Alopecurus Aequalis Research Articles

Detection of Two Common ACCase Mutations Associated with High Levels of Fenoxaprop-P-Ethyl Resistance in Shortawn Foxtail (Alopecurus aequalis) Using Loop-Mediated Isothermal Amplification

Abstract The resistance to fenoxaprop-P-ethyl, a herbicide that inhibits acetyl-CoA carboxylase (ACCase), has emerged in shortawn foxtail (Alopecurus aequalis Sobol.) since the 1990s, presenting a considerable challenge to wheat (Triticum aestivum L.) production in China. One of the primary mechanisms responsible for this high-level resistance is the presence of mutations at codons 1781, 2041, and 2078 in the ACCase gene. However, the conventional methods used to detect these mutations, such as polymerase chain reaction (PCR) and gene sequencing, are time-consuming and labor-intensive. To address this issue and enable the prompt and effective detection of these common ACCase mutations in A. aequalis, a loop-mediated isothermal amplification (LAMP) strategy was developed. The LAMP assay specifically targets the Ile-1781-Leu and Asp-2078-Gly mutations within the ACCase gene of A. aequalis. Through the optimization of primers, systems, and conditions, the LAMP assay enables rapid differentiation between wild-type individuals and mutants of A. aequalis carrying either of these two mutations. By including SYBR Green I dye in the final reaction mixtures, the target mutation can be visually detected through a noticeable color change that can be observed with the naked eye. It is noteworthy that the sensitivity of the LAMP assay was approximately 104-fold greater than that of conventional PCR methods. Additionally, a derived cleaved amplified polymorphic sequence (dCAPS) assay was established for each mutation to distinguish between homozygous and heterozygous mutants. Overall, the developed LAMP assay could efficiently detect the Ile-1781-Leu and Asp-2078-Gly mutations in the ACCase gene of A. aequalis, offering significant advantages for the monitoring and management of fenoxaprop-P-ethyl resistance.

Chemical Synthesis, Herbicidal Activity, Crop Safety, and Molecular Basis of ortho-Fluoroalkoxy Substituted Sulfonylureas as Novel Acetohydroxyacid Synthase Inhibitors.

In the face of increasing resistance to the currently used commercial herbicides and the lack of success in identifying new herbicide targets, alternative herbicides need to be developed to control unwanted monocotyledon grasses in food crops. Here, a panel of 29 novel sulfonylurea-based compounds with ortho-fluoroalkoxy substitutions at the phenyl ring were designed and synthesized. Pot assays demonstrated that two of these compounds, 6d and 6u, have strong herbicidal activities against Echinochloa crus-galli, Eleusine indica, Alopecurus aequalis, and Alopecurus japonicus Steudel at a dosage of 15 g ha-1. Furthermore, these two compounds exhibited <5% inhibition against wheat at a dosage of 30 g ha-1 under post-emergence conditions. 6u also exhibited <5% inhibition against rice at a dosage of 30 g ha-1 under both post-emergence and pre-emergence conditions. A kinetics study demonstrated that 6d and 6u are potent inhibitors of Arabidopsis thaliana acetohydroxyacid synthase (AHAS; EC 2.2.1.6) with potent Ki values of 18 ± 1.1 and 11.9 ± 4.0 nM, respectively. The crystal structure of 6u in complex with A. thaliana (At)AHAS has also been determined at 2.7 Å resolution. These new compounds represent new alternative herbicide choices to protect wheat or rice from invading grasses.

Metabolism-Based Nontarget-Site Mechanism Is the Main Cause of a Four-Way Resistance in Shortawn Foxtail (Alopecurus aequalis Sobol.).

