Dual Effect of Nanomaterials on Germination and Seedling Growth: Stimulation vs. Phytotoxicity

Due to recent active research, a large amount of data has been accumulated regarding the effects of different nanomaterials (mainly metal oxide nanoparticles, carbon nanotubes, chitosan nanoparticles) on different plant species. Most studies have focused on seed germination and early seedling development, presumably due to the simplicity of these experimental systems. Depending mostly on size and concentration, nanomaterials can exert both positive and negative effects on germination and seedling development during normal and stress conditions, thus some research has evaluated the phytotoxic effects of nanomaterials and the physiological and molecular processes behind them, while other works have highlighted the favorable seed priming effects. This review aims to systematize and discuss research data regarding the effect of nanomaterials on germination and seedling growth in order to provide state-of-the-art knowledge about this fast developing research area.

Activated sludge treatment for promoting the reuse of a synthetic produced water in irrigation

Large volumes of produced water are generated as a byproduct in activities of oil and gas exploitation, which can be reused in agriculture after a treatment process. Activated sludge treatment has been successfully used to remove oil from wastewater, but systematic studies on the toxicity of this effluent using this treatment are scarce in the literature. In this study, it was investigated the performance of an activated sludge system in the treatment of a synthetic produced water under different initial conditions in terms of salinity and oil and grease concentration. Furthermore, it was evaluated this effluent phytotoxicity in the germination, and seedling and plant growths of sunflower and corn seeds using untreated and treated synthetic produced water. Results revealed the activated sludge effectiveness in oil and grease and salinity removal from produced water, viz. high removal efficiency of 99.01 ± 0.28 and 91.07 ± 0.39%., respectively. Untreated produced water showed considerable toxic effects on the germination (74.67 ± 2.31% and 82.67 ± 2.31 for sunflower and corn seeds, respectively) and growth stages of sunflower and corn seed plants. The germination percentage was approximately 100% for both types of seed. The seedling and plant growth of the two seeds irrigated with treated produced water had similar performance when used tap water. These results highlighted the potential reuse as an unconventional water resource for plant irrigation of the synthetic produced water treated by an activated sludge process, which technology has showed high removal performance of salinity and oil.

Changes in the physiological and biochemical state of peanut plants (Arachis hypogaea L.) induced by exposure to green metallic nanoparticles

Different types of nanoparticles (NPs) are increasingly used in multiple sectors such as industry, medicine and agriculture. This application has increased the possibility of NPs accumulating and contaminating the environment. Plants are one of the essential building blocks of all ecosystems and the interaction between NPs and plants is an indispensable aspect of risk assessment. To understand the effects of NPs in agricultural systems, in the present study we investigated the effects of exposure of Ag, Cu and Cu/Ag phytonanoparticles in Arachis hypogaea L. plants at a physiological and biochemical level, for which NPs solutions were applied foliarly at concentrations of 250, 500, 750 and 1000 ppm for 48 days. Parameters such as leaf length, chlorophyll and concentration of phytohormones showed that phytonanoparticles could cause serious damage to plant growth and development. Plants exposed to phytonanoparticles showed an increase in total phenols, proline, PAL activity and antioxidant enzymes, this to mitigate the stress caused. The alteration in the composition and content of fatty acids in the peanut kernels after exposure to different NPs indicated that they could affect the yield and quality of crop. Therefore, it is necessary to investigate its potential impact on food quality. Statement of noveltyIn this manuscript, we report for the first time that green nanoparticles induced a lower degree of toxicity in plants compared to commercial nanoparticles.Our results indicate that the mechanisms by which peanut plants respond to the application of nanoparticles were an increase in the activity of phenylalanine ammonia-lyase and antioxidant enzymes. So far there are few studies on the effect of nanoparticles on plant hormones, our results revealed a significant decrease in indole-3 acetic acid and induced the synthesis of gibberellins. The modification in the composition and content of fatty acids in the peanut kernels indicated that the nanoparticles could affect the quality of the crop.

Phytotoxic Effects and Mechanism of Action of Essential Oils and Terpenoids

Weeds are one of the major constraints in crop production affecting both yield and quality. The excessive and exclusive use of synthetic herbicides for their management is increasing the development of herbicide-resistant weeds and is provoking risks for the environment and human health. Therefore, the development of new herbicides with multitarget-site activity, new modes of action and low impact on the environment and health are badly needed. The study of plant–plant interactions through the release of secondary metabolites could be a starting point for the identification of new molecules with herbicidal activity. Essential oils (EOs) and their components, mainly terpenoids, as pure natural compounds or in mixtures, because of their structural diversity and strong phytotoxic activity, could be good candidates for the development of new bioherbicides or could serve as a basis for the development of new natural-like low impact synthetic herbicides. EOs and terpenoids have been largely studied for their phytotoxicity and several evidences on their modes of action have been highlighted in the last decades through the use of integrated approaches. The review is focused on the knowledge concerning the phytotoxicity of these molecules, their putative target, as well as their potential mode of action.

