Dissipation of nicosulfuron and rimsulfuron in surface soil

Many factors influencing herbicide dissipation have been studied; however, the effect of the presence of one herbicide on another herbicide\u27s dissipation rate has not been extensively investigated. Field studies were established in 1997 and 1998 on a Sequatchie silt loam in Knoxville, TN. Treatments applied to tilled, bare ground included nicosulfuron (0.046 kg ai ha-1), rimsulfuron (0.046 kg ai ha-1), nicosulfuron (0.046 kg ai ha-1) + rimsulfuron (0.046 kg ai ha-1), and an untreated control. Samples (0-8 cm) were collected from 0 to 31 days after treatment (DAT) in 1997 and 1998. Laboratory studies were also conducted using the same soil. Soil was fortified at 50 ppb (µg g-1) nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron. Samples for the laboratory study were removed from the incubator 0, 1, 2, 3, and 7 DAT and frozen until extraction. All samples were extracted twice with 90:10 (v:v) 0.1 M aqueous ammonium carbonate/ acetone for 20 minutes. Solid phase extraction C18 and silica columns were used for sample cleanup and samples were analyzed using an HPLC. Neither rimsulfuron nor nicosulfuron dissipation was influenced by the presence of the other herbicide. Field studies in 1997 and 1998 determined that both herbicides alone and in mixture disappeared quickly. Rainfall within 12 hr of application in each year and a soil pH of 5.7 encouraged rapid degradation. In 1997, the half-life (DT50; of nicosulfuron was 5.3 d and the DT50 of rimsulfuron was 3.1 d. When the two herbicides were applied in combination, the DT50 of nicosulfuron was 4.2 d and the rimsulfuron DT50; was 3.5 d. In 1998, all DT50 were \u3c 2.2 d. Rapid degradation was observed in the soil fortification experiments with DT50 for all treatments \u3c 3.5 d

Association Genetics for Agronomic Traits in Rice and Cloning of ALS Herbicide Resistant Genes from Coreopsis Tinctoria Nutt

We have evaluated the potential of discriminant analysis (DA) to detect candidate markers associated with twelve economically important traits in a large population of unrelated U.S. and Asian inbred lines of rice. Associated marker alleles detected by DA mapped within the same genetic intervals when compared with previous traditional QTL mapping experiments that evaluated progeny derived from various controlled crosses. New markers identified by DA suggest that the procedure can also uncover relevant genetic regions not possible by standard genetic tests. With the same dataset, we also compared different modern regression approaches for selecting molecular markers associated with the twelve agronomic traits. These methods included stepwise forward regression (SFR), least angle regression (LAR) and least absolute shrinkage and selection operator (LASSO) selection. The epistatic model based on stepwise forward regression did successfully identify several interacting loci that explained a relatively high proportion of the observed variation for all the twelve agronomically important traits. Moreover, the loci identified by the epistatic model mapped within previously known QTL regions that underscores the genetic basis of the selected markers. It was concluded that stepwise forward regression with consideration for population structure, epistatic interactions, and missing data (multiple imputation) was a robust method, compared to the general linear model, to identify markers associated with complex agronomic traits. Acetolactate synthase (ALS), also known as acetohydroxy acid synthase (AHAS), which catalyzes the first step in the biosynthesis of the branched-chain amino acids valine, leucine and isoleucine in plants, is a target of five herbicide groups, including sulfonylurea and imidazolinone. A recently discovered group of Coreopsis tinctoria Nutt. mutants from the field showed high levels of resistance to both sulfonylurea and imidazolinone herbicides. In this study the mutants were compared by chemical, genetic, and molecular analyses with “normal” or wild-type Coreopsis. A phylogenetic analysis revealed that the ALS gene can serve as a useful molecular tool for evaluating evolutionary relationships among plant species. Due to pending patent applications by the Louisiana State University Agricultural Center and restrictions of patent applications, specific results from this research cannot be presented in this dissertation