Alopecurus aequalis Sobol. is a predominant grass weed in Chinese winter wheat fields, posing a substantial threat to crop production owing to its escalating herbicide resistance. This study documented the initial instance of an A. aequalis population (AHFT-3) manifesting resistance to multiple herbicides targeting four distinct sites: acetyl-CoA carboxylase (ACCase), acetolactate synthase, photosystem II, and 1-deoxy-d-xylulose-5-phosphate synthase. AHFT-3 carried an Asp-to-Gly mutation at codon 2078 of ACCase, with no mutations in the remaining three herbicide target genes, and exhibited no overexpression of any target gene. Compared with the susceptible population AHFY-3, AHFT-3 metabolized mesosulfuron-methyl, isoproturon, and bixlozone faster. The inhibition and comparison of herbicide-detoxifying enzyme activities indicated the participation of cytochrome P450s in the resistance to all four herbicides, with glutathione S-transferases specifically linked to mesosulfuron-methyl. Three CYP72As and a Tau class glutathione S-transferase, markedly upregulated in resistant plants, potentially played pivotal roles in the multiple-herbicide-resistance phenotype.

Design, Synthesis, and Biological Evaluation of Pyridazinone-Containing Derivatives As Novel Protoporphyrinogen IX Oxidase Inhibitor.

Protoporphyrinogen IX oxidase (PPO, E.C. 1.3.3.4) plays a pivotal role in chlorophyll biosynthesis in plants, making it a prime target for herbicide development. In this study, we conducted an investigation aimed at discovering PPO-inhibiting herbicides. Through this endeavor, we successfully identified a series of novel compounds based on the pyridazinone scaffold. Following structural optimization and biological assessment, compound 10ae, known as ethyl 3-((6-fluoro-5-(6-oxo-4-(trifluoromethyl)pyridazin-1(6H)-yl)benzo[d]thiazol-2-yl)thio)propanoate, emerged as a standout performer. It exhibited robust activity against Nicotiana tabacum PPO (NtPPO) with an inhibition constant (Ki) value of 0.0338 μM. Concurrently, we employed molecular simulations to obtain further insight into the binding mechanism with NtPPO. Additionally, another compound, namely, ethyl 2-((6-fluoro-5-(5-methyl-6-oxo-4-(trifluoromethyl)pyridazin-1(6H)-yl)benzo[d]thiazol-2-yl)thio)propanoate (10bh), demonstrated broad-spectrum and highly effective herbicidal properties against all six tested weeds (Leaf mustard, Chickweed, Chenopodium serotinum, Alopecurus aequalis, Poa annua, and Polypogon fugax) at the dosage of 150 g a.i./ha through postemergence application in a greenhouse. This work identified a novel lead compound (10bh) that showed good activity in vitro and excellent herbicidal activity in vivo and had promising prospects as a new PPO-inhibiting herbicide lead.

Herbicidal Activity of Cinmethylin against Grass Weeds and Its Safety for Use with Different Wheat Varieties

Cinmethylin is a potential pre-emergence herbicide that could be used to control grass weeds in winter cereals. To determine the herbicidal activity of cinmethylin against common gramineous weeds in wheat fields in China and its level of safety on wheat, we conducted the following experiments: (i) assessing the efficacy of cinmethylin against 11 grass weeds and (ii) determining its safety against 19 wheat varieties. The results showed that cinmethylin had good herbicidal efficacy against annual bluegrass (Poa annua L.), shortawn foxtail (Alopecurus aequalis Sobol.), slender meadow foxtail (Alopecurus myosuroides Huds.), Japanese foxtail (Alopecurus japonicus Steud.), Italian ryegrass (Lolium multiflorum Lam.), British timothy (Phleum paniculatum Huds.), Asia Minor bluegrass (Polypogon fugax Nees ex Steud.), Helictotrichon tibeticum (Roshev.) Holub., and wild oat (Avena fatua L.), with a GR50 (the herbicide dose resulting in 50% growth inhibition) value of 4.50–99.21 g a.i. ha−1 in plant height and 1.43–70.34 g a.i. ha−1 in fresh weight. However, cinmethylin cannot control Japanese brome (Bromus japonicus L.) or Tausch’s goatgrass (Aegilops tauschii Coss.) at a dose of 200 g a.i. ha−1. Different wheat varieties varied in their phytotoxicity to cinmethylin. Overall, there is a phytotoxicity risk when using cinmethylin on wheat, mainly to wheat roots, with a reduction in root length of 40.81–64.09% at a dose of 400 g a.i. ha−1. These findings indicate that the pre-emergence herbicide cinmethylin provides good efficacy against most grass weeds and may possess potential for weed management in wheat fields. However, attention should be given to the application dosage and the sensitivity of wheat varieties when using cinmethylin in wheat fields.

