Nontarget site-based resistance to nicosulfuron and identification of candidate genes in Cucumis melo L. var. agrestis Naud. via RNA-Seq transcriptome analysis.

Herbicide resistance is a worldwide concern for weed control. Cucumis melo L. var. agrestis Naud. (C. melo) is an annual trailing vine weed that is commonly controlled by nicosulfuron, acetolactate synthase (ALS)-inhibiting herbicides. However, long-term use of this herbicide has led to the emergence of resistance and several nicosulfuron resistant populations of C. melo have been found. Here we identified a resistant (R) C. melo population exhibiting 7.31-fold resistance to nicosulfuron compared with a reference sensitive (S) population. ALS gene sequencing of the target site revealed no amino acid substitution in R plants, and no difference in enzyme activity, as shown by ALS activity assays in vitro. ALS gene expression was not significantly different before and after the application of nicosulfuron. Pretreatment with the cytochrome P450 monooxygenase (P450) inhibitor malathion reduced nicosulfuron resistance in the R population. RNA-Seq transcriptome analysis was used to identify candidate genes that may confer metabolic resistance to nicosulfuron. We selected genes with annotations related to detoxification functions. A total of 20 candidate genes (7 P450 genes, 1 glutathione S-transferase (GST) gene, 2 ATP-binding cassette (ABC) transporters, and 10 glycosyltransferase (GT)) were identified; 12 of them (7 P450s, 1 GST, 2 ABC transporters, and 2 GTs) were demonstrated significantly differential expression between R and S by quantitative real-time RT-PCR (qRT-PCR). Our findings revealed that the resistance mechanism in C. melo was nontarget-site based. Our results also provide a valuable resource for studying the molecular mechanisms of weed resistance.

Protective mechanisms of neral as a plant-derived safener against fenoxaprop-p-ethyl injury in rice.

BACKGROUND: The use of herbicide safeners effectively minimises crop damage while maintaining the full efficacy of herbicides. The present study aimed to assess the potential protective effects of neral (NR) as a safener, in order to mitigate injury caused by fenoxaprop-p-ethyl (FE) on rice. RESULTS: The alleviating effect of NR was similar to that of the safener isoxadifen-ethyl (IE). The root elongation of rice was significantly promoted under the FE + NR and FE + IE treatments, as compared to the FE treatment. The transcriptome analysis further suggested that the effects of NR treatment on plant metabolic pathways differed from those of IE treatment. In total, 895 and 47 up-differentially expressed genes induced by NR (NR-inducible genes) and IE (IE-inducible genes) were identified. NR-inducible genes were mainly enriched in phytohormone synthesis and signalling response, including 'response to brassinosteroid', 'response to jasmonic acid', 'response to ethylene', 'brassinosteroid metabolic process', 'brassinosteroid biosynthesis' and 'plant hormone signal transduction'. In contrast, IE-inducible genes were predominantly enriched in glutathione metabolism. The activity of glutathione S-transferase was found to be increased after IE treatment, whereas no significant increase was observed following NR treatment. Moreover, several transcription factor genes, such as those encoding AP2/ERF-ERF and (basic helix-loop-helix) bHLH were found to be significantly induced by NR treatment. CONCLUSION: This is the first report of the utilisation of NR as an herbicide safener. The results of this study suggest the toxicity of FE to rice is mitigated by NR through a distinct mechanism compared to IE. © 2023 Society of Chemical Industry.

Genetic diversity analysis of volunteer wheat based on SSR markers.

Volunteer wheat is a kind of wheat with weed characteristics, distributed widely in the main wheat-producing areas of China. It seriously damages the yield and quality of cultivated wheat. To study the genetic diversity and population structure within and between volunteer wheat and cultivated wheat (Triticum aestivum L.), 195 volunteer wheat seeds and 29 cultivated wheat seeds were analysed based on 16 pairs of highly-polymorphic microsatellite simple sequence repeats (SSR) primers and a microchip capillary electrophoresis (MCE) detection system. A total of 110 polymorphic alleles were detected by MCE with each pair of primers identifying 2-15 alleles with an average of 6.875 alleles. The polymorphic information content (PIC) ranged from 0.1089 to 0.7843, with an average of 0.5613. Genetic diversity arguments from 224 samples showed that the volunteer wheat was more varied than cultivated wheat. Based on the SSR information, the 224 samples were classified into seven groups, which corresponded to the volunteer wheats and cultivated wheats through principal coordinates analysis (PCA). We propose that the volunteer wheat and cultivated wheat have rather distant phylogenetic relationships. Hence, it is important for wheat breeding to study the genetic relationship between volunteer wheat and cultivated wheat.

