Fluxofenim. Articles on uses as Safener for herbicides applied to wheat seeds

FLUORIDE ACTION NETWORK PESTICIDE PROJECT

Fluxofenim. Articles on uses as Safener for herbicides applied to wheat seeds.

From: http://jgg.unl.edu/articles/safener.htm

(Undated article; downloaded Nov 8, 2001)

Safening Herbicides for Selective Control of Jointed Goatgrass

By Dr. Brian Jenks, North Dakota State University

Many winter wheat producers look forward to the day when a new product enters the market that will selectively control troublesome winter annual grasses like jointed goatgrass and volunteer rye in winter wheat. The close genetic relationship of winter wheat and jointed goatgrass will probably preclude any such finding in the near future. However, rather than attempting to discover a new selective herbicide, Washington State University researchers at Pullman, WA, are investigating substances (safeners) that, when applied to wheat seeds, reduce herbicide injury to winter wheat while maintaining activity against weedy grasses.

The concept of safening a crop from herbicidal injury has been used successfully with corn herbicides. A compound called dichlormid has been used to reduce corn injury from the herbicide EPTC (Eptam). Another compound, benoxacor, has been shown to increase levels of glutathione S-transferase (GST), an enzyme in corn that breaks down certain corn herbicides and reduces or eliminates crop injury. Consequently, the safener concept could be used to increase enzyme levels in wheat to allow the use of herbicides that would otherwise cause unacceptable crop injury.

Dr. Dean Riechers, Dr. Pat Fuerst, and others at Washington State University have screened approximately 80 wheat lines and relatives to identify those with naturally high GST levels and those with even higher GST levels in response to treatment with a safener. Seeds of wheat lines and relatives were treated with the safeners fluxofenim and cloquintocet-mexyl, and were compared to an unsafened control for their ability to produce greater levels of GST and, in turn, reduce herbicide injury to wheat. The herbicide used was dimethenamid (Frontier), a corn and soybean herbicide that controls grassy weeds.

Results showed that the hexaploid wheats (common bread wheats) responded better to the safeners than did the tetraploid wheats (durum) or the hexaploid triticale. Riechers indicated that the D genome (which is present in the hexaploid wheats, but not the tetraploid wheats or hexaploid triticale) may be the source of GST enzymes that metabolize the herbicide dimethenamid (Frontier). They also found that the safener fluxofenim (Concep III) consistently increased GST levels more than another safener, cloquintocet-mexyl. Those wheats that had the highest safener-increased GST levels also demonstrated the highest tolerance to the herbicide. The durum wheats, which produced lower GST levels, also were less tolerant to the herbicide.

Although the safener fluxofenim increased tolerance to the herbicide dimethenamid, the injury sustained was still considered unacceptable. Riechers recently obtained the gene for this GST, which will enable scientists to efficiently screen for herbicide-tolerant and safener-responsive lines. This trait could be incorporated into future wheat varieties and may yet allow the use of a herbicide in tandem with a seed-applied safener to control winter annual grass weeds in winter wheat.

This work is part of the National Jointed Goatgrass Research program that was organized to develop integrated management strategies to control jointed goatgrass. State and federal researchers involved in this program are investigating a broad spectrum of approaches (including cultural and biological) to control jointed goatgrass. For additional information, contact the National Jointed Goatgrass Extension Coordinator:

Eric Zakarison

Dept of Crop & Soil Sciences

Washington State University

Pullman, WA 99164-6420

ezak@wsu.edu

V: (509) 335-2451

Visit the jointed goatgrass Web site at http://jgg.unl.edu

From: http://ianrsearch.unl.edu/jgg/jgg/projects/1996proj/mint.htm

Innovative Safener Treatments for Jointed Goatgrass Management

Innovative Safener Treatments for Jointed Goatgrass Management

Personnel:

PI: Pat Fuerst; cooperators: Dean Riechers, Jerry Irzyk, Ken Yang, Stephen Jones

Time Line: start 1994 finish 1996

Summary of Progress: We are attempting to develop the technology to use a herbicide in combination with a safener to control jointed goatgrass in wheat. We identified possible herbicide-safener combinations (dimethenamid plus cloquintocet-mexyl or fluxofenim) but the margin of herbicide selectivity was inadequate. We believe that wheat lines can be developed that show a more dramatic safener response. We developed laboratory assays that proved to be effective biochemical markers to evaluate safener response in wheat germplasm. We have purified the enzyme involved in the metabolism of dimethenamid and we are developing the technology for an even more efficient and reliable test for safener-responsive germplasm.

