Kriton K. Hatzios

Herbicide Antidotes: Development, Chemistry, and Mode of Action

Publisher Summary This chapter discusses the development, chemistry, and mode of action of herbicide antidotes. Organic herbicides represent the most effective weapon available to farmers worldwide in their war against weeds. A fundamental reason for the widespread use of these chemicals in modern agriculture is their ability to control selectively a wide spectrum of weeds in a variety of crops. The concept of using herbicide antidotes offers a potential alternative for increasing the selectivity of available herbicides. A desirable herbicide antidote is a chemical agent that selectively protects crops from herbicide injury without protecting weeds. This selectivity is the result of either a very specific crop–herbicide–antidote interaction or a selective treatment such as the dressing of crop seeds with the antidote. Herbicide antidotes are developed primarily through random screening techniques that involve most combinations of important herbicides, major crops, and candidate antidotes. The timing of herbicide and antidote applications to the crop as well as differential intraspecific tolerance of crop cultivars to combinations of herbicides plus antidotes needs to be established for optimum effectiveness of herbicide antidotes in the field.

Role of glutathione and glutathione S-transferase in the selectivity of acetochlor in maize and wheat

Abstract The role of shoot and root glutathione (GSH) content and glutathione S-transferase (GST) activity in the response of the ‘A632 × A635’ and ‘Anjou SC256’ hybrids of maize (Zea mays L.) and of ‘Jubilejnaja 50’ wheat (Triticum aestivum L.) to the chloroacetanilide herbicide acetochlor was evaluated. The concentrations of root-applied acetochlor causing a 50% inhibition of plant shoot height were 20 μM for the tolerant ‘A632 × A635’ maize, 1 μM for the sensitive ‘Anjou SC256’ maize, and 0.1 μM for the very sensitive ‘Jubilejnaja 50’ wheat. The nonprotein thiol (mainly GSH) level in the roots of the tolerant ‘A632 × A635’ maize hybrid was 2-fold greater than that found in the roots of the sensitive maize hybrid and of wheat. Pretreatment with 10 μM of acetochlor induced the root nonprotein thiol levels of all three genotypes. The highest induction of root thiol content compared to controls was observed at 48 hr after acetochlor treatment and was 2.23-fold in the tolerant maize and 1.72-fold for the sensitive wheat. GST activities of etiolated maize and wheat seedlings were evaluated using both CDNB (1-chloro-2,4-dinitrobenzene) and [14C]-acetochlor as substrates. GST(CDNB) activity was greater in the roots than in the shoots of both maize hybrids. The shoot GST(CDNB) activity of both maize genotypes was similar, but the tolerant ‘A632 × A635’ maize had slightly higher root GST(CDNB) activity. In the sensitive wheat, similar shoot and root GST(CDNB) activities were observed. GST(CDNB) activity in roots of the maize hybrids and of wheat was enhanced by 70–100% at 48 hr after pretreatment with 10 μM of acetochlor. Shoot GST(CDNB) activity of maize or wheat was not induced significantly by acetochlor pretreatment. Root and shoot GST(acetochlor) activities of the maize hybrids and wheat were much lower than GST(CDNB) activities. Root GST(acetochlor) activities of the two maize hybrids were greater and more inducible by acetochlor pretreatment than those of the sensitive wheat. These results demonstrate the important role of endogenous levels of GSH and of GST activity in chloroacetanilide herbicide detoxication and selectivity.

Weed and Herbicide-Resistant Soybean (Glycine max) Response to Glufosinate and Glyphosate Plus Ammonium Sulfate and Pelargonic Acid1

