Physiological Basis for the Mechanism of Selectivity of Tripyrasulfone between Rice (Oryza sativa) and Barnyard Grass (Echinochloa crus-galli).

Tripyrasulfone is currently the only HPPD-inhibiting herbicide that possesses outstanding selectivity even for direct-seeded rice (Oryza sativa) when applied POST to control grass weeds; however, the underlying mechanisms remain unclear. In this study, the inhibitory effects of the real active HDT of tripyrasulfone on recombinant 4-hydroxyphenylpyruvate dioxygenase (HPPDs) from rice and barnyard grass (Echinochloa crus-galli) were similar, with consistent structural interactions and similar binding energies predicted by molecular docking. However, the HPPD expression level in rice was significantly greater than that in barnyard grass after tripyrasulfone treatment. Tripyrasulfone was rapidly taken up and hydrolyzed into HDT, which was similarly distributed within the whole plants of rice and barnyard grass at 24 h after treatment. Compared with barnyard grass, rice has more uniform epicuticular wax in the cuticle of its leaves, absorbing less tripyrasulfone and metabolizing much more tripyrasulfone. Overall, to a greater extent, the different sensitivities to tripyrasulfone between barnyard grass and rice resulted from metabolic variations.

Enhanced Herbicide Metabolism and Target Site Mutation Enabled the Multiple Resistance to Cyhalofop-butyl, Florpyrauxifen-benzyl, and Penoxsulam in Echinochloa crus-galli.

This study investigated the multiple herbicide resistance (MHR) mechanism of one Echinochloa crus-galli population that was resistant to florpyrauxifen-benzyl (FPB), cyhalofop-butyl (CHB), and penoxsulam (PEX). This population carried an Ala-122-Asn mutation in the acetolactate synthase (ALS) gene but no mutation in acetyl-CoA carboxylase (ACCase) and transport inhibitor response1 (TIR1) genes. The metabolism rate of PEX was 2-fold higher, and the production of florpyrauxifen-acid and cyhalofop-acid was lower in the resistant population. Malathion and 4-chloro-7-nitrobenzoxadiazole (NBD-Cl) could reverse the resistance, suggesting that cytochrome P450 (CYP450) and glutathione S-transferase (GST) contribute to the enhanced metabolism. According to RNA-seq and qRT-PCR validation, two CYP450 genes (CYP71C42 and CYP71D55), one GST gene (GSTT2), two glycosyltransferase genes (rhamnosyltransferase 1 and IAAGLU), and two ABC transporter genes (ABCG1 and ABCG25) were induced by CHB, FPB, and PEX in the resistant population. This study revealed that the target mutant and enhanced metabolism were involved in the MHR mechanism in E. crus-galli.

Utilization of the neighborhood design to evaluate suitable cover crops and their density for Echinochloa colona management.

Summer weed species, including Echinochloa colona, are becoming problematic in the eastern grain region of Australia, but cover crops can be useful to suppress weeds during the summer fallow period. The present study evaluated the growth and seed production of E. colona grown alone or with four and eight cover crop plants per pot (i.e., 80 and 160 plants m-2). Four legume (cowpea, lablab, pigeonpea, and soybean) and two grass (forage sorghum and Japanese millet) cover crops were used. Interference by cover crops reduced the height, the number of leaves and tillers, inflorescence number, seed production, and biomass of this weed than when it was grown alone. Cover crops differed in their ability to suppress the growth and seed production of E. colona. The effect of cover crop density on the studied attributes was non-significant in most cases. Pigeonpea as a cover crop was the least effective in suppressing the growth and seed production of E. colona. In general, leguminous cover crops exhibited less suppression of E. colona than grasses. Forage sorghum was most efficient in reducing the growth of this weed. Forage sorghum and Japanese millet reduced E. colona leaf and tiller numbers per plant by 90 and 87%, respectively. These cover crops reduced E. colona leaf number to only 17 per plant as against 160 per plant recorded without cover crops. Inflorescence number per E. colona plant growing alone was as high as 48. However, it was reduced by 20-92% when this weed was grown with cover crop plants. E. colona's seed production was significantly suppressed by all the cover crops, except pigeonpea. Biomass of E. colona was suppressed largely by forage sorghum and Japanese millet compared to other cover crops. Among the cover crops, pigeonpea produced the lowest biomass of 11 g pot-1, and the highest biomass (114 g pot-1) was produced by forage sorghum. The study demonstrated the usefulness of cover crops, especially forage sorghum and Japanese millet, to suppress the growth and seed output of E. colona.

