Controlling weeds with fungi, bacteria and viruses: a review

Selective biotic stressors' action on seed germination: A review

In the realm of plant biology and agriculture, seed germination serves as a fundamental process with far-reaching implications for crop production and environmental health. This comprehensive review seeks to unravel the intricate web of interactions between some biotic stressors and seed germination, addressing the pertinent issue of how these stressors influence seed germination. Different chemicals produced by interacting plants (different parts), fungi, bacteria, or insects can either promote or inhibit seed germination. Releasing chemicals that modulate signaling pathways and cellular processes significantly disrupt essential cellular functions. This disruption leads to diverse germination outcomes, introducing additional layers of complexity to this regulatory landscape. The chemicals perturb enzyme activity and membrane integrity, imposing unique challenges on the germination process. Understanding the mechanisms- how allelochemicals, mycotoxins, or bacterial toxins affect seed germination or the modes of action holds promise for more sustainable agricultural practices, enhanced pest control, and improved environmental outcomes. In sum, this review contributes to a fundamental exposition of the pivotal role of biotic stressors in shaping the germination of seeds.

Effects of Bipolaris yamadae strain HXDC-1-2 as a bioherbicide against Echinochloa crus-galli in rice and dry fields

BACKGROUND

Barnyardgrass (Weed Science Society of America recommended) or Barnyard grass (Britannica recommended) (Echinochloa crus-galli (L.) P. Beauv.) is one of the most problematic and dominant weeds in world agricultural systems, especially in paddy fields, where tillering and grain yield can be reduced by 50-70% because of its competitive pressure. The frequent use of chemical herbicides to control E. crus-galli has led to the evolution of herbicide resistance. Developing bioherbicides using pathogenic fungi to control E. crus-galli could be an alternative option.

RESULTS

In a previous study we showed that a strain of Bipolaris yamadae (HXDC-1-2) was promising in controlling gramineous weeds. Here we present a study that evaluated this fungus as a mycoherbicide against E. crus-galli in greenhouse and paddy fields, characterized mycelium growth and conidial production, and examined the infection development. The median effective dose (ED50) and 90% effective dose (ED90) values of microcapsulated B. yamadae strain HXDC-1-2 on E. crus-galli in the greenhouse were 7.17 × 102 and 9.35 × 103 conidia mL-1, respectively. Conidial germination, mycelial growth, and attachment formation occurred on E. crus-galli leaves within 1 to 6 h. The hyphae directly invaded cells and stomata, primarily from the appressorium on the epidermis, and necrotic lesions were observed on the leaf surface within 20 to 24 h. Applied to E. crus-galli plants at 1 × 105 conidia mL-1, the fungus reduced the weed's fresh weight of 75%.

CONCLUSION

B. yamadae strain HXDC-1-2 has the potential to be developed as a bioherbicide against E. crus-galli plants, especially in rice fields. © 2024 Society of Chemical Industry.

Emerging technologies for the removal of pesticides from contaminated soils and their reuse in agriculture

Pesticides are becoming more prevalent in agriculture to protect crops and increase crop yields. However, nearly all pesticides used for this purpose reach non-target crops and remain as residues for extended periods. Contamination of soil by widespread pesticide use, as well as its toxicity to humans and other living organisms, is a global concern. This has prompted us to find solutions and develop alternative remediation technologies for sustainable management. This article reviews recent technological developments for remediating pesticides from contaminated soil, focusing on the following major points: (1) The application of various pesticide types and their properties, the sources of pesticides related to soil pollution, their transport and distribution, their fate, the impact on soil and human health, and the extrinsic and intrinsic factors that affect the remediation process are the main points of focus. (2) Sustainable pesticide degradation mechanisms and various emerging nano- and bioelectrochemical soil remediation technologies. (3) The feasible and long-term sustainable research and development approaches that are required for on-site pesticide removal from soils, as well as prospects for applying them directly in agricultural fields. In this critical analysis, we found that bioremediation technology has the potential for up to 90% pesticide removal from the soil. The complete removal of pesticides through a single biological treatment approach is still a challenging task; however, the combination of electrochemical oxidation and bioelectrochemical system approaches can achieve the complete removal of pesticides from soil. Further research is required to remove pesticides directly from soils in agricultural fields on a large-scale.

Trichoderma koningiopsis fermentation in airlift bioreactor for bioherbicide production

During scaling of fermentations, choosing a bioreactor is fundamental to ensure the product's quality. This study aims to produce bioherbicides using Trichoderma koningiopsis fermentation, evaluating process parameters in an Airlift bioreactor. As a response, we quantified the production of enzymes involved in the bioherbicide activity (amylase, cellulase, laccase, lipase, and peroxidase). In addition, it evaluated the agronomic efficiency of the fermented extract optimized through tests that promoted soybean growth and nodulation, soybean seed germination, and in vitro phytopathogen control. As a result of optimizing the scaling bioprocess, it was possible to obtain an adequate fermentation condition, which, when applied to soybean seeds, had beneficial effects on their growth. It allowed the production of an enzyme cocktail. These results add a crucial biotechnological potential factor for the success of the optimized formulation in the Airlift bioreactor, in addition to presenting relevant results for the scientific community.

Sustainable synthesis of bionanomaterials using non-native plant extracts for maintaining ecological balance: A computational bibliography analysis

Biological approaches via biomolecular extracts of bacteria, fungi, or plants have recently been introduced as an alternative approach to synthesizing less or nontoxic nanomaterials, compared to conventional physical and chemical approaches. Among these biological methods, plant-mediated approaches (phytosynthesis) are reported to be highly beneficial for large-scale, nontoxic nanomaterial synthesis. However, plant-mediated synthesis of nanomaterials using native plant extract can lead to bioprospecting issues and deforestation challenges. On the other hand, non-native or invasive plants are non-indigenous to a particular geographic location that can grow and spread rapidly, ultimately disrupting the local and endogenous plant communities or ecosystems. Thus, controlling or eradicating these non-native plants before they damage the ecosystem is necessary. Even though mechanical, chemical, and biological approaches are available to control non-native plants, all these methods possess certain limitations, such as environmental toxicity, disturbance in the nutrient cycle, and loss of genetic integrity. Therefore, non-native plants were recently proposed as a novel sustainable source of phytochemicals for preparing nanomaterials via green chemistry, mainly metallic nanoparticles, as an alternative to native, agriculture-based, or medicinal plants. This work aims to cover a literature gap on plant-mediated bionanomaterial synthesis with an overview and bibliography analysis of non-native plants via novel data mining and advanced visualization tools. In addition, the potential of non-native plants as a sustainable, green chemistry-based alternative for bionanomaterial preparation for maintaining ecological balance, the mechanism of formation via phytochemicals, and their possible applications to promote their control and spread were also discussed. The bibliography analysis revealed that only an average of 4 articles have been published in the last 10 years (2013-2023) on non-native/invasive plants for nanomaterial synthesis, which shows the significance of this article.