Cypyrafluone, a 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor to Control Weed in Wheat Fields.

As a bleaching herbicide, cypyrafluone was applied postemergence in wheat fields for annual weed control; especially, this herbicide possesses high efficacy against cool-season grass weed species such as Alopecurus aequalis and Alopecurus japonicus. In this study, the target of action of cypyrafluone on 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibition was confirmed. This herbicide caused severe foliar whitening symptoms at 5-7 days after treatment (DAT) and death of the whole plant within 10 DAT. Significant increases in phytoene content and significant decreases in kinds of carotenoid and chlorophyll pigments were observed. The content of chlorophyll pigments in cypyrafluone-treated Spirodela polyrhiza decreased upon the addition of homogentisic acid (HGA), which indicated that cypyrafluone prevents the HGA production, possibly by inhibiting the catalytic activity of 4-HPPD. Indeed, cypyrafluone strongly inhibited the catalytic activity of Arabidopsis thaliana HPPD produced by Escherichia coli, which was approximately 2 times less effective than mesotrione. In addition, overexpression of Oryza sativa HPPD in rice and A. thaliana both conferred a high tolerance level to cypyrafluone on them. Molecular docking found that cypyrafluone bonded well to the active site of the HPPD and formed a bidentate coordination interaction with the Fe2+ atom, with distances of 2.6 and 2.7 Å between oxygen atoms and the Fe2+ atom and a binding energy of -8.0 kcal mol-1.

Molecular mechanism of resistance to mesosulfuron-methyl in shortawn foxtail (Alopecurus aequalis) from China

AbstractShortawn foxtail (Alopecurus aequalis Sobol.) is an obligate wetland plant that is widely distributed throughout Europe, temperate Asia, and North America. In China, it is widespread in the middle and lower reaches of the Yangtze River as a noxious weed in winter cropping fields with a rice (Oryza sativa L.) rotation. The acetolactate synthase (ALS)-inhibiting herbicide mesosulfuron-methyl has been widely used to control annual grass and broadleaf weeds, including A. aequalis, in wheat (Triticum aestivum L.) fields, leading to the selection of herbicide-resistant weeds. In this study, an A. aequalis population, AHFT-4, that survived mesosulfuron-methyl at the field-recommended rate (9 g ai ha−1) was collected in Anhui Province. Single-dose testing confirmed that the suspected resistant AHFT-4 had evolved resistance to mesosulfuron-methyl. Target gene sequencing revealed a resistance mutation of Pro-197-Ala in ALS1 of the resistant plants, and a derived cleaved amplified polymorphic sequence marker was developed to specifically detect the mutation. A relative expression assay showed no significant difference in ALS expression between AHFT-4 and a susceptible population without or with mesosulfuron-methyl treatment. Whole-plant dose–response bioassays indicated that AHFT-4 had evolved broad-spectrum cross-resistance to ALS-inhibiting herbicides of all five chemical families tested, with GR50 resistance index (RI) values ranging from 21 to 206. However, it remained susceptible to the photosystem II inhibitor isoproturon. Pretreatment with the cytochrome P450 inhibitor malathion or the glutathione S-transferase inhibitor 4-chloro-7-nitrobenzoxadiazole had no significant effects on the resistance of AHFT-4 to mesosulfuron-methyl. To our knowledge, this study reports for the first time the ALS gene Pro-197-Ala substitution conferring broad-spectrum cross-resistance to ALS-inhibiting herbicides in A. aequalis.

