Thesis (Ph. D.)--University of Idaho, 2005. / Also available online in PDF format. Abstract. "December 2005." Includes bibliographical references.

Thesis (Ph.D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Field and greenhouse experiments were conducted in 2008, 2009, and 2010 to evaluate the efficacy of glyphosate combined with other broadleaf herbicides on herbicide-resistant and -susceptible weeds in Illinois. In the field, the addition of lactofen or fomesafen to glyphosate provided the greatest consistency and control of problematic target weeds including common waterhemp and giant ragweed. Applications of glyphosate tank-mixtures at EPOST provided 10% greater control of giant ragweed compared with the same treatments at POST. The addition of a tank-mix herbicide with glyphosate provided the greatest impact on weed control when applied to glyphosate-resistant common waterhemp with control increasing by 67% compared with glyphosate applied alone. The addition of a tank-mix herbicide with glyphosate had little impact on control of PPO-resistant and herbicide-susceptible common waterhemp. Generally, the addition of an adjuvant to herbicide mixtures with glyphosate did not influence weed control 14 DAT compared with no additional adjuvant. However, the addition of PO-HSOC and SO-HSOC to glyphosate tank-mixtures containing fomesafen and cloransulam increased annual morningglory control compared with no additional adjuvant. In the greenhouse, PPO-inhibiting herbicides (fomesafen, lactofen, flumiclorac, fluthiacet) applied with glyphosate resulted in additive and antagonistic responses depending on the PPO-inhibitor used and the common waterhemp biotype. Generally, glyphosate tank-mixtures applied to PPO-resistant and herbicide-susceptible common waterhemp biotypes resulted in a greater frequency of antagonism than that of a glyphosate-resistant biotype. The efficacy of glyphosate tank-mixtures was also influenced by environmental conditions shortly before and after the herbicide application. Glyphosate tank-mixtures usually resulted in greater efficacy on common waterhemp when applied at 24 C with 75% RH than at 32 C with 40% RH, regardless of tank-mix herbicide or common waterhemp biotype. Although this research supports an improvement in control of glyphosate-resistant common waterhemp with the addition of PPO-inhibiting herbicides to glyphosate, the overall herbicide efficacy was still somewhat variable with evidence for environmental conditions that may alter efficacy of the tank mixtures. Thus, the use of preemergence, soil residual herbicides are still justified to reduce reliance on these postemergence herbicide mixtures for weed control in soybean and ultimately deter further selection of common waterhemp populations resistant to glyphosate and PPO-inhibiting herbicides.

Doctor of Philosophy / Department of Agronomy / Kassim Al-Khatib / Growth chamber, greenhouse and field experiments using conventional grain sorghum were conducted to 1) evaluate the differential response of grain sorghum hybrids to POST application of mesotrione at various rates and application timings, and 2) determine the physiology of tolerance of grain sorghum hybrids to mesotrione. Sorghum response ranged from susceptible to tolerant. Mesotrione dose-response studies on four sorghum hybrids revealed that injury symptoms were greatest in Pioneer 85G01 and least in Asgrow Seneca. Mesotrione applied EPOST (early POST) injured sorghum more than when applied at MPOST (mid POST) or LPOST (late POST) timings. Observed injury symptoms were not well correlated with grain yield and were transient, thus injury did not reduce sorghum grain yield. Foliar absorption or translocation of mesotrione in tolerant hybrids did not differ with that of susceptible hybrids but metabolism was more rapid in tolerant than in susceptible hybrids. Initial grain sorghum injury was severe and will likely be a major concern to producers. Field and growth chambers studies were conducted on herbicide-resistant grain sorghum to 1) determine the effect of quizalofop rates, application timings, and herbicide tank mixes on acetyl-coenzyme A carboxylase (ACCase)-resistant grain sorghum injury and yield, and 2) determine if herbicide metabolism is an additional mechanism that could explain the resistance of ACCase- and acetolactate synthase (ALS)-resistant grain sorghum. Depending on rate, EPOST application caused the greatest injury while the least injury occurred with LPOST application. Crop injury from quizalofop was more prominent at rates higher than the proposed use rate (62 g ha [superscript]-1) in grain sorghum. Sorghum grain yield was not affected by quizalofop regardless of rates or application timings. Weed control was greater when quizalofop was applied with other herbicides than when applied alone. Herbicide treatments except those that included 2,4-D caused slight to no sorghum injury. Results of the quizalofop metabolism study do not support the involvement of differential metabolism in the observed response of grain sorghum to quizalofop. Rimsulfuron metabolism by ALS-resistant sorghum is more rapid than the susceptible genotypes, thus explaining the observed rapid recovery of grain sorghum plants from rimsulfuron injury in the field.