Abstract:u2009The effects of ammonium sulfate and pelargonic acid on weed control with glufosinate and glyphosate and safety to glufosinate-resistant and glyphosate-resistant soybean were investigated in the greenhouse and field. Annual and perennial weeds varied in their sensitivity to the herbicides. Based on fresh weight reduction 10 d after treatment (DAT), common milkweed was more tolerant to glufosinate, and horsenettle was more tolerant to glyphosate. Giant foxtail was highly sensitive to both herbicides. The activity of glufosinate on common milkweed and of glyphosate on horsenettle was enhanced with the addition of 5% (wt/v) ammonium sulfate. The addition of pelargonic acid at 3% (v/v) did not enhance the activity of glufosinate or glyphosate on any weed, and it antagonized common lambsquarters and giant foxtail control with glufosinate and with glyphosate. Glyphosate was more effective than glufosinate in suppressing the regrowth of the perennial weeds horsenettle and common milkweed, but addition of ammonium sulfate and pelargonic acid was not beneficial with either herbicide. Under field conditions, the addition of ammonium sulfate or pelargonic acid to glufosinate or glyphosate did not improve efficacy on annual weeds. The addition of pelargonic acid improved yellow nutsedge control with glufosinate, but only at 6 DAT. Glufosinate and glyphosate applied alone or in combination with ammonium sulfate were safe to transgenic soybeans resistant to the respective herbicide. The addition of pelargonic acid to glufosinate or glyphosate in the greenhouse caused a rate-dependent reduction in soybean fresh weight. In the field, slight soybean injury with the addition of pelargonic acid was evident 6 DAT, but not 23 DAT. Addition of ammonium sulfate can increase the efficacy of glufosinate and glyphosate on perennial weeds without negatively affecting soybean yield. Nomenclature: Glufosinate; glyphosate; pelargonic acid; common lambsquarters, Chenopodium album L. #3 CHEAL; common milkweed, Asclepias syriaca L. # ASCSY; giant foxtail, Setaria faberi Herrm. # SETFA; horsenettle, Solanum carolinense L. # SOLCA; yellow nutsedge, Cyperus esculentus L. # CYPES; soybean, Glycine max (L.) Merr. ‘Asgrow 5547LL’ and ‘Asgrow 4501RR’. Additional index words: Herbicide additives, Amaranthus retroflexus, Ambrosia artemisifolia, Ipomoea hederacea, Ipomoea lacunosa, Senna obtusifolia, glufosinate-resistant soybean, glyphosate-resistant soybean, AMARE, AMBEL, ASCSY, CASOB, CHEAL, CYPES, IPOHE, IPOLA, SETFA, SOLCA. Abbreviations: DAT, days after treatment; GR50, 50% growth reduction (the herbicide rate needed to achieve a 50% reduction in fresh weight).

The mechanism of resistance to aryloxyphenoxypropionate and cyclohexanedione herbicides in a johnsongrass biotype

Abstract Acetyl-coenzyme A carboxylase (ACCase) assays and absorption, translocation, and metabolism experiments were conducted to investigate the mechanism(s) responsible for resistance in a johnsongrass biotype that exhibited low levels of resistance to the cyclohexanedione (CHD) herbicide sethoxydim and the aryloxyphenoxypropionate (APP) herbicides quizalofop-P and fluazifop-P. The rate of [14C]quizalofop-ethyl absorption was significantly higher in the resistant compared to the susceptible biotype 8, 24, and 48 h after treatment (HAT), but by 72 HAT, there was no significant difference in the amount of [14C]quizalofop-ethyl detected in either biotype. Additionally, little or no differences in the translocation of [14C]quizalofop-ethyl were observed in the resistant and susceptible biotypes at any time interval after application. In [14C]quizalofop-ethyl metabolism experiments, similar levels of quizalofop-ethyl and quizalofop metabolites were observed in the resistant and susceptible biotypes 8, 24, 48, and 72 HAT, but slightly higher levels of quizalofop acid were detected in the resistant biotype 48 and 72 HAT. In ACCase assays, the concentrations of quizalofop-P, clethodim, and sethoxydim that inhibited ACCase activity by 50% (I50) were statistically similar in the two biotypes, indicating that the resistant johnsongrass biotype contains an ACCase that is sensitive to the APP and CHD herbicides. In the absence of APP or CHD herbicides, however, the specific activity of ACCase in the resistant biotype was two to three times greater than that of the susceptible biotype. The specific activity of ACCase in the resistant biotype was also significantly greater than that of the susceptible biotype in the presence of all concentrations of quizalofop-P and sethoxydim and in the presence of 0.1, 1, and 10 µM clethodim. These results suggest that resistance to quizalofop-P and sethoxydim is conferred by an overproduction of ACCase in the resistant johnsongrass biotype. Nomenclature: Clethodim; fluazifop-P; quizalofop-P; sethoxydim; johnsongrass, Sorghum halepense (L.) Pers. SORHA.