Design, Synthesis, and Biological Activities of Novel 2-Cyanoacrylate Compounds Containing Substituted Pyrazolyl or 1,2,3-Triazolyl Moiety.

To develop novel 2-cyanoacrylate derivatives with potential bioactivity, a number of 2-cyanoacrylate compounds, including substituted pyrazole or 1,2,3-triazole ring, were designed, prepared, and structurally detected by 1H NMR, 13C NMR, and elemental analysis. The biological assessment displayed that some designed compounds had significant herbicidal activities against Brassica juncea, Chenopodium serotinum, Rumex acetosa, Alopecurus aequalis, Polypogon fugax, and Poa annua at a dosage of 1500 g/ha. Furthermore, some derivatives still expressed satisfactory herbicidal activities against Brassica juncea, Chenopodium serotinum, and Rumex acetosa when the dosage was lowered to 150 g/ha, especially the inhibitory effects of compounds 9a, 9d, 9f, 9i, 10a, 10b, 10e, and 10n against Brassica juncea were all over 80%, compounds 9d, 9f, 9g, 9h, 9i, 10h, 10i, 10m, 10n, and 10o possessed more than 70% inhibition rates against Chenopodium serotinum, and compound 9d indicated 70% herbicidal activity against Rumex acetosa. These results provided an important basis for further design and discovery of biologically active 2-cyanoacrylate compounds.

Comparative analysis of fungal communities between herbicide-resistant and -susceptible Alopecurus aequalis.

Alopecurus aequalis is a grass species invading Chinese canola and wheat fields. An A. aequalis KMN-R population surviving mesosulfuron-methyl treatment with recommended rates was acquired from wheatland. Here, we aimed to confirm the resistance profiles of KMN-R to acetolactate synthetase (ALS) inhibiting herbicides and explore the possible resistance mechanisms to mesosulfuron-methyl in this weed population. The dose-response tests performed in our study were used to test the toxicity of A. aequalis to ALS-inhibiting herbicides. Sanger sequencing was used to analyze the ALS gene of mesosulfuron-methyl -resistant and -susceptible A. aequalis. RNA sequencing analysis was used to find candidate genes that may confer metabolic resistance to the mesosulfuron-methyl in resistant A. aequalis population. Mesosulfuron-methyl -resistant and -susceptible A. aequalis populations fungal composition was measured via Illumina MiSeq Sequencing. Dose-response results indicated that KMN-R population evolved resistance to mesosulfuron-methyl and other tested ALS-inhibiting herbicides. Known resistance-conferring Trp-574-Leu gene mutation in A. aequalis ALS was detected in the KMN-R population. Pretreatment with 4-chloro-7-nitrobenzoxadiazole reversed mesosulfuron-methyl resistance in KMN-R. Glutathione S-transferases (GST) gene GSTZ2 and GSTT3 were highly expressed in KMN-R population. In addition, we evaluated the alpha diversity in A. aequalis, centering on OTU abundance, equality, and multiplicity, and found that the fungal community composition had more unexplained variance between KMN-R and KMN-S A. aequalis. We also observed higher abundances of specific fungi in KMN-R A. aequalis. The results proved that resistance to mesosulfuron-methyl in A. aequalis KMN-R population is probably caused by target site- and non-target site-based relating GST and provided the basis for further research between fungal interaction and herbicide resistance.

Loop-mediated isothermal amplification for detecting the Ile-2041-Asn mutation in fenoxaprop-P-ethyl-resistant Alopecurus aequalis.