Adaptability and Germination Characteristics of Volunteer Wheat in China's Main Wheat-Producing Areas.

Volunteer wheat commonly occurs and spreads rapidly in the main wheat-producing areas of China, seriously impacting cultivated wheat production. Limited information is currently available regarding the adaptability and germination traits of volunteer wheat. Therefore, this study's aim was to evaluate the effects of environmental conditions on the germination and emergence of volunteer wheat seeds through laboratory experiments. The results showed that the germination percentages and viability of volunteer wheat were significantly higher than those of cultivated wheat at a low temperature of 5 °C, and they were lower than those of cultivated wheat at high temperatures of above 30 °C. Compared to cultivated wheat, volunteer wheat was able to tolerate higher salinity and lower osmotic potential, especially long-dormancy volunteer wheat. The secondary germination ability of volunteer wheat was higher than that of cultivated wheat after water immersion. Furthermore, volunteer wheat could not emerge normally when the seeding depth was greater than 8 cm, and the emergence ability of the volunteer wheat was weaker than that of the cultivated wheats when the seeding depth was 4-8 cm, which indicates that the deep tillage of cultivated land could effectively prevent the spread of volunteer wheat. This study revealed differences in the germination characteristics of volunteer wheat and cultivated wheat under the influence of different environmental factors, which provides a basis for future studies concerning the control of volunteer wheat.

Transcriptomic analysis of maize uncovers putative genes involved in metabolic detoxification under four safeners treatment.

Isoxadifen-ethyl (IDF) and cyprosulfamide (CSA) can effectively protect maize from nicosulfuron (NIC) injury, while mefenpyr-diethyl (MPR) and fenchlorazole-ethyl (FCO) did not. Their chemical diversity and requirement to use them in combination with the corresponding herbicides suggest that their elicitation of gene expression are complex and whether it is associated with the safening activity remains elusive. In this study, our first objective was to determine whether or not the ability of four safeners to enhance the metabolic rate of nicosulfuron. It was found that nicosulfuron degradation in maize was accelerated by IDF and CSA, but not by FCO and MPR. Transcriptomic analysis showed that the number of genes induced by IDF and CSA were larger than that induced by FCO and MPR. Overall, 34 genes associated with detoxification were identified, including glutathione S-transferase (GST), cytochrome P450 (CYP450), UDP-glucosyltransferase (UGT), transporter and serine. Moreover, 14 detoxification genes were screened for further verification by real-time PCR in two maize inbred lines. Two maize inbred lines exhibited high expression levels of four genes (GST31, GST39, AGXT2 and ADH) after IDF treatment. GST6, GST19, MATE, SCPL18 and UF3GT were specifically up-regulated in telerant maize inbred line under IDF and IDF + NIC treatments. Seven genes, namely GST31, GST6, GST19, UF3GT, MATE, ADH and SCPL18, are induced by IDF and CSA to play a vital role in regulating the detoxification process of NIC. Accordingly, the GST activity in maize was accelerated by IDF and CSA, but not by FCO and MPR. This result is consistent with transcriptome and metabolic data.These results indicate that the mitigation of NIC damage is associated with enhanced herbicide metabolism. IDF and CSA were more effective in protecting maize from NIC injury due to their ability to enhance the detoxification of specific types of herbicides, compared to FCO and MPR. The chemical specificity of four safeners is attributed to the up-regulated genes related to the detoxification pathway.

The mechanism of exogenous gibberellin A3 protecting sorghum shoots from S-metolachlor Phytotoxicity.