Essential Oil of Calotropis procera: Comparative Chemical Profiles, Antimicrobial Activity, and Allelopathic Potential on Weeds

Plants are considered green resources for thousands of bioactive compounds. Essential oils (EOs) are an important class of secondary compounds with various biological activities, including allelopathic and antimicrobial activities. Herein, the present study aimed to compare the chemical profiles of the EOs of the widely distributed medicinal plant Calotropis procera collected from Saudi Arabia and Egypt. In addition, this study also aimed to assess their allelopathic and antimicrobial activities. The EOs from Egyptian and Saudi ecospecies were extracted by hydrodistillation and analyzed via GC-MS. The correlation between the analyzed EOs and those published from Egypt, India, and Nigeria was assessed by principal component analysis (PCA) and agglomerative hierarchical clustering (AHC). The allelopathic activity of the extracted EOs was tested against two weeds (Bidens pilosa and Dactyloctenium aegyptium). Moreover, the EOs were tested for antimicrobial activity against seven bacterial and two fungal strains. Ninety compounds were identified from both ecospecies, where 76 compounds were recorded in Saudi ecospecies and 33 in the Egyptian one. Terpenes were recorded as the main components along with hydrocarbons, aromatics, and carotenoids. The sesquiterpenes (54.07%) were the most abundant component of EO of the Saudi sample, while the diterpenes (44.82%) represented the mains of the Egyptian one. Hinesol (13.50%), trans-chrysanthenyl acetate (12.33%), 1,4-trans-1,7-cis-acorenone (7.62%), phytol (8.73%), and myristicin (6.13%) were found as the major constituents of EO of the Saudi sample, while phytol (38.02%), n-docosane (6.86%), linoleic acid (6.36%), n-pentacosane (6.31%), and bicyclogermacrene (4.37%) represented the main compounds of the Egyptian one. It was evident that the EOs of both ecospecies had potent phytotoxic activity against the two tested weeds, while the EO of the Egyptian ecospecies was more effective, particularly on the weed D. aegyptium. Moreover, the EOs showed substantial antibacterial and antifungal activities. The present study revealed that the EOs of Egyptian and Saudi ecospecies were different in quality and quantity, which could be attributed to the variant environmental and climatic conditions. The EOs of both ecospecies showed significant allelopathic and antimicrobial activity; therefore, these EOs could be considered as potential green eco-friendly resources for weed and microbe control, considering that this plant is widely grown in arid habitats.

Ecotoxicity Evaluation of Pristine and Indolicidin-coated Silver Nanoparticles in Aquatic and Terrestrial Ecosystem

BACKGROUND

Metallic nanoparticles (NPs) are highly exploited in manufacturing and medical processes in a broad spectrum of industrial applications and in the academic sectors. Several studies have suggested that many metallic nanomaterials including those derived by silver (Ag) are entering the ecosystem to cause significant toxic consequences in cell culture and animal models. However, ecotoxicity studies are still receiving limited attention when designing functionalized and non.-functionalized AgNPs.

OBJECTIVE

This study aimed to investigate different ecotoxicological profiles of AgNPs, which were analyzed in two different states: in pristine form uncoated AgNPs and coated AgNPs with the antimicrobial peptide indolicidin. These two types of AgNPs are exploited for a set of different tests using Daphnia magna and Raphidocelis subcapitata, which are representatives of two different levels of the aquatic trophic chain, and seeds of Lepidium sativum, Cucumis sativus and Lactuca sativa.

RESULTS

Ecotoxicological studies showed that the most sensitive organism to AgNPs was crustacean D. magna, followed by R. subcapitata and plant seeds, while AgNPs coated with indolicidin (IndAgNPs) showed a dose-dependent decreased toxicity for all three.

CONCLUSION

The obtained results demonstrate that high ecotoxicity induced by AgNPs is strongly dependent on the surface chemistry, thus the presence of the antimicrobial peptide. This finding opens new avenues to design and fabricate the next generation of metallic nanoparticles to ensure the biosafety and risk of using engineered nanoparticles in consumer products.

