Chemical composition and allelopathic potential of Schinus molle L. (Anacardiaceae) essential oils against common weeds of wheat crop

This study aims to determine the chemical composition of essential oil (EO) extracted from the aerial parts of Schinus molle L., as well as its phytotoxicity on germination and seedling growth against some invasive weed species of cereal crops and wheat (Triticum durum, cultivar Chen'S). Gas chromatography/mass spectrometry (GC-MS) identified 51 components (representing 95.26% of the total EO composition). Shyobunone (10.14%), 1-phellandrene (9.63%), α-cadinol (7.46%), δ-cadinene (7.45%), and germacrene D (7.09%) were the most abundant compounds. The effect of EO on weed species germination, root and shoot growth was moderate to strong. When 0.02% and 0.03% of the oil were applied, EO had a strong phytotoxic effect, resulting in 100% failure of Bromus rigidus germination. In addition to determining the responsible compound, the observed phytotoxicity suggestedthat S. molle essential oil could be used as an environmentally friendly biopesticide.

LC-MS/MS-Guided Molecular Networking for Targeted Discovery of Undescribed and Bioactive Ophiobolins from Bipolaris eleusines

An integrated purification procedure through the LC-MS/MS-based molecular networking strategy combined with bioactive evaluation was first ushered for discovering bioactive ophiobolins from Bipolaris eleusines. Ophiobolins were mainly dispersed in five clusters, which were classified based on different ring systems and functional groups. Nine undescribed ophiobolins (1-6 and 9-11) and an undescribed natural product (8) along with two known analogs (7 and 12) were isolated in target. The undescribed structures were characterized by HR-ESI-MS, NMR spectra, and X-ray diffraction experiments. Compounds 3-12 exhibited strong phytotoxic effects on green foxtails by producing visible lesions, and compounds 1-10 and 12 displayed different levels of cytotoxic activities against cancer cell lines B16, Hep G2, and MCF-7, from which the possible structure-activity relationships were then suggested. The results have supported that bioactivity-guided molecular networking is an efficient strategy to expedite the discovery of undescribed bioactive natural products.

Effects of Microplastic Contamination on the Aquatic Plant Lemna minuta (Least Duckweed)

Microplastics are widely spread in aquatic environments. Although they are considered among the most alarming contaminants, toxic effects on organisms are unclear, particularly on freshwater plants. In this study, the duckweed Lemna minuta was grown on different concentrations (50, 100 mg/L) of poly(styrene-co-methyl methacrylate) microplastics (MP) and exposure times (T0, T7, T14, T28 days). The phytotoxic effects of MP were investigated by analyzing several plant morphological and biochemical parameters (frond and root size, plant growth, chlorophyll, and malondialdehyde content). Observations by scanning electron microscope revealed MP adsorption on plant surfaces. Exposition to MP adversely affected plant growth and chlorophyll content with respect to both MP concentrations and exposure times. Conversely, malondialdehyde measurements did not indicate an alteration of oxidative lipid damage in plant tissue. The presence of MP induced root elongation when compared to the control plants. The effects of MP on L. minuta plants were more evident at T28. These results contribute to a better understanding of MP's impact on aquatic plants and highlight that MP contamination manifests with chronic-type effects, which are thus detectable at longer exposure times of 7 days than those traditionally used in phytotoxicology tests on duckweeds.

HPLC-DAD-MS Identification and Quantification of Phenolic Components in Japanese Knotweed and American Pokeweed Extracts and Their Phytotoxic Effect on Seed Germination

We performed a detailed HPLC-MSn analysis of the phenolic compounds from the extracts of two invasive alien plant species (IAPS): Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decr.) and American pokeweed (Phytolacca americana L.). The major phenolic groups were hydroxycinnamic acids and flavanols in Japanese knotweed (J. knotweed) and flavonols, hydroxycinnamic acids, and stilbenes in American pokeweed (A. pokeweed). We investigated the influence of solvent type and extraction time on the extraction efficiency of the phenolic compounds. The solvent 80% methanol had a higher polyphenolic extraction efficiency than water, since 14.5 times more flavonols and 2.3 times more stilbenes were extracted from J. knotweed and 5.2 times more flavonols and 2.6 times more stilbenes were extracted from A. pokeweed. In contrast, with water, we obtained a 52% higher hydroxycinnamic acids (HCA) content from J. knotweed. Hydroxycinnamic acids were best extracted in water after 24 h, flavanols after 12 h, stilbenes between 12 and 24 h, and flavonol glycosides after 48 h of extraction. We also tested the allelopathic effect of the aqueous extract of A. pokeweed and J. knotweed on seed germination and shoot and root growth of perennial ryegrass. The results showed that the water extract of J. knotweed resulted in 38 to 48% lower seed germination of perennial ryegrass, and the extract of A. pokeweed resulted in 83 to 90% lower seed germination. The phytotoxic effect of the extract of J. knotweed and A. pokeweed was also reflected in a characteristic reduced growth of shoots and roots of perennial ryegrass. The phytotoxic action of IAPS could also be applied for beneficial purposes, since this would be an effective strategy for their control and a reduction of their spread in the environment.