BACKGROUND: S-metolachlor (MET) was used to prevent weed infestation in sorghum fields, but inappropriate application could result in phytotoxicity on sorghum. Exogenous gibberellin A3 (GA3 ) has been applied for alleviating the phytotoxicity of MET. However, its detoxification mechanism is still not well known. RESULTS: Leaf deformity of sorghum caused by 200 mg/L MET was alleviated by treating sorghum shoots with 800 mg/L GA3 , and the injury recovery rate of growth index was over 73%. More importantly, GA3 could not accelerate the metabolic rate of MET in sorghum. The result of phytohormone metabolomics showed that endogenous GA3 content in sorghum decreased by 78.10% with MET treatment, while abscisic acid (ABA) content increased by 120.2%, resulting in 10.3-fold increase of ABA/GA3 ratio. Content of ABA and GA3 increased by 11.9- and 21.1-fold with MET and GA3 treatment, respectively, leading to ABA/GA3 ratio restoration. Moreover, MET inhibited the expression of genes encoding key enzymes related to GA synthesis including CPS1, KO2, KAO, GA20ox1D and ABA8ox gene related to ABA metabolism. The transcription levels of GA metabolism-related genes CYP714D1 and GA2ox were up-regulated by 11.2- and 7.2-fold, while ABA synthesis-related genes NCED and ZEP were up-regulated by 8.0- and 3.0-fold, respectively, with MET and GA3 treatment. CONCLUSION: In this study, exogenous GA3 protecting sorghum shoots from MET phytotoxicity was due to supplement the MET-induced GA3 deficiency by absorbing exogenous GA3 , and restore homeostasis of ABA and GA3 by promoting ABA synthesis, which provides novel insights for mechanism of GA3 alleviating MET phytotoxicity. © 2022 Society of Chemical Industry.

Transcriptome analysis and the identification of genes involved in the metabolic pathways of fenoxaprop-P-ethyl in rice treated with isoxadifen-ethyl hydrolysate.

Fenoxaprop-P-ethyl (FE) is a highly effective weed control agent for rice fields, but it causes phytotoxicity in crops. A whole-plant bioassay has revealed that isoxadifen-ethyl hydrolysate (IH) can significantly improve the tolerance of rice to FE, but the molecular mechanisms underlying this phenomenon are still unclear. In this study, we performed RNA-Seq analysis using rice seedlings treated with FE and IH to determine the IH-regulated candidate genes involved in metabolic resistance to FE. We also analyzed spatiotemporal expression using quantitative reverse transcription polymerase chain reaction to reveal the expression patterns of these genes under different treatments. The results showed that genes encoding metabolic enzymes, such as cytochrome P450 monooxygenases, glutathione-s-transferases, UDP-glycosyltransferase, carboxylesterase, and ATP-binding cassette transporter, were influenced by the application of IH. Most of these genes were upregulated, and their products were involved in various stages of FE metabolism. Tolerance to FE was primarily mediated by CarE15, CYP86A1, GSTU6, GST4, UGT13248, UGT79, and ABCC4, all of which played a vital role in regulating the detoxification process of FE. Our findings elucidated the protective mechanisms of IH, which can help alleviate the phytotoxic effects of FE and expand its potential for application in agriculture.

Adsorption and degradation of imazapic in soils under different environmental conditions.

Imazapic is widely used in peanut production, and its residues can cause damage to succeeding crops planted in the following year. The planting area of peanut is large in Henan province. Inceptisol is the main soil type in Henan Province and was used in laboratory experiments that were conducted to investigate imazapic degradation in soil under various environmental conditions. The results indicated that the imazapic degradation rate increased with an increase in temperature, soil pH, and soil moisture, and decreased with organic matter content. The use of biogas slurry as a soil amendment accelerated imazapic degradation. The half-life of imazapic in sterilized soil (364.7 d) was longer than in unsterilized soil (138.6 d), which suggested that there was a significant microbial contribution to imazapic degradation. Imazapic adsorption was also examined and was found to be well described by the Freundlich isotherm. The results indicate that soil has a certain adsorption capacity for imazapic.

Effects of bensulfuron-methyl residue on photosynthesis and chlorophyll fluorescence in leaves of cucumber seedlings.