Phytotoxicity, Morphological, and Metabolic Effects of the Sesquiterpenoid Nerolidol on Arabidopsis thaliana Seedling Roots

Natural herbicides that are based on allelopathy of compounds, can offer effective alternatives to chemical herbicides towards sustainable agricultural practices. Nerolidol, a sesquiterpenoid alcohol synthesized by many plant families, was shown to be the most effective allelopathic compound in a preliminary screening performed with several other sesquiterpenoids. In the present study, Arabidopsis thaliana seedlings were treated for 14 d with various cis-nerolidol concentrations (0, 50, 100, 200, 400, and 800 µM) to investigate its effects on root growth and morphology. To probe the underlying changes in root metabolome, we conducted untargeted gas chromatography mass spectrometry (GC-MS) based metabolomics to find out the specificity or multi-target action of this sesquiterpenoid alcohol. Oxidative stress (measured as levels of H₂O₂ and malondialdehyde (MDA) by-product) and antioxidant enzyme activities, i.e., superoxide dismutase (SOD) and catalase (CAT) were also evaluated in the roots. Nerolidol showed an IC₅₀ (120 µM), which can be considered low for natural products. Nerolidol caused alterations in root morphology, brought changes in auxin balance, induced changes in sugar, amino acid, and carboxylic acid profiles, and increased the levels of H₂O₂ and MDA in root tissues in a dose-dependent manner. Several metabolomic-scale changes induced by nerolidol support the multi-target action of nerolidol, which is a positive feature for a botanical herbicide. Though it warrants further mechanistic investigation, nerolidol is a promising compound for developing a new natural herbicide.

Phytotoxic Activity of the Natural Compound Norharmane on Crops, Weeds and Model Plants

Norharmane is a secondary metabolite that appears in different species of land plants. In this paper, we investigated for the first time the specificity of norharmane through germination and growth tests on some crops as Zea mays L. (maize), Triticum aestivum L. (wheat), Oryza sativa L. (rice) and Lactuca sativa L. (lettuce) and weeds as Amaranthus retroflexus L. (amaranth), Echinochloa crus-galli L. (barnyard grass), Plantago lanceolata L. (ribwort), Portulaca oleracea L. (common purslane) and Avena fatua L. (wild oat), and its phytotoxic capacity on the metabolism of adult Arabidopsis thaliana L. (thale cress) by measuring chlorophyll a fluorescence, pigment content, total proteins, osmotic potential and morphological analysis. Norharmane had an inhibitory effect on the germination of A. fatua and P. lanceolata, and the growth of P. oleracea, E. crus-galli and A. retroflexus. On adult A. thaliana plants, the compound was more effective to watering, leading to water stress that compromised the growth of the plants and ultimately affected the photosynthetic apparatus. Therefore, this research shows that norharmane not only affects seedlings’ metabolism, but also damages the metabolism of adult plants and can be a potential model for a future bioherbicide given its specificity.

Potential Effects of Essential Oils Extracted from Mediterranean Aromatic Plants on Target Weeds and Soil Microorganisms

Essential oils (EOs), extracted from aromatic plants, have been proposed as candidates to develop natural herbicides. This study aimed to evaluate the herbicidal potential of Thymbra capitata (L.) Cav., Mentha × piperita L. and Santolina chamaecyparissus L. essential oils (EOs) on Avena fatua L., Echinochloa crus-galli (L.) P. Beauv, Portulaca oleracea L. and Amaranthus retroflexus L. and their effects on soil microorganisms. A pot experiment was set up and three EOs at three doses were applied by irrigation. Efficacy and effects of EOs on weed growth were determined. Soil microbial biomass carbon and nitrogen, microbial respiration, and the main microbial groups were determined at days 7, 28 and 56. EOs demonstrated herbicidal activity, increasing their toxicity with the dose. T. capitata was the most effective against all weeds at the maximum dose. P. oleracea was the most resistant weed. Soil microorganisms, after a transient upheaval period induced by the addition of EOs, recovered their initial function and biomass. T. capitata EO at the highest dose did not allow soil microorganisms to recover their initial functionality. EOs exhibited great potential as natural herbicides but the optimum dose of application must be identified to control weeds and not negatively affect soil microorganisms.