No abstract available. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009. / Submitted to the African Centre for Crop Improvement. Full text also available online. Scroll down for electronic link.

Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming

Weed infestation is one of the yield limiting factors in crop production. Weeds have negative effect on crop growth and productivity due to competition, allelopathy or hosting other harmful organisms. For large-scale wheat production, the use of wide spectrum pre-emergence or post-emergence herbicides remains the most valuable weed control tool. In South Africa, annual grass weeds are a major wheat production constraint, which is usually managed through application of pre-emergence herbicides. Due to limited water availability and low soil moisture content, these herbicides can often become ineffective and result into high weed infestations, which then have to be managed by manual cultivation or post-emergence herbicidal applications. However, there are no effective selective post-emergence herbicides available to control grass weeds in wheat. There is also limited option to use broad-spectrum post-emergent herbicides because they non-selectively kill the crop and weeds. Consequently, the use of herbicide resistant crops is a viable weed management system in wheat production. Breeding herbicide resistant crop varieties would allow farmers to safely use post-emergence herbicides without damaging the crop. Subsequently yield and quality losses will be reduced significantly. Thus, the development of herbicide resistant crop varieties through mutation breeding is a novel approach for effective weed management under both small-scale and commercial farmers. Mutagenesis has been recognized as one of the most efficient method to induce genetic variation in plants. Through induced mutations, development of new variants is possible that could be manipulated in plant breeding programs. Mutation leads to alteration of various traits in crop plants including plant height, improved nutritional quality, shorter growing period, increased tolerance or resistance to abiotic and biotic stresses. Ethylmethanesulphonate (EMS) is one of the most widely used chemical mutagens to induce mutagenesis in crop plants. The objectives of this study were to: 1) determine the optimum EMS concentration, treatment temperature and duration that would provide desired germination percentage and vigorous and healthy seedlings for effective mutagenesis in wheat, 2) investigate variations in agro-morphological traits in two selected wheat varieties (SST56 and SST875) after EMS mutagenesis and 3) select herbicide resistant wheat germplasm after inducing genetic variation using EMS using two selected wheat varieties (SST56 and SST875). The objectives were achieved through three independent studies as outlined below: In the first study seeds of four selected wheat varieties (B936, B966, SST387 and SST875) were treated in two replicates with three EMS concentrations (0.3, 0.5, and 0.7%), three temperature regimes (30, 32.5 and 35 °C) at four time durations (0.5, 1, 1.5 and 2 hrs). Results showed highly significant interactions (P<0.01) among varieties, EMS concentrations, temperature and exposure time on seedling emergence, germination and seedling height. Seeds treated with the highest EMS dose (0.7%), temperature (35ºC) and long exposure time (2 hr) showed delayed emergence by 18 days. At 30ºC, 0.5hr and 0.3% EMS varieties B936, B966 and SST875 had early emergence (6 days). B936 and SST387 had 50% while B966 and SST875 had 53% and 57% germination, respectively. These results were observed at EMS level of 0.7%, 300C and 1.5 hr exposure time in B936 and EMS at 0.5%, 350C and 1.5 hr in B966. SST387 and SST875 required EMS dose at 0.5%, 32.50C and 2 hr treatment time. Other low or high treatment combinations were invariably ineffective comparedto untreated control. During the second study two selected varieties (SST56 and SST875) were subjected to EMS mutagenesis using 0.5% v/v