Enantioselective and Synergistic Herbicidal Activities of Common Amino Acids Against Amaranthus tricolor and Echinochloa crus-galli.

Amino acids have a wide range of biological activities, which usually rely on the stereoisomer presented. In this study, glycine and 21 common α-amino acids were investigated for their herbicidal property against Chinese amaranth (Amaranthus tricolor L.) and barnyard grass (Echinochloa crus-galli (L.) Beauv.). Both d- and l-isomers, as well as a racemic mixture, were tested and found that most compounds barely inhibited germination but moderately suppressed seedling growth. Various ratios of d:l-mixture were studied and synergy between enantiomers was found. For Chinese amaranth, the most toxic d:l-mixtures were at 3:7 (for glutamine), 8:2 (for methionine), and 5:5 (for tryptophan). For barnyard grass, rac-glutamine was more toxic than the pure forms; however, d-tryptophan exhibited greater activity than racemate and l-isomer, indicating the sign of enantioselective toxicity. The mode of action was unclear, but d-tryptophan caused bleaching of leaves, indicating pigment synthesis of the grass was inhibited. The results highlighted the enantioselective and synergistic toxicity of some amino acids, which relied upon plant species, chemical structures, and concentrations. Overall, our finding clarifies the effect of stereoisomers, and provides a chemical clue of amino acid herbicides, which may be useful in the development of herbicides from natural substances.

Comparison of Efficacy and Detection of Clethodim and Glyphosate Applied with Dicamba and 2,4-D through Tank Mixture and Sequential Applications.

Greenhouse studies were planted at the R.R. Foil Plant Science Research Center in Starkville, MS. In the efficacy trial, pots were seeded with barnyardgrass (Echinochloa crus-galli), broadleaf signalgrass (Urochloa platyphylla), and giant foxtail (Setaria faberi). In the lab detection trial, only barnyardgrass was seeded. Both studies consisted of 16 treatments with four replications per treatment. The treatments consisted of clethodim, glyphosate, dicamba, and 2,4-D applied singularly and in combination with each other. Each herbicide combination was applied with three application methods: tank mixture, sequential applications where the synthetic auxin was applied first (auxin applied first), and sequential applications where glyphosate or clethodim was applied first (auxin applied second). The auxin applied second method had higher visual estimations of control ratings and lower biomass weights compared to the other two methods. The auxin applied second method had more glyphosate and clethodim detected with the use of liquid chromatography tandem mass spectrometry.

Design, Synthesis, and Herbicidal Activity of N-Benzyl-5-cyclopropyl-isoxazole-4-carboxamides.

Based on the structures of isoxaflutole (IFT) and N-isobutyl-N-(4-chloro-benzyl)-4-chloro-2-pentenamide, a series of N-benzyl-5-cyclopropyl-isoxazole-4-carboxamides was designed by connecting their pharmacophores (i.e., a multitarget drug design strategy). A total of 27 N-benzyl-5-cyclopropyl-isoxazole-4-carboxamides were prepared from 5-cyclopropylisoxazole-4-carboxylic acid and substituted benzylamines, and their structures were confirmed by NMR and MS. Laboratory bioassays indicated that I-26 showed 100% inhibition against Portulaca oleracea and Abutilon theophrasti at a concentration of 10 mg/L, better than the positive control butachlor (50% inhibition for both weeds). A strong growth inhibition was observed, but a typical bleaching phenomenon of IFT could not be observed in the Petri dish assay. I-05 displayed excellent postemergence herbicidal activity against Echinochloa crusgalli and A. theophrasti at a rate of 150 g/ha, and bleaching symptoms were observed in the leaves of treated weeds. The bleaching effect of Chlamydomonas reinhardtii treated by I-05 could be reversed by adding homogentisate. Enzymatic bioassays indicated that I-05 could not inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD) activity, but II-05, an isoxazole ring-opening product of I-05, could inhibit HPPD activity with an EC50 value of 1.05 µM, similar to that of mesotrione (with an EC50 value of 1.35 µM). Detailed discussion about observed herbicidal symptoms is provided in the Results and Discussion section. This investigation provided a proof-of-concept foundation that a multitarget drug design strategy could be applied in agrochemical research.