Antibacterial Activity of Essential Oils and Trametes versicolor Extract against Clavibacter michiganensis subsp. michiganensis and Ralstonia solanacearum for Seed Treatment and Development of a Rapid In Vivo Assay

Clavibacter michiganensis subsp. michiganensis (Smith) Davis et al. (Cmm) and Ralstonia solanacearum Yabuuchi et al. (Smith) (Rs) are important seed-borne bacterial pathogens of tomato (Solanum lycopersicum) listed as A2 pests in the EPPO (European and Mediterranean Plant Protection Organization) region. At present, there are few strategies to control these pathogens, and seed control with eco-compatible approaches is widely encouraged. In this work, the essential oils (EOs) of oregano (Origanum vulgare), garlic (Allium sativum), basil (Ocimum basilicum), cinnamon (Cinnamomum zeylanicum), clove buds (Syzygium aromaticum), thyme (Thymus vulgaris), and Trametes versicolor extract (Tve) were tested in vitro for their antimicrobial activity against Cmm and Rs (broth microdilution method). The tested EOs and the Tve extract caused a significant inhibition of bacterial growth, with very promising MBC (minimum bactericidal concentration) and MIC90 (minimum inhibitory concentration causing a 90% growth inhibition) values. Moreover, an in vivo germination test showed no major reduction in seed germination when the substances were applied as seed treatment. A rapid molecular screening method has been developed, through real-time PCR, for the specific quantification of Cmm in the presence of a vegetable matrix to test in vivo the antimicrobial efficacy of oregano and cinnamon oil on seed treatment without resorting to whole plant essays, which are time- and space-consuming.

Phytotoxicity of Essential Oils: Opportunities and Constraints for the Development of Biopesticides. A Review

The extensive use of chemical pesticides leads to risks for both the environment and human health due to the toxicity and poor biodegradability that they may present. Farmers therefore need alternative agricultural practices including the use of natural molecules to achieve more sustainable production methods to meet consumer and societal expectations. Numerous studies have reported the potential of essential oils as biopesticides for integrated weed or pest management. However, their phytotoxic properties have long been a major drawback for their potential applicability (apart from herbicidal application). Therefore, deciphering the mode of action of essential oils exogenously applied in regards to their potential phytotoxicity will help in the development of biopesticides for sustainable agriculture. Nowadays, plant physiologists are attempting to understand the mechanisms underlying their phytotoxicity at both cellular and molecular levels using transcriptomic and metabolomic tools. This review systematically discusses the functional and cellular impacts of essential oils applied in the agronomic context. Putative molecular targets and resulting physiological disturbances are described. New opportunities regarding the development of biopesticides are discussed including biostimulation and defense elicitation or priming properties of essential oils.

Concentration of exopolysaccharides produced by Fusarium fujikuroi and application of bioproduct as an effective bioherbicide

Exopolysaccharides are secondary metabolites produced by microorganisms and are a subject of research in many fields of science and industry due to some of their confirmed properties, especially in the pharmaceutical and agrochemical areas. In this context, the objectives of this work were to evaluate the potential of Fusarium fujikuroi for producing exopolysaccharides and to concentrate such compounds in order to increase the herbicidal activity. Exopolysaccharides were produced by submerged fermentation and different concentration methods (membranes, lyophilization, and evaporation) were evaluated. The phytotoxic effects were assessed through absorption assays in detached leaves of Cucumis sativus and evaluated on the seventh day after application. The surface tension was evaluated for each concentration method. The production of exopolysaccharides in the crude broth without concentration was 5.94 g/L. When using the lyophilization method, a maximum yield of exopolysaccharides of 10.64 g/L was obtained. The membranes also presented satisfactory results of exopolysaccharides: 9.60 g/L. The increase of bioherbicidal activity and the lower surface tension are proportionally related to the increase of the concentration of exopolysaccharides.

Bioherbicide Potential of Eucalyptus saligna Leaf Litter Essential Oil

We aimed to evaluate the bioherbicide potential of Eucalyptus saligna leaf litter essential oil, its fractions and major compounds. Six essential oil fractions were obtained by preparative thin-layer chromatography and analyzed by gas chromatography/mass spectrometry. Effects of the oil, its fractions and major compounds (1,8-cineole and/or α-pinene) diluted in aqueous solution were assessed on germination and seedling growth. Recipient species were Lactuca sativa (model), Amaranthus viridis (weed), Eragrostis plana (weed), and Paspalum notatum (forage). The essential oil was more phytotoxic on A. viridis and L. sativa, followed by E. plana, and caused no effects on P. notatum. Amaranthus viridis was inhibited by all treatments, mainly the essential oil, α-pinene and fraction 6, whereas E. plana was more affected by the oil fractions. Results revealed the species-specific phytotoxic effects of E. saligna essential oil, indicating its potential use for controlling A. viridis and E. plana. Phytotoxic effects of essential oils or their components should not be generalized, as effects may change according to recipient species.