EMS at 32.5oC for 1 hr. Field trials were carried out at Ukulinga research farm of the University of KwaZulu-Natal in the randomized complete block design with two replicates. Data on nine important agro-morphological traits were collected and analyzed using the analysis of variance (ANOVA), correlation and principal component analysis (PCA) procedures. Significant variations were found among the agro-morphological traits between M1 individuals compared to untreated checks. The mutagenesis significantly reduced seed germination in the field at 40% in both varieties. The treatment significantly delayed days to heading by 8 days and shortened days to maturity by 13 days in both varieties. EMS treatment also significantly reduced plant height at 18 cm in SST56 and 21 cm in SST875 and spike length reduced by ~2.5 cm in both varieties. Plant height had positive and significant correlation with number of tillers, number of seeds per spike, flag leaf length and 100 seed weight. However, it had negative correlation with the number of days to maturity. The PCA revealed that three principal components (PC1, PC2 and PC3) accounted to 57% of the total variations among the agro-morphological traits in both varieties. PC1 alone contributed to 27.7% of the variation which was well-correlated with plant height (0.767), tiller number (0.812), number of seeds per spike (0.599) and seed yield (0.720). PC2 explained 15.6% of the variation and well-correlated with germination percentage (0.784), spike length (0.554) and flag leaf length (0.772). PC3 accounted to 12.4% of the variation and had negative correlation with days to maturity (-0.730). In the last study, seeds of two selected wheat varieties (SST56 and SST875) were treated with EMS at 0.5% concentration for 2 hr at 32.5ºC. Treated seeds and comparative controls were planted at the experimental farm of the University of KwaZulu-Natal using the randomized complete block design. Four weeks after planting M1 plants and untreated standard checks were sprayed with two herbicides, i.e. metsulfuron-methyl and bromoxynil at three different doses viz. 2x, 4x and 8x above the recommended rate of 4 g ha-1 and 2 kg ha-1, respectively. Two weeks after the treatment herbicide resistance were assessed. Results showed significant difference among varieties, tested herbicides and doses used. The EMS treated wheat lines showed variable degree of herbicide resistance compared to untreated controls. Overall, the study established the requirement of variety specific EMS dose and treatment temperature and duration that could be used for inducing large-scale mutation to select targeted mutant individuals in wheat. Further, the study found that EMS has the potential to increase agro-morphological variations in wheat to select useful and novel mutants with desired phenotypic traits and herbicide resistance which will be subjected for further selections to identify stable and herbicide resistance lines. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Crop production provides the food and fiber necessary to sustain the world\'s population. Effective weed management is critical to maintaining agricultural productivity. Intensive or continuous use of herbicides that act on the same target site, or are detoxified by similar processes within crops and target weeds frequently results in the development of weeds resistant to a specific herbicide or class of herbicides. Weed resistance due to the extensive use of glyphosate in glyphosate tolerant crop systems has become one of the most serious issues facing agriculture today. Thus PPO-inhibitor herbicides are an alternative mechanism of action that have the potential to mitigate the development of resistant weeds in weed control systems where crop tolerance is sufficient to allow them to be effectively deployed. While there are few reports of weed resistance to PPO-inhibitor herbicides it has not developed to the extent that it is a commercial problem for growers. When used at recommended doses, they typically have favorable