A potted soil experiment was conducted to investigate the effects of bensulfuron-methyl (BSM) residue on the growth and photosynthesis of seedlings of a local cucumber variety (Xia Feng No.1). When the residue of bensulfuron-methyl in soil exceeded 50µg kg-1, it significantly inhibited the growth of cucumber, chlorophyll content and photosynthetic capacity of cucumber. BSM treatment caused significant decreases in the biomass, chlorophyll content, net photosynthesis rate, stomatal conductance, and transpiration rate, photosystem II (PSII) maximum quantum yield, actual quantum yield, photochemical quenching coefficient, and electron transport rate in cucumber seedlings, but increased the minimal fluorescence yield and dark respiration rate. Moreover, comparisons of the patterns of absorbed light energy partitioning revealed that the fractions of excess and thermally dissipated energy increased with rising concentrations of the BSM residue, but the fraction of PSII photochemistry declined. The BSM residues caused reversible destruction in the PSII reaction centers and decreased the proportion of available excitation energy used in PSII photochemistry. The results suggested that rice or wheat fields sprayed with BSM will not be suitable for planting cucumbers in succession or rotation.

The expression of detoxification genes in two maize cultivars by interaction of isoxadifen-ethyl and nicosulfuron.

Herbicide safeners protect crop plants from herbicide phytotoxicity, but an understanding of their molecular mechanisms is still lacking. We investigated the effects of the safener isoxadifen-ethyl and/or nicosulfuron on the expression of 10 genes, 8 glutathione transferases (GSTs), 1 glutathione transporter and 1 multidrug resistance protein gene in two maize cultivars. Nicosulfuron and isoxadifen-ethyl induce different detoxification enzyme genes. The expression analyses of the 10 genes revealed that most were expressed much higher in 'Zhengdan958' than those in 'Zhenghuangnuo No.2', both in control and in isoxadifen-ethyl- and/or nicosulfuron-treated plants. The expression levels of ZmGSTIV, ZmGST6, ZmGST31 and ZmMRP1 in two maize cultivars were up-regulated by isoxadifen-ethyl only, or in combination with nicosulfuron, whereas nicosulfuron down-regulated the expression of eight genes. Thus, ZmGSTIV, ZmGST6, ZmGST31 and ZmMRP1 could be considered safener-responsive and may be the core genes responsible for isoxadifen-ethyl increasing the tolerance of maize to nicosulfuron.

Effect of Environmental Conditions on the Degradation of Florasulam in Typical Soils of Northern China.

The widespread use of florasulam in China makes residues from this herbicide in soil a serious concern due to their potential to pollute the soil environment and groundwater. Accelerating the degradation of these residues will reduce their pollution potential. In this study, we investigated the degradation and adsorption of florasulam in four typical soils in northern China and examined the degradation of florasulam in Inceptisols at different temperatures, soil moisture contents, and pH values, as well as the influence of microorganisms and the use of organic matter and biogas slurry as soil amendments. The half-lives of florasulam in the four soils were 13.6 d (Ultisols), 13.9 d (Vertisols), 15.1 d (Alfisols), and 19.3 d (Inceptisols), and the adsorption ability of the four soils followed the order Inceptisols > Alfisols > Vertisols > Ultisols. Florasulam degradation rates increased as temperature and soil moisture increased and as soil pH decreased (from 8.0 to 6.0). Adding a small amount of organic matter to the soil increased the florasulam degradation rates. The use of biogas slurry also increased the degradation rates. Florasulam half-life in unsterilized soil ( = 19.3 d) was significantly shorter than in sterilized soil ( = 113.4 d). These results provide agricultural producers and environmental managers useful information for reducing the environmental risk associated with florasulam use.

Influence of environmental factors on Cucumis melo L. var. agrestis Naud. seed germination and seedling emergence.

Cucumis melo L. var. agrestis Naud. (field muskmelon) is an annual invasive weed in many parts of Asia. However, there is very little available information about the germination and emergence of this species. Therefore, laboratory experiments were conducted to evaluate the effects of light, temperature, salt stress, osmotic stress, pH, and depth of planting on field muskmelon germination and seedling emergence. Light had no effect on seed germination, and the seeds germinated at a wide range of temperatures. More than 90% of the seeds germinated at constant temperatures between 20°C and 35°C, and fluctuating day/night temperatures between 15/25 and 30/40°C. The seeds were tolerant to salinity as germination occurred up to the 200 mM NaCl treatment. However, the seeds were sensitive to osmotic stress as seed germination was completely inhibited at -0.6 MPa. The seeds germinated over a pH range of 4 to 10, which suggested that pH was not a limiting factor for germination. Seedling emergence was greatest (97.86%) when the seeds were planted on the soil surface, but emergence declined as the burial depth increased. Information from this study can be used to predict future infestations in China and help develop strategies to manage this species.