Turpentine Derived Secondary Amines for Sustainable Crop Protection: Synthesis, Activity Evaluation and QSAR Study.

In this study, we will report on the synthesis and application of efficient botanical agrochemicals from turpentine for sustainable crop protection. Two series of turpentine derived secondary amines were synthesized and identified by FT-IR, 1H NMR, 13C NMR, and HRMS. The herbicidal activities against Echinochloa crus-galli were evaluated. The potential toxicity of the synthesized compounds was tested by MTT cytotoxicity analysis. The effect of structure of the synthesized secondary amines and corresponding Schiff base compounds on their activities was investigated by quantitative structure-activity relationship (QSAR) study. All target products were found to be low toxicity, with similar or higher herbicidal activities than commercial herbicides diuron and Glyphosate. Results of QSAR study showed that a best four-descriptor QSAR model with R2 of 0.880 and Rloo2 of 0.818 was obtained. The four descriptors most relevant to the herbicidal activities are the min valency of a N atom, the max total interaction for a C-H bond, the relative number of aromatic bonds, and the min partial charge (Qmin).

Herbicidal Activity of Thymbra capitata (L.) Cav. Essential Oil.

The bioherbicidal potential of Thymbra capitata (L.) Cav. essential oil (EO) and its main compound carvacrol was investigated. In in vitro assays, the EO blocked the germination and seedling growth of Erigeron canadensis L., Sonchus oleraceus (L.) L., and Chenopodium album L. at 0.125 µL/mL, of Setaria verticillata (L.) P.Beauv., Avena fatua L., and Solanum nigrum L. at 0.5 µL/mL, of Amaranthus retroflexus L. at 1 µL/mL and of Portulaca oleracea L., and Echinochloa crus-galli (L.) P.Beauv. at 2 µL/mL. Under greenhouse conditions, T. capitata EO was tested towards the emergent weeds from a soil seedbank in pre and post emergence, showing strong herbicidal potential in both assays at 4 µL/mL. In addition, T. capitata EO, applied by spraying, was tested against P. oleracea, A. fatua and E. crus-galli. The species showed different sensibility to the EO, being E. crus-galli the most resistant. Experiments were performed against A. fatua testing T. capitata EO and carvacrol applied by spraying or by irrigation. It was verified that the EO was more active at the same doses in monocotyledons applied by irrigation and in dicotyledons applied by spraying. Carvacrol effects on Arabidopsis root morphology were also studied.

Sensitivity of yellow foxtail (Setaria glauca L.) and barnyardgrass (Echinochloa crus-galli L.) to aqueous extracts or dry biomass of cover crops.

BACKGROUND: The common weeds Echinochloa crus-galli L. and Setaria glauca L. were studied for their sensitivity to aqueous extracts or dry biomass of the following cover crops (CCs): Brassicaceae (Sinapis alba, Raphanus sativus var. Oleiformis, Camellina sativa), Fagopyrum esculentum and Guizotia abyssinica. RESULTS: Treating E. crus-galli with aqueous extracts of mixed CCs or individual brassica CC significantly reduced germination. Treating S. glauca with aqueous extracts of C. sativa or G. abyssinicia reduced germination. Aqueous extracts of all CCs significantly reduced radicle length of E. crus-galli and S. glauca, with C. sativa and mixed CCs showing the greatest effect. Aqueous extracts of nearly all CCs delayed start and middle germination of E. crus-galli and S. glauca, with S. alba and R. sativus showing the strongest effects. Aqueous extracts of Brassicaceae leaf and flower significantly reduced germination, coleoptile length, radicle length and seedling biomass of E. crus-galli and S. glauca. Brassicaceae leaves and flowers contained higher phenolics than other tissues. Adding 4 or 8% S. alba and R. sativus dry powder to soil significantly reduced growth of E. crus-galli and S. glauca; even concentrations of 1% measurably slowed growth of E. crus-galli. CONCLUSIONS: Brassicaceae may be allelopathic to S. glauca and E. crus-galli. Aqueous extracts of leaves and flowers showed greater phytotoxic activity than other tissues and also contained more phenolics. Therefore Brassicaceae CCs may be most effective against S. glauca and E. crus-galli if incorporated into soil during their flowering stage. © 2020 Society of Chemical Industry.