Application of an Endophyte Enterobacter sp. TMX13 to Reduce Thiamethoxam Residues and Stress in Chinese Cabbage (Brassica chinensis L)

A strain of thiamethoxam-degrading endophyte, named TMX13, was isolated from roots of mulberry (Morus alba L.) and was identified as Enterobacter sp. Inoculating Chinese cabbage (Brassica chinensis L) with strain TMX13-gfp (gfp-labeled TMX13) could significantly reduce thiamethoxam residues in the aboveground part (edible portion) of the vegetable. The theoretical daily intake (TDI) of thiamethoxam via consumption of TMX13-gfp inoculated Chinese cabbage was 0.17 μg/kg body weight per day, far less than the prescribed acceptable daily intake (ADI) for this pesticide. TMX13-gfp colonization could increase the leaf chlorophyll content and plant biomass and promote the development of plant roots. Compared with the uninoculated treatment, the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) and the activity of superoxide dismutase (SOD) in leaves of the TMX13-gfp inoculated plants decreased by 18.4%-60.2%, suggesting that TMX13-gfp colonization could alleviate the oxidative stress induced by thiamethoxam exposure. The total amounts of organic acids and amino acids in root exudates from the TMX13-gfp inoculated Chinese cabbage decreased by 9.2% and 85.2%, respectively. Results of this study lead to the conclusion that the isolated endophyte Enterobacter sp. TMX13 could reduce thiamethoxam residues in edible vegetables, promote plant growth, and alleviate the phytotoxic effects induced by thiamethoxam exposure.

Nutrient status and phytotoxicity analysis of goat manure discharged from farms in South Korea

The present study evaluated the phytotoxicity effect of goat manure (GM) collected from six different regions in South Korea, namely, Chupungnyeong (T1), Hoengseong (T2), Goesan (T3), Sancheong (T4), Jangsu (T5) and Namwon (T6). Phytotoxicity was assessed by means of the analysis of germination index (GI), relative seed germination (RSG), relative root elongation (RRE) and vigor index (VI) using five commercial crop varieties, namely, sesame (Sesamum indicum L.), chrysanthemum (Chrysanthemum indicum L.), carrot (Daucus carota), radish (Raphanus sativus) and cabbage (Brassica rapa). Physico-chemical parameter values were recorded at appreciable levels in all GM extracts. The effect of seedling growth was significantly different (p ≤ .05) due to the variability of nutrient content and phytotoxic effect of the extracts on the different crop seeds. Of the extracts, Goesan (T3) and Sancheong (T4) recorded the best results in the range of GI (%) (54.1-128.8) and VI (930.7-1044) and GI (%) (70.1-167.3) and VI (609.2-3034), respectively, and also showed no inhibitory effect in any of the crop seeds. Overall results also revealed that radish crops showed excellent and non-phytotoxic results in all manure extracts compared to the other crops.

Phoma crystallifera with phytotoxic effects and pathogenic potential against field bindweed (Convolvulus arvensis L.) in Iran

AIMS

To identify a potential pathogenic isolate of fungus on Convolvulus arvensis and to determine its phytotoxic activity, which revealed the presence of toxic metabolites responsible for the toxicity against the target weed.

METHODS AND RESULTS

A high virulent isolate of the fungus, Phoma crystallifera was isolated from symptomatic field bindweed in the west of Iran and was screened for the production of phytotoxins, which promoted necrosis on the detached leaves and seedlings of field bindweed in the bioassays. The isolate was distinct from other isolates of the fungi on the basis of morphological characteristics and the combined sequence database of the ITS region, partial LSU rDNA and β-tubulin gene. Isolate P. crystalifera P6 produced the highest amount of phytotoxins after 21 days in a shacked culture of Richard's broth. The active metabolites were isolated from a cell-free culture filtrate by ethyl-acetate and purified by thin layer chromatography. The result indicated that six out of nine spots had phytotoxic activity in the bioassays, with R_f values of 0·16, 0·30, 0·36, 0·43, 0·57 and 0·81.

CONCLUSIONS

Phoma crystallifera P6 and its active metabolites showed significant phytotoxic effects on the detached leaves of C. arvensis.

SIGNIFICANCE AND IMPACT OF THE STUDY

To date, there are no reports of possible biocontrol agent(s) on C. arvensis in Iran. Thus, P. crystallifera P6 is introduced here as a severe pathogenic fungus and which can be used as a biocontrol agent against C. arvensis.