelochemicals. Further studies are recommended in identifying the specific allelochemicals and exploring their practical implementation in the field.

Root microbiome diversity and structure of the Sonoran desert buffelgrass (Pennisetum ciliare L.).

Buffelgrass (Pennisetum ciliare) is an invasive plant introduced into Mexico's Sonoran desert for cattle grazing and has converted large areas of native thorn scrub. One of the invasion mechanisms buffelgrass uses to invade is allelopathy, which consists of the production and secretion of allelochemicals that exert adverse effects on other plants' growth. The plant microbiome also plays a vital role in establishing invasive plants and host growth and development. However, little is known about the buffelgrass root-associated bacteria and the effects of allelochemicals on the microbiome. We used 16S rRNA gene amplicon sequencing to obtain the microbiome of buffelgrass and compare it between samples treated with root exacknudates and aqueous leachates as allelochemical exposure and samples without allelopathic exposure in two different periods. The Shannon diversity values were between H' = 5.1811-5.5709, with 2,164 reported bacterial Amplicon Sequence Variants (ASVs). A total of 24 phyla were found in the buffelgrass microbiome, predominantly Actinobacteria, Proteobacteria, and Acidobacteria. At the genus level, 30 different genera comprised the buffelgrass core microbiome. Our results show that buffelgrass recruits microorganisms capable of thriving under allelochemical conditions and may be able to metabolize them (e.g., Planctomicrobium, Aurantimonas, and Tellurimicrobium). We also found that the community composition of the microbiome changes depending on the developmental state of buffelgrass (p = 0.0366; ANOSIM). These findings provide new insights into the role of the microbiome in the establishment of invasive plant species and offer potential targets for developing strategies to control buffelgrass invasion.

Drought stress intensifies the phytotoxicity of five Asteraceae exotic invasive plants

Abstract The phytotoxicity of exotic invasive plants (EIP) is vital for their successful invasion. At the family level, Asteraceae contains the largest number of EIP species in China. Drought stress may affect the phytotoxicity of EIP by altering the production and secretion of allelochemicals. Therefore, it is important to estimate the phytotoxicity of multiple EIP under drought stress. In this study, the phytotoxicity of five Asteraceae EIP, i.e., Solidago canadensis L., Aster subulatus Michx., Bidens pilosa L., Erigeron annuus (L.) Pers., and Conyza canadensis (L.) Cronq., were estimated using leaf extracts. Their effects on seed germination and seedling growth of the horticultural Asteraceae species Lactuca sativa L. under drought stress (simulated by polyethylene glycol-6000) were assessed. These five Asteraceae EIP, particularly S. canadensis, inhibited seed germination of L. sativa. Aster subulatus, B. pilosa, E. annuus, and C. canadensis increased seedling growth of L. sativa. The phytotoxicity of these five Asteraceae EIP decreased in the following order: S. canadensis > E. annuus > A. subulatus > B. pilosa ≈ C. canadensis. Drought stress intensified the phytotoxicity of all five Asteraceae EIP. The level of stress intensity mediated by these five Asteraceae EIP, particularly by S. canadensis, A. subulatus, and B. pilosa, increased with increasing degree of drought stress. Thus, an increasing growing degree of drought stress may accelerate the invasion process of these five Asteraceae EIP via the effects of intensified phytotoxicity on growth performance of adjacent species, particularly on seed germination and seedling growth.

