Understanding the Differential Response of Setaria viridis L. (green foxtail) and Setaria pumila Poir. (yellow foxtail) to Pyroxsulam.

Green foxtail [Setaria viridis (L) Beauv.] and yellow foxtail [Setaria pumila (Poir.) Roem. & Schult.] are among the most abundant and troublesome annual grass weeds in cereal crops in the Northern Plains of the United States and the Prairie Provinces of Canada. Greenhouse and laboratory experiments were conducted to examine the differential responses of both weed species to foliar applications of the new triazolopyrimidine sulfonamide acetolactate synthase-inhibiting herbicide, pyroxsulam, and to determine the mechanism(s) of differential weed control. Foliar applications of pyroxsulam resulted in >90% control of yellow foxtail at rates between 7.5 and 15 g ai ha-1, whereas the same rates resulted in a reduced efficacy on green foxtail (≤81%). The absorption and translocation of [14C]pyroxsulam in green and yellow foxtail were similar and could not explain the differential whole-plant efficacy. Studies with [14C]pyroxsulam revealed a higher percentage of absorbed pyroxsulam was metabolized into an inactive metabolite in the treated leaf of green foxtail than in the treated leaf of yellow foxtail. Metabolism studies demonstrated that, 48 h after application, 50 and 35% of pyroxsulam in the treated leaf was converted to 5-hydroxy-pyroxsulam in green and yellow foxtail, respectively. The acetolactate synthase (ALS) inhibition assay showed that ALS extracted from green foxtail was more tolerant to pyroxsulam than the enzyme extracted from yellow foxtail was. The in vitro ALS assay showed IC50 values of 8.39 and 0.26 µM pyroxsulam for green and yellow foxtail, respectively. The ALS genes from both green and yellow foxtail were sequenced and revealed amino acid differences; however, the changes are not associated with known resistance-inducing mutations. The differential control of green and yellow foxtail following foliar applications of pyroxsulam was attributed to differences in both metabolism and ALS sensitivity.

Pro-insecticidal approach towards increasing in planta activity.

BACKGROUND: The adrenergic mode of action was investigated for the development of potential new insecticides. Clonidine-related analogs were tested against Myzus persicae (Sulzer) and Bemisia tabaci (Gennadius). Clonidine analogs lack translation owing to a possible vacuole-trapping mechanism. Physical property modulation via a prodrug approach was attempted to overcome this mechanism. RESULTS: Clonidine showed insecticidal activity against M. persicae and B. tabaci. A prodrug of a known open-chain analog of clonidine was developed. While the prodrug had decreased pKa and increased lipophilicity and displayed good activity against M. persicae B. tabaci, the activity did not translate to cotton. Metabolic studies showed that the prodrug was quickly metabolized to the parent compound, and was further metabolized to a known vacuole-trapped oxazoline analog. CONCLUSIONS: Adrenergic active compounds, such as clonidine analogs, show potential as insecticides; however, a designed prodrug approach did not overcome the lack of translation in this case. Studies confirmed that the synthesized prodrug analog metabolized in planta to the proposed vacuole-trapped compound. One possible explanation for the failure of this approach is that the rate of metabolism and vacuole trapping is faster than translaminar flow, and therefore the released pesticide is not biologically available to the target organism. © 2016 Society of Chemical Industry.

Mevalocidin: a novel, phloem mobile phytotoxin from Fusarium DA056446 and Rosellinia DA092917.

A multiyear effort to identify new natural products was built on a hypothesis that both phytotoxins from plant pathogens and antimicrobial compounds might demonstrate herbicidal activity. The discovery of one such compound, mevalocidin, is described in the current report. Mevalocidin was discovered from static cultures of two unrelated fungal isolates designated Rosellinia DA092917 and Fusarium DA056446. The chemical structure was confirmed by independent synthesis. Mevalocidin demonstrated broad spectrum post-emergence activity on grasses and broadleaves and produced a unique set of visual symptoms on treated plants suggesting a novel mode of action. Mevalocidin was rapidly absorbed in a representative grass and broadleaf plant. Translocation occurred from the treated leaf to other plant parts including roots confirming phloem as well as xylem mobility. By 24 hr after application, over 20 % had been redistributed through-out the plant. Mevalocidin is a unique phytotoxin based on its chemistry, with the uncommon attribute of demonstrating both xylem and phloem mobility in grass and broadleaf plants.

