Diclofop‐resistant Lolium rigidum from northern Greece with cross‐resistance to ACCase inhibitors and multiple resistance to chlorsulfuron

Repeated use of ACCase‐ and ALS‐inhibiting herbicides in northern Greece has resulted in the evolution of a population of Lolium rigidum resistant to diclofop and chlorsulfuron. The biotype from Athos was highly resistant to diclofop and also exhibited differential cross‐resistance to clodinafop, fluazifop, tralkoxydim and sethoxydim. Assay of ACCase activity confirmed that the resistant biotype was tenfold more resistant to diclofop than the susceptible biotype, suggesting that the resistance mechanism could involve an altered target site. The diclofop‐resistant biotype has also exhibited multiple resistance to chlorsulfuron and the mechanism for this is unknown. Seed‐bioassay was found to be a rapid, cheap and reliable method to identify populations of L rigidum resistant to ACCase inhibitors and chlorsulfuron. Moreover, root elongation in the seed bioassay was more sensitive to ACCase inhibitors and chlorsulfuron than shoot elongation. © 2000 Society of Chemical Industry     

7‐(4,6‐Dimethoxypyrimidinyl)oxy‐ and ‐thiophthalides as novel herbicides: Part 1. CGA 279 233: a new grass‐killer for rice

A series of novel types of 7‐(4,6‐dimethoxypyrimidin‐2‐yl)oxy ‐ and ‐thio‐3‐methyl‐1 (3H)‐isobenzofuranones were discovered at Dr R Maag AG. From the thio‐isobenzofuranyl series, CGA 279 233—BSI‐proposed common name pyriftalid—was chosen for further development as a grass herbicide for use in rice. General synthetic approaches to these new phthalic acid‐derived compounds are given, with emphasis on the synthesis of pyriftalid and its physico‐chemical behaviour. © 2001 Society of Chemical Industry     

Selectivity of foramsulfuron + thiencarbazone‐methyl and classic herbicides in sensitive and non‐sensitive sugar beet genotypes

A new herbicide for sugar beet cultivation using the ALS‐inhibiting active ingredients foramsulfuron and thiencarbazone‐methyl is under approval in the EU member states. Sugar beet genotypes that are non‐sensitive to this herbicide are currently under development. Selectivity of the ALS‐inhibiting herbicide and yield response of the non‐sensitive genotypes might be relevant to meet the requirements for variety registration. To evaluate these issues, six field trials were conducted in Germany in 2013 and 2014. Classic herbicides and the ALS‐inhibitor herbicide were applied in dosages of up to fourfold the authorised (or applied for) application rates. The ALS‐inhibitor herbicide did not cause any significant phytotoxicity and had no effect on leaf area index at a single, double or fourfold dosage. By contrast, classic herbicides had significant negative effects at the single dosage. At fourfold dosage, they caused 41% phytotoxicity and reduced leaf area index by 35%. The relative yield difference between ALS‐inhibitor and classic herbicide treatments was 8.6% and 17.4% of white sugar yield at double and fourfold dosage respectively. The ALS‐inhibitor herbicide thus showed higher selectivity than the classic herbicides. In the registration process, the resulting yield advantage could balance a possible yield penalty of non‐sensitive genotypes. The introduction of a new system for weed control could improve application flexibility and control of troublesome weeds in sugar beet.     

In‐field classification of herbicide‐resistant Papaver rhoeas and Stellaria media using an imaging sensor of the maximum quantum efficiency of photosystem II

Reliable in‐season and in‐field tools for rapidly quantifying herbicide efficacy in dicotyledonous weeds are missing. In this study, the maximum quantum efficiency of photosystem II (F_v/F_m) of susceptible and resistant Papaver rhoeas and Stellaria media populations in response to treatments with acetolactate synthase (ALS) inhibitors were examined. Seedlings (4–6 leafs) were transplanted into the field immediately after the application of the ALS inhibitors florasulam, metsulfuron‐methyl and tribenuron‐methyl. The F_v/F_m values were assessed 1–7, 9 and 14 days after treatment (DAT). Based on the F_v/F_m values of all fluorescing pixels in the images of herbicide‐treated plants, discriminant maximum‐likelihood classifiers were created. Based on this classifier, an independent set of images were classified into ‘susceptible’ or ‘resistant’ plants. The classifiers’ accuracy, false‐positive rate and false‐negative rate were calculated. The F_v/F_m values of sensitive P. rhoeas and S. media plants decreased within 3 DAT by 28–43%. The F_v/F_m values of the resistant plants of both species were 20% higher than those of the sensitive plants in all herbicide treatments. The classifier separated sensitive and resistant plants 3 DAT with accuracies of 62–100%. False‐positive and false‐negative classifications decreased with increasing DAT. We conclude that by the assessment of the F_v/F_m value in combination with the classification sensitive and resistant P. rhoeas and S. media populations could be separated 3 DAT. This technique can help to select effective control methods and speed up the monitoring process of susceptible and resistant weeds.     