Allelopathy and Allelochemicals in Grasslands and Forests

Plants can produce and release allelochemicals to interfere with the establishment and growth of conspecific and interspecific plants. Such allelopathy is an important mediator among plant species in natural and managed ecosystems. This review focuses on allelopathy and allelochemicals in grasslands and forests. Allelopathy drives plant invasion, exacerbates grassland degradation and contributes to natural forest regeneration. Furthermore, autotoxicity (intraspecific allelopathy) frequently occurs in pastures and tree plantations. Various specialized metabolites, including phenolics, terpenoids and nitrogen-containing compounds from herbaceous and woody species are responsible for allelopathy in grasslands and forests. Terpenoids with a diversity of metabolites are qualitative allelochemicals occurring in annual grasslands, while phenolics with a few specialized metabolites are quantitative allelochemicals occurring in perennial forests. Importantly, allelochemicals mediate below-ground ecological interactions and plant–soil feedback, subsequently affecting the biodiversity, productivity and sustainability of grasslands and forests. Interestingly, allelopathic plants can discriminate the identity of neighbors via signaling chemicals, adjusting the production of allelochemicals. Therefore, allelochemicals and signaling chemicals synergistically interact to regulate interspecific and intraspecific interactions in grasslands and forests. Allelopathy and allelochemicals in grasslands and forests have provided fascinating insights into plant–plant interactions and their consequences for biodiversity, productivity and sustainability, contributing to our understanding of terrestrial ecosystems and global changes.

Impact of the Alien Aquatic Plant Ludwigia hexapetala on the Native Utricularia australis: Evidence from an Indoor Experiment

Ludwigia hexapetala is an alien aquatic plant considered highly invasive in Europe since it alters freshwater habitats by forming dense mats both in water and along banks, outcompeting natives. Ludwigia effects on the native carnivorous plant Utricularia australis were investigated here. A 21-day indoor experiment was performed by setting up some separate tests in which Utricularia was made to grow both alone (control tests) and together with Ludwigia (arena tests). Water chemical and physical parameters and growth and morphological traits of Utricularia and Ludwigia were analysed weekly. Water samples were also analysed by UV-visible spectra to verify allelochemical (quercitrin) production by Ludwigia. In arena tests, oxygen concentration and pH were lower and conductivity higher than in control tests. Utricularia grew significantly less in arena tests in both shoot length and internode number, and its fresh weight, trap number and internode length decreased more than the control. Quercitrin was found only in arena tests as an allelochemical product released by Ludwigia. Overall, this study demonstrated Ludwigia significantly alters water parameters and negatively affects the growth of Utricularia, showing aggressive and competitive behaviour against this native species. Such evidence suggest that the widespread of L. hexapetala can represent a serious threat to the conservation of native plant diversity occurring in the freshwater habitats it invades.

Cytogenotoxic, insecticidal, and phytotoxic activity from biomass extracts of the freshwater algae Nitella furcata

ABSTRACT Agroecology, the application of ecological concepts to agricultural production, has been developing over the last years with consequent promotion for discovery of bioactive compounds to control pests and abolish crop diseases. In this context, algae from Nitella genus are characterized by high potential for bioeconomic applications due to (1) available biomass for harvesting or cultivation and (2) production of allelochemicals, which present a potential to protect field crops from insect infestation. Therefore, this study aimed to determine primary and secondary metabolites derived from aqueous and hydroethanolic extracts of Nitella furcata and to evaluate phytotoxic, cytogenotoxic, insecticidal, and pro-oxidative activities of these extracts. Determination of metabolites showed the presence predominantly of carbohydrates, proteins, phenols, and flavonoids in hydroethanolic extract. Both extracts of N. furcata interfered in the germination of seeds and development of seedlings of Lactuca sativa, with hydroethanolic extract exhibiting greater inhibition. Both extracts also interfered with meristematic cells of Allium cepa as evidenced by chromosomal alterations and higher pro-oxidative activity. Aqueous extract at 5 and 0 mg/ml produced 100% insect mortality. Further, hydroethanolic extract at 0 mg/ml was lethal immediately upon exposure. Therefore, results demonstrate that N. furcata is potential algae species to be considered for development of environmental and ecotoxicological studies as a source of compounds with potential use in agroecological strategies.

Allelopathic potential in rice - a biochemical tool for plant defence against weeds.