Effect of weed water stress on postemergence herbicide activity

Shattercane (Sorghum bicolor (L.) Moench) and woolly cupgrass (Eriochloa villosa (Thunb.) Kunth) growing under water stress conditions suffer morphological and physiological changes that may affect the activity of postemergence herbicides. Morphological and physiological changes in shattercane and woolly cupgrass growing under different levels of water stress were determined. Leaf area expansion was the growth variable most affected in both species. Both plants exhibit decreased dry matter accumulation due to water stress treatments. Woolly cupgrass stomatal conductance was more affected by water stress than shattercane. Photosynthesis was greatly reduced in both weeds, but only partially related to decreased stomatal conductance, indicating the possibility than non-stomatal factors superimpose their action on stomatal control, thus reducing the carbon exchange rate. Maximum accumulation of epicuticular wax was determined for shattercane and woolly cupgrass plants growing under moderate water stress conditions (-0.4 MPa of soil water potential). Abscisic acid content of shattercane and woolly cupgrass leaves and indole-3-acetic acid content of woolly cupgrass leaves increased with increasing intensity and duration of water stress. Additionally, the effect of differential water status on the activity, retention, uptake, and translocation of nicosulfuron (2-(((4,6-dimethoxypyrimidin-2-yl) aminocarbonyl) aminosulfonyl) -N,N-dimethyl-3-pyridinecarboxamide), and primisulfuron-methyl (3-(4,6-bis-(difluoromethoxy) -pyrimidin-2-yl) -1-(2-methoxycarbonylphenylsulfonyl)urea) was studied. Maximum herbicide activity was demonstrated on well-watered plants. Increasing plant water stress reduced herbicide activity in both species. Shattercane uptake of nicosulfuron and primisulfuron-methyl was not affected by soil water potential. However, woolly cupgrass uptake of both herbicides was affected by soil water potential, demonstrating reduced herbicide absorption due to water stress. Both species accumulated herbicides in the cuticles. The total amount of herbicide translocated was significantly affected by water stress treatments in both species

Glyphosate resistance in annual ryegrass (Lolium rigidum Gaud.) with multiple resistance mechanisms.

Glyphosate (N-(phosphonomethyl)glycine) is a post-emergent, systemic and non-selective herbicide for the control of annual and perennial weeds. This herbicide has very low toxicity to the mammals. The target enzyme for glyphosate in plants is 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Glyphosate inhibits the biosynthesis of the aromatic amino acids phenylalanine, tyrosine and tryptophan in the plant. The first case of glyphosate resistance was reported in Lolium rigidum in Australia after 15 years of persistence use of this herbicide and the number weeds reported resistant to glyphosate has increased around the world. So far, two mechanisms known to be involved in resistance to glyphosate are target-site mutation and reduced herbicide translocation. Recently, two populations of L. rigidum from Australia have been discovered with very high levels of resistance to glyphosate. This project aims to determine the levels of glyphosate resistance in these populations, investigate glyphosate resistance mechanisms in the populations and finally assess the mode of inheritance of resistance. In this project, four resistant (NLR70, SLR77, SLR80 and SLR88) and one susceptible (VLR1) L. rigidum populations were evaluated for their response to glyphosate. From the dose response experiments, the susceptible population of VLR1 was completely controlled with the recommended rate of glyphosate (450 g a.e ha⁻ ¹). In contrast, the resistant populations were not fully controlled by this herbicide rate. There was considerable variation between the populations in their resistance to glyphosate. In comparison to the susceptible population VLR1, SLR77 was 2.2 to 3.5 fold resistant to glyphosate, NLR70 was 3.7 to 8.4 fold resistant to glyphosate, SLR88 was 5.6 to 11.4 fold resistant to glyphosate and SLR80 was 8.2 to 76.7 fold resistant to glyphosate. The mechanism of glyphosate resistance in the populations was investigated. ¹⁴ C-glyphosate was used to determine the absorption and translocation of glyphosate among the populations. There was no significant difference on the absorption of ¹⁴ C-glyphosate 48 hours after treatment in the population. However, the accumulation of ¹⁴ C-glyphosate in the stem region was higher in the susceptible VLR1 population (25.9%) and in resistant SLR77 (25%) than the other three populations. The resistant populations NLR70, SLR88 and SLR80 had about half the amount of glyphosate accumulating in the stem region. These three resistant populations appear to be resistant to glyphosate as a result of reduced translocation of glyphosate to the shoot meristem. Part of the EPSP synthase gene of the susceptible and four resistant populations was amplified and sequenced to identify any changes in the nucleotide sequence. The predicted amino acid sequence from the susceptible population VLR1 was the same as the consensus sequence from other plant species in the conserved region sequenced. However, the resistant populations of NLR70, SLR77, SLR80 and SLR88 showed polymorphisms within the nucleotide sequence in this region. Single nucleotide substitutions of A for C at codon 106 were observed in the resistant populations SLR77 and SLR80. This nucleotide change is predicted to substitute threonine for proline at position 106. In the resistant population SLR88, a nucleotide substitution of T for C was observed at the same codon. This nucleotide substitution is predicted to change the amino acid from proline 106 to serine. Therefore, these three populations appear to be resistant to glyphosate as a result of a target-site mutation. An inheritance study was conducted by cross pollinating the susceptible VLR1 and resistant SLR88 population. From the dose response, the parent susceptible was completely killed with the recommended rate of glyphosate and higher rates of glyphosate were required to control parental resistant and both F₁ progenies (maternal susceptible and resistant). Both F₁ progenies showed an intermediate response to glyphosate compared with the parental populations. This indicated that the resistance to glyphosate in population SLR88 is inherited by nuclear gene(s) through the transfer of pollen during the cross pollination. It is suggested that SLR88 and SLR80 population contain both glyphosate resistant mechanisms due to the cross pollination between individuals with different resistant mechanisms. Having two resistant mechanisms results in populations being highly resistant to glyphosate compared to those with one resistance mechanism. The higher level of glyphosate resistance in these multiple glyphosate resistance populations will likely make them harder to manage.Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 201