Shortawn foxtail (Alopecurus aequalis Sobol.), a competitive grass weed severely infesting overwintering crops worldwide, has evolved resistance to the highly efficient acetyl-CoA carboxylase (ACCase)-inhibiting herbicide fenoxaprop-P-ethyl. The Ile-to-Asn substitution at codon position 2041 of ACCase is a dominant resistance mutation that has been associated with fenoxaprop-P-ethyl resistance in A.aequalis. However, its detection based on conventional methods such as polymerase chain reaction (PCR) and gene sequencing is rather labor- and time-consuming. In order to facilitate its detection in field populations of A.aequalis, a simple and efficient method with high sensitivity to the Ile-2041-Asn mutation was developed based on loop-mediated isothermal amplification (LAMP). A set of four primers was designed to target a 244-bp fragment of ACCase comprising codon position 2041. Using the special primers and genomic DNA of A.aequalis, the concentrations of reaction components, temperature and time each were optimized. The LAMP reaction for the detection of the Ile-2041-Asn mutation was processed at 65 °C for 45 min followed by 80 °C for 10min to stop the reaction. The LAMP method developed was 1000-fold more sensitive than the conventional PCR method, and the detection was also practicable when using crude DNA of A.aequalis as a template. The low cost, simplicity and high sensitivity of the developed LAMP assay make the detection of the Ile-2041-Asn mutation easier and quicker, which may contribute to the monitoring and management of resistance development to fenoxaprop-P-ethyl in A.aequalis. © 2022 Society of Chemical Industry.

Cytochrome P450 CYP709C56 metabolizing mesosulfuron-methyl confers herbicide resistance in Alopecurus aequalis.

Multiple herbicide resistance in diverse weed species endowed by enhanced herbicide detoxification or degradation is rapidly growing into a great threat to herbicide sustainability and global food safety. Although metabolic resistance is frequently documented in the economically damaging arable weed species shortawn foxtail (Alopecurus aequalis Sobol.), relevant molecular knowledge has been lacking. Previously, we identified a field population of A. aequalis (R) that had evolved metabolic resistance to the commonly used acetolactate synthase (ALS)-inhibiting herbicide mesosulfuron-methyl. RNA sequencing was used to discover potential herbicide metabolism-related genes, and four cytochrome P450s (CYP709C56, CYP71R18, CYP94C117, and CYP94E14) were identified with higher expressions in the R vs. susceptible (S) plants. Here the full-length P450 complementary DNA transcripts were each cloned with identical sequences between the S and R plants. Transgenic Arabidopsis overexpressing CYP709C56 became resistant to the sulfonylurea herbicide mesosulfuron-methyl and the triazolo-pyrimidine herbicide pyroxsulam. This resistance profile generally but does not completely in accordance with what is evident in the R A. aequalis. Transgenic lines exhibited enhanced capacity for detoxifying mesosulfuron-methyl into O-demethylated metabolite, which is in line with the detection of O-demethylated herbicide metabolite in vitro in transformed yeast. Structural modeling predicted that mesosulfuron-methyl binds to CYP709C56 involving amino acid residues Thr-328, Thr-500, Asn-129, Gln-392, Phe-238, and Phe-242 for achieving O-demethylation. Constitutive expression of CYP709C56 was highly correlated with the metabolic mesosulfuron-methyl resistance in A. aequalis. These results indicate that CYP709C56 degrades mesosulfuron-methyl and its up-regulated expression in A. aequalis confers resistance to mesosulfuron-methyl.

Carbon decomposition and nitrogen mineralization of foxtail and milk vetch incorporated into paddy soils for different durations of organic farming