Strategies for mitigation of pesticides from the environment through alternative approaches: A review of recent developments and future prospects

Chemical-based peticides are having negative impacts on both the healths of human beings and plants as well. The World Health Organisation (WHO), reported that each year, >25 million individuals in poor nations are having acute pesticide poisoning cases along with 20,000 fatal injuries at global level. Normally, only ∼0.1% of the pesticide reaches to the intended targets, and rest amount is expected to come into the food chain/environment for a longer period of time. Therefore, it is crucial to reduce the amounts of pesticides present in the soil. Physical or chemical treatments are either expensive or incapable to do so. Hence, pesticide detoxification can be achieved through bioremediation/biotechnologies, including nano-based methodologies, integrated approaches etc. These are relatively affordable, efficient and environmentally sound methods. Therefore, alternate strategies like as advanced biotechnological tools like as CRISPR Cas system, RNAi and genetic engineering for development of insects and pest resistant plants which are directly involved in the development of disease- and pest-resistant plants and indirectly reduce the use of pesticides. Omics tools and multi omics approaches like metagenomics, genomics, transcriptomics, proteomics, and metabolomics for the efficient functional gene mining and their validation for bioremediation of pesticides also discussed from the literatures. Overall, the review focuses on the most recent advancements in bioremediation methods to lessen the effects of pesticides along with the role of microorganisms in pesticides elimination. Further, pesticide detection is also a big challenge which can be done by using HPLC, GC, SERS, and LSPR ELISA etc. which have also been described in this review.

Evaluation of Bipolaris yamadae as a bioherbicidal agent against grass weeds in arable crops

BACKGROUND

Weeds are among the most damaging pests of agriculture, causing ≈10% worldwide reduction in crop productivity each year. Over-reliance on synthetic chemical herbicides has caused weeds around the world to evolve resistance. Bioherbicides may be an alternative. However, among their many constraints including strict environmental requirements, complicated mass-production and high product costs, limited pathogenicity and a narrow spectrum of activity are frequently encountered and are major barriers to commercialization.

RESULTS

We isolated a pathogenic fungus, HXDC-1-2, from diseased leaves of a gramineous weed, stiltgrass [Microstegium vimineum (Trin.) A. Camus], from the edge of farmland in Guizhou province, China. HXDC-1-2 was identified as the fungal species Bipolaris yamadae based on the morphological characteristics and ITS-GPDH-EF1α multiple primer analysis. Its potential as a bioherbicide was evaluated by determining its weed control efficacy and crop safety. The ED50 and ED90 values of HXDC-1-2 on Echinochloa crus-galli were 3.22 × 103 and 1.32 × 105 conidia mL-1 , respectively. Host range tests revealed that 20 gramineous weeds including Setaria viridis, Leptochloa chinensis, Eleusine indica, Pseudosorghum zollingeri, Leptochloa panicea, Bromus catharticus, E. crus-galli plants, were extremely susceptible whereas 77 crop species from 27 plant families including rice, wheat, barley, corn, soybean and cotton (excluding cowpea and sorghum) were unaffected.

CONCLUSION

Bipolaris yamadae strain HXDC-1-2 has great potential to be developed as a commercial broad-spectrum bioherbicidal agent for controlling grass weeds in arable crops. © 2023 Society of Chemical Industry.

Action of the fungal compound citrinin, a bioherbicide candidate, on photosystem II

BACKGROUND

Bioherbicides are becoming more attractive as safe weed control tools towards sustainable agriculture. Natural products constitute an important source chemicals and chemical leads for discovery and development of novel pesticide target sites. Citrinin is a bioactive compound produced by fungi of the genera Penicillium and Aspergillus. However, its physiological-biochemical mechanism as a phytotoxin remains unclear.

RESULTS

Citrinin causes visible leaf lesions on Ageratina adenophora similar to those produced by the commercial herbicide bromoxynil. Phytotoxicity bioassay tests using 24 plant species confirmed that citrinin has a broad activity spectrum and therefore has potential as a bioherbicide. Based on chlorophyll fluorescence studies, citrinin mainly blocks PSII electron flow beyond plastoquinone QA at the acceptor side, resulting in the inactivation of PSII reaction centers. Furthermore, molecular modeling of citrinin docking to the A. adenophora D1 protein suggests that it binds to the plastoquinone QB site by a hydrogen bond between the O1 hydroxy oxygen atom of citrinin and the histidine 215 of the D1 protein, the same way as classical phenolic PSII herbicides do. Finally, 32 new citrinin derivatives were designed and sorted according to free energies on the basis of the molecular model of an interaction between the citrinin molecule and the D1 protein. Five of the modeled compounds had much higher ligand binding affinity within the D1 protein compared with lead compound citrinin.

CONCLUSION

Citrinin is a novel natural PSII inhibitor that has the potential to be developed into a bioherbicide or utilized as a lead compound for discovery of new derivatives with high herbicidal potency. © 2023 Society of Chemical Industry.

Endophytic fungi: an overview on biotechnological and agronomic potential

Abstract Endophytic fungi colonize the inter- and/or intracellular regions of healthy plant tissues and have a close symbiotic relationship with their hosts. These microorganisms produce antibiotics, enzymes, and other bioactive compounds that enable them to survive in competitive habitats with other microorganisms. In addition, secondary metabolites confer protection to their host plant against other bacterial and fungal pathogens and/or can promote plant growth. Endophytic fungi are viewed as a promising source of bioactive natural products, which can be optimized through changes in growing conditions. The exploration of novel bioactive molecules produced by these microorganisms has been attracting attention from researchers. The chemical and functional diversity of natural products from endophytic fungi exhibits a broad spectrum of applications in medicine, agriculture, industry and the environment. Fungal endophytes can also enhance the photoprotective effects and photochemical efficiency in the host plants. Modern omic approaches have facilitated research investigating symbiotic plant-endophytic fungi interactions. Therefore, research on endophytic fungi can help discovery novel biomolecules for various biotechnological applications and develop a sustainable agriculture.

Can nanotechnology improve the application of bioherbicides?

Bioherbicides are composed of microorganisms or natural compounds and are used for weed control; however, they have specific weaknesses and constraints that hinder their development and success under field conditions. Nanotechnology can help to overcome these limitations by providing a good starting point for the design of specific formulations and carriers that minimize the deficiencies of natural compounds and microorganisms, such as low solubility, short shelf life or a loss of viability. In addition, nanoformulations can help to improve the efficacy of bioherbicides by increasing their effectiveness and bioavailability, reducing the amount required for a treatment, and enhancing their ability to target specific weeds while preserving the crop. However, it is important to choose the right materials and nanodevices depending on specific needs and considering several factors inherent to nanomaterials such as production cost, safety or possible toxic effects. © 2023 Society of Chemical Industry.