Response of glyphosate-resistant and susceptible biotypes of Echinochloa colona to low doses of glyphosate in different soil moisture conditions.

To evaluate the hormetic effect of glyphosate on Echinochloa colona, two pot studies were done in the screenhouse at the Gatton Campus, the University of Queensland, Australia. Glyphosate was sprayed at the 3-4 leaf stage using different doses [(0, 5, 10, 20, 40, 80 and 800 g a.e. ha-1) and (0, 2.5, 5, 10, 20 and 800 g a.e. ha-1)] in the first and second study, respectively. In the second study, two soil moistures (adequately-watered and water-stressed), and two E. colona biotypes, glyphosate-resistant and glyphosate-susceptible, were included. In both studies, plants that were treated with glyphosate at 2.5-40 g ha-1 grew taller and produced more leaves, tillers, inflorescences and seeds than the control treatment. In the first study, 5 g ha-1 glyphosate resulted in the maximum aboveground biomass (increase of 34% to 118%) compared with the control treatment. In the second study, the adequately-watered and glyphosate low dose treatments caused an increase in all the measured growth parameters for both biotypes. For example, total dry biomass was increased by 64% and 54% at 5 g ha-1 in the adequately-watered treatments for the resistant and susceptible biotypes, respectively, compared with the control treatment. All measured traits tended to decrease with increasing water stress and the stimulative growth of low doses of glyphosate could not compensate for the water stress effect. The results of both studies showed a hormetic effect of low doses of glyphosate on E. colona biotypes and such growth stimulation was significant in the range of 5 to 10 g ha-1 glyphosate. Water availability was found to be effective in modulating the stimulatory outcomes of glyphosate-induced hormesis. No significant difference was observed between the resistant and susceptible biotypes for hormesis phenomenon. The study showed the importance of precise herbicide application for suppressing weed growth and herbicide resistance evolution.

Growth behavior and glyphosate resistance level in 10 populations of Echinochloa colona in Australia.

Recently, poor control of Echinochloa colona with glyphosate has been reported in no-till agriculture systems of the northern grain region (NGR) of Australia. Two experiments were conducted using 10 populations of E. colona selected from the NGR of Australia to understand differences in their growth behavior and resistance pattern. Growth studies revealed that these populations differed in plant height (53-70 cm plant-1), tiller production (30-52 tillers plant-1), leaf production (124-186 leaves plant-1) and seed head production (37-65 seed heads plant-1). Days taken to seed heads and shoot biomass in these populations ranged between 40-48 d and 21-27 g plant-1, respectively. Seed production in these populations ranged between 5380 and 10244 seeds plant-1; lowest for population B17/25 and highest for population B17/13. Correlation studies revealed that seed number plant-1 had a positive correlation with tiller number plant-1 (r = 0.73) and negative relation with days taken to seed head initiation (r = - 0.65). The glyphosate dose-response study showed a wide range of responses in these populations and the glyphosate dose required to kill 50% plants (LD50 values) was estimated between 161 to 2339 g a.e. glyphosate ha-1. LD50 values of populations B17/16, B 17/34 and B17/35 were 1086, 2339 and 1153 g ha-1, respectively, making them 6.7, 15.1 and 7.2-fold resistant to glyphosate compared with the susceptible population B17/37. Growth behavior and seed production potential in these populations had no correlation with the resistance index. These results suggest that some populations of E. colona are highly problematic; for example, population B17/34 was not only highly glyphosate-resistant, but also produced a high seed number (9300 seeds plant-1). This study demonstrated that there is a possibility of great risk with the increased use of glyphosate for managing E. colona in the NGR of Australia. The results warrant integrated weed management strategies and improved stewardship guidelines are required for managing glyphosate-resistant populations of E. colona and to restrict further movement of resistant populations to other regions of Australia.

The response of glyphosate-resistant and glyphosate-susceptible biotypes of Echinochloa colona to carbon dioxide, soil moisture and glyphosate.