Bioremediation of Hexavalent Chromium by Chromium Resistant Bacteria Reduces Phytotoxicity

Chromium (Cr) (VI) has long been known as an environmental hazard that can be reduced from aqueous solutions through bioremediation by living cells. In this study, we investigated the efficiency of reduction and biosorption of Cr(VI) by chromate resistant bacteria isolated from tannery effluent. From 28 screened Cr(VI) resistant isolates, selected bacterial strain SH-1 was identified as Klebsiella sp. via 16S rRNA sequencing. In Luria–Bertani broth, the relative reduction level of Cr(VI) was 95%, but in tannery effluent, it was 63.08% after 72 h of incubation. The cell-free extract of SH-1 showed a 72.2% reduction of Cr(VI), which indicated a higher activity of Cr(VI) reducing enzyme than the control. Live and dead biomass of SH-1 adsorbed 51.25 mg and 29.03 mg Cr(VI) per gram of dry weight, respectively. Two adsorption isotherm models—Langmuir and Freundlich—were used for the illustration of Cr(VI) biosorption using SH-1 live biomass. Scanning electron microscopy (SEM) analysis showed an increased cell size of the treated biomass when compared to the controlled biomass, which supports the adsorption of reduced Cr on the biomass cell surface. Fourier-transform infrared analysis indicated that Cr(VI) had an effect on bacterial biomass, including quantitative and structural modifications. Moreover, the chickpea seed germination study showed beneficial environmental effects that suggest possible application of the isolate for the bioremediation of toxic Cr(VI).

Bioaccumulation and Phytotoxicity and Human Health Risk from Microcystin-LR under Various Treatments: A Pot Study

Microcystin-LR (MC-LR) is prevalent in water and can be translocated into soil-crop ecosystem via irrigation, overflow (pollution accident), and cyanobacterial manure applications, threatening agricultural production and human health. However, the effects of various input pathways on the bioaccumulation and toxicity of MCs in terrestrial plants have been hardly reported so far. In the present study, pot experiments were performed to compare the bioaccumulation, toxicity, and health risk of MC-LR as well as its degradation in soils among various treatments with the same total amount of added MC-LR (150 μg/kg). The treatments included irrigation with polluted water (IPW), cultivation with polluted soil (CPS), and application of cyanobacterial manure (ACM). Three common leaf-vegetables in southern China were used in the pot experiments, including Ipomoea batatas L., Brassica juncea L., and Brassica alboglabra L. All leaf vegetables could bioaccumulate MC-LR under the three treatments, with much higher MC-LR bioaccumulation, especially root bioconcentration observed in ACM treatment than IPW and CPS treatments. An opposite trend in MC-LR degradation in soils of these treatments indicated that ACM could limit MC-LR degradation in soils and thus promote its bioaccumulation in the vegetables. MC-LR bioaccumulation could cause toxicity to the vegetables, with the highest toxic effects observed in ACM treatment. Similarly, bioaccumulation of MC-LR in the edible parts of the leaf-vegetables posed 1.1~4.8 fold higher human health risks in ACM treatment than in IPW and CPS treatments. The findings of this study highlighted a great concern on applications of cyanobacterial manure.

Genome-Wide Investigation of 2,4-Diacetylphloroglucinol Protection Genes in Arabidopsis thaliana

The compound 2,4-diacetylphloroglucinol (DAPG) is a well-known secondary metabolite produced by Pseudomonas spp. that are used as biocontrol agents. DAPG displays a remarkably broad spectrum of toxic activity against pathogens of plants. Yet high concentrations of DAPG may also have negative effect on plants, but the phytotoxicity of DAPG is not clearly understood. Here, we used genome-wide activation, tagging Arabidopsis plants as the model plant to investigate the plant response to DAPG. A total of 15 lines were selected as DAPG-tolerant plants from among 62,000 lines investigated. The DAPG-responsible genes were then identified via thermal asymmetric interlaced PCR and quantitative reverse transcription PCR, and the gene ontology analysis showed the distribution of these genes having different biological processes, cellular regulations, and molecular functional properties. Collectively, these findings suggest that plants may rely on several pathways to prevent DAPG phytotoxicity.

