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Tripleurospermum inodorum (L.) Sch. Bip. is one of the most economically important and yield-reducing weeds in cereals in Europe. Random and systematic monitoring of this weed might provide an early warning for the farmers and slow down the pace of the evolution of herbicide resistance. This study aimed to identify resistant populations of T. inodorum in the Czech Republic and elucidate their possible resistance mechanism/s. Monitoring and screening of T. inodorum for herbicide resistance against acetolactate synthase (ALS) inhibitors and synthetic auxins was carried out. Greenhouse experiments and molecular-genetics studies were conducted to characterize the resistance. While all the tested populations were found to be susceptible to synthetic auxins, two populations (MATIN 2 and MATIN 4) were found to be resistant against tribenuron (ALS inhibitor). However, their cross-resistance to florasulam was not confirmed. The resistance mechanism detected was the target-site substitution of Pro197 at the ALS gene. The two populations carried different point mutations: Pro197Ser (MATIN 2) and Pro197Gln (MATIN 4). This is the first study in the Czech Republic to identify the survival mechanism in T. inodorum for resistance to ALS-inhibiting herbicides. Our results from this research will provide basis for resistance management in T. inodorum in the Czech Republic and other countries.

Abstract Background Acetolactate synthase (ALS)-inhibiting herbicide tribenuron-methyl (TBM) is an efficient gametocide that can cause rapeseed (Brassica napus L.) to become male sterile and outcrossing. To find the reason the TBM treatment leads to male sterility, an integrated study using cytological, physiological, and transcriptomic methods was conducted. Results Some temporary symptoms, including the discoloration of young leaves and a short halt of raceme elongation, were observed in the rapeseed plants exposed to TBM at an application rate of 1 μg per plant. Both chloroplasts in young leaves and plastids in anthers were deformed. TBM also reduced the leaf photosynthetic rate and the contents of chlorophyll, soluble sugar and pyruvate. Both the tapetal cells and uni-nucleate microspores in the treated plants showed large autophagic vacuoles, and the tissue degenerated quickly. A transcriptomic comparison with the control identified 200 upregulated and 163 downregulated differential expression genes in the small flower buds of the TBM treatment. The genes encoding functionally important proteins, including glucan endo-1,3-beta-glucosidase A6, QUARTET3 (QRT3), ARABIDOPSIS ANTHER 7 (ATA7), non-specific lipid-transfer protein LTP11 and LTP12, histone-lysine N-methyltransferase ATXR6, spermidine coumaroyl-CoA acyltransferase (SCT), and photosystem II reaction centre protein psbB, were downregulated by TBM exposure. Some important genes encoding autophagy-related protein ATG8a and metabolic detoxification related proteins, including DTX1, DTX6, DTX35, cytosolic sulfotransferase SOT12, and six members of glutathione S-transferase, were upregulated. In addition, several genes related to hormone stimulus, such as 1-aminocyclopropane-1-carboxylate synthase 8 (ACS8), ethylene-responsive factor ERF1A, ERF1, ERF71, CRF6, and RAP2-3, were also upregulated. The transcriptional regulation is in accordance with the functional abnormalities of pollen wall formation, lipid metabolism, chloroplast structure, ethylene generation, cell cycle, and tissue autophagy. Conclusion The results suggested that except for ALS, the metabolic pathways related to lipid metabolism, pollen exine formation, photosynthesis and hormone response are associated with male sterility induced by TBM. The results provide new insight into the molecular mechanisms of inducing male sterility by sulfonylurea.

This study included the determination of the effect of the herbicide Tribenuron methyl on pseudomonas aeruginosa isolated from wheat field soil in Thi-Qar governorate district at the range of 1.6, 2.9, 4.0ppmconcentration.The results showed that the number of pseudomonas aeruginosa reached to (21×108) in control,but the numbers decreased to(11.4×108,17.1×108 )withTribenuron methyl in the concentration (4, 1.6 ppm)respectively . While the numbers increased to (21.8×108)with Tribenuron methyl in concentration( 2.9 ppm). The results showed that pseudomonas aeruginosa are able to convert Tribenuron methyl to other compounds in the laboratory. [ABSTRACT FROM AUTHOR]