Seedbank persistence,germination and early growth of glyphosate‐resistant Kochia scoparia

This study describes the seedbank persistence of glyphosate‐resistant (GR) Kochia scoparia at two sites in western Canada and examines if GRK. scoparia from western Canada and mid‐western United States (USA) differ from their susceptible counterparts in seed germination and early growth characteristics at low‐temperature regimes. Site or depth of seed burial (surface, 2.5 cm, 10 cm) did not affect seed viability over time and time to 50% and 90% loss of viability averaged 210 and 232 days respectively. Glyphosate‐resistant K. scoparia generally germinated later and had lower cumulative germination than glyphosate‐susceptible (GS) K. scoparia from Saskatchewan, Canada; and Kansas, USA; but not Colorado, USA. Similarly, time to 10% first leaf of GSK. scoparia from Saskatchewan and Kansas tended to be sooner than that of GRK. scoparia, with a greater percentage of GS vs. GR seedlings of populations from all regions having attained first leaf by the end of the experiment. The short seedbank longevity and delayed and reduced germination and time to first leaf of GRK. scoparia may potentially be exploited to maximise management efficacy through delayed preseeding weed control or alternatively by early seeding date to enhance crop competitiveness.     

甲硫嘧磺隆对后茬玉米安全性评价

选用种植面积较大的玉米品种漯湘玉1号为指示植物,通过室内生测方法研究新型除草剂甲硫嘧磺隆对后茬作物玉米的安全性。结果表明,当甲硫嘧磺隆浓度低于5mg／L时,对后茬玉米无影响;但当浓度高于15mg／L时,其对后茬玉米有明显的药害,建议与其他农药混配使用以提高其对后茬作物的安全性。     

Target-site basis for resistance to acetolactate synthase inhibitor in Water chickweed (Myosoton aquaticum L.)

Water chickweed is a widespread and competitive winter annual or biennial weed of wheat in China. One Water chickweed population (HN02) resistant to several acetolactate synthase (ALS) inhibitors was found in Henan province of China. Whole-plant bioassays showed that HN02 was high resistance to tribenuron (292.05-flod). In vitro ALS assays revealed that resistance was due to reduced sensitivity of the ALS enzyme to tribenuron. The I₅₀ value for HN02 was 85.53 times greater respectively than that of susceptible population (SD05). This altered ALS sensitivity in the resistant population was due to a mutation in the ALS gene resulting in a Pro197 to Ser substitution. Cross-resistance experiments indicated that HN02 exhibited various resistance patterns to pyrithiobac-sodium, florasulam and pyroxsulam, without resistance to imazethapyr. This is the first report of tribenuron-resistant Water chickweed in Henan province of China, target-site based resistance was established as being due to an insensitive form of ALS, resulting from a Pro to Ser substitution at amino acid position 197 in the ALS gene.     

Soil‐less bioassays for early screening for resistance to imazapyr in sunflower (Helianthus annuus L.)

BACKGROUND: Rapid and efficient diagnostic tests for early screening of herbicide resistance are convenient alternatives to field screening methods. There is a need for a quick, reliable and cost‐effective method for rapid diagnosis of imidazolinone resistance in sunflower (Helianthus annuus L.). RESULTS: Two seed germination bioassays were developed. Seeds from three sunflower inbred lines differing in resistance to imidazolinones were germinated either on solid culture medium or placed in plastic pots filled with commercial perlite. After 8 days incubation under controlled conditions, both assays successfully distinguished susceptible genotype from the resistant and intermediate ones. The susceptible genotype showed arrested root growth at all herbicide treatments (root length < 1 cm). The resistant genotype developed a complete root system even when exposed to the highest dose of herbicide. However, no definite differences were observed for the intermediate and resistant genotypes with respect to root growth under the different herbicide treatments. CONCLUSION: The simple and rapid screening assays described in the present study were useful in discriminating imidazolinone resistance at the seedling stage. Therefore, these bioassays could be potential tools for early screening of imidazolinone resistance genes from large sunflower populations. Copyright © 2009 Society of Chemical Industry     

Design,synthesis and structure–activity relationships of novel ALS inhibitors

The paper describes the biophore models of sulfonylurea, imidazolinone, triazolopyrimidinesulfonamide and 5‐pyrimidyltriazolo‐3‐sulfonamides established by the Apex‐3D method. A series of N‐phenylsulfonyl‐N ′‐(thiadiazol‐2‐yl)oxamides and three types of triazolopyrimidinesulfonamide were synthesised and their herbicidal activities determined to assess the validity of the model. In general, the model gave useful leads to activity, although the actual level was not always predicted accurately. In only a few cases did compounds predicted as being active prove to be inactive in the bioassay, and compounds with little or no activity were clearly indicated. As a result of this work, the compound N,N ′‐[1‐(5,7‐dimethyl‐1,2,4‐triazolo[1,5‐a]pyrimidin‐2‐yl‐thio)butane‐2,3‐di‐imino]bis(2‐chlorobenzenesulfonamide) was selected as showing good activity against a range of species, and will be used as a lead for further development. © 2000 Society of Chemical Industry