Broad host-range pathogens as bioherbicides: managing nontarget plant disease risk

Plant pathogens with a broad host range are commercially more attractive as microbial bioherbicides than strictly host-specific pathogens as a result of the wider market potential of a product capable of controlling multiple species. However, the perceived spatiotemporal disease risk to nontarget plants is a barrier to their adoption for weed control. We consider two approaches to managing this risk. First, we consider safety zones and withholding periods for bioherbicide treatment sites. These must ensure inoculum spreading from, or surviving at the site, exposes nontarget plants to no more inoculum than from natural sources. They can be determined using simple dispersal models. We show that a ratio of added:natural inoculum of 1.0 is biologically reasonable as an 'acceptable risk' and a sound basis for safety zones and withholding periods. These would be analogous to the 'conditions of use' for synthetic chemical herbicides aimed at minimizing collateral damage to susceptible plants from spray drift and persistent soil residues. Second, weed-specific isolates of broad host-range pathogens may avoid the need for safety zones and withholding periods. Such isolates have been found in many broad host-range pathogen species. Their utilization as bioherbicides may more easily meet the requirements of regulators. Mixtures of different weed-specific isolates of a pathogen could provide bioherbicides with commercially attractive spectrums of weed control activity. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Potential of utilizing pathogen-derived mycotoxins as alternatives to synthetic herbicides in controlling the noxious invasive plant Xanthium italicum

Discovery of environmentally friendly agents for controlling alien invasive species (AIS) is challenging and in urgent need as their expansion continues to increase. Xanthium italicum is a notorious invasive weed that has caused serious ecological and economic impacts worldwide. For the purpose of exploring the possibility of utilizing herbicidal mycotoxins to control this species, three compounds, a new compound, curvularioxide (1), a new naturally occurring compound, dehydroradicinin (2), and a known compound, radicinin (3), were isolated via activity-guided fractionation from the secondary metabolites of the pathogenic Curvularia inaequalis, which was found to infect X. italicum in natural habitats. All isolated compounds exhibited potent herbicidal activity on receiver species. It is noteworthy to mention that their effects on X. italicum in our bioassays were equivalent to the commercial herbicide glyphosate. Subsequent morphological analysis revealed that application of radicinin (3) severely hindered X. italicum seedlings' hypocotyl and root development. Malondialdehyde content and the activity of catalase and peroxidase of the seedlings were also significantly different from the control, implying the occurrence of induced oxidative stress. Our results suggest that pathogens infecting invasive plants might be valuable resources for developing safer herbicides for controlling weeds. © 2023 Society of Chemical Industry.

Biological Control of Weeds in turfgrass: opportunities and misconceptions

Turfgrass systems may offer opportunities for overcoming some constraints on the successful implementation of weed biocontrol. Of the roughly 16.4 million ha of turfgrass in the USA, ≈60-75% are in residential lawns and 3% are golf turf. Annual expenditures for a standard herbicide treatment regimen for residential turf are estimated to be ≈US$326 ha-1 , about 2-3-fold greater than that for USA corn and soybean growers. Expenditures can be >US$3000 ha-1 for control of certain weeds such as Poa annua in high-value areas including golf fairways or greens, but those applications are made to far smaller areas. Regulatory actions and consumer preferences are creating market opportunities for alternatives to synthetic herbicides in both commercial and consumer markets, but the size of these markets and willingness-to-pay are poorly documented. Turfgrass sites are intensively managed, yet despite the ability to modify site conditions through irrigation, mowing and fertility management, microbial biocontrol agents tested thus far have not provided the consistently high levels of weed control expected in the market. Recent advances in microbial bioherbicide products may offer a path to overcome many of the obstacles to success. No single herbicide will control the diversity of turfgrass weeds, nor will any single biocontrol agent or biopesticide. Successful development of weed biocontrol for turfgrass systems will require numerous, effective biocontrol agents for the many weed species found in turfgrass environments, as well as a deeper understanding of different turfgrass market segments, and weed management expectations for each segment. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Fungus-based bioherbicides on circular economy

This review aimed to show that bioherbicides are possible in organic agriculture as natural compounds from fungi and metabolites produced by them. It is discussed that new formulations must be developed to improve field stability and enable the commercialization of microbial herbicides. Due to these bottlenecks, it is crucial to advance the bioprocesses behind the formulation and fermentation of bio-based herbicides, scaling up, strategies for field application, and the potential of bioherbicides in the global market. In this sense, it proposed insights for modern agriculture based on sustainable development and circular economy, precisely the formulation, scale-up, and field application of microbial bioherbicides.

Chinee Apple (Ziziphus mauritiana): A Comprehensive Review of Its Weediness, Ecological Impacts and Management Approaches

Ziziphus mauritiana Lam. (Rhamnaceae) (Chinee Apple, Indian Jujube, or Ber) is a significant woody weed in the drier tropics of northern Queensland, Western Australia, and the Northern Territory. Throughout these regions, its densely formed thickets influence the structure, function, and composition of rangeland ecosystems by outcompeting native pasture species. Despite this, the recent literature is heavily focused on the horticultural value of domesticated Ziziphus species in South Asia (China, India, and Pakistan), particularly its potential for poverty alleviation in arid or semi-arid areas. In fact, there has been comparatively little research undertaken on its invasiveness or associated ecological factors in pastoral contexts. Currently, the management of Z. mauritiana is limited to the application of synthetic herbicides or mechanical clearing operations. There is also considerable interest in the exploitation of host-specific, natural enemies (biological control agents, herbivorous insects, fungi, bacteria, or viruses) for limiting the vigour, competitiveness, or reproductive capacity of Z. mauritiana in northern Australia. The development of a "bioherbicide" in lieu of synthetic counterparts may foster a more resilient coexistence between agricultural systems and the natural environment owing to its reduced environmental persistence and increased target specificity. This review summarises the current literature on the weediness, ecological impacts, and current management of this problematic weed, thereby identifying (i) opportunities for further research and (ii) recommendations for improved management within its invasive range.

New frontiers of soil fungal microbiome and its application for biotechnology in agriculture

The fungi-based technology provided encouraging scenarios in the transition from a conventionally based economic system to the potential security of sources closely associated with the agricultural sphere such as the agriculture. In recent years, the intensification of fungi-based processes has generated significant gains, additionally to the production of materials with significant benefits and strong environmental importance. Furthermore, the growing concern for human health, especially in the agriculture scenario, has fostered the investigation of organisms with high biological and beneficial potential for use in agricultural systems. Accordingly, this study offered a comprehensive review of the diversity of the soil fungal microbiome and its main applications in a biotechnological approach aimed at agriculture and food chain-related areas. Moreover, the spectrum of opportunities and the extensive optimization platform for obtaining fungi compounds and metabolites are discussed. Finally, future perspectives regarding the insurgency of innovations and challenges on the broad rise of visionary solutions applied to the biotechnology context are provided.

Abutilon theophrasti's Resilience against Allelochemical-Based Weed Management in Sustainable Agriculture - Due to Collection of Highly Advantageous Microorganisms?