The aim of this work was to verify and assess the tolerance of the PR63E82 (ExpressSun) sunflower cultivar to tribenuron, propaquizafop and their tank-mix combination in two rates under various weather conditions. Three small-plot field trials were carried out on sunflower in Prague, Czech Republic, from 2015 to 2017. High phytotoxicity (25–56%) of tribenuron (TBM) + non-ionic surfactant was observed in 2015 and 2016 when the sunflower was sown in mid-April. In 2017, phytotoxicity was significantly lower (4–6%), probably due to a later sowing of sunflower (May), and hence higher temperatures. The main symptoms of TBM phytotoxicity were leaf chlorosis, necrosis and growth retardation. Propaquizafop (PQF) injury was minimal in 2015 and 2017. A higher phytotoxicity (10–13%) was recorded in 2016, probably due to a hail which occurred 2 days after T2 (second application term (sunflower BBCH 14)) application. Plant injury had puckered leaves and also made more side branches. TBM + PQF damaged sunflower plants most of the tested herbicide treatments (phytotoxicity 3–62%). High phytotoxicity caused stem branching, increased number of sunflower heads and decreased yield. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Descurainia sophia L., a problematic weed in winter wheat fields in China, has developed high resistance to tribenuron‐methyl. Amino acid substitutions at sites Pro197, Asp376 and Trp574 in the target acetohydroxyacid synthase (AHAS) were primarily responsible for D. sophia resistance to tribenuron‐methyl. In this study, purified subpopulations of D. sophia plants individually homozygous for a specific resistance mutation (Pro197Leu, Pro197His, Pro197Ser, Pro197Thr, Asp376Glu or Trp574Leu) in AHAS were generated, and the effects of resistance mutations on D. sophia resistance and AHAS characteristics were investigated. RESULTS: All resistance mutations in this study not only caused D. sophia to evolve 152‐ to 811‐fold resistance to tribenuron‐methyl but also greatly reduced AHAS sensitivity to tribenuron‐methyl and increased AHAS binding affinity for the substrate pyruvate, which was primarily responsible for D. sophia resistance. The molecular docking results indicated that these resistance mutations altered AHAS binding affinity for tribenuron‐methyl by reducing the hydrogen bonds and changing hydrophobic interactions. Compared with the wild‐type AHAS, these resistance mutations exhibited no significant effects on AHAS feedback inhibition by branched‐chain amino acids (BCAAs) at concentrations <0.08 m m. The altered AHAS sensitivity to feedback inhibition by BCAAs did not necessarily increase or decrease the free BCAAs in resistant D. sophia plants. CONCLUSION: The AHAS resistance mutations conferred D. sophia resistance to tribenuron‐methyl by decreasing the binding affinity for tribenuron‐methyl and/or increasing the binding affinity for pyruvate, but the mutations did not necessarily affect the biosynthesis of BCAAs in plants. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Rate-response experiments with nine putative resistant wild mustard ( Sinapis arvensis ) populations from Greece showed cross-resistance to tribenuron and imazamox. The calculated GR 50 values [herbicide rate (g ai ha − 1 ) required for 50% reduction of fresh weight] of the nine resistant (R) populations ranged from 51.8 to 555.6 g ai tribenuron ha − 1 and from 66.3 to 900.4 g ai imazamox ha − 1 . Regarding the susceptible population, GR 50 value was not estimated for tribenuron as its lower treatment reduced fresh weight by > 95%, whereas the respective value for imazamox was 0.5 g ai ha − 1 . Gene sequencing of als revealed that a point mutation at Trp574 position, leading to amino acid substitution by Leu in the ALS enzyme was present and the likely cause of resistance. The in vitro activity of the ALS enzyme indicated I 50 values (herbicide concentration required for 50% reduction of the ALS activity) ranging from 19.11 to 217.45 μM for tribenuron, whereas the respective value for the S population was 1.17 μM. All populations were susceptible to MCPA at the recommended rate. These results strongly support that cross-resistance of 9 S. arvensis populations was due a point mutation of the als gene, which resulted in a less sensitive ALS enzyme. [ABSTRACT FROM AUTHOR]

Target-site and non-target-site resistance mechanisms to ALS inhibitors were investigated in multiple resistant (tribenuron-methyl and 2,4-D) and only 2,4-D resistant, Spanish corn poppy populations. Six amino-acid replacements at the Pro197 position (Ala197, Arg197, His197, Leu197, Thr197 and Ser197) were found in three multiple resistant populations. These replacements were responsible for the high tribenuron-methyl resistance response, and some of them, especially Thr197 and Ser197, elucidated the cross-resistant pattern for imazamox and florasulam, respectively. Mutations outside of the conserved regions of the ALS gene (Gly427 and Leu648) were identified, but not related to resistance response. Higher mobility of labeled tribenuron-methyl in plants with multiple resistance was, however, similar to plants with only 2,4-D resistance, indicating the presence of non-target-site resistance mechanisms (NTSR). Metabolism studies confirmed the presence of a hydroxy imazamox metabolite in one of the populations. Lack of correlation between phenotype and genotype in plants treated with florasulam or imazamox, non-mutated plants surviving imazamox, tribenuron-methyl translocation patterns and the presence of enhanced metabolism revealed signs of the presence of NTSR mechanisms to ALS inhibitors in this species. On this basis, selection pressure with ALS non-SU inhibitors bears the risk of promoting the evolution of NTSR mechanisms in corn poppy. [ABSTRACT FROM AUTHOR]