Rice is a key crop for meeting the global food demand and ensuring food security. However, the crop has been facing great problems to combat the weed problem. Synthetic herbicides pose a severe threat to the long-term viability of agricultural output, agroecosystems, and human health. Allelochemicals, secondary metabolites of allelopathic plants, are a powerful tool for biological and eco-friendly weed management. The dynamics of weed species in various situations are determined by crop allelopathy. Phenolics and momilactones are the most common allelochemicals responsible for herbicidal effects in rice. The dispersion of allelochemicals is influenced not only by crop variety but also by climatic conditions. The most volatile chemicals, such as terpenoids, are usually emitted by crop plants in drought-stricken areas whereas the plants in humid zones release phytotoxins that are hydrophilic in nature, including phenolics, flavonoids, and alkaloids. The allelochemicals can disrupt the biochemical and physiological processes in weeds causing them to die finally. This study insight into the concepts of allelopathy and allelochemicals, types of allelochemicals, techniques of investigating allelopathic potential in rice, modes of action of allelochemicals, pathways of allelochemical production in plants, biosynthesis of allelochemicals in rice, factors influencing the production of allelochemicals in plants, genetical manipulation through breeding to develop allelopathic traits in rice, the significance of rice allelopathy in sustainable agriculture, etc. Understanding these biological phenomena may thus aid in the development of new and novel weed-control tactics while allowing farmers to manage weeds in an environmentally friendly manner.

Root placement patterns in allelopathic plant-plant interactions.

Plants actively respond to their neighbors by altering root placement patterns. Neighbor-modulated root responses involve root detection and interactions mediated by root-secreted functional metabolites. However, chemically mediated root placement patterns and their underlying mechanisms remain elusive. We used an allelopathic wheat model system challenged with 60 target species to identify root placement responses in window rhizobox experiments. We then tested root responses and their biochemical mechanisms in incubation experiments involving the addition of activated carbon and functional metabolites with amyloplast staining and auxin localization in roots. Wheat and each target species demonstrated intrusive, avoidant or unresponsive root placement, resulting in a total of nine combined patterns. Root placement patterns were mediated by wheat allelochemicals and (-)-loliolide signaling of neighbor species. In particular, (-)-loliolide triggered wheat allelochemical production that altered root growth and placement, degraded starch grains in the root cap and induced uneven distribution of auxin in target species roots. Root placement patterns in wheat-neighbor interactions were perception dependent and species dependent. Signaling (-)-loliolide induced the production and release of wheat allelochemicals that modulated root placement patterns. Therefore, root placement patterns are generated by both signaling chemicals and allelochemicals in allelopathic plant-plant interactions.

Competition induces negative conspecific allelopathic effects on seedling recruitment.

Some plant species suppress competitors through release of chemical compounds into the environment. As the production of allelochemicals may be costly, it would be beneficial if their production would only be induced when plants experience competition. We tested whether two plant species that frequently co-occur show evidence for induced allelopathy in response to intra- and interspecific competition. We used the annual forb Crepidiastrum sonchifolium and the perennial forb Achyranthes bidentata, which are native to China and predominantly occur in ruderal communities, as focal species. We first grew the species without competition, with intraspecific competition and in competition with each other. We chemically analysed aqueous extracts made from these plants to test for evidence that the competition treatments affected the metabolomic profiles of the species. We then tested the effects of the aqueous extracts on seed germination and seedling growth of both plant species. Metabolomic analysis revealed that competition treatments modified the chemical profiles of the two study species. The root lengths of A. bidentata and C. sonchifolium seedlings were reduced by the aqueous plant extracts. For seedling root length of A. bidentata, heterospecific allelopathy was more negative than conspecific allelopathy, but for germination of C. sonchifolium seeds, the reverse was true. Moreover, conspecific allelopathic effects on germination of A. bidentata seeds and on seedling root length of both species were most negative when the aqueous extracts were made from plants that had experienced competition. In the case of seedling root length of A. bidentata, this effect was most negative when the plants had experienced interspecific instead of intraspecific competition. We showed that plants change their metabolomic profiles in response to competition, and that this correlated with allelopathic inhibition of conspecific seed germination and seedling growth. We suggest that autoallelopathy for seed germination could function as a mechanism to avoid strong competition by keeping the seeds in a dormant state.

Allelopathy as an evolutionary game.