Abutilon theophrasti Medik. (velvetleaf) is a problematic annual weed in field crops which has invaded many temperate parts of the world. Since the loss of crop yields can be extensive, approaches to manage the weed include not only conventional methods, but also biological methods, for instance by microorganisms releasing phytotoxins and plant-derived allelochemicals. Additionally, benzoxazinoid-rich rye mulches effective in managing common weeds like Amaranthus retroflexus L. have been tested for this purpose. However, recent methods for biological control are still unreliable in terms of intensity and duration. Rye mulches were also ineffective in managing velvetleaf. In this review, we present the attempts to reduce velvetleaf infestation by biological methods and discuss possible reasons for the failure. The resilience of velvetleaf may be due to the extraordinary capacity of the plant to collect, for its own survival, the most suitable microorganisms from a given farming site, genetic and epigenetic adaptations, and a high stress memory. Such properties may have developed together with other advantageous abilities during selection by humans when the plant was used as a crop. Rewilding could be responsible for improving the microbiomes of A. theophrasti.

Agriculture without paraquat is feasible without loss of productivity-lessons learned from phasing out a highly hazardous herbicide

A small proportion of the thousands of pesticides on the market today are associated with a disproportionately high incidence of severe acute pesticide poisoning and suicide. Paraquat stands out as one of the most lethal pesticides in common use, frequently involved in fatal incidents due to suicides or accidental exposure. Even though paraquat has been banned in over 67 countries, it is still widely used in many others, particularly in Asia and Latin America. Based on a literature review and consultations, this paper identifies options for replacing paraquat and distils practical lessons from numerous successes around the world. Our aim is to support regulators, policymakers, agronomists and the supply chain sector with practical information related to phasing out paraquat. Production data consistently failed to show any negative effects of banning paraquat on agricultural productivity. A wide range of alternative approaches to weed management and crop defoliation are available, many of which do not rely on herbicides. Over 1.25 million farmers in low- and middle-income countries (LMICs) successfully produce a range of crops for private voluntary standards (PVS) in food and fiber supply chains which prohibit paraquat use. We conclude from the findings of this study that eliminating paraquat will save lives without reducing agricultural productivity. Less hazardous and more sustainable alternatives exist. To enhance successful adoption and uptake of these methods on a wide scale, farmers require training and support within an enabling policy environment.

Effect of Mycotoxin Cytochalasin A on Photosystem II in Ageratina adenophora

Biological herbicides have received much attention due to their abundant resources, low development cost, unique targets and environmental friendliness. This study reveals some interesting effects of mycotoxin cytochalasin A (CA) on photosystem II (PSII). Our results suggested that CA causes leaf lesions on Ageratina adenophora due to its multiple effects on PSII. At a half-inhibitory concentration of 58.5 μΜ (I₅₀, 58.5 μΜ), the rate of O₂ evolution of PSII was significantly inhibited by CA. This indicates that CA possesses excellent phytotoxicity and exhibits potential herbicidal activity. Based on the increase in the J-step of the chlorophyll fluorescence rise OJIP curve and the analysis of some JIP-test parameters, similar to the classical herbicide diuron, CA interrupted PSII electron transfer beyond Q_A at the acceptor side, leading to damage to the PSII antenna structure and inactivation of reaction centers. Molecular docking model of CA and D1 protein of A. adenophora further suggests that CA directly targets the Q_B site of D1 protein. The potential hydrogen bonds are formed between CA and residues D1-His215, D1-Ala263 and D1-Ser264, respectively. The binding of CA to residue D1-Ala263 is novel. Thus, CA is a new natural PSII inhibitor. These results clarify the mode of action of CA in photosynthesis, providing valuable information and potential implications for the design of novel bioherbicides.

Herbicidal characteristics and structural identification of a potential active compound produced by Streptomyces sp. KRA18-249

The KRA18-249 strain, isolated from a natural recreational forest near Jeongseon, Gangwon-do, when applied to plants induced signs of wilting within 24 h, leading to plant death. The isolated actinomycete was identified as Streptomyces gardneri based on 16S rRNA gene homogeneity analysis. The culture filtrate was solvent fractionated to obtain the active substance, and the active compound 249-Y1 was isolated from the purified fractions via a herbicide activity test using Digitaria ciliaris. NMR and ESI-MS analyses revealed that the molecular formula of 249-Y1 is C₂₀H₁₆O₆ [MW = 352.0947] and is an anthraquinone (rubiginone D2) produce by polyketide synthetase system. The active compound 249-Y1 showed strong (100%) herbicidal activity against several weeds at 500 μg mL^-1 concentration. Twisting symptoms began to appear within 24 h of treatment and intensified over time. The KRA18-249 strain produced the herbicidal compound under specific culture conditions, that is, at 200 rpm, 35 °C, for eight days at an initial pH of 10. We also found that 249-Y1 inhibited chlorophyll, but was not a radical generator. Overall, the secondary metabolite 249-Y1, produced by KRA18-249, can be used as a new biological agent for weed control.

Achievements, Developments and Future Challenges in the Field of Bioherbicides for Weed Control: A Global Review

The intrusion of weeds into fertile areas has resulted in significant global economic and environmental impacts on agricultural production systems and native ecosystems, hence without ongoing and repeated management actions, the maintenance or restoration of these systems will become increasingly challenging. The establishment of herbicide resistance in many species and unwanted pollution caused by synthetic herbicides has ushered in the need for alternative, eco-friendly sustainable management strategies, such as the use of bioherbicides. Of the array of bioherbicides currently available, the most successful products appear to be sourced from fungi (mycoherbicides), with at least 16 products being developed for commercial use globally. Over the last few decades, bioherbicides sourced from bacteria and plant extracts (such as allelochemicals and essential oils), together with viruses, have also shown marked success in controlling various weeds. Despite this encouraging trend, ongoing research is still required for these compounds to be economically viable and successful in the long term. It is apparent that more focused research is required for (i) the improvement of the commercialisation processes, including the cost-effectiveness and scale of production of these materials; (ii) the discovery of new production sources, such as bacteria, fungi, plants or viruses and (iii) the understanding of the environmental influence on the efficacy of these compounds, such as atmospheric CO₂, humidity, soil water stress, temperature and UV radiation.

Microbe Related Chemical Signalling and Its Application in Agriculture

The agriculture sector has been put under tremendous strain by the world’s growing population. The use of fertilizers and pesticides in conventional farming has had a negative impact on the environment and human health. Sustainable agriculture attempts to maintain productivity, while protecting the environment and feeding the global population. The importance of soil-dwelling microbial populations in overcoming these issues cannot be overstated. Various processes such as rhizospheric competence, antibiosis, release of enzymes, and induction of systemic resistance in host plants are all used by microbes to influence plant-microbe interactions. These processes are largely founded on chemical signalling. Producing, releasing, detecting, and responding to chemicals are all part of chemical signalling. Different microbes released distinct sorts of chemical signal molecules which interacts with the environment and hosts. Microbial chemicals affect symbiosis, virulence, competence, conjugation, antibiotic production, motility, sporulation, and biofilm growth, to name a few. We present an in-depth overview of chemical signalling between bacteria-bacteria, bacteria-fungi, and plant-microbe and the diverse roles played by these compounds in plant microbe interactions. These compounds’ current and potential uses and significance in agriculture have been highlighted.