Physiological and growth responses of two Australian Echinochloa colona biotypes (glyphosate-resistant and susceptible, produced from a single population) to different concentrations of carbon dioxide (CO2) (ambient ~450 ppm and elevated ~750 ppm) and soil moisture (well-watered and water-stressed) were analyzed. Elevated CO2 and well-watered conditions resulted in E. colona plants with greater biomass, height and numbers of tillers and leaves in both biotypes; however, no significant response was observed for seed production or the amount of photosynthesis pigments with increasing CO2 at both soil moisture levels. In addition, water availability was more influential for growth than CO2 concentration. The mean shoot biomass of the susceptible biotype under elevated CO2 and well-watered conditions was significantly greater than the resistant biotype. Although the susceptible biotype showed more vegetative and reproductive growth than the resistant biotype, no significant difference was observed for seed production between the biotypes in the water-stressed condition. In a second experiment, different doses of glyphosate (0, 180, 360, 720 and 1440 g a.e ha-1) were applied to both biotypes grown at two soil moisture levels (well-watered and water-stressed). In the water-stressed condition, glyphosate efficacy was decreased in both biotypes. The resistant biotype in the well-watered condition had only 19% survival at 1440 g ha-1 glyphosate (double the recommended rate), but this value increased in the water-stressed condition by 62%. Our study suggests that future climate change can affect the physiological and growth processes of weeds and their responses to herbicides. Knowledge of their adapting behaviors will be critical to weed management strategies.

Herbicidal Polyketides and Diketopiperazine Derivatives from Penicillium viridicatum.

Herbicidal activity-guided isolation from the fermentation extract of Penicillium viridicatum had obtained two herbicidal series of polyketides (1-7) and diketopiperazine derivatives (8-11), especially including three novel polyketides (1-3). The structures and absolute configurations of new polyketides 1-3 were elucidated by extensive spectroscopic analyses, as well as comparisons between measured and calculated ECD spectra. Novel polyketides 1-3 and known 4, all bearing the heptaketide skeleton with a trans-fused decalin ring of 8-CH3 substitution, could significantly inhibit the radicle growth of Echinochloa crusgalli seedlings with a dose-dependent relationship. Especially at the concentration of 10 µg/mL, 1-4 exhibited the inhibition rates with 81.5% ± 2.0, 76.4% ± 0.8, 79.6% ± 1.1, and 80.0 ± 1.8%, respectively, even better than the commonly used synthetic herbicide of acetochlor with 76.1 ± 1.4%. Further greenhouse bioassay revealed that 4 showed pre-emergence herbicidal activity against E. crusgalli with the fresh-weight inhibition rate of 74.1% at a dosage of 400 g ai/ha, also better than acetochlor, while the other isolated metabolites (5-11) exhibited moderate herbicidal activities. The structure-activity differences of isolated polyketides indicated that the heptaketide skeleton, characterized by a trans-fused decalin ring with 8-CH3 substitution, should be the key factor of their herbicidal activities, which could give new insights for the bioherbicide developments.

Bioherbicidal activity of terpenes and phenylpropenes against Echinochloa crus-galli.

This study was undertaken to evaluate the herbicidal activity of twelve natural compounds belonging to monoterpenes, phenylpropenes, and sesquiterpenes against Echinochloa crus-galli under laboratory and glasshouse conditions. Experiments were conducted to determine the impact of different concentrations (0.5, 1, 2, 4 and 8 mM) of these compounds on the seed germination and root and shoot growth of barnyard grass. trans-Cinnamaldehyde, eugenol, and thymol caused the highest impact on barnyard grass reducing its seed germination and shoot growth. p-Cymene (EC50 = 0.22 mM) and trans-cinnamaldehyde (EC50 = 0.34 mM) were the most potent compounds in limiting the root growth of the E. crus-galli. In a post-emergent experiment, thymol, trans-cinnamaldehyde, eugenol, farnesol, and nerolidol significantly reduced the shoot growth, fresh and dry weight of two-leaf stage barnyard grass after 2 days of the foliar treatment with the concentrations of 0.5, 1.0 and 2.0%. These compounds induced severe visible injury symptoms where trans-cinnamaldehyde, eugenol, farnesol and nerolidol showed a complete weed control at 1.0 and 2.0%. These compounds were successfully formulated as emulsifiable concentrates and showed higher herbicidal activities against barnyard grass. Altogether, our data showed that trans-cinnamaldehyde, eugenol, thymol, farnesol, and nerolidol can be developed as novel bioherbicides for managing E. crus-galli.

