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Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 137-139). Also available via the Internet.

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Italian ryegrass growth and production from positionally selective applications and sublethal rates of a nonselective herbicide were compared to growth and production when treated with diuron applied preemergence as a broadcast treatment and safened by activated carbon applied over the crop row. In the positionally selective treatments, herbicide spray was directed to leave an untreated zone over the crop row at planting. Growth analysis indicated no detectable differences when Italian ryegrass safened by directed spray was compared to Italian ryegrass safened by activated carbon. The major difference between systems was greater weed control in the crop row for carbon-safened treatments. The non-safened application superimposed sublethal diuron rates over Italian ryegrass and rattail fescue grown in varying densities and proportiors. Growth analysis of monoculture stands indicated differences due to planted density, species, and herbicide, whereas growth analysis of plants grown as space-planted individuals indicated difference due to species only. Diuron at the rates applied did not affect seed yield or above ground dry weight. Soil samples were taken in crop rows where diuron was applied as directed spray or broadcast spray safened by carbon. Samples were assayed and soil profile concentrations mapped. To assist future investigators' understanding of the role rainfall plays in herbicide movement from directed applications, elementary rainfall depth and occurrence models were examined. The Markov and mixed-exponential models adequately described rainfall occurrence and depth patterns for Corvallis, Oregon. / Graduation date: 1992

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Clomazone is a herbicide used for grass weed control in paddy rice. However, label rate may not provide efficient control for some weed species. For this reason many times it is necessity to increase the rate to improve weed control efficiency. Clomazone selectivity in rice is affected for soil type, the rate of the herbicide and the cultivar used, been necessary the use of safener to protect the plants when high rates are used. Though, it is necessary to adjust those factors for better use of this technology. For this reason, it were conducted two greenhouse experiments, the first with the objective of quantify the selectivity of clomazone in sand and clay soils, to quantify the protection of the dietholate on rice plants in these soil conditions. The second experiment had the objective of verify if phorate provides similar protective effect as dietholate provides for clomazone. The results allowed to conclude that the cultivars IRGA 409 and IRGA 417 are equally sensible to clomazone. In regards of soil type, clomazone cause higher injury to rice cultivated in sandy soil. The application of dietholate allows the increase of dose of clomazone. As much in the sandy soil as in the clay soil, dietholate as treatment of seeds allowed increase of the dose of clomazone in up to three times the dose in relation to the treatment without dietholate. Organophosphate phorate is capable to act as safener for rice when clomazone is applied, with similar safening ability as dietholate, conferring to the crop capability to support higher rates of clomazone. / O herbicida clomazone é utilizado para controle de poáceas na cultura do arroz irrigado. Porém, sua dose de registro para essa cultura não proporciona controle eficiente para determinadas espécies de plantas daninhas. Assim, há a necessidade de elevar sua dose para melhorar a eficácia sobre estas espécies. A seletividade do clomazone no arroz irrigado está condicionada ao tipo de solo, à dose do herbicida e a cultivar semeada, necessitando-se o uso de protetor de plantas quando se praticam altas doses de clomazone. Entretanto, há a necessidade de adequar esses fatores para melhor uso da tecnologia. Em vista do exposto, instalaram-se dois experimentos em casa de vegetação. O primeiro, com o objetivo de quantificar a seletividade de doses de clomazone em solo com característica arenosa e argilosa e verificar a ação do protetor de plantas dietholate sobre cultivares de arroz. O segundo experimento objetivou verificar se o organofosforado phorate proporciona efeito protetor semelhante àquele proporcionado pelo dietholate. Os resultados permitiram concluir que as cultivares IRGA 409 e IRGA 417 são igualmente sensíveis ao clomazone, e respondem igualmente aos tratamentos com dietholate. Tanto no solo arenoso como no solo argiloso, o dietholate como tratamento de sementes permitiu aumento da dose de clomazone em até três vezes a dose em relação ao tratamento sem dietholate. O phorate apresenta papel protetor na cultivar de arroz IRGA 417, contra a ação do herbicida clomazone, de forma equivalente ao protetor dietholate.

Determining the basis of intraspecific herbicide tolerance was expected to be a useful way of revealing factors which are regulated by safeners in providing their protective effect. Differential tolerance to the chloroacetanilide herbicide metolachlor and the thiocarbamate herbicide EPTC was examined in 11 corn hybrids. Tolerance to one of these herbicides does not imply similar tolerance to the other. Detoxication of these herbicides in plants is mediated via conjugation with glutathione (GSH). GSH levels from 1.8 to 2.4 µmol/g fresh weight were determined for the eleven corn hybrids tested. There was no correlation between GSH content and herbicide tolerance. The monooxygenase inhibitor piperonyl butoxide (PBO) acted synergistically with EPTC on 8 of the tested corn hybrids. A Similar antagonism by the oxygen evolving compound calcium peroxide provided additional evidence for the importance of oxidative processes in EPTC tolerance which were not important in determining metolachlor tolerance. The more rapid absorption and greater accumulation of ¹⁴C-metolachlor by 'Northrup-King 9283' corn relative to 'Cargill 7567' corn at least partially explains the increased susceptibility of the former hybrid to metolachlor. The in vitro metabolism of ¹⁴C-metolachlor was similar for both hybrids. A lag in the expression of glutathione S-transferase (GST) activity during early seedling development of 'Northrup-King 9283' corn may be of additional significance in its limited tolerance to metolachlor. The safener benoxacor was effective in protecting 'Northrup-King 9283' and other susceptible corn hybrids from metolachlor injury. Benoxacor had no effect on metolachlor uptake or the rate of non-enzymatic conjugation of metolachlor. Seedlings of 'Cargill 7567' and 'Northrup-King 9283' treated with 1 µM benoxacor metabolized metolachlor to the GS-conjugate at a rate 1.7 times that of untreated seedlings. GST activity was stimulated by 35% by similar treatment. GST isozymes with metolachlor conjugating activity (GST-metolachlor activity) were found in the cytosol and microsomal fractions of corn extracts. At least two GST-metolachlor isozymes were separated by DEAE-Sepharose chromatography. The activity of both isozymes was increased by benoxacor treatment. It appears that benoxacor regulates metolachlor tolerance by inducing GST isozymes that consequently increase the rate of metolachlor detoxication. / Ph. D.