Physiological basis for isoxadifen-ethyl induction of nicosulfuron detoxification in maize hybrids.

Isoxadifen-ethyl can effectively alleviate nicosulfuron injury in the maize. However, the effects of safener isoxadifen-ethyl on detoxifying enzymes in maize is unknown. The individual and combined effects of the sulfonylurea herbicide nicosulfuron and the safener isoxadifen-ethyl on the growth and selected physiological processes of maize were evaluated. Bioassays showed that the EC50 values of nicosulfuron and nicosulfuron plus isoxadifen-ethyl for maize cultivar Zhengdan958 were 18.87 and 249.28 mg kg-1, respectively, and were 24.8 and 275.51 mg kg-1, respectively, for Zhenghuangnuo No. 2 cultivar. Evaluations of the target enzyme of acetolactate synthase showed that the I50 values of nicosulfuron and nicosulfuron plus isoxadifen-ethyl for the ALS of Zhengdan958 were 15.46 and 28.56 µmol L-1, respectively, and were 0.57 and 2.17 µmol L-1, respectively, for the acetolactate synthase of Zhenghuangnuo No. 2. The safener isoxadifen-ethyl significantly enhanced tolerance of maize to nicosulfuron. The enhanced tolerance of maize to nicosulfuron in the presence of the safener, coupled with the enhanced injury observed in the presence of piperonyl butoxide, 1-aminobenzotriazole, and malathion, suggested cytochrome P450 monooxygenases may be involved in metabolism of nicosulfuron. We proposed that isoxadifen-ethyl increases plant metabolism of nicosulfuron through non-P450-catalyzed routes or through P450 monooxygenases not inhibited by piperonyl butoxide, 1-aminobenzotriazole, and malathion. Isoxadifen-ethyl, at a rate of 33 mg kg-1, completely reversed the effects of all doses (37.5-300 mg kg-1) of nicosulfuron on both of the maize cultivars. When the two compounds were given simultaneously, isoxadifen-ethyl enhanced activity of glutathione S-transferases (GSTs) and acetolactate synthase activity in maize. The free acid 4,5-dihydro-5,5-diphenyl-1,2-oxazole-3-carboxylic was equally effective at inducing GSTs as the parent ester and appeared to be the active safener. GST induction in the maize Zhenghuangnuo No. 2 was faster than in Zhengdan 958.

Degradation of Mesotrione Affected by Environmental Conditions.

With the widespread use of mesotrione, its residues have become increasingly serious and caused a series of environmental problems in northern China. To reduce the harm of these residues, we investigated the degradation effect of mesotrione in typical soils in northern China at different temperatures, soil moisture, pH values and initial concentrations. We also examined the influence of soil type, microorganisms and the use of organic matter and biogas slurry as soil amendments. Mesotrione degradation rates increased as the temperature, soil moisture, soil pH and the content of biogas slurry increased; and decreased as the organic content and the initial concentration of mesotrione increased. The degradation rates were different in the three soils. Microorganisms played an important role in the degradation process. These result may offer a theoretical basis for decreasing mesotrione residue when using this product in northern China.

N'-Nitro-2-hydrocarbylidenehydrazinecarboximidamides: design, synthesis, crystal structure, insecticidal activity, and structure-activity relationships.

A novel series of acyclic imine-substituted nitenpyram analogues were designed and synthesized from nitroaminoguanidine, and their structures were confirmed using X-ray diffraction crystallography. Preliminary bioassays showed that the target molecules exhibited good activities against aphids in laboratory (Myzus persicae Sulzer) and field trials (M. persicae Sulzer and Brevicoryne brassicae Linnaeus). Comparative molecular field analysis and comparative molecular similarity indices analysis were employed to develop a three-dimensional quantitative structure-activity relationship model that describes the insecticidal activity of 21 neonicotinoid derivatives. Simple synthesis, low cost, and good insecticidal activity have made this series of compounds become very promising candidates for future commercial pesticides.