Target-Site and Metabolic Resistance Mechanisms to Penoxsulam in Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv).

Herbicide resistance identification is essential for effective chemical weed control. In this study, we quantified the differences in growth response between penoxsulam resistant (R) and sensitive (S) Echinochloa crus-galli populations, explored the changes in ALS, and performed genetic analyses to identify metabolic genes that are up-regulated by the application of penoxsulam and other common herbicides. The R population showed a 26.0-fold higher resistance to penoxsulam and varied resistance to most tested herbicides with indices ranging from 4.9 to 145.9. A Trp-574-Arg amino acid mutation in ALS and low penoxsulam ALS sensitivity were the main mechanisms underlying herbicide resistance. The penoxsulam resistance can be significantly reversed by two P450s inhibitors and one GST inhibitor. By RNA-Seq, thirty-six highly expressed contigs were selected, and 30 of them were up-regulated in the R population treated by penoxsulam. Many of these genes were significantly expressed when treated with pyroxsulam, metamifop, and quinclorac. These upregulated genes appear to be complementary for plant resistance to penoxsulam and other common herbicides.

Chemical profiling, cytotoxicity and phytotoxicity of foliar volatiles of Hyptis suaveolens.

In the present study, the essential oil (EO) of Hyptis suaveolens has been explored for the first time for its phytotoxic and cytotoxic activities. The phytotoxic activity was assessed against rice (Oryza sativa) and its major troublesome weed, Echinochloa crus-galli, under laboratory and screenhouse conditions. GC-MS analysis revealed EO to be monoterpenoid (~ 79% monoterpenes) in nature with α-phellandrene (22.8%), α-pinene (10.1%) and limonene (8.5%) as the major chemical constituents. The laboratory bioassay showed a complete growth inhibitory effect of EO (≥ 2 mg mL-1) towards the germination and seedling growth of E. crus-galli. However, the inhibitory effect on rice was much less (~40% inhibition). EO caused visible injury, reduction in chlorophyll content, cell viability and ultimately led to complete wilting of E. crus-galli plants. In addition, EO altered the cell division in the meristematic cells of Allium cepa as depicted by ~63% decrease in mitotic index. EO exposure induced several aberrations at chromosomal (c-mitosis, anaphase bridges, chromosomal breakage, vagrant chromosomes, and sticky chromosomes) and cytological level (cytoplasm destruction, peripheral nuclei, and bi-nucleate cells). The present study concludes that H. suaveolens EO possesses phytotoxic activity due to its mito-depressive activity, and could serve as a natural herbicide under sustainable agricultural practices.

Bioactive Resorcylic Acid Lactones with Different Ring Systems from Desert Plant Chaetosphaeronema hispidulum. [corrected].

Five new resorcylic acid lactones (RALs) hispidulactones A-E (1, 4, 5, 8, and 9), a new natural product (2), and four known ones (3, 6, 7, and 10) with different ring systems were isolated from the desert plant Chaetosphaeronema hispidulum. [corrected]. The new compounds were characterized by NMR data, CD spectra, and X-ray experiment. The new natural product (2) displayed strongly biological effects on the seedlings growth of Arabidopsis thaliana, Digitaria sanguinalis, and Echinochloa crusgalli with a dose-dependent relationship. Compounds 1, 2, and 6 were also tested cytotoxic activities against three cancer cell lines HCT116, Hela, and MCF7 and only did the new natural product (2) display biological activities with IC50 values at 54.86 ± 1.52, 4. 90 ± 0.02, and 20.04 ± 4.00 µM, respectively, whereas the IC50 values of the positive control cis-platinum were 11.36 ± 0.42, 3.54 ± 0.12, and 14.32 ± 1.01 µM, respectively.

Evaluation of weed control efficacy and crop safety of the new HPPD-inhibiting herbicide-QYR301.