regulatory profiles. Furthermore, most of them are highly compatible with no-tillage agriculture. However, PPO-inhibitor herbicides are typically more active on dicots than monocots. This thesis provides information with regards to effectiveness of certain binary mixtures of PPO herbicides as weed control agents. The mixtures showed synergistic effects and could control monocots as Echinochloa crus-galli and volunteer corn besides control the dicots species. Regarding the compounds studied, trifludimoxazin and flumioxazin required less amount of compound to inhibit 50% of PPO2 activity in all plants species tested, while sulfentrazone and saflufenacil, one of the best mixtures in the field, showed that needed bigger concentrations to inhibit 50% of the PPO2 compared to other compounds evaluated.The absorption and translocation of these compounds individually or in mixtures, showed that as single compounds, the absorption was slower in maize than E. crus-galli and there was no difference among the herbicides except trifludimoxazin, that was significantly lower than the other compounds. Saflufenacil was the herbicide that showed the best translocation out of treated leaf point, while trifludimoxazin has not shown any translocation out of leaf treated. In mixtures, the compounds showed some differences in absorption and translocation, which it was variable according to species studied. Some traits of PPO-tolerant were also evaluated in Arabidopsis thaliana which indicates potential traits to be developed in crops of interest. / Agricultura é responsável por fornecer alimento e fibras necessárias para sustentar a população mundial. Controle de plantas daninhas é essencial para obter uma boa produtividade. O uso intensivo de herbicidas que age no mesmo sitio de ação ou são detoxificados por processos similares pelas plantas daninhas resulta geralmente no desenvolvimento de plantas daninhas resistentes a um herbicida específico ou à uma classe de herbicidas. A resistência de plantas daninhas devido ao uso de culturas tolerantes à glifosato tem se tornado um dos mais sérios problemas na agricultura. Inibidores da PPO pode ser uma ferramenta para mitigar o desenvolvimento de plantas daninhas resistentes. Há poucos relatos de plantas daninhas resistentes a este mecanismo de ação. Quando aplicados na dose recomendada, apresentam perfil toxicológico favorável e além disso, a maioria dos herbicidas deste grupo são compatíveis com plantio direto. No entanto, são mais eficientes em dicotiledôneas do que em monocotiledôneas. O objetivo dessa tese foi fornecer informações em relação a associação binária de herbicidas inibidores da PPO no controle de plantas daninhas. As associações mostraram efeito sinérgico no controle de Echinochloa crus-galli e milho voluntário, além do controle de dicotiledôneas. Avaliou-se também a atividade de alguns inibidores da PPO na inibição de 50% da enzima PPO2 e observou-se que para inibir 50% da PPO2 necessitou de menor quantidade de trifludimoxazin e flumioxazin em todas as plantas testadas, enquanto que sulfentrazone e saflufenacil, que associados apresentaram a melhor eficácia nos ensaios de campo, mostraram que precisar de maiores concentrações para inibir a PPO2 comparada aos outros produtos. A absorção e translocação destes produtos, isolados ou em mistura, mostraram que a absorção foi mais lenta em milho do que em E. crus-galli. Os herbicidas apresentaram comportamentos similares, sendo absorvidos quase 95% até 72 horas após aplicação, com exceção do trifludimoxazin, que foi significativamente mais lento que os outros. Saflufenacil foi o herbicida que apresentou melhor translocação na folha aplicada, enquanto trifludimoxazin não apresentou nenhuma translocação. Em relação às associações, os produtos mostraram diferenças na absorção e translocação, variando conforme as plantas daninhas estudadas. Alguns eventos tolerantes a inibidores da PPO foram avaliados em Arabidopsis thaliana e indicaram como potenciais eventos para ser desenvolvidos nas culturas de interesse.