Neurotoxicological Profiling of Paraquat in Zebrafish Model

Paraquat is a polar herbicide protecting plant products against invasive species, it requires careful manipulation and restricted usage because of its harmful potentials. Exposure to paraquat triggers oxidative damage in dopaminergic neurons and subsequently causes a behavioral defect in vivo. Thereby, persistent exposure to paraquat is known to increase Parkinson's disease risk by dysregulating dopaminergic systems in humans. Therefore, most studies have focused on the dopaminergic systems to elucidate the neurotoxicological mechanism of paraquat poisoning, and more comprehensive neurochemistry including histaminergic, serotonergic, cholinergic, and GABAergic systems has remained unclear. Therefore, in this study, we investigated the toxicological potential of paraquat poisoning using a variety of approaches such as toxicokinetic profiles, behavioral effects, neural activity, and broad-spectrum neurochemistry in zebrafish larvae after short-term exposure to paraquat and we performed the molecular modeling approach. Our results showed that paraquat was slowly absorbed in the brain of zebrafish after oral administration of paraquat. In addition, paraquat toxicity resulted in behavioral impairments, namely, reduced motor activity and led to abnormal neural activities in zebrafish larvae. This locomotor deficit came with a dysregulation of dopamine synthesis induced by the inhibition of tyrosine hydroxylase activity, which was also indirectly confirmed by molecular modeling studies. Furthermore, short-term exposure to paraquat also caused simultaneous dysregulation of other neurochemistry including cholinergic and serotonergic systems in zebrafish larvae. The present study suggests that this neurotoxicological profiling could be a useful tool for understanding the brain neurochemistry of neurotoxic agents that might be a potential risk to human and environmental health.

Phytotoxic Azaphilones From the Mangrove-Derived Fungus Penicillium sclerotiorum HY5

Mangrove is a unique marine ecosystem growing in the intertidal zone of tropical and subtropical coast, with the characteristics of hypoxia tolerance, high salinity, and high humidity. In order to discover novel leading compounds with potent phytotoxicity, seven pairs of azaphilones E/Z isomers, isochromophilone H (1a/1b), sclerotiorins A and B (2a/2b and 3a/3b), ochlephilone (4a/4b), isochromophilone IV (5a/5b), isochromophilone J (6a/6b), and isochromophilone I (7a/7b), were isolated from the culture broth of the mangrove-derived fungus, the Penicillium sclerotiorum HY5, by various chromatographic methods. Among them, 1a, 1b, 2a, 3a, 4a, 5a, 6a, and 6b were new compounds. Their chemical structures and absolute configurations were elucidated based on high resolution electrospray ionization mass spectroscopy (HRESIMS), 1D/2D nuclear magnetic resonance (NMR) spectroscopic analysis, and comparisons of electronic circular dichroism (ECD) data. Compounds 3, 4, and 7 exhibited potent phytotoxicity against the growth of radicle and plumule on Amaranthus retroflexus L., with EC₅₀ values ranging from 234.87 to 320.84 μM, compared to the positive control glufosinate-ammonium, with EC₅₀ values of 555.11 μM for radicle, and 656.04 μM for plumule. Compounds 4 and 7 also showed inhibitory effects on the growth of velvetleaf (Abutilon theophrasti Medikus), with EC₅₀ values ranging from 768.97 to 1,201.52 μM. This study provides new leading compounds for the research and development of marine-derived bioherbicides.

Pathogenic potential and phytotoxic effects of Coniolariella gamsii Iran 2506C on Iranian knapweed (Centaurea depressa)

Application of fungal phytotoxins is one of the possible solutions to reduce the use of chemical products in agricultural fields. Phytotoxic compounds isolated from phytopathogenic fungi provide a promising source of environmentally friendly herbicides. This paper focuses on the phytotoxic fungus Coniolariella gamsii Iran 2506C as a fungal pathogen against Iranian knapweed (Centaurea depressa) in the western Iran and investigate its phytotoxic constituents. The fungal pathogen was identified on the basis of morphological characteristics and confirmed by sequencing of the internal transcribed spacer (ITS) region and partial LSU rDNA gene. Pathogenicity tests were conducted on the weed seedlings and C. gamsii Iran 2506C isolate with high disease severity was selected for phytotoxin studies. Phytotoxic activity of the isolate was checked by screening the production of phytotoxins, which interestingly inhibited seed germination and seedling growth of Iranian knapweed as compared to wheat in the bioassays. The active metabolites were extracted from cell-free culture filtrate (CFCF) by ethyl acetate and separated by thin layer chromatography (TLC). The results indicated that two out of four spots had phytotoxicity with R_f values of 0.43 and 0.82 on the weed, whereas wheat was not sensitive in the bioassays. Using Gas Chromatography-Mass spectrometry (GC-MS), 3-Carene and Oleic acid were identified as the main constituents and quantified by a gas chromatographic method with 12.7 ± 0.03 and 2.9 ± 0.01 μg ml^-1 respectively. This is the first finding presented on the phytotoxic effects of the active metabolites of C. gamsii Iran 2506C and highlights its herbicidal potential which can be used as a biocontrol agent of C. depressa.

Diacetoxyscirpenol, a Fusarium exometabolite, prevents efficiently the incidence of the parasitic weed Striga hermonthica

BACKGROUND

Certain Fusarium exometabolites have been reported to inhibit seed germination of the cereal-parasitizing witchweed, Striga hermonthica, in vitro. However, it is unknown if these exometabolites will consistently prevent S. hermonthica incidence in planta. The study screened a selection of known, highly phytotoxic Fusarium exometabolites, in identifying the most potent/efficient candidate (i.e., having the greatest effect at minimal concentration) to completely hinder S. hermonthica seed germination in vitro and incidence in planta, without affecting the host crop development and yield.

RESULTS

In vitro germination assays of the tested Fusarium exometabolites (i.e., 1,4-naphthoquinone, equisetin, fusaric acid, hymeglusin, neosolaniol (Neo), T-2 toxin (T-2) and diacetoxyscirpenol (DAS)) as pre-Striga seed conditioning treatments at 1, 5, 10, 20, 50 and 100 µM, revealed that only DAS, out of all tested exometabolites, completely inhibited S. hermonthica seed germination at each concentration. It was followed by T-2 and Neo, as from 10 to 20 µM respectively. The remaining exometabolites reduced S. hermonthica seed germination as from 20 µM (P < 0. 0001). In planta assessment (in a S. hermonthica-sorghum parasitic system) of the exometabolites at 20 µM showed that, although, none of the tested exometabolites affected sorghum aboveground dry biomass (P > 0.05), only DAS completely prevented S. hermonthica incidence. Following a 14-d incubation of DAS in the planting soil substrate, bacterial 16S ribosomal RNA (rRNA) and fungal 18S rRNA gene copy numbers of the soil microbial community were enhanced; which coincided with complete degradation of DAS in the substrate. Metabolic footprinting revealed that the S. hermonthica mycoherbicidal agent, Fusarium oxysporum f. sp. strigae (isolates Foxy-2, FK3), did not produce DAS; a discovery that corresponded with underexpression of key genes (Tri5, Tri4) necessary for Fusarium trichothecene biosynthesis (P < 0.0001).