Objective: Because jointed goatgrass and wheat are so closely related, there are currently no herbicides to selectively control jointed goatgrass in wheat. Seed-applied safeners might be used to protect wheat from a herbicide that would control jointed goatgrass. Our work was designed to use a laboratory assay to screen a large number of wheat lines (and wheat relatives) as a rapid test to determine whether there are wheat lines tolerant to the herbicide, dimethenamid, and to identify lines that had high potential for safening from herbicide injury.

Progress: (See attached publication.) Our greenhouse and field studies showed that the herbicide, dimethenamid ('Frontier', from Sandoz), had the greatest potential for both safening in wheat and inhibiting jointed goatgrass growth. Dimethenamid controls jointed goatgrass and downy brome when soil moisture conditions are favorable. Our research also showed that the safeners cloquintocet-mexyl (CGA-185072) and fluxofenim (Concep III) had the greatest potential for safening whet. The safeners are applied as wheat seed treatments so that only wheat is protected from the herbicide. Safening is due to stimulation of herbicide detoxification We have shown that the enzyme, glutathione S-transferase is responsible for this herbicide detoxification; this work was published in the Journal of Agricultural and Good Chemistry.

The level of safening achieved with these safeners was inadequate for commercial application, so we initiated research that could lead to the development of wheat lines with greater safener response. We evaluated two laboratory assays for glutathione S-transferase to rapidly screen for wheat lines for safener response, and evaluated the merit of these assays with greenhouse evaluations of safener responses. Out of approximately 80 wheat lines, we identified four that showed the greatest response (increased glutathione S-transferase) in laboratory assays, which also had the greatest herbicide tolerance in the greenhouse. We concluded that one of these laboratory assays for glutathione S-transferase can be used as a biochemical marker to select wheat germplasm for safener response.

More recent research has focused on biochemical studies that would lead to more efficient development of wheat lines with dimethenamid tolerance and stronger safener response. We purified the major enzyme responsible for dimethenamid metabolism in wheat. We obtained several amino acid sequences from the enzyme, and we are isolating the cDNA clone. Isolation of the full-length clone will allow development of very specific assays to select for dimethenamid tolerance and safener response. We hope to collaborate with breeders in the near future to develop safener-responsive wheat lines.

Most of the above research was conducted by Dean Riechers, as part of his doctoral dissertation

Awards: Dean Riechers received three awards in the course of his doctoral studies: first place in the American chemical Society Predoctoral Award in Agrochemistry, 1995; first place in the Graduate Student Papers, Basic Sciences, from the Western Society of Weed Science, 1996; and Outstanding Graduate Student, Weed Science Society of America 1997.

Publications, Refereed:

Riechers, D.E., K.Yang, G.P. Irzyk, S.S. Jones, and E.P. Fuerst. 1996. Variability of glutathione S-transferase levels and dimethenamid tolerance in safener-treated wheat and wheat relatives. Pestic. Biochem. Physiol. (In Press, attached).

Riechers, D.E., E.P. Fuerst, and K.D. Miller. 1996. Initial metabolism of dimethenamid in safened and unsafened wheat. J. Agricultural and Food Chemistry 44: 1558-1564.

Riechers, D.E., G.P. Irzyk, and E.P. Fuerst. 1997. Partial characterization of glutathione S-transferases from wheat (Triticum spp.) and Purification of a safener-induced GST from Triticum tauschii. Plant Physiol. (submitted 12/96).

Publication, Non-Refereed:

C.M. Boerboom, E.P. Fuerst, and D.E. Riechers. 1993. Wheat safener research targeted for jointed goatgrass control. Pages 77-78 in: Department of Crop and Soil Sciences Technical Report 93-4, "1993 Field Day Proceedings: Highlights of Research Progress", B. Miller, ed.

Riechers, D.E., E.P. Fuerst, and C.M. Boerboom. 1994. Advancements in the development of seed-applied herbicide safeners for wheat. Page 102 in: Department of Crop and Soil Sciences Technical Report 94-6, "1994 Field Day Proceedings: Highlights of Research Progress", B. Miller, ed.

Abstracts:

Riechers, D.E., G.P. Irzyk, S.S. Jones, and E.P. Fuerst. 1996. Purification and cloning of a safener-induced glutathione S-transferase from. NATO Advanced Research Workshop (Kallithea, Greece): Regulation of Enzymatic Systems Detoxifying Xenobiotics in Plants: Abstr., p. 63.

Riechers, D.E., G.P. Irzyk, E.P. Fuerst, S. Potter, and E. Ward. 1997. Mechanism of action of safeners in wheat: Purification and cloning of GST-D from safener-treated Triticum Tauschii. Abstr. Weed Sci. Soc. Am. 37: (In Press).

Riechers, D.E., K. Yang, G.P. S.S. Jones, and E.P. Fuerst. 1996 Genetic variability of safener-increased glutathione S-transferase levels in wheat germplasm. Proc. West. Soc. Weed Sci. 49: 103.