Rehmannia glutinosa Replant Issues: Root Exudate-Rhizobiome Interactions Clearly Influence Replant Success

Production of medicinal tubers of Rehmannia glutinosa is severely hindered by replanting issues. However, a mechanistic understanding of the plant-soil factors associated with replant problems is currently limited. Thus, we aimed to identify the R. glutinosa root exudates, evaluate their potential phytotoxicity and profile the interactions between the plant and its associated rhizobiome. Stereomicroscopy and liquid chromatography coupled to a quadrupole/time of flight mass spectrometer were used to monitor and identify secreted metabolites, respectively. Seedling bioassays were used to evaluate the phytotoxicity of R. glutinosa root exudates. Two complimentary experiments were performed to investigate allelochemical fate in rhizosphere soil and profile the associated microbiota. Root specific microbes were further isolated from R. glutinosa rhizosphere. Impacts of isolated strains were evaluated by co-cultivation on plate and on seedlings in tissue culture, with a focus on their pathogenicity. Interactions between key R. glutinosa root exudates and isolated rhizobiomes were investigated to understand the potential for plant-soil feedbacks. Quantification and phytotoxic analysis of metabolites released from R. glutinosa indicated catalpol was the most abundant and bioactive metabolite in root exudates. Subsequent microbial profiling in soil containing accumulated and ecologically significant levels of catalpol identified several taxa (e.g., Agromyces, Lysobacter, Pseudomonas, Fusarium) that were specifically shifted. Isolation of R. glutinosa rhizobiomes obtained several root specific strains. A significant antagonistic effect between strain Rh7 (Pseudomonas aeruginosa) and two pathogenic strains Rf1 (Fusarium oxysporum) and Rf2 (Fusarium solani) was observed. Notably, the growth of strain Rh7 and catalpol concentration showed a hormesis-like effect. Field investigation further indicated catalpol was increasingly accumulated in the rhizosphere of replanted R. glutinosa, suggesting that interactions of biocontrol agents and pathogens are likely regulated by the presence of bioactive root exudates and in turn impact the rhizo-ecological process. In summary, this research successfully monitored the release of R. glutinosa root exudates, identified several abundant bioactive R. glutinosa secreted metabolites, profiled associated root specific microbes, and investigated the plant-soil feedbacks potentially regulated by catalpol and associated rhizobiomes. Our findings provide new perspectives toward an enhanced understanding R. glutinosa replant problems.

Acaricidal effects of methyl benzoate against Tetranychus urticae Koch (Acari: Tetranychidae) on common crop plants

BACKGROUND

Methyl benzoate (MB) is a small, hydrophobic organic compound isolated from the freshwater fern Salvinia molesta (Salviniales: Salviniaceae). It is used as a fragrance and flavor enhancer owing to its pleasant smell. It has also demonstrated potential as a green pesticide for various groups of insects. However, its effects on mites are yet to be studied.

RESULTS

Here, we assessed the acaricidal and repellent effects of MB against the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), under laboratory and greenhouse conditions. MB demonstrated concentration-dependent contact toxicity against eggs and adults of the mite. A leaf-dipping assay using 1% MB prevented the hatching of 92.7% of eggs and killed 100% of adults within 48 h of treatment. Concentration-mortality statistics were subjected to probit analysis, and the median lethal concentration (LC₅₀ ) values for eggs and adults were 0.25% and 0.5%, respectively. Treatment with 1% MB showed the highest mortality (100%), with a median lethal time (LT₅₀ ) estimated of 8.1 h. The efficacy of MB against adults of T. urticae on tomato plants under greenhouse conditions was 97.5% within 96 h post-treatment. Further, MB showed significant repellent activity against adult females of T. urticae, although this declined with time. Spraying with 1% MB (three times per plant) was not phytotoxic to bean, cucumber, pepper, or tomato plants.

CONCLUSION

MB is highly acaricidal and repellent, but not phytotoxic, and is a promising green pesticide.

Involvement of Allelopathy in the Invasive Potential of Tithonia diversifolia

Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae) is native to Mexico and Central America. The species is spreading quickly and has naturalized in more than 70 countries. It has often been recorded as a harmful invasive plant that disturbs native plant communities. Phytotoxic chemical interactions such as allelopathy between invasive plants and native plants have been reported to play an important role in the invasion. Evidence for allelopathy of T. diversifolia has accumulated in the literature over 30 years. Thus, the objective of this review was to discuss the possible involvement of allelopathy in the invasive potential of T. diversifolia. The extracts, root exudates, and plant residues of T. diversifolia inhibited the germination and growth of other plant species. The soil water and soil collected from T. diversifolia fields also showed inhibitory growth effects. The decomposition rate of T. diversifolia residues in soil was reported to be high. Phytotoxic substances such as sesquiterpene lactones were isolated and identified in the extracts of T. diversifolia. Some phytotoxic substances in T. diversifolia may be released into the soil through the decomposition of the plant residues and the exudation from living tissues of T. diversifolia, including its root exudates, which act as allelopathic substances. Those allelopathic substances can inhibit the germination and growth of neighboring plants and may enhance the competitive ability of the plants, make them invasive.