CONCLUSIONS

Among the tested Fusarium exometabolites, DAS exhibited the most promising herbicidal potential against S. hermonthica. Thus, it could serve as a new biocontrol agent for efficient S. hermonthica management. Further examination of DAS specific mode of action against the target weed S. hermonthica at low concentrations (≤ 20 µM), as opposed to non-target soil organisms, is required.

Nano-enabled agrochemicals/materials: Potential human health impact, risk assessment, management strategies and future prospects

Nanotechnology is a rapidly developing technology that will have a significant impact on product development in the next few years. The technology is already being employed in cutting-edge cosmetic and healthcare products. Nanotechnology and nanoparticles have a strong potential for product and process innovation in the food industrial sector. This is already being demonstrated by food product availability made using nanotechnology. Nanotechnologies will have an impact on food security, packaging materials, delivery systems, bioavailability, and new disease detection materials in the food production chain, contributing to the UN Millennium Development Goals targets. Food products using nanoparticles are already gaining traction into the market, with an emphasis on online sales. This means that pre- and post-marketing regulatory frameworks and risk assessments must meet certain standards. There are potential advantages of nanotechnologies for agriculture, consumers and the food industry at large as they are with other new and growing technologies. However, little is understood about the safety implications of applying nanotechnologies to agriculture and incorporating nanoparticles into food. As a result, policymakers and scientists must move quickly, as regulatory systems appear to require change, and scientists should contribute to these adaptations. Their combined efforts should make it easier to reduce health and environmental impacts while also promoting the economic growth of nanotechnologies in the food supply chain. This review highlighted the benefits of a number of nano enabled agrochemicals/materials, the potential health impacts as well as the risk assessment and risk management for nanoparticles in the agriculture and food production chain.

Weeds harbor an impressive diversity of fungi, which offers possibilities for biocontrol

The use of herbicides for weed control is very common, but some of them represent a threat to human health, are environmentally detrimental and stimulate herbicide resistance. Therefore, using microorganisms as natural herbicides appears as a promising alternative. The mycoflorae colonizing different species of symptomatic and asymptomatic weeds were compared to characterize the possible mycoherbicidal candidates associated with symptomatic weeds. A collection of 475 symptomatic and asymptomatic plants belonging to 23 weed species was established. A metabarcoding approach based on amplification of the internal transcribed spacer (ITS) region combined with high-throughput amplicon sequencing revealed the diversity of fungal communities hosted by these weeds: 542 fungal genera were identified. The variability of the composition of fungal communities revealed a dispersed distribution of taxa governed neither by geographical location nor by the botanical species, suggesting a common core displaying non-specific interactions with host plants. Beyond this core, specific taxa were more particularly associated with symptomatic plants. Some of these, such as Alternaria, Blumeria, Cercospora, Puccinia, are known pathogens, while others such as Sphaerellopsis, Vishniacozyma and Filobasidium are not, at least on crops, and constitute new tracks to be followed in the search for mycoherbicidal candidates. IMPORTANCE: This approach is original because the diversity of weed-colonizing fungi has rarely been studied before. Furthermore, targeting both the ITS1 and ITS2 regions to characterize the fungal communities i) highlighted the complementarity of these two regions, ii) revealed a great diversity of weed-colonizing fungi, and iii) allowed for the identification of potential mycoherbicides, among which unexpected genera.

Phytotoxic compounds from endophytic fungi

Weeds represent one of the most challenging biotic factors for the agricultural sector, responsible for causing significant losses in important agricultural crops. Traditional herbicides have managed to keep weeds at bay, but overuse has resulted in negative environmental and toxicological impacts, including the increase of herbicide-resistant species. Within this context, the use of biologically derived (bio-)herbicides represents a promising solution because they are able to provide the desired phytotoxic effects while causing less toxic environmental damage. In recent years, bioactive secondary metabolites, in particular those bio-synthesized by endophytic fungi, have been shown to be promising sources of novel compounds that can be exploited in agriculture, including their use in weed control. Endophytic fungi have the ability to produce volatile and nonvolatile compounds with broad phytotoxic activity. In addition, as a result of the beneficial relationships they establish with their host plants, they are part of the colonization mechanism and can provide protection for their hosts. As such, endophytic fungi can be exploited as bioherbicides and as research tools. In this review, we cover 100 nonvolatile secondary metabolites with phytotoxic activity and more than 20 volatile organic compounds in a mixture, produced by 28 isolates of endophytic fungi from 21 host plant families, collected in 8 countries. This information can form the basis for the application of endophytic fungal compounds in weed control. KEY POINTS: • Endophytic fungi produce a wide variety of secondary metabolites with unique and complex structures. • Fungal endophytes produce volatile and nonvolatile compounds with promising phytotoxic activity. • Endophytic fungi are a promising source of useful bioherbicides.

Effects of the Fungal Bioherbicide, Alternaria cassia on Peroxidase, Pectinolytic and Proteolytic Activities in Sicklepod Seedlings

Certain plant pathogens have demonstrated potential for use as bioherbicides for weed control, and numerous studies have been published on this subject for several decades. One of the early examples of an important fungal bioherbicide is Alternaria cassiae, isolated from the weed sicklepod (Senna obtusifolia). To gain further insight into biochemical interactions of this fungus and its host weed, we examined the effects of this bioherbicide on various enzymes associated with plant defense. Young sicklepod seedlings were challenged with A. cassiae spore inoculum and enzyme activities associated with plant defense (peroxidase, proteolytic, and pectinolytic) were assayed periodically over a 96-h time course on plants grown in continuous darkness or continuous light. Peroxidase activity increased with time in untreated control seedlings in both light and dark, but the effect was greater in the light. In A. cassiae-treated plants, peroxidase was elevated above that in control tissue at all sample times resulting in a 1.5 -fold increase above control in light-grown tissue and a 2- to 3-fold increase in dark-grown tissue over 48-96 h. Differences in leucine aminopeptidase activity in control versus A. cassiae-treated tissues were not significant until 48-96 h, when activity was inhibited in fungus-treated tissues by about 32% in light-grown tissue and 27% in dark-grown tissue after 96 h. Proteolytic activity on benzoyl-arginine-p-nitroanilide was not significantly different in treated versus control tissue in either light or dark over the time course. Pectinase activity increased in treated tissues at all time points as early as 16 h after spore application in light- or dark-grown plants. The greatest increases were 1.5-fold above control levels in light-grown plants (40-64 h) and 2-fold in plants grown in darkness (72-96 h). Data suggests that peroxidase may be involved as defense mechanism of sicklepod when challenged by A. cassia and that this mechanism is operative in young seedlings under both light and dark growth conditions. Differential proteolytic activity responses on these two substrates suggests the presence of two different enzymes. Increased pectinase activity during pathogenesis suggests that A. cassiae-sicklepod interaction results in an infectivity mechanism to degrade pectic polymers important to sicklepod cell wall integrity. These studies provide important information on some biochemical interactions that may be useful for improvements to biological weed control programs utilizing plant pathogens. Such information may also be useful in genetic selection and manipulation of pathogens for weed control.