Riechers, D.E., G.P. Irzyk, and E.P. Fuerst. 1996. Purification of a safener-induced glutathione S-transferase from Triticum tauschii. Abstr. Weed Sci. Soc. Am. 36: 54.

Riechers, D.E., E.P. Fuerst, G.P. Irzyk, and K.D. Miller. 1995. Safener-increased metabolism of the herbicide dimethenamid is mediated by isozymes of glutathione S-transferase in winter wheat. Abstr., Amer. Chem. Soc., Div. Agrochem.

Riechers, D.E., E.P. Fuerst, G.P. Irzyk, and S.S. Jones. 1995. Genetic evaluation of safener-induced glutathione S-transferases in winter wheat. Abstr. Weed Sci. Weed Sci. Soc. Am. 35: 73.

Riechers, D.E., E.P. Fuerst, and C.M. Boerboom. 1994. Optimization and mechanism of action of seed-applied herbicide safeners in winter wheat. Proc. West. Soc. Weed Sci. 47: 108-109.

Riechers, D.E., E.P. Fuerst, and C.M. Boerboom. 1994. Optimization and mechanism of action of seed-applied herbicide safeners in winter wheat. Abstr. Weed Sci. Soc. Am. 34: 62.

Riechers, D.E., E.P. Fuerst, G.P. Irzyk, and K.D. Miller. 1994. Safener-increased metabolism of the herbicide dimethenamid is mediated by isozymes of glutathione S-transferase in winter wheat. Plant Physiol. 105 (suppl.): 125.

Kennedy, A.C., T.L. Stubbs, and E.P. Fuerst. 1995. Biological control of jointed goatgrass (Aegilops cylindrica). Abstr. Weed Sci. Soc. Am. 35: 61.

Technology Transfer Activities: Wheat breeders, especially Steve Jones (a cooperator on this project) will be informed of those wheat lines that we consider to have the greatest potential, and we will encourage them to include them in a breeding program. The development and marketing of a new safener-treated wheat line also depends upon the cooperation of chemical companies involved, and we have kept Sandoz informed of our progress.

Variability of Glutathione S-Transferase Levels and Dimethenamid Tolerance in Safener-Treated Wheat and Wheat Relatives

Dean E. Riechers, Ken Yang, Gerard P. Irzyk, Stephen S. Jones, and E. Patrick Fuerst

Introduction

Jointed goatgrass (Aegilops cylindrica Host) and downy brome (Bromus tectorum L.) are problem winter annual grass weeds in winter wheat production in the United States. Jointed goatgrass cannot be controlled selectively with herbicides that are currently labeled for used in winter wheat (1). The chloro-acetamide herbicide dimethenanamid, currently used for weed control in corn and soybeans, has activity on these grass weeds (Riechers and Fuerst, unpublished results). However, wheat is also injured to an unacceptable level by dimethenamid. Herbicide safeners are often used to increase crop tolerance to herbicides (2). We have evaluated the use of seed-applied herbicide safeners to protect winter wheat from dimethenamid injury (3). Field and greenhouse studies have concentrated on safening "Madsen" winter wheat, which is the most commonly grown wheat cultivar in Washington State (4). These studies have shown that the level of safening achieved with fluxofenim, cloquintocet-mexyl, and benoxacor may not be adequate for used of dimethenamid in the field at rates needed to control annual grass weeds. Therefore, increasing the seed-applied safeners requires further improvement.

Most herbicide safeners protect crop species by increasing the rate of herbicide metabolism and detoxification (5-8). For example, the safener-increased tolerance to a chloro-acetamide herbicide in sorghum was attributed to increased herbicide metabolism via glutathione conjugation (9); this safener-increased metabolism was attributed to the increase in glutathione S-transferase (GST³; EC 2.5 1,18) activity (10). Constitutive levels of GST activity in maize hybrids (11) have also been correlated with tolerance to the chloroacetamide herbicide metolachlor. GST activity with herbicide metolachlor. GST activity with herbicide substrates in maize and weed species correlated well with their respective level of tolerance to the herbicide (12). We have demonstrated that safener treatment increased the rate of dimethenamid metabolism via glutathione conjugation in wheat (13).