ABSTRACT Foxtail (Alopecurus aequalis) and milk vetch (Astragalus sinicus) are typical winter weeds grown in single-cropping rice fields during the fallow season in central Japan. These winter weeds are generally incorporated into the soil as green manure during plowing, and before rice transplanting, to improve soil fertility and rice yield. To understand the carbon (C) decomposition and nitrogen (N) mineralization behavior of fallow weeds in organic rice farming, we carried out two experiments. Firstly, we examined the effect of adding 1% foxtail to soils that were sampled from fields that were farmed conventionally or organically for different durations (4–12 years). The results showed that net N mineralization of incorporated foxtail was not affected by the duration of organic farming, although the N mineralization of indigenous soil increased with organic farming duration. Secondly, 1% pulverized young and old foxtail (YF and OF; C/N ratios of 47.0 and 54.9, respectively), and milk vetch (YM and OM; C/N ratios of 13.0 and 14.6, respectively), were mixed with soil samples from fields that had been farmed organically for 15 years to determine the role of each plant. More than half of weed C was decomposed during 4 weeks of anaerobic incubation at 30°C. In addition, the net weed C decomposition potentials were significantly higher in YF and YM than those in OF and OM. The lower C/N ratio of milk vetch was contributed to a net N mineralization rate that was 8.4 times higher than that of foxtail. The percentage of N mineralized from milk vetch was significantly higher (about 2.3 times) than that from foxtail. Even though foxtail incorporation can contribute to the growth of organic rice as an N nutrient source, it should be noted that net N immobilization occurred for 2 weeks of incubation at 30°C, and sometimes extended to 4 weeks before net N mineralization became tangible. Considering this early net N immobilization following incorporation of foxtail, it is recommended to wait at least 4 weeks between the start of flooding after weed incorporation and transplanting rice to facilitate initial growth and avoid N exhaustion.

Beaver-created microhabitats in a small water body and their impact on flora and fauna (the Khoper River floodplain, Russia)

This study shows how beaver digging activity can affect water body morphology and local biota under modern environmental conditions in a small floodplain lake. The total area of microhabitats created by beavers was found to reach 7% of water body area and 30% of littoral-zone area. It was noted that the zoogenic microhabitats are different when depth is greater and plant cover is smaller, especially of emergent vegetation. HelophytesSparganium erectumandAlopecurus aequaliswere found to prefer the beaver-unaffected part of the littoral. InvertebratesNaucorissp. andHydrophilussp. prefer beaver microhabitats, whereasPlanorbis planorbis,Lymnaea palustris, andHydroussp. prefer thickets of emergent plants in beaver-unaffected littoral areas. Adult crucian carpsCarassius carassiusproved to be abundant in the beaver-unaffected part of the water body, while the adult weatherfishMisgurnus fossilisprefers beaver burrows, and its fry inhabit beaver-unaffected sites. A similar situation was observed for marsh frogsPelophylax ridibundus: adults prefer beaver microhabitats in June, but frog tadpoles mainly inhabit a beaver-unaffected littoral. Tadpoles ofPelobates vespertinusproved to be slightly aggregated near beaver burrows in July. The beaver activity was found to slightly increase β-diversity within the water body according to Jaccard indices. The results confirm that the beaver-created heterogeneity is important for aquatic biota under conditions of shallowing of floodplain water bodies.

Microhabitat Variation in Egg Diapause Incidence in Summer Within a Local Population: An Adaptation to Decline in Host-Plant Suitability in Trigonotylus caelestialium (Hemiptera: Miridae).

Diapause induction in multivoltine insects is an ecophysiological event that is generally triggered by seasonal cues such as photoperiod and temperature. The rice leaf bug, Trigonotylus caelestialium (Kirkaldy), feeds on various Poaceae grasses and produces several generations a year. Previous studies have shown that adults produce diapause and nondiapause eggs under short-day and long-day conditions, respectively. However, there is a distinct mid-summer peak in diapause incidence before an autumnal increase in diapause incidence in the field, which cannot be explained by the laboratory results. The present study was performed to examine the environmental factors affecting the diapause incidence in mid-summer and the adaptive significance of this phenomenon. Seasonal trends in diapause incidence differed significantly among three sites located 150-400 m apart from each other and with different host plants. The suitability of host plants differs depending on species and seasonally. Therefore, the microhabitat difference in diapause trend is believed to be due to the difference in host plants. When field-collected female adults laying diapause eggs in late June were fed a seasonally deteriorating host (the orange foxtail, Alopecurus aequalis Sobol. [Poales: Poaceae]), they kept laying diapause eggs, whereas when fed a suitable host (the wheat, Triticum aestivum L. [Poales: Poaceae]) for 5 d, they changed oviposition mode to lay nondiapause eggs. These results indicate that host-plant suitability affects the oviposition mode of T. caelestialium. Diapause-egg oviposition in mid-summer in T. caelestialium has adaptive significance as a bet-hedging strategy against unpredictable dietary conditions.