Control of Italian ryegrass (Lolium perenne L. spp. multiflorum Lam. Husnot) in wheat (Triticum spp.) and evaluation of resistance to acetyl-CoA carboxylase inhibiting herbicides

Control of Italian ryegrass is important to Tennessee wheat producers. Control of Italian ryegrass has become more difficult over the years due to diclofop resistance. Italian ryegrass resistance to diclofop has been documented in several countries including the US. Tennessee producers have begun to notice that ryegrass escapes are becoming more prevalent than in years past. The purpose of this research was to use glasshouse methods to screen selected populations of Italian ryegrass for resistance to diclofop and to a more recent wheat herbicide pinoxaden and to utilize field experiments to develop herbicide programs for control Italian ryegrass in the field. Resistance to diclofop was found in eight TN populations. The eight populations did not show cross-resistance to pinoxaden. One population from Union County, NC (R1) was found to be resistant to both diclofop and pinoxaden. The level of resistance to pinoxaden of the R1 population was 14 x that of the susceptible population.Field experiments demonstrated preemergence (PRE) Italian ryegrass control with chlorsulfuron (71 to 94%) and flufenacet + metribuzin (84 to 96%). Italian ryegrass control with pendimethalin applied PRE or delayed preemergence (DPRE) was variable (0 to 85%). Postemergence control of Italian ryegrass was good with pinoxaden, mesosulfuron, flufenacet + metribuzin, and chlorsulfuron + flucarbazone (\u3e80%). Timing of application and herbicide treatment had no effect upon wheat yield, except for diclofop and pendimethalin treatments where Italian ryegrass was not controlled. Pinoxaden is in the phenylpyrazolin herbicide family which offers control of Italian ryegrass but is not toxic to wheat. Pinoxaden has only been on the market for three years yet several wheat producers have suspected resistance in Italian ryegrass biotypes.An experiment was conducted to identify Italian ryegrass biotypes resistant to pinoxaden and to determine the mechanism of resistance using derived Cleaved Amplified Polymorphic Sequence (dCAPS) methods. Two populations were found resistant to pinoxaden, one from the state of Washington (R2) and the other from North Carolina (R1). The substitution of isoleucine by leucine at the 1781 ACCase residue was identified in the R1 biotype but not in the R2. The NC1 biotype is the first known pinoxaden resistant Italian ryegrass population to be documented having the 1781 target-site mutation

Ecological, Physiological, and Molecular Characterization of Annual Bluegrass (Poa annua L.) Herbicide Resistance and Its Control on Golf Courses