Wheat and barley varieties have been screened in the greenhouse for the safening activity of R-32822 against thiocarbamate herbicide injury, and variability existed for tolerance to the herbicides (with and without safener) (14). It is possible that a more rapid and sensitive laboratory assay for herbicide tolerance could be developed. The objectives of our study were to (1) identify wheat lines or wheat relatives with higher constitutive GST levels, and/or higher safener-increased GST levels, than "Madsen" wheat, and (2) to determine if GST levels could be used to predict wheat seedling tolerance to dimethenamide. GST proteins were determined by an enzyme-linked immunosorbent assay (GST-ELISA) and GST activity by an assay using dimethe-namid as a substrate (GST-D). All experiments were conducted with young wheat seedlings, since chloroacetamide herbicides and their safeners are most active in emerging shoots of grasses (5, 15). The ability to identify either high constitutive and/or safener-increased GST levels would be a useful biochemical marker for dimethenamid tolerance in wheat or wheat relatives and might allow for the development of a wheat variety with increased tolerance to dimethenamid.

from: http://ianrsearch.unl.edu/jgg/jgg/denver/smboerbo.htm

Current Research in Jointed Goatgrass at Washington State University

Chris M. Boerboom
Extension Weed Specialist
Washington State University

Herbicide Safeners. We are evaluating a chemical approach where seed-applied safeners protect wheat against herbicides that control jointed goatgrass. This research is being coordinated by Drs. Fuerst, Boerboom, and Ogg. Safeners have been evaluated as protectants for wheat against trifluralin (Treflan), trifluralin plus triallate (Buckle), clomazone (Command), metribuzin (Sencor), and the choloroacetamide herbicides of metolachlor (Dual), acetochlor (Harness), and dimethenamid (Frontier). In greenhouse studies, numerous safeners did not protect wheat against metribuzin injury. However, various safeners were able to protect wheat from trifluralin, trifluralin plus triallate, clomazone, and acetochlor. For the different herbicides, the best safener increased seedling fresh weights from 2.4 to 5.8 times the weight of nonsafened herbicide treated wheat. On a relative basis, the greatest safening was observed against trifluralin where oxabetrinil (Concep II) increased the seedling fresh weight 5.8 fold. In a subsequent field study, oxabetrinil or CGA 185072 did not provide significant safening from trifluralin at 0.75 and 1.5 lb ai/a when the wheat was seeded into the treated zone.

Safening wheat from the chloroacetamide herbicides has been easier to achieve even though initial test only showed a 4 fold increase in fresh weight when safened from acetochlor. Among evaluated chloroacetamide herbicides, dimethenamid and acetochlor were more phytotoxic than metolachlor to wheat, jointed goatgrass and downy brome per pound active ingredient. The dimethenamid rate required to reduce weight 50% was approximately 0.5 lb ai/a for wheat and jointed goatgrass and less than 0.25 lb ai/a for downy brome. Several safeners protected wheat from dimethenamid in greenhouse tests including oxabetrinil, fluxofenim (Concep III), and benoxacor. This safening response was also demonstrated in a field study where oxabetrinil and benoxacor provided safening of two wheat varieties from dimethenamid applied at 1.5 and 3.0 lb ai/a. As a result of these findings, a four state cooperative project was initiated in the fall of 1993 to evaluate the potential to safen wheat from dimethenamid under a range of environments and the efficacy of dimethenamid on jointed goatgrass, downy brome, and wild oat.

The mechanism by which these safeners are acting is also being studied. Initial studies suggest that the antidotes are safening wheat from chloroacetamide herbicides by inducing the expression of glutathione-S-transferase (GST) isozymes. The resulting GST enzymes can rapidly detoxify chloroacetamide herbicides so that injury does not occur. Safeners that protect corn and sorghum from herbicides like metolachlor, alachlor, and acetochlor have a similar mechanism.

Biological Control. A potential biological method of jointed goatgrass control is the use of a Pseudomonas soil bacteria to suppress jointed goatgrass germination and subsequent growth. This research is being conducted by Dr. Kennedy, USDA-ARS. Over 2,000 naturally occurring strains of Pseudomonas bacteria have been screened for activity against jointed goatgrass and wheat. Approximately 3% of the strains inhibit jointed goatgrass by greater than 70% in the initial agar screen without causing significant effects to wheat. Further greenhouse testing has limited the number of potential bacterial isolates to 7. The primary effect of the bacteria appears to be a suppression of root growth, which results in reduced shoot growth. In a field nursery in the 1992-93 season, one isolate reduced jointed goatgrass shoot biomass by 30% and in 1989-90 another isolate reduced the jointed goatgrass stand by 60%.

This biocontrol system is similar to an extensive project on bacterial control of downy brome. Both projects are challenged in trying to maximize the bacteria's survival after application to ensure activity. Dry encapsulated formulations have increased the bacteria's survival compared to applications of liquid suspensions. With the downy brome project, all accessions of downy brome are equally susceptible to isolates with activity against that weed. The situation appears more complex with jointed goatgrass. Jointed goatgrass accessions vary in their susceptibility to different bacterial isolates. This may suggest that greater diversity exists in the germplasm among jointed goatgrass than among downy brome.

Ongoing biocontrol research involves screening for active isolates, evaluating the mechanism of the bacteria's suppressive action and population dynamics, and developing technology to improve survival.