Herbicide safeners (protectants, antidotes) are used to protect crop plants from herbicide injury. Currently our understanding of the mechanisms involved in the protection of plants by safeners is not well defined; therefore, investigations were conducted to elucidate the mechanism(s) of action of the oxime ether safeners. Molecular comparisons of selected herbicide-safener combinations using computer-aided molecular modeling revealed that the chemical structures of safeners and herbicides are very similar at the molecular level; and, indicate that these compounds could bind at the same active site of the target protein or they may serve as inducers of metabolic enzymes which detoxify herbicides. Metolachlor at 10 μM and seed-applied CGA-133205 had no effect on germination while treatment with seed-applied oxabetrinil significantly reduced germination of grain sorghum. Results from experiments on ¹⁴C-acetate incorporation into lipids indicate that metolachlor and the oxime ether safeners influence lipid metabolism causing a redistribution of carbon in the lipid fractions of germinating sorghum roots. Results from studies with acetyl-CoA carboxylase indicate that this enzyme is not a target site for either metolachlor or the oxime ether safeners. Metolachlor and the oxime ether safeners enhanced glutathione levels in grain sorghum seedlings at 12 to 48 hr after imbibition was initiated with oxabetrinil being more stimulatory than metolachlor or CGA-133205. Glutathione reductase activity was also stimulated in safener-treated grain sorghum seedlings. Both safeners slightly enhanced nonenzymatic and enzymatic conjugation of metolachlor with reduced glutathione. Oxabetrinil conjugated enzymatically or nonenzymatically with reduced glutathione at a slow rate, but CGA-133205 did not. These data suggest that during the early stages of seed germination and seedling development of grain sorghum, safeners can enhance the detoxication of metolachlor by enhancing glutathione levels and enzymatic and nonenzymatic conjugation of metolachlor with glutathione. It appears that oxabetrinil and CGA-133205 are conferring protection to grain sorghum by increasing the rate of metolachlor metabolism. / Ph. D.

CGAr92194 {α-[1,3-dioxolan-2-yl-methoxy)imino]benzeneacetonitrile} is a herbicide safener that is used as a seed dressing agent (1.25 g ai/kg seeds) to protect grain sorghum [<i>Sorghum bicolor</i> (L.) Moench] against metolachlor [2-chloroi-<u>N</u>-(2-ethyl-6-methylphenyl-<u>N</u>-(2-methoxy1-methylethyl)acetamide] injury. The potential adverse phytotoxic effects and the mechanisms of the protective action of this safener were studied in laboratory experiments. Adverse phytotoxicity was assessed by comparing CGA-92194 and the herbicide safeners cyometrinil {(Z)-α[(cyanomethoxy)imino]benzeneacetonitrile} and flurazole [phenylmethyl 2-chloro-4-(trifluromethyl)-5-thiazolecarboxylate] for their effects on CO₂ fixation, protein, DNA, RNA and lipid syntheses of enzymatically isolated leaf cells of soybean [<u>Clycine max</u> (L.) Merr]. At physiological concentrations of less than 10 μM, CGA-92194, cyometrinil and flurazole were stimulatory of all metabolic processes. At 100 μM, the safeners were inhibitory of the five processes with flurazole being the most potent. The mechanisms of the safening action of CGA-92194 were studied by examining the potential interactions of this safener with metolachlor at the levels of uptake and macromolecular syntheses in enzymatically isolated leaf mesophyll protoplasts of grain sorghum. The influence of CGA-92194 on the <i>in vitro</i> reactivity of metolachlor with glutathione (GSH) and it metabolism by sorghum seedlings were also examined. When CGA-92194 and metolachlor were given simultaneously, CGA-92194 enhanced the uptake of ¹⁴C-metolachlor into the sorghum protoplasts in a concentration-dependent pattern. Thus, interference with herbicide uptake is not involved in the protective action of this safener Treatments with metolachlor and CGA-92194 in combination inhibited the incorporation of ¹⁴C-uracil, ³H-thymidine and ¹⁴C-acetate into sorghum protoplast macromolecules less than metolachlor given alone, suggesting the potential involvement of a competitive antagonism in the mechanism of action of CGA-92194. The metabolic activity and growth of sorghum seedlings grown from CGA-92194-pretreated seeds was significantly lower than that of seedlings grown from untreated seeds at 10 or 20 days after planting, The relationship of these effects of CGA-92194 to its safening action is unclear at the present time. CGA-92194 increased the <i>in vitro</i> chemica1 reactivity of metolachlor for GSH in a concentration-dependent pattern, Sorghum seedlings grown from safener-pretreated seeds enhanced ¹⁴C-metolachlor absorption and stimulated its metabolism <u>via</u> conjugation to GSH. This stimulation was reduced by tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethy1)- oxirane] a potent inhibitor of plant GSH-<u>S</u>-transference enzymes, These results indicate that a safener-induced stimulation of the spontaneous or enzymatic conjugation of metolachlor with GSH is most likely involved in the protective action of CGA-92194. It is suggested that the safening mechanism of action of CGA—92194 involves a sequence of multilevel interactions which together contribute to the overall protection of grain sorghum from metolachlor injury. / Ph. D. / incomplete_metadata