Evaluation of the mechanism of action of the bleaching herbicide SC-0051 by HPLC analysis

Abstract The accumulation of leaf pigments in soybean [ Glycine max (L.) Merr. cv. Essex] plants treated with the bleaching herbicides norflurazon (20 ppm, w w ) and SC-0051 (2.5 ppm, w w ) was investigated by means of high-performance liquid chromatography analysis. SC-0051 is a new experimental herbicide whose chemistry has not been released. Both SC-0051 and norflurazon reduced the relative concentrations of xanthophylls, chlorophylls, and colored carotenoids and induced the accumulation of the colorless carotene, phytoene, in the leaves of treated soybeans. These results confirm that the mechanism of the bleaching action of the herbicide SC-0051 is similar to that of norflurazon and includes the inhibition of the desaturation reactions of carotenoid biosynthesis. In addition to their phytoene-accumulating activity, both SC-0051 and norflurazon induced the accumulation of an additional pigment which was not present in leaf extracts obtained from untreated soybeans. Although the exact identity of this pigment is unknown, it appears to be a derivative of phytoene.

Absorption, translocation, and metabolism of CGA 362622 in cotton and two weeds

Abstract Absorption, translocation, and metabolism of the herbicide CGA 362622 were studied in cotton, spurred anoda, and smooth pigweed. 14C-labeled CGA 362622 was foliarly applied to cotton at the cotyledon to the one-leaf growth stage or at the two- to three-leaf growth stage and to spurred anoda and smooth pigweed at the four- to six-leaf growth stage. Differential absorption, translocation, and metabolism contributed to the differential tolerance of cotton, spurred anoda, and smooth pigweed to CGA 362622. Rapid translocation and a slow rate of metabolism appear to explain the susceptibility of smooth pigweed. Reduced absorption and translocation as well as rapid metabolism contribute to the CGA 362622 tolerance of cotton at the two growth stages. Limited translocation may explain the intermediate tolerance of spurred anoda to CGA 362622. Nomenclature:u2003CGA 362622, N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; cotton, Gossypium hirsutum L. GOSHI; smooth pigweed, Amaranthus hybridus L., AMACH; spurred anoda, Anoda cristata (L.) Schlecht., ANVCR.

Influence of the herbicides hexazinone and chlorsulfuron on the metabolism of isolated soybean leaf cells

Abstract The effects of the herbicides hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] and chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesulfonamide) on the metabolism of enzymatically isolated leaf cells from soybean [Glycine max (L.) Merr., cv. ‘Essex’] were examined. Photosynthesis, protein, ribonucleic acid (RNA), and lipid syntheses were assayed by the incorporation of specific radioactive substrates into the isolated soybean leaf cells. These specific substrates were NaH14CO3, [14C]leucine, [14C]uracil, and [14C]acetate, respectively. Time-course and concentration studies included incubation periods of 30, 60, and 120 min and concentrations of 0.1, 1, 10, and 100 μM of both herbicides. Photosynthesis was the most sensitive and first metabolic process inhibited by hexazinone. RNA and lipid syntheses were also inhibited significantly by hexazinone whereas the effect of this herbicide on protein synthesis was less. The most sensitive and first metabolic process inhibited by chlorsulfuron was lipid synthesis. Photosynthesis, RNA, and protein syntheses were affected significantly only by the highest concentration of this herbicide and longest exposure. Although these two herbicides may exert their herbicidal action by affecting other plant metabolic processes not examined in this study, hexazinone appears to be a strong photosynthetic inhibitor, while the herbicidal action of chlorsulfuron appeared to be related to its effects on lipid synthesis.

Biotechnology Applications in Weed Management: Now and in the Future

Publisher Summary This chapter examines the applications of biotechnology in the field of weed management. The concept of deliberately using organisms to control a pest constitutes the fundamental basis of all biological pest control systems. The bioherbicide approach employs the massive, usually annual, release of a biocontrol agent into specific weed-infested fields to infect and kill susceptible weeds. The concept of using fungi, bacteria, and even viruses as bioherbicides is biologically feasible with several host-pathogen combinations. The potential commercialization of a microbial phytopathogenic agent is dependent greatly on whether this microbe possesses properties that allow it to be handled like a chemical herbicide or not. Utilization of innovative approaches for large-scale production and stabilization under field conditions has resulted in the commercialization and registration of two fungi as mycoherbicides. Pathogen strain improvement may be also achieved by mutagenesis induced either by irradiation or by chemical treatment. This approach seems particularly promising for the selection of strains of bioherbicides that are tolerant to chemical pesticides. Increased activity of a target enzyme is a mechanism that may confer resistance to selected herbicides. The genetic manipulation of crop tolerance to herbicides is also elaborated.