Unravelling the effect of two herbicide resistance mutations on acetolactate synthase kinetics and growth traits.

Gene mutations conferring herbicide resistance are hypothesized to have negative pleiotropic effects on plant growth and fitness, which may in turn determine the evolutionary dynamics of herbicide resistance alleles. We used the widespread, annual, diploid grass weed Alopecurus aequalis as a model species to investigate the effect of two resistance mutations-the rare Pro-197-Tyr mutation and the most common mutation, Trp-574-Leu-on acetolactate synthase (ALS) functionality and plant growth. We characterized the enzyme kinetics of ALS from two purified A. aequalis populations, each homozygous for the resistance mutation 197-Tyr or 574-Leu, and assessed the pleiotropic effects of these mutations on plant growth. Both mutations reduced sensitivity of ALS to ALS-inhibiting herbicides without significant changes in extractable ALS activity. The 197-Tyr mutation slightly decreased the substrate affinity (corresponding to an increased Km for pyruvate) and maximum reaction velocity (Vmax) of ALS, whereas the 574-Leu mutation significantly increased these kinetics. Significant decrease or increase in plant growth associated, respectively, with the 197-Tyr and 574-Leu resistance mutations was highly correlated with their impact on ALS kinetics, suggesting more likely persistence of the 574-Leu mutation than the 197-Tyr mutation if herbicide application is discontinued.

Incorporation of winter grasses suppresses summer weed germination and affects inorganic nitrogen in flooded paddy soil

ABSTRACT Laboratory experiments were conducted to investigate how incorporation of the winter grasses foxtail (Alopecurus aequalis) and milk vetch (Astragalus sinicus) into flooded paddy soil affects the germination of summer weeds and soil inorganic nitrogen (N) levels. Polyethylene terephthalate (PET) vessels (10.0 × 8.0 × 15.0 cm) were filled with 0.7 kg air-dried soil that had been collected from organic paddy fields located in Tochigi, Japan. Foxtail and milk vetch were then independently incorporated into the soil at rates of 0% (untreated control), 0.25%, 0.5%, 1%, and 1.5%, with four repetitions per treatment. The PET vessels were placed in a growth chamber (Biotron) set to day/night temperatures and humidities of 27/18°C and 70%/65%, respectively, and with an illuminance of 40,000 lx (12 h) for 28 days, and the total number of weeds and changes in the electrical conductivity (EC) of the surface water were investigated throughout this period, while changes in soil inorganic N were determined at the ends of the experiments. The incorporation of both foxtail and milk vetch significantly suppressed the germination of summer weeds by 56% and 50%, respectively, at incorporation rates of 1% and by 78% and 77%, respectively, at incorporation rates of 1.5% compared with their respective controls. There was a high and significant positive correlation between both the rate of winter grass incorporation and the degree of growth suppression and EC. Incorporation of foxtail at rates of 0.25% and 0.5% significantly increased the inorganic N contents of the sub-layer by an average of 68% compared with the control but had no significant effect in the top layer, whereas the incorporation of milk vetch at a rate of 1% significantly increased the inorganic N contents of both the top layer and sub-layer by 200% and 316%, respectively, compared with the control. Furthermore, the effect of milk vetch on inorganic N significantly increased with an increase in the rate of incorporation. These findings demonstrate that incorporation of the winter grasses foxtail and milk vetch into flooded organic paddy soil can suppress weed growth and act as a source of inorganic N.