Evaluation of the herbicidal potential of some fungal species against Bidens pilosa, the coffee farming weeds

Weeds are the most productive limiting factor, especially in organic farming systems where the uses of synthetic herbicides are not allowed due to their negative impacts. Hence, synthetic herbicides need to be replaced with biological herbicides for weed management. Thus, the present study was designed to evaluate the herbicidal activity of conidia suspensions from Aspergillus niger, Trichoderma asperlium, Trichoderma atroviride, Trichoderma hamatum, Trichoderma harzanium, Trichoderma longibrachatum and Trichoderma viride against Bidens pilosa weed via a series of laboratory and lath-house conditions that laid out in a CRD and RCBD, respectively, with three replications for each bioassay. The results revealed that all fungi, except T. longibrachatum, had significantly reduced seed germination as well as early growth of the target weed compared to the untreated control. The inhibitory effects were measured to be varied among the types of conidia suspensions of fungal species and their level of concentration. The highest rate of inhibition was observed for conidia suspension from A. niger which suppressed with the maximum seed germination inhibitory level (65%) over control. Likewise, the plumule and radicle growth length of the target weed also significantly inhibited by the tested fungi (ranging from 10 to 85% and 34 to 97%) compared to the control, respectively. Based on their efficacy in the laboratory bioassay, the herbicidal potential of selected fungi was further evaluated in pot experiments. In contrarily to laboratory observations, the effect of different fungal conidia suspensions on various growth parameters of the targeted weed was insignificant in the lath-house experiments. In conclusion, the application of A. niger displayed some potential green light to be investigated as a biocontrol agent with promising retarding in the germination and early growth of B. pilosa. Hence, we recommend further investigation of those fungi under field conditions on different coffee weed species.

Prospective of fungal pathogen-based bioherbicides for the control of water hyacinth: A review

Over the decades the presence of aquatic weeds has caused immense biodiversity loss to the ecosystem. The use of herbicides has arisen emergence of herbicide-resistant weeds and loss of inherent flora and fauna due to the recalcitrant nature of the chemicals used. Hence, there is a need to use nontoxic, ecosustainable, low-cost, and efficient biological molecules that are analogous to chemical herbicides. Various plants, bacteria, fungi as well a few viruses are reported to secrete allelopathic biomolecules that inhibit the growth and development of weeds. However, majorly fungal pathogens and their metabolites are found to be effective biocontrol agents for the water hyacinth. The present review puts forward major findings and interventions in the biological control of the weed, water hyacinth. The biosynthesis, mechanism of action and factors regulating the activity of bioherbicides are discussed. In addition, the issues associated with the in situ application of these bioherbicides are also conferred focusing on the available mode of applications and formulation used. The major factors include the type and concentration of allelopathic biomolecules, age, type, and morphology of targeted weed, formulation type, mode of application and other physiological and environmental factors. Among various modes for the application of bioherbicides, emulsions are found to be most effective for the control of water hyacinth. Most of the toxicity studies indicated no toxicity of this fungal pathogen to other ecological plant species except water hyacinth. Yet, in-depth investigations are needed of these allelochemicals and toxins before field applications. Overall, lab-scale studies have shown promising results and highlighted a few potential fungi that need to be further explored for optimizing their bioherbicidal activity.

Mycoherbicides for the Noxious Meddlesome: Can Colletotrichum be a Budding Candidate?

Invasive plant species are a major threat to biodiversity and agricultural productivity. Hence, efforts to manage these menace involves extensive and effective use of chemical herbicides amongst others. However, not only is the impact of control with chemical herbicides short-lived but also leads to negative impact on human health and environment due to non-target herbicide-drift and runoff from the sprayed areas. This has ushed in much-anticipated nature-based potential regulators of weed species, in an attempt to lower the utilisation of chemical herbicides. Mycoherbicides have been seen as a benign, eco-friendly, host-specific, and replacement for chemical herbicides. There are several noteworthy genera of fungus that have been proved to be effective against weeds. They either produce strong phytotoxins or are often used as spore/conidia-based solutions and applied as a spray in growth media. One of such potential genera is Colletotrichum Corda 1831. Compared to other potent fungal genera, with well-established roles in conferring herbicidal activities by producing competent phytotoxins, only a few species under genus Colletotrichum are known to produce fungal metabolites be used as phytotoxins. This article elucidates the current understanding of using spore suspension/phytotoxin of Colletotrichum as a weedicide. We also discuss the interaction between fungal metabolites release and Colletotrichum-target plant, from a molecular and biochemical point of view. This review article has been written to accentuate on the potency of Colletotrichum, and to serve as an eye-opener to consider this genus for further fruitful investigations. However, inconsistency associated with mycoherbicides in terms of viability and efficacy under field conditions, production of bioactive compound, slow natural dispersal ability, etc., have often reduced their utility. Hence, our study emphasizes on the need to do extensive research in elucidating more phytotoxins from necrotrophic phytopathogenic microorganisms with novel mode of action for field application.

Bioprospecting Trichoderma: A Systematic Roadmap to Screen Genomes and Natural Products for Biocontrol Applications

Natural products derived from microbes are crucial innovations that would help in reaching sustainability development goals worldwide while achieving bioeconomic growth. Trichoderma species are well-studied model fungal organisms used for their biocontrol properties with great potential to alleviate the use of agrochemicals in agriculture. However, identifying and characterizing effective natural products in novel species or strains as biological control products remains a meticulous process with many known challenges to be navigated. Integration of recent advancements in various "omics" technologies, next generation biodesign, machine learning, and artificial intelligence approaches could greatly advance bioprospecting goals. Herein, we propose a roadmap for assessing the potential impact of already known or newly discovered Trichoderma species for biocontrol applications. By screening publicly available Trichoderma genome sequences, we first highlight the prevalence of putative biosynthetic gene clusters and antimicrobial peptides among genomes as an initial step toward predicting which organisms could increase the diversity of natural products. Next, we discuss high-throughput methods for screening organisms to discover and characterize natural products and how these findings impact both fundamental and applied research fields.

Bioherbicides: An Eco-Friendly Tool for Sustainable Weed Management

Weed management is an arduous undertaking in crop production. Integrated weed management, inclusive of the application of bioherbicides, is an emerging weed control strategy toward sustainable agriculture. In general, bioherbicides are derived either from plants containing phytotoxic allelochemicals or certain disease-carrying microbes that can suppress weed populations. While bioherbicides have exhibited great promise in deterring weed seed germination and growth, only a few in vitro studies have been conducted on the physiological responses they evoke in weeds. This review discusses bioherbicide products that are currently available on the market, bioherbicide impact on weed physiology, and potential factors influencing bioherbicide efficacy. A new promising bioherbicide product is introduced at the end of this paper. When absorbed, phytotoxic plant extracts or metabolites disrupt cell membrane integrity and important biochemical processes in weeds. The phytotoxic impact on weed growth is reflected in low levels of root cell division, nutrient absorption, and growth hormone and pigment synthesis, as well as in the development of reactive oxygen species (ROS), stress-related hormones, and abnormal antioxidant activity. The inconsistency of bioherbicide efficacy is a primary factor restricting their widespread use, which is influenced by factors such as bioactive compound content, weed control spectrum, formulation, and application method.