Discovery and characterization of sulfoxaflor, a novel insecticide targeting sap-feeding pests.

The discovery of sulfoxaflor [N-[methyloxido[1-[6-(trifluoromethyl)-3-pyridinyl]ethyl]-λ(4)-sulfanylidene] cyanamide] resulted from an investigation of the sulfoximine functional group as a novel bioactive scaffold for insecticidal activity and a subsequent extensive structure-activity relationship study. Sulfoxaflor, the first product from this new class (the sulfoximines) of insect control agents, exhibits broad-spectrum efficacy against many sap-feeding insect pests, including aphids, whiteflies, hoppers, and Lygus, with levels of activity that are comparable to those of other classes of insecticides targeting sap-feeding insects, including the neonicotinoids. However, no cross-resistance has been observed between sulfoxaflor and neonicotinoids such as imidacloprid, apparently the result of differences in susceptibility to oxidative metabolism. Available data are consistent with sulfoxaflor acting via the insect nicotinic receptor in a complex manner. These observations reflect the unique structure of the sulfoximines compared with neonicotinoids.

The impact of uptake, translocation and metabolism on the differential selectivity between blackgrass and wheat for the herbicide pyroxsulam.

BACKGROUND: Wheat shows selectivity to pyroxsulam, a new broad-spectrum herbicide with high activity on blackgrass. Studies were performed to establish whether uptake, translocation or metabolism were responsible for the differential activity in wheat compared with blackgrass. In addition, the effect of the safener cloquintocet-mexyl on metabolism was evaluated in wheat and blackgrass shoots. RESULTS: Root uptake of pyroxsulam in blackgrass was significantly higher than in wheat, suggesting a possible activity enhancement in blackgrass owing to root uptake. Translocation to foliage from root uptake as well as translocation out of treated foliage following foliar applications was low in wheat compared with blackgrass, likely owing to the rapid metabolism of pyroxsulam in wheat. Wheat metabolized pyroxsulam significantly faster than blackgrass to the less active O-dealkylation product. Wheat shoots metabolized pyroxsulam faster when the safener cloquintocet-mexyl was present, but cloquintocet-mexyl did not increase the rate of metabolism in blackgrass. CONCLUSIONS: The selectivity of pyroxsulam to wheat relative to blackgrass was connected primarily with differences in the rate of metabolism and generation of an inactive metabolite. Metabolism in wheat restricted subsequent movement of radioactivity out of the treated leaf. The rapid metabolism in wheat was increased by the addition of cloquintocet-mexyl.

Uptake, translocation and metabolism of the herbicide florasulam in wheat and broadleaf weeds.

Florasulam is a triazolopyrimidine sulfonanilide post-emergence broadleaf herbicide for use in wheat (Triticum aestivum L.). The selectivity of florasulam to wheat has been determined to be related primarily to a differential rate of metabolism between wheat with a half-life of 2.4 h and broadleaf weeds with half-lives ranging from 19 to >48 h. To a lesser extent, selectivity, at least for the broadleaf weed cleavers (Galium aparine L.), involves uptake differences. Rate of metabolism data were generated using greenhouse-grown plants injected with radiolabelled florasulam and subsequent extraction and processing by high-performance liquid chromatography (HPLC). Structures of metabolites were determined by isolation for nuclear magnetic resonance and liquid chromatography/mass spectrometry. Wheat plants metabolised florasulam by hydroxylation of the aniline ring para to the nitrogen, followed by conjugation to glucose. Metabolism by broadleaf weeds was so slow that isolation of metabolite was not possible, but comparison of HPLC data suggested hydroxylation as the major pathway.