Characterization of cytochrome P450-mediated bensulfuron-methyl O-demethylation in rice☆

Abstract The cytochrome P450-mediated metabolism of the herbicide bensulfuron-methyl (BSM) was investigated in rice ( Oryza sativa L., cv. Lemont) seedlings. Shoots and roots of rice seedlings were harvested at 0, 4, 8, 12, 24, and 48xa0h following treatment with 1xa0μM [ 14 C]BSM. BSM and its metabolites were extracted from plant tissues with aqueous methanol, purified by TLC, and identified by HPLC and mass spectrometry procedures using authentic metabolite standards. The major BSM metabolites identified in rice roots were: methyl- a -(4-hydroxy-6-methoxypyrimidin-2-yl)carbamoylsulfamoyl- o -toluate (M1, 4-hydroxy BSM)); methyl-( a -aminosulfonyl)- o -toluate (M2); and N -4,6-dimethoxypyrimidin-2yl urea (M4). Crude microsomal preparations from roots of 5-day etiolated rice seedlings were treated with digitonin and purified by fast protein liquid chromatography (FPLC) using Superose 12 HR gel column, phenyl superose HR5/5 column, Mono Q anion column, and Mono P chromatofocusing column. SDS–PAGE analysis showed that the purified rice P450 migrated to a single protein band with a molecular mass of about 60xa0kDa. P450 activity was determined using BSM as substrate and 4-hydroxy-BSM as a product. The optimum pH of the rice P450 catalyzing the O-demethylation of BSM was 7.2. P450 activity was inhibited in vivo and in vitro by known P450 inhibitors such as ABT, PBO, and TET and cytochrome c . Ethanol, the safeners NA and dymuron, and BSM induced the in vivo activity of the rice P450. The results of this study demonstrate that a P450-mediated O-demethylation of BSM plays an important role in the metabolism of BSM by rice seedlings.

Uptake, translocation, and metabolism of [14C]pretilachlor in fenclorim-safened and unsafened rice seedlings

Abstract The influence of the safener fenclorim and of the synergist tridiphane on the uptake, translocation, and metabolism of the herbicide pretilachlor by 15-day-old rice seedlings was studied under greenhouse conditions. Water sown rice ( Oryza sativa L., var. “Lemont”) seedlings were grown hydroponically in a nutrient solution containing 10 μ M of [ 14 C]pretilachlor and harvested following 6, 24, and 48 hr of exposure. Fenclorim and tridiphane were also used at 10 μ M in the nutrient solution when needed. The uptake of root-applied pretilachlor by control or fenclorim-treated rice seedlings increased steadily with time. Fenclorim and tridiphane significantly reduced the root uptake of pretilachlor by rice seedlings at 24 and 48 hr after application of [ 14 C]pretilachlor. TLC analysis of water-soluble extracts from rice roots and shoots revealed five major metabolites of pretilachlor. Fenclorim enhanced the metabolism of pretilachlor via conjugation to reduced glutathione (GSH) at all time intervals. This safener-induced enhancement of the glutathione-mediated metabolism of pretilachlor was coupled with a concomitant decrease in the amount of radioactivity corresponding to the parent herbicide and was more pronounced in root extracts than in shoot extracts. Tridiphane slightly reduced the formation of the glutathione conjugate of pretilachlor in both roots and shoots of treated rice seedlings only at the 48-hr time period. The effect of fenclorim on the nonenzymatic formation of the glutathione conjugate of pretilachlor was also studied. Fenclorim used over a range of concentrations (1 to 160 μ M ) increased the reactivity of pretilachlor with GSH in a concentration-dependent manner. The results of the present study show that the protection afforded by fenclorim to rice appears to result from a fenclorim-mediated reduction in the root uptake of pretilachlor and an enhancement of the metabolism of pretilachlor via enzymatic or nonenzymatic conjugation with GSH.