In plants, most competition is resource competition, where one plant simply preempts the resources away from its neighbors. Interference competition, as the name implies, is a form of direct interference to prevent resource access. Interference competition is common among animals that can physically fight, but in plants, one of the main mechanisms of interference competition is allelopathy. Allelopathic plants release cytotoxic chemicals into the environment which can increase their ability to compete with surrounding organisms for limited resources. The circumstances and conditions favoring the development and maintenance of allelochemicals, however, are not well understood. Particularly, despite the obvious benefits of allelopathy, current data suggest it seems to have only rarely evolved. To gain insight into the cost and benefit of allelopathy, we have developed a 2×2 matrix game to model the interaction between plants that produce allelochemicals and plants that do not. Production of an allelochemical introduces novel cost associated with both synthesis and detoxifying a toxic chemical but may also convey a competitive advantage. A plant that does not produce an allelochemical will suffer the cost of encountering one. Our model predicts three cases in which the evolutionarily stable strategies are different. In the first, the nonallelopathic plant is a stronger competitor, and not producing allelochemicals is the evolutionarily stable strategy. In the second, the allelopathic plant is the better competitor, and production of allelochemicals is the more beneficial strategy. In the last case, neither is the evolutionarily stable strategy. Instead, there are alternating stable states, depending on whether the allelopathic or nonallelopathic plant arrived first. The generated model reveals circumstances leading to the evolution of allelochemicals and sheds light on utilizing allelochemicals as part of weed management strategies. In particular, the wide region of alternative stable states in most parameterizations, combined with the fact that the absence of allelopathy is likely the ancestral state, provides an elegant answer to the question of why allelopathy seems to rarely evolve despite its obvious benefits. Allelopathic plants can indeed outcompete nonallelopathic plants, but this benefit is simply not great enough to allow them to go to fixation and spread through the population. Thus, most populations would remain purely nonallelopathic.

Kin discrimination in allelopathy and consequences for agricultural weed control.

Among all biotic stress types (i.e. pathogens, pests and weeds), weeds have the largest potential for yield reduction (larger than the other two combined) (Oerke, 2006). Chemical control of weeds is coming under increasing pressure due to concerns about their health- and environmental impacts and increasing herbicide resistance of weeds. As a consequence there is an increased interest in ecological weed control, of which development of weed-suppressive crops can be an important part (Bastiaans, Paolini, & Baumann, 2008). In the current issue, Xu, Cheng, Kong, and Meiners (2021) for the first time, show that kin recognition (the ability of plants to distinguish genetically related individuals from strangers) can make rice plants more competitive against weeds potentially being a new strategy in ecological weed control. This article is protected by copyright. All rights reserved.

Intra-specific kin recognition contributes to inter-specific allelopathy: A case study of allelopathic rice interference with paddy weeds.

Species interactions and mechanisms affect plant coexistence and community assembly. Despite increasing knowledge of kin recognition and allelopathy in regulating inter-specific and intra-specific interactions among plants, little is known about whether kin recognition mediates allelopathic interference. We used allelopathic rice cultivars with the ability for kin recognition grown in kin versus non-kin mixtures to determine their impacts on paddy weeds in field trials and a series of controlled experiments. We experimentally tested potential mechanisms of the interaction via altered root behaviour, allelochemical production and resource partitioning in the dominant weed competitor, as well as soil microbial communities. We consistently found that the establishment and growth of paddy weeds were more inhibited by kin mixtures compared to non-kin mixtures. The effect was driven by kin recognition that induced changes in root placement, altered weed carbon and nitrogen partitioning, but was associated with similar soil microbial communities. Importantly, genetic relatedness enhanced the production of intrusive roots towards weeds and reduced the production of rice allelochemicals. These findings suggest that relatedness allows allelopathic plants to discriminate their neighbouring collaborators (kin) or competitors and adjust their growth, competitiveness and chemical defense accordingly.

