Response of Corn and Palmer amaranth to Mesotrione

Mesotrione is a herbicide used for the selective pre- and post-emergence control of a wide range of broadleaf and grass weeds in corn (Zea mays). It inhibits the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD) which leads to stop biosynthesis of plastoquinone, a key factor in the synthesis of carotenoid pigment. The depletion of carotenoids leading to bleaching symptoms followed by necrosis in sensitive plants. Palmer amaranth (Amaranth Palmeri) is one of the major weeds in corn production system. This study was conducted to test the hypothesis that mesotrione may be effective to control Palmer amaranth and safe for use in corn. Therefore, the objective of this research was to evaluate response of corn and Palmer amaranth to mesotrione. Corn and Palmer amaranth plants were treated with mesotrione at 105 g ai ha-1,and plant survival data was collected at 3 week after application. There was no injury reported to any of the corn plant, and plant survival rate was reported 100%. However, Palmer amaranth plants showed bleaching symptoms followed by necrosis and plant death. Only 12.5% Palmer amaranth plants survived after mesotrione application. These results demonstrated the tolerance of corn and sensitivity of Palmer amaranth to mesotrione

Dose Responses of Silvery-thread Moss to Carfentrazone-ethyl

As compared with label recommendations, this research suggests that lower carfentrazone-ethyl rates and longer intervals may be effective for silvery- thread moss (STM; Bryum argenteum Hedw.) control in putting greens

Herbicide-Resistant Palmer amaranth (Amaranthus palmeri S. Wats.) in the United States — Mechanisms of Resistance, Impact, and Management

Palmer amaranth, a dioecious summer annual species, is one of the most troublesome weeds in the agronomic crop production systems in the United States. In the last two decades, continuous reliance on herbicide(s) with the same mode of action as the sole weed management strategy has resulted in the evolution of herbicide-resistant (HR) weeds, including Palmer amaranth. By 2015, Palmer amaranth biotypes had been confirmed resistant to acetolactate synthase (ALS)-inhibitors, dinitroanilines, glyphosate, hydroxyphenylpyruvate dioxygenase (HPPD)-inhibitors, and triazine herbicides in some parts of the United States along with multiple HR biotypes. Mechanisms of herbicide-resistance in Palmer amaranth are discussed in this chapter. Preplant herbicide options including glufosinate, 2,4-D, and dicamba provide excellent Palmer amaranth control; however, their application is limited before planting crops, which is often not possible due to unfavorable weather conditions. Agricultural biotechnology companies are developing new multiple HR crops that will allow the post-emergence application of respective herbicides for management of HR weeds, including Palmer amaranth. For the effective in-crop management of Palmer amaranth, and to reduce the potential for the evolution of other HR weeds, growers should apply herbicides with different modes of action in tank-mixture and should also incorporate cultural practices including inversion tillage and cover crops along with herbicide programs

Reduced Translocation of Glyphosate and Dicamba in Combination Contributes to Poor Control of Kochia scoparia: Evidence of Herbicide Antagonism

Citation: Ou, Junjun, Curtis R. Thompson, Phillip W. Stahlman, Nicholas Bloedow, and Mithila Jugulam. “Reduced Translocation of Glyphosate and Dicamba in Combination Contributes to Poor Control