Annual bluegrass (Poa annua L.) is one of the most pervasive, adaptable, and variable plant species in the world and is the most problematic winter annual weed in managed turfgrass. Its prolific seedhead production regardless of mowing height, clumping growth habit, and lack of tolerance to stress reduces turfgrass aesthetic quality and playability on golf courses. Its ability to germinate almost year-round influences cultural practices and herbicide use. Herbicides are an integral part of a weed control program for all weeds that invade a desirable turfgrass stand. However, inappropriate use of herbicides results in herbicide resistance issues. In recent years, the number of annual bluegrass populations on golf courses resistant to herbicides has increased. Currently, this weed is resistant to 9 mechanisms of action worldwide. Most recently, resistance has evolved to acetolactate synthase (ALS) inhibitors and glyphosate, both of which are integral herbicides for annual bluegrass control. Therefore, the purpose of this research was to investigate ecological, physiological, and molecular characteristics of resistance to these herbicides in order to increase the understanding of annual bluegrass herbicide resistance. Studies included diagnosing resistant biotypes, assays of enzyme activity, DNA sequencing, and simulation modeling. Beyond the issue of herbicide resistance, control remains difficult in all commercial turfgrass situations. Additional studies investigated annual bluegrass control in creeping bentgrass putting greens and bermudagrass fairways overseeded with perennial ryegrass with current and experimental herbicides and plant growth regulators to determine best management practices for controlling annual bluegrass. To diagnose resistance to ALS-inhibiting herbicides in biotypes from South Carolina and Georgia, dose-response experiments and ALS activity assays were conducted on mature annual bluegrass plants using trifloxysulfuron, foramsulfuron, and bispyribac-sodium. For dose-response experiments, I50 values for susceptible (S) biotypes were 13.6 g ai ha-1 for trifloxysulfuron, 7.0 g ai ha-1 for foramsulfuron, and 38.3 g ai ha-1 for bispyribac-sodium. Fifty percent shoot biomass reduction was not observed in either the South Carolina (CI) or Georgia (FP) biotypes at eight times the labeled field rate of all ALS-inhibiting herbicides tested. For in vivo tests of ALS activity, the CI biotype yielded I50 values 3650, 3290, and 13 times S biotypes following treatment with trifloxysulfuron, foramsulfuron, and bispyribac-sodium, respectively. Similarly, I50 values for the FP biotype were 316, 140 and 64 times greater than S biotypes following the same herbicide treatments. This confirms high levels of annual bluegrass resistance to multiple ALS-inhibiting herbicides in South Carolina and Georgia. Further investigations into enzyme and growth characteristics of ALS-resistant annual bluegrass were conducted with a biotype from Alabama (GN) containing a mutation in the ALS gene resulting in a Trp574 to Leu amino acid substitution. Compared to the susceptible (VS) biotype, the GN biotype exhibited a 27- and 10-fold resistance to trifloxysulfuron at the whole plant level and under in vitro conditions, respectively. No significant differences were observed in Km (pyruvate) or extractable ALS activity between biotypes, but the Vmax was higher for the GN biotype. The feedback inhibition of ALS activity by the branched-chain amino acids was higher for the GN biotype than the VS biotype, with leucine, valine, and isoleucine inhibiting ALS activity 20, 6, and 4% more in the R biotype, respectively. The GN biotype produced more inflorescences and seeds per plant in comparison with the VS biotype, but relative growth rates between biotypes were similar at all harvest intervals. This provides baseline information regarding ALS enzyme response, vegetative growth, and reproduction characteristics of annual bluegrass biotypes resistant and susceptible to ALS-inhibiting herbicides. Glyphosate is used in the transition zone to control annual bluegrass in fully dormant warm-season grasses. A suspected resistant (CN) biotype of annual bluegrass was identified on a golf course in South Carolina after at least 10 consecutive years of glyphosate application. Resistance was confirmed after 4.4 times more glyphosate was required to reduce growth 50% compared to a standard susceptible (VS) biotype. Further studies were conducted to determine the mechanism conferring glyphosate resistance in the CN biotype. Leaf discs of both biotypes accumulated shikimate in response to increasing glyphosate concentration, but the I50 for EPSP synthase inhibition in the CN biotype was 3.5-fold higher than the S biotype. At the whole plant level, similar levels of shikimate accumulation were observed between biotypes at 6 and 24 hours after treatment (HAT) with glyphosate, but greater shikimate accumulation occurred in the VS biotype at 72, 120, and 168 HAT. Shikimate levels decreased in the CN biotype after 72 HAT. There were no differences in 14C-glyphosate uptake between biotypes. However, more 14C-glyphosate translocated out of the treated leaf in the CN biotype and into root tissues over time compared to the VS biotype. Partial sequencing of the EPSP synthase gene revealed a heterozygous mutation at Pro106 which resulted in a substitution of Ala. These results represent the first documentation of a Pro106 to Ala substitution as the mechanism of glyphosate resistance in annual bluegrass and the first report of glyphosate-resistant annual bluegrass in South Carolina. A basic simulation model was developed for the evaluation of herbicide resistance evolution in golf course populations of annual bluegrass, to understand key biological parameters of annual bluegrass which result in high resistance risks, to evaluate several annual bluegrass management programs for golf course fairways and their relative risks for selecting resistance, and to compare two herbicides (i.e., glyphosate and ALS-inhibitors) to determine how their respective characteristics influence resistance evolution in turfgrass systems. Annual bluegrass biological characteristics, typical turfgrass weed management strategies, and several genetic parameters were used in the simulations. Values and ranges for parameters were determined via review of the literature and field observations. In these simulations, the first population with evolved herbicide resistance was predicted after 5 and 9 yr of annual use of ALS-inhibitors and glyphosate, respectively. Several herbicide use strategies were subsequently simulated to assess their potential for managing resistance and included using alternate mechanisms of action in rotation or using these herbicides in combination with PRE or POST herbicides for early annual bluegrass control. The most effective use strategy for glyphosate was rotating mechanism of action. In comparison, the most effective resistance management strategy for ALS-inhibitors was applying a PRE or POST herbicide for early control followed by rotating ALS-inhibitors with an alternate mechanism of action in late winter. Regardless of which strategy was used, \u3e90% resistance risk was predicted for either herbicide after 40 years. Biological parameters including seed bank density, annual germination proportion, and seed removal had significant influence on resistance evolution. These simulations suggest annual bluegrass population dynamics contribute to its propensity to develop herbicide resistance and highlight the need for integrated control programs to manage resistance. Field trials in creeping bentgrass putting greens revealed the best currently labeled annual bluegrass management options is multiple applications of paclobutrazol in fall and spring. This provided 70%. All methiozolin treatments provided \u3e70% control after two years at two locations, but this herbicide is not currently registered for use. When it becomes registered, the best program in the transition zone will be multiple applications at low rates during the fall and spring. All other treatments failed to provide satisfactory control or seedhead suppression. In overseeded ryegrass, methiozolin and amicarbazone either did not consistently control annual bluegrass or damaged ryegrass beyond an acceptable threshold. Single herbicide applications in overseeded ryegrass will not provide acceptable control. The best program consists of a preemergence herbicide, an early postemergence application with a sulfonylurea herbicide, and a postemergence application with either ethofumesate or bispyribac-sodium. In summary, annual bluegrass remains as the most problematic weed for managed turfgrasses. Herbicide resistance to many mechanisms of action increases the difficulty of control of this weed. There are only three labeled mechanisms of action for turfgrass where annual bluegrass has not evolved resistance. Thus, turfgrass managers must use integrated programs to prevent resistance from developing. Where resistance to a single herbicide exists, it is of utmost importance to develop sound herbicide use practices such that multiple resistance will not evolve. Future research should continue to investigate herbicide resistant populations of annual bluegrass, management programs which are best suited to delay or prevent resistance, and new herbicides which provide alternative mechanisms of action for its control