Crop production provides the food and fiber necessary to sustain the world\'s population. Effective weed management is critical to maintaining agricultural productivity. Intensive or continuous use of herbicides that act on the same target site, or are detoxified by similar processes within crops and target weeds frequently results in the development of weeds resistant to a specific herbicide or class of herbicides. Weed resistance due to the extensive use of glyphosate in glyphosate tolerant crop systems has become one of the most serious issues facing agriculture today. Thus PPO-inhibitor herbicides are an alternative mechanism of action that have the potential to mitigate the development of resistant weeds in weed control systems where crop tolerance is sufficient to allow them to be effectively deployed. While there are few reports of weed resistance to PPO-inhibitor herbicides it has not developed to the extent that it is a commercial problem for growers. When used at recommended doses, they typically have favorable regulatory profiles. Furthermore, most of them are highly compatible with no-tillage agriculture. However, PPO-inhibitor herbicides are typically more active on dicots than monocots. This thesis provides information with regards to effectiveness of certain binary mixtures of PPO herbicides as weed control agents. The mixtures showed synergistic effects and could control monocots as Echinochloa crus-galli and volunteer corn besides control the dicots species. Regarding the compounds studied, trifludimoxazin and flumioxazin required less amount of compound to inhibit 50% of PPO2 activity in all plants species tested, while sulfentrazone and saflufenacil, one of the best mixtures in the field, showed that needed bigger concentrations to inhibit 50% of the PPO2 compared to other compounds evaluated.The absorption and translocation of these compounds individually or in mixtures, showed that as single compounds, the absorption was slower in maize than E. crus-galli and there was no difference among the herbicides except trifludimoxazin, that was significantly lower than the other compounds. Saflufenacil was the herbicide that showed the best translocation out of treated leaf point, while trifludimoxazin has not shown any translocation out of leaf treated. In mixtures, the compounds showed some differences in absorption and translocation, which it was variable according to species studied. Some traits of PPO-tolerant were also evaluated in Arabidopsis thaliana which indicates potential traits to be developed in crops of interest. / Agricultura é responsável por fornecer alimento e fibras necessárias para sustentar a população mundial. Controle de plantas daninhas é essencial para obter uma boa produtividade. O uso intensivo de herbicidas que age no mesmo sitio de ação ou são detoxificados por processos similares pelas plantas daninhas resulta geralmente no desenvolvimento de plantas daninhas resistentes a um herbicida específico ou à uma classe de herbicidas. A resistência de plantas daninhas devido ao uso de culturas tolerantes à glifosato tem se tornado um dos mais sérios problemas na agricultura. Inibidores da PPO pode ser uma ferramenta para mitigar o desenvolvimento de plantas daninhas resistentes. Há poucos relatos de plantas daninhas resistentes a este mecanismo de ação. Quando aplicados na dose recomendada, apresentam perfil toxicológico favorável e além disso, a maioria dos herbicidas deste grupo são compatíveis com plantio direto. No entanto, são mais eficientes em dicotiledôneas do que em monocotiledôneas. O objetivo dessa tese foi fornecer informações em relação a associação binária de herbicidas inibidores da PPO no controle de plantas daninhas. As associações mostraram efeito sinérgico no controle de Echinochloa crus-galli e milho voluntário, além do controle de dicotiledôneas. Avaliou-se também a atividade de alguns inibidores da PPO na inibição de 50% da enzima PPO2 e observou-se que para inibir 50% da PPO2 necessitou de menor quantidade de trifludimoxazin e flumioxazin em todas as plantas testadas, enquanto que sulfentrazone e saflufenacil, que associados apresentaram a melhor eficácia nos ensaios de campo, mostraram que precisar de maiores concentrações para inibir a PPO2 comparada aos outros produtos. A absorção e translocação destes produtos, isolados ou em mistura, mostraram que a absorção foi mais lenta em milho do que em E. crus-galli. Os herbicidas apresentaram comportamentos similares, sendo absorvidos quase 95% até 72 horas após aplicação, com exceção do trifludimoxazin, que foi significativamente mais lento que os outros. Saflufenacil foi o herbicida que apresentou melhor translocação na folha aplicada, enquanto trifludimoxazin não apresentou nenhuma translocação. Em relação às associações, os produtos mostraram diferenças na absorção e translocação, variando conforme as plantas daninhas estudadas. Alguns eventos tolerantes a inibidores da PPO foram avaliados em Arabidopsis thaliana e indicaram como potenciais eventos para ser desenvolvidos nas culturas de interesse.