QYR301, 1,3-Dimethyl-1H-pyrazole-4-carboxylic acid 4-[2-chloro-3-(3,5-dimethyl-pyrazol-1-ylmethyl)-4-methanesulfonyl-benzoyl]-2,5-dimethyl-2H-pyrazol-3-yl ester, is a novel HPPD-inhibiting herbicide and was evaluated to provide a reference for post-emergence (POST) application under greenhouse and field conditions. The crop safety (180 and 360 g active ingredient (a.i.) ha-1 treatments) experiment revealed that wheat, paddy, garlic and corn were the only four crops without injury at both examined herbicide rates. The weed control efficacy (60 and 120 g a.i. ha-1) experiment showed that QYR301 exhibited high efficacy against many weeds, especially weeds infesting paddy fields. Furthermore, it is interesting that both susceptible and multiple herbicide resistant Echinochloa crus-galli (L.) Beauv. and Echinochloa phyllopogon (Stapf) Koss, two notorious weed species in paddy field, remained susceptible to QYR301. Further crop tolerance results indicated that 20 tested paddy hybrids displayed different levels of tolerance to QYR301, with the japonica paddy hybrids having more tolerance than indica paddy hybrids under greenhouse conditions. Results obtained from field experiments showed that QYR301 POST at 135 to 180 g a.i. ha-1 was recommended to provide satisfactory full-season control of E. crus-galli and Leptochloa chinensis (L.) Nees and to maximize rice yields. These findings indicate that QYR301 possesses great potential for the management of weeds in paddy fields.

Ecological Relevance of the Major Allelochemicals in Lycopersicon esculentum Roots and Exudates.

Stigmasterol, bergapten, and α-tomatine were isolated from tomato roots. The preliminary phytotoxic activities of stigmasterol and α-tomatine were evaluated in a wheat-coleoptile bioassay, and α-tomatine was more active than stigmasterol. To confirm its phytotoxic activity, α-tomatine was tested on Lactuca sativa and two weeds ( Lolium perenne and Echinochloa crus-galli), and it was active in all cases. The stimulatory activities of α-tomatine and stigmasterol on parasitic-plant germination were also evaluated, and α-tomatine was found to be active on Phelipanche ramosa, a parasitic plant of tomato. α-Tomatine was identified in root exudates by LC-MS/MS. This confirms that α-tomatine is exuded by roots into the environment, where it could act as both an allelochemical and a stimulator of P. ramosa, a parasitic plant of tomato.

Inhibitory Effects of a Variety of Aldehydes on Amaranthus tricolor L. and Echinochloa crus-galli (L.) Beauv.

Thirty-seven commercial aldehydes containing aliphatic chains and aromatic rings as well as heteroaromatic rings were evaluated for their inhibitory activities against Chinese amaranth (Amaranthus tricolor L.) and barnyardgrass (Echinochloa crus-galli (L.) Beauv). Polysorbate 80 (Tween® 80) was used as a surfactant and the research was preliminarily conducted at 400 µM of all aldehydes. Among these aldehydes, (E)-cinnamaldehyde (7) showed the greatest inhibitory effect on seed germination, shoot and root growth of Chinese amaranth by 54.55%, 75.53%, and 85.13% respectively. Similarly, (E)-crotonaldehyde (5), a related α,ß-unsaturated aldehyde, inhibited the germination and seedling growth of the tested species at a high percentage. Apart from these two unsaturated aldehydes, no other aliphatic aldehydes had a harmful effect on Chinese amaranth. In terms of benzaldehyde (6), it had no effect on the tested plant; however, many of its derivatives displayed some inhibitory activity. Furthermore, for the ten common heteroaromatic aldehydes, picolinaldehyde (32) had a high inhibitory effect on Chinese amaranth which closely related to the effect of (E)-crotonaldehyde (5) and (E)-cinnamaldehyde (7), whereas, other heteroaromatic aldehydes showed lower effects. In the case of a monocot plant, barnyardgrass, no tested aldehydes reduced seed germination, however, (E)-cinnamaldehyde (7), 2,4,6-trimethoxybenzaldehyde (16) and 4-(dimethylamino)benzaldehyde (24) could inhibit the seedling growth of the plant with low to moderate levels. The herbicidal effects of the most active aldehydes were then further investigated in order to find the minimum concentration of these aldehydes suppressing the germination and growth of the tested plants. At concentrations as low as 50-100 µM some aldehydes could inhibit the seedling growth of the tested species. The structure-activity relationship (SAR) study reported here demonstrates the chemical clues governing the inhibitory activity of aldehydes which could be utilized in the development of highly effective herbicides in the near future.