Dispersal and genetic variability of Sonchus oleraceus L. in relation to its resistance to ALS-inhibiting herbicides.

The work described in this thesis investigates the existence and level of acetolactate synthase (ALS)-inhibiting herbicide resistance in Sonchus oleraceus in Australia. It further discusses the sensitivity of different S. oleraceus populations to different dose rate treatments of the ALS-inhibiting herbicide, chlorsulfuron. Thirdly the movement or not of the resistance gene between S. oleraceus plants. Gene movement is investigated in light of S. oleraceus being self pollinated and possessing a wind dispersed seed. Finally using molecular tools the genetic diversity and seed movement in S. oleraceus is investigated. Although much is known about the evolution of plant based genetic resistance to herbicides there is less known as to the specific resistance gene movement in differing weed species. The first approach undertaken in this study was to collect a broad spectrum of S. oleraceus seed from a number of Australian states and test the progeny from this seed for resistance to chlorsulfuron. Subsequent to this DNA extractions were made from S. oleraceus plant material for use in AFLP and sequencing techniques. The results of this study indicate that ALS-inhibiting herbicide resistance to chlorsulfuron in S. oleraceus is now widespread in Australia. The movement of the resistance gene within populations is low (<4%), however, population dendrograms indicate seed has been dispersed across large distances in Australia facilitating the movement of the resistance gene. In addition sequence analysis indicates numerous independent mutation events. With the identification of previously unknown levels of resistance in Australia and gene movement knowledge, extension of improved management practises is possible.Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 201