The reliable gene expression analysis of a reverse transcription quantitative polymerase chain reaction (qRT-PCR) mainly depends on selecting suitable reference genes that can express stably under different experimental conditions. Thus far, no reference genes have been identified in flixweed. In this paper, 7 supposed reference genes were selected to evaluate their expression stabilities by qRT-PCR in flixweed under three conditions including different sampling times after tribenuron treatment, different organs, and different growth stages using geNorm, NormFinder, and BestKeeper statistical algorithms. The results showed that ACT7 , UBC and 18SrRNA were the stable reference genes in all of the tested samples. ACT7 and UBC showed high stability in different sampling times after the tribenuron treatment. UBC and 18SrRNA were the most suitable genes for different organs and growth stages. This work confirmed the suitable reference genes of flixweed for a relatively accurate gene expression analysis under different experimental conditions. [ABSTRACT FROM AUTHOR]

The decline of arable species characteristic of winter cereal fields has often been attributed to different factors related to agricultural intensification but most importantly to herbicide use. Herbicide phytotoxicity is most frequently assessed using short-term endpoints, primarily aboveground biomass. However, short-term sensitivity is usually not sufficient to detect actual effects because plants may or may not recover over time following sublethal herbicide exposures. Therefore, it is important to assess the long-term effects of herbicide applications. Annual species rely on renewable seed production to ensure their persistence; hence, assessment of herbicide sensitivity is more accurately estimated through effects on reproduction. Here we aim to assess the phytotoxicity of two commonly used herbicides: tribenuron and 2,4-D on eight plant species belonging to four families, each with one rare and one more common species. Specifically we examined the pattern of sensitivity using short-term and long-term endpoints (total aboveground biomass, total seed biomass and number of seeds) of these species; we determined the levels of and time to recovery in terms of stem length and fruit number, and assessed whether their rarity relates to their sensitivity to herbicide application. Our results suggest that although differences in herbicide sensitivity are not a direct cause of rarity for all species, it may be an important driver of declining arable plants. [ABSTRACT FROM AUTHOR]

Background: Acetolactate synthase (ALS)-inhibiting herbicide tribenuron-methyl (TBM) is an efficient gametocide that can cause rapeseed (Brassica napus L.) to become male sterile and outcrossing. To find the reason the TBM treatment leads to male sterility, an integrated study using cytological, physiological, and transcriptomic methods was conducted. Results: Some temporary symptoms, including the discoloration of young leaves and a short halt of raceme elongation, were observed in the rapeseed plants exposed to TBM at an application rate of 1 μg per plant. Both chloroplasts in young leaves and plastids in anthers were deformed. TBM also reduced the leaf photosynthetic rate and the contents of chlorophyll, soluble sugar and pyruvate. Both the tapetal cells and uni-nucleate microspores in the treated plants showed large autophagic vacuoles, and the tissue degenerated quickly. A transcriptomic comparison with the control identified 200 upregulated and 163 downregulated differential expression genes in the small flower buds of the TBM treatment. The genes encoding functionally important proteins, including glucan endo-1,3-beta-glucosidase A6, QUARTET3 (QRT3), ARABIDOPSIS ANTHER 7 (ATA7), non-specific lipid-transfer protein LTP11 and LTP12, histone-lysine N-methyltransferase ATXR6, spermidine coumaroyl-CoA acyltransferase (SCT), and photosystem II reaction centre protein psbB, were downregulated by TBM exposure. Some important genes encoding autophagy-related protein ATG8a and metabolic detoxification related proteins, including DTX1, DTX6, DTX35, cytosolic sulfotransferase SOT12, and six members of glutathione S-transferase, were upregulated. In addition, several genes related to hormone stimulus, such as 1-aminocyclopropane-1-carboxylate synthase 8 (ACS8), ethylene-responsive factor ERF1A, ERF1, ERF71, CRF6, and RAP2-3, were also upregulated. The transcriptional regulation is in accordance with the functional abnormalities of pollen wall formation, lipid metabolism, chloroplast structure, ethylene generation, cell cycle, and tissue autophagy. Conclusion: The results suggested that except for ALS, the metabolic pathways related to lipid metabolism, pollen exine formation, photosynthesis and hormone response are associated with male sterility induced by TBM. The results provide new insight into the molecular mechanisms of inducing male sterility by sulfonylurea. [ABSTRACT FROM AUTHOR]