Allelopathy of Sorghum Residues on Weed Establishment Is Affected by Hybrid, Phenolic Acid Contents and Environment

Sorghum species are well known for allelopathic potential toward weeds and other crops. Sorghum above-ground residues mediate allelopathic activity through production and release of many allelochemicals including phenolic acids. Information is limited on selection of grain sorghum hybrids with high allelopathic potential and assessment of sorghum residue phenolic activity in soil under field conditions. This study was carried out to investigate several grain sorghum hybrids for allelopathic potential for suppressing weed growth in the field in the subsequent growing season; and to investigate the involvement of phenolic substances released into soil on the establishment of weeds. The weed seedbank was affected by environmental conditions that led to different weed densities subjected to suppression by residues in soil. Differential allelopathy was identified among the sorghum hybrids suggesting that improved selection may increase production and release of allelochemicals in new hybrids to control weeds inexpensively, easily, and environmentally friendly. Tillage type (till vs no-till) had variable effects on weed suppression. Soil type, environment, sorghum hybrid traits and cultural practices complicate the use of allelopathy in weed control and benefits gained from this potentially environment friendly weed control practice. Well-planned management will be required to successfully integrate allelopathic crops into sustainable crop production.

Phenotyping of Weedy Rice to Assess Root Characteristics Associated with Allelopathy

Weedy rice is a species of Oryza, and is a wild relative of cultivated rice. The weed possesses unique hardiness that allows them to thrive in dynamic and stressful environments. These characteristics suggest that weedy rice is a stored source of novel genes for competitive traits. One such trait is allelopathy, where a species releases secondary metabolites that suppress the growth and development of neighboring species. Weed competition is a limiting factor in rice production systems; therefore, it is critical to identify specific allelopathic weedy rice accessions to determine the genetic pathways and mechanisms associated with allelopathy to be used in breeding programs. Due to the complex nature of allelochemical production and the lack of knowledge of allelopathy mechanisms in weedy rice, phenotypic traits, particularly root traits, can be used to overcome this limitation and serve as target characteristics for breeding weed suppressive rice varieties. Five weedy rice accessions were chosen from preliminary screenings of larger sample sizes with the ability to suppress barnyardgrass weed seedling growth. Another five weedy rice with low barnyardgrass suppression was selected for the current root phenotypic study. Five cultivated rice lines were used as a comparison. All plants were propagated in a transparent germination pouch for four weeks. Roots were scanned and analyzed for root length and area covered. No differences were found in the seedling root area among weedy rice and rice accessions; however, allelopathic weedy rice plants exhibited a 14% increase in root length than non-allelopathic weedy rice plants. The allelopathic weedy rice accession B2 possessed the most extended root system (22.4 cm root length). The highly allelopathic weedy rice accessions (including B2) screened and phenotyped in this study are ideal candidates for identifying the genetic controls of early root length, a possible trait contributing to underground allelopathic production and competitive advantage.

Inhibition or Facilitation? Contrasted Inter-Specific Interactions in Sphagnum under Laboratory and Field Conditions.

In a natural environment, plants usually interact with their neighbors predominantly through resource competition, allelopathy, and facilitation. The occurrence of the positive effect of allelopathy between peat mosses (Sphagnum L.) is rare, but it has been observed in a field experiment. It is unclear whether the stability of the water table level in peat induces positive vs. negative effects of allelopathy and how that is related to phenolic allelochemical production in Sphagnum. Based on field experiment data, we established a laboratory experiment with three neighborhood treatments to measure inter-specific interactions between Sphagnum angustifolium (Russ.) C. Jens and Sphagnum magellanicum Brid. We found that the two species were strongly suppressed by the allelopathic effects of each other. S. magellanicum allelopathically facilitated S. angustifolium in the field but inhibited it in the laboratory, and relative allelopathy intensity appeared to be positively related to the content of released phenolics. We conclude that the interaction type and intensity between plants are dependent on environmental conditions. The concentration of phenolics alone may not explain the type and relative intensity of allelopathy. Carefully designed combined field and laboratory experiments are necessary to reveal the mechanism of species interactions in natural communities.