Characterization and phylogenetic analysis of the complete plastome of Alopecurus japonicus (Gramineae), an annual weed

Alopecurus japonicus is a weed in summer crop field, which is harmful to wheat crops. The complete plastome of A. japonicus was reported in this study. The genome was 136,408 bp in length, consisting of an 80,512 bp large single-copy region, a 12,836 bp small single-copy region, and two 21,530 bp inverted repeat regions. The GC content of this plastome was 38.3%. A total of 112 genes were annotated for the plastome of A. japonicus, containing 78 protein-coding genes (PCGs), 30 tRNAs, and 4 rRNAs. Phylogenetic analysis showed that A. japonicus was sister to Alopecurus aequalis.

A phytosociological study of spring-type rice field vegetation in Angye Plains, South Korea

This phytosociological study was carried out on spring-type rice field vegetation in the Angye Plains. Field surveys were based on the method developed by the Zürich–Montpellier School of Phytosociology, which emphasizes species composition and homogeneity of the phytocenosis, and 75 relevés were obtained. We analyzed the species performance of 63 plant species appearing in the obtained relevés through 9 levels of combined cover degree and relative net contibution degree (r-NCD). We classified syntaxa by grouping the relevés. Two associations, one subassociation, and one community were classified: the Stellario-Alopecuretum amurensis (typicum subassociation and persicaretosum hydropiperae subasso. nov. hoc loco), Alopecuro-Ranunculetum scelerati, Hemistepto-Capsellietum drabetosum nemorosae, and Cardamine fallax–Alopecurus aequalis community. This study identified the Stellario-Alopecuretum persicaretosum hydropiperae and Cardamine fallax–Alopecurus aequalis communities for the first time. The spring-type rice field vegetation in the Angye Plains was considered rice field vegetation of the dry type, which reflects impact of frequent human activity and rainless climate of the Daegu regional bioclimatic subdistrict.

Seasonal Changes and Differences in Vegetation, and Interactions between the Vegetation and Two Mirid Bugs（Hemiptera: Miridae）Causing Pecky Rice in Rice Paddy Levees

We investigated the vegetation management and occurrence of two mirid bugs, Trigonotylus caelestialium（Kirkaldy）（Hemiptera: Miridae）and Stenotus rubrovittatus（Matsumura）（Hemiptera: Miridae）, causing pecky rice, in rice paddy levees over an area measuring 10 ha in Niigata Prefecture, Japan. Mowing and herbicide application were carried out on the levees several times to manage weeds during the growing period of rice. Major poaceous plants on the investigated levees were Poa annua, Alopecurus aequalis, Digitaria ciliaris, and Echinochloa crus-galli. The two mirid bug species existed either separately or together on levees infested with ear-emerged poaceous plants. In July and August, which are important periods for forecasting the two bugs, D. ciliaris was the major plant and occurrence of the two mirid bugs was almost entirely restricted to the levees infested with ear-emerged D. ciliaris. Ears of D. ciliaris vanished after mowing or herbicide application and re-emerged with growth. As a result, the locations of levees infested with ear-emerged D. ciliaris changed over short periods. The observation results were similar over 3 years, and there were no significant changes in weed management, vegetation, and occurrence of the two bugs in the area. In levees infested with ear-emerged D. ciliaris, the spatial distribution pattern of T. caelestialium was aggregated, and that of S. rubrovittatus was even more aggregated. Despite the difference in the distribution, the locations and areas of levees infested with ear-emerged poaceous plants could be used in indices for regionally forecasting the occurrence of the two bugs.

Characterization of the complete plastome of Alopecurus aequalis (Poaceae), a widespread weed

Alopecurus aequalis is a predominant weed species that distributes widely in North temperate regions. The complete plastome of A. aequalis is reported here. It is a circular molecular of 136,382 bp in length and consists of a large single-copy region (LSC: 80,455 bp), a small single-copy region (SSC: 12,849 bp), and two inverted repeats regions (IRs: 21,539 bp). GC content is 38.3%. This plastome encodes 112 unique genes, including 78 protein-coding genes, 30 tRNAs, and 4 rRNAs. Phylogenetic tree shows that A. aequalis is sister to Poa annua.