Phytotoxic and Antimicrobial Activities of Teucrium polium and Thymus decussatus Essential Oils Extracted Using Hydrodistillation and Microwave-Assisted Techniques

Essential oils (EOs) have been described as promising eco-friendly secondary products of aromatic plants with several biological activities. The present study aimed to characterize the chemical composition and explore phytotoxic and antimicrobial activities of Teucrium polium and Thymus decussatus EOs extracted using hydrodistillation (HD) and microwave-assisted extraction (MAE) methods. Twenty-seven and twenty-eight compounds were identified from HD and MAE extracted EOs of T. polium, respectively. The oxygenated sesquiterpenes (57.68%) were characterized as the main components of the hydrodistilled EO with a prominence of 6-epi-shyobunol (33.00%), while sesquiterpene hydrocarbons (54.48%) were the main components of the MAE method, with a prominence of delta-cadinene (25.13%). Eighteen and nineteen compounds, were characterized in T. decussatus EOs extracted using HD and MAE methods, respectively, and oxygenated monoterpenes represented the main components of both EOs with carvacrol (94.40% and 75.91%, respectively) as the main compound. The EOs extracted using the MAE method were slightly more phytotoxic than those extracted using the HD method. The T. decussatus EO extracted using the MAE method showed a higher inhibitory effect than T. polium by 16-, 32-, and 24-fold, regarding seed germination, shoot, and root growth of lettuce, respectively. Moreover, EOs extracted by HD method showed a similar pattern with 16-, 28-, and 14-fold effects. Both T. decussatus EOs exhibited potent inhibitory effect against all tested bacteria with an inhibition zone of 34–39 mm and the lowest minimum inhibitory concentration (MIC) of 0.49, 0.98, and 1.95 μg/mL against Aspergillus niger, Escherichia coli, and Staphylococcus aureus, respectively. However, the EOs of T. polium showed weak antibacterial activity and no antifungal effect. Further studies are needed for the characterization of bioactive major compounds, either singular or synergistic, at field scale and to determine their modes of action and safety.

Isolation, characterization, and decolorization of Disperse Blue 60 by newly isolated bacterial strains from Kashan textile wastewater

Wastewaters are a source of water pollution and the environment. Therefore, the decolorization ability of isolated strains from textile wastewater for Disperse Blue 60 dye was measured. After sampling from different parts of textile waste, four decolorizer strains were isolated. The effects of various factors were evaluated on decolorization. Decolorization ability of strains was measured after incubation up to 72 hr, the range of pH 6-9, different dye concentrations from 50 to 400 mg/L, and different carbon sources. The four newly bacterial strains showed high decolorization ability to dye. The highest decolorization (90%-95%) was observed after 72 hr, pH 7-9, 50 mg/L concentration of dye and glucose as carbon source. According to findings from the present study, the decolorization ability of F52, C43, C19, and C25 strains was 93%, 96%, 100%, and 98.33%, respectively. The phytotoxicity test confirmed the nontoxic effect of the dye decolorization products compared with the toxic Disperse Blue 60 on seeds of Raphanus sativus L. Based on the biochemical characterization and 16s rDNA gene sequencing analysis, the selected bacterial strains were identified as Alishewanella, Halomonas, Jonesia, and Pseudomonas genera. High decolorization ability of the bacterial isolates showed they could effectively use in the biological treatment of wastewater. PRACTITIONER POINTS: Isolation of powerful and effective strains from Kashan textile wastewater Increasing of decolorization by improving environmental conditions Alishewanella, Halomonas, Jonesia, and Pseudomonas genera can be used for biological treatment of wastewater.