A Path Forward: Promoting Microbial-Based Methods in the Control of Invasive Plant Species

In this review, we discuss the unrealized potential of incorporating plant-microbe and microbe-microbe interactions into invasive plant management strategies. While the development of this as a viable strategy is in its infancy, we argue that incorporation of microbial components into management plans should be a priority and has great potential for diversifying sustainable control options. We advocate for increased research into microbial-mediated phytochemical production, microbial controls to reduce the competitiveness of invasive plants, microbial-mediated increases of herbicidal tolerance of native plants, and to facilitate increased pathogenicity of plant pathogens of invasive plants.

Selection of rhizobacteria isolates with bioherbicide potential against Palmer amaranth (Amarathus palmeri S. Wats.)

Crop yield and quality are affected by the presence of weeds such as Palmer amaranth. Chemical control is the most commonly used method to eradicate weeds, due to its quickness and efficacy. However, the inappropriate use of chemical herbicides can lead to resistant weed biotypes, as well as problems related to environmental pollution and human health hazards. One ecological alternative to combat weeds is the use of deleterious rhizobacteria (DRB). We evaluated the potential bioherbicidal effect in 15 DRB isolates from the rhizosphere of Palmer amaranth, both in vitro and in greenhouse tests. Isolates TR10 and TR18 inhibited seed germination in vitro, whereas the TR25 and TR36 isolates showed the potential to inhibit Palmer amaranth plant development in growth room assays without affecting maize and common bean germination and growth. These four isolates were molecularly identified as either Pseudomonas sp. (TR10 and TR36), Enterobacter sp. (TR18), or Bacillus sp. (TR25). In addition, the production of volatiles and diffusible metabolites were identified as possible mechanisms of germination arrestment and plant development inhibition. This study suggests the bioherbicide potential of some indigenous rhizobacteria against Palmer amaranth.

Field application of allelopathic bacteria to control invasion of little seed canary grass in wheat

Development of successful biological weed control can help to resolve various environmental challenges created by the chemical and mechanical weed control. The current study is aimed at investigating the potential of allelopathic bacteria (hereinafter as AB) for biological weed control in wheat rather than the traditional areas of plant allelopathy, phyto-pathology, and insect biocontrol agents. Eleven strains of AB were obtained that were inhibitory to little seed canary grass of which 5 also inhibited wheat in our previous studies. The remaining strains indicated the potential for biological control of this weed in wheat. Five efficient strains were selected for this purpose to conduct pot and field trials. Seeds of little seed canary grass were sown together in potted soils with wheat seeds inoculated with AB strains. A subsequent field trial was conducted at a site selected based on chronic infestations of canary grass. Seeds of the weed and inoculated wheat were co-seeded directly in field soil. For inoculation, these strains were formulated in sterilized peat and applied to seeds. In pot trials, the invasion of little seed canary grass in wheat reduced wheat grain yield up to 59.9%. Four strains suppressed the weed which resulted in recovery wheat grain yield losses from 20.1 to 66.9%. The field trial showed that the invasion of little seed canary grass reduced wheat grain yields up to 53.9%. Four strains suppressed the weed which resulted into recovery of grain wheat grain yield losses 34.3 to 64.3%. These findings were consistent with improvement of other agronomic, physiological, and chemical parameters of the crop where the four strains of AB (L9, T42, 7O₀, and O₀10) were applied.

Herbicidal Characteristics and Structural Identification of the Potential Active Compounds from Streptomyces sp. KRA17-580

Weeds are notorious plant species exhibiting a harmful impact on crops. Biological weed control is an efficient and environmentally friendly technique, usually constitutes naturally derived compounds, including bioherbicidal metabolites produced by Streptomyces sp. The isolation and structural identification of phytotoxic compounds from Streptomyces have recently been proposed as an effective way to the discovery of novel bioherbicides. In the screening of bioherbicidal agents, isolated Streptomyces strain KRA17-580 demonstrated significant phytotoxic activity against Digitaria ciliaris. Phylogenetic analysis of the 16S rRNA sequence indicated that isolated KRA17-580 is similar to Streptomyces olivochromogenes. The bacterial culture conditions were optimized for temperature, agitation, and initial pH. Streptomyces strain KRA17-580 showed intense phytotoxic activity and high cell mass at an initial pH of 5.5-7.0, more than 150 rpm, and 25-30 °C. The herbicidal compounds isolated from the culture filtrate of strain KRA17-580 were purified by solvent partition, C₁₈, Sephadex LH20 column chromatography, and high-performance liquid chromatography. By 1D-NMR, 2D-NMR, and electrospray ionization mass spectrometry analysis, the 580-H1 and 580-H2 compounds were identified as a cinnoline-4-carboxamide (M_W, 173.0490; C₉H₇N₃O₂) and cinnoline-4-carboxylic acid (M_W, 174.0503; C₉H₆N₂O₂), respectively. Only these two herbicidal compounds showed strong phytotoxic activity against D. ciliaris in foliar applications. However, compound 580-H2 was more phytotoxic than 580-H1 and the toxicity was dose-dependent. The herbicidal metabolite KRA17-580 produced by Streptomyces sp. is a new bioherbicidal candidate that may provide a new lead molecule for more efficient phytotoxic compounds.

Effect of Ammonia and Indole-3-acetic Acid Producing Endophytic Klebsiella pneumoniae YNA12 as a Bio-Herbicide for Weed Inhibition: Special Reference with Evening Primroses

Information on the use of endophytic bacteria as a bio-herbicide for the management of weed control in agricultural fields is limited. The current study aimed to isolate endophytic bacteria from evening primroses and to screen them for their bio-herbicidal activity. Two isolated endophytic bacteria (Pantoea dispersa YNA11 and Klebsiella pneumoniae YNA12) were initially screened for citrate utilization and for indole-3-acetic acid (IAA) and catalase production. The preliminary biochemical assessment showed YNA12 as a positive strain. Ammonia, catalase, and IAA in its culture filtrate were quantified. Gas Chromatography/Mass Spectroscopy- Selective Ion Monitoring (GC/MS-SIM) analysis revealed the production of IAA by YNA12 in a time-dependent manner. YNA12 also exhibited significant ammonia-producing potential and catalase activity against hydrogen peroxide. The YNA12 culture filtrate significantly inhibited the germination rate of evening primrose seeds, resulting in a marked reduction in seedling length and biomass compared with those of the control seeds. Moreover, the culture filtrate of YNA12 significantly accelerated the endogenous abscisic acid (ABA) production and catalase activity of evening primrose seedlings. Macronutrient regulation was adversely affected in the seedlings exposed to the culture filtrate of YNA12, leading to inhibition of seed germination. The current results suggest that endophytic YNA12 may be used as a potent bio-herbicidal agent for controlling weed growth and development.