Perspectives and challenges of micro/nanoplastics-induced toxicity with special reference to phytotoxicity

Plastic pollution has become a global concern for ecosystem health and biodiversity conservation. Concentrations of plastics are manifold higher in the terrestrial system than the aquatic one. Micro/nanoplastics (M/NP) have the ability to alter soil enzymatic system, soil properties and also affect soil borne microorganisms and earthworms. Despite, the knowhow regarding modulatory effects of plastics are acquired from the study on aquatic system and reports on their phytotoxic potentials are limited. The presence of cell wall that could restrict M/NP invasion into plant roots might be the putative cause of this limitation. M/NP inhibit plant growth, seed germination and gene expression; and they also induce cytogenotoxicity by aggravating reactive oxygen species generation. Dynamic behavior of cell wall; the pores formed either by cell wall degrading enzymes or by plant-pathogen interactions or by mechanical injury might facilitate the entry of into roots M/NP. This review also provides a possible mechanism of large sized microplastics-induced phytotoxicity especially for those that cannot pass through cell wall pores. As M/NP affect soil microbial community and soil parameters, it is hypothesized that they could have the potential to affect N₂ fixation and research should be conducted in this direction. Reports on M/NP-induced toxicity mainly focused only on one polymer type (polystyrene) in spite of the toxicological relevancies of other polymer types like polyethylene, polypropylene etc. So, the assessment of phytotoxic potential of M/NP should be done using other plastic polymers in real environment as they are known to intract with other environmental stressors as well as can alter the the soil-microbe-plant interaction.

Zinc Oxide Nanoparticles Damage Tobacco BY-2 Cells by Oxidative Stress Followed by Processes of Autophagy and Programmed Cell Death

Nanomaterials, including zinc oxide nanoparticles (ZnO NPs), have a great application potential in many fields, such as medicine, the textile industry, electronics, and cosmetics. Their impact on the environment must be carefully investigated and specified due to their wide range of application. However, the amount of data on possible negative effects of ZnO NPs on plants at the cellular level are still insufficient. Thus, we focused on the effect of ZnO NPs on tobacco BY-2 cells, i.e., a widely accepted plant cell model. Adverse effects of ZnO NPs on both growth and biochemical parameters were observed. In addition, reactive oxygen and nitrogen species visualizations confirmed that ZnO NPs may induce oxidative stress. All these changes were associated with the lipid peroxidation and changes in the plasma membrane integrity, which together with endoplasmatic reticulum and mitochondrial dysfunction led to autophagy and programmed cell death. The present study demonstrates that the phytotoxic effect of ZnO NPs on the BY-2 cells is very complex and needs further investigation.

Evaluation of Allelopathic Activity of Chinese Medicinal Plants and Identification of Shikimic Acid as an Allelochemical from Illicium verum Hook. f

This study focused on the potential allelopathy of 50 species of Chinese medicinal plants, which are mainly distributed in the Xinjiang Uyghur Autonomous Region, Inner Mongolia, and Yunnan Province. The “sandwich method” was adopted and used for the screening for allelopathic potential among these plant species. Further phytotoxic evaluation of the candidate species was conducted by applying plant extracts to crops and weed species. The results of this study indicated that among the 50 medicinal plant species evaluated, the fruits of Illicium verum Hook. f. (star anise) showed the most significant allelopathic potential through the leaf leachates. Shikimic acid was identified to be the main bioactive compound (about 7% dry weight) in star anise by reversed-phase High Performance Liquid Chromatography (RP-HPLC) analysis. The phytotoxic bioassay indicated that both the crude extract of the Chinese star anise and the synthetic shikimic acid showed strong inhibitory activity on the radicle and hypocotyl growth of lettuce. The radicle growth inhibition of lettuce caused by the crude extract of star anise could be explained by the contribution of the biological activity of shikimic acid. In conclusion, shikimic acid could be a putative allelochemical in the fruits of Illicium verum and could be utilized in sustainable weed management.

Allelochemical Activity of Eugenol-Derived Coumarins on Lactuca sativa L

Coumarins are widely distributed substances in plant species that promote phytotoxic effects, allowing them to be exploited as herbicides less harmful to the environment, since many invasive species have demonstrated resistance to commercially available products. The derived coumarins used in this study had not been tested in plant models and their effect on plants was unknown. The objective of this study was to evaluate the phytotoxic action of these coumarins in bioassays with Lactuca sativa L., in order to select the most responsive substance whose toxicity was best elucidated by chromosomal complement and enzymatic antioxidant metabolism studies. From the phytotoxicity assays, coumarin 8-methoxy-2-oxo-6-(prop-2-en-1-yl)-2H-chromene-3-carboxylic acid (A1), reported here for the first time, was selected as the most responsive and caused a reduction in the following parameters: number of normal seedlings, fresh biomass, root length and shoot length. Subsequent studies demonstrated that this coumarin is cytogenotoxic due to damage caused to the cell cycle and the occurrence of chromosomal abnormalities. However, it did not interfere with antioxidant enzyme activity and did not cause lipid peroxidation. The changes caused by coumarin A1 described herein can contribute to better understanding the allelochemical actions of coumarins and the potential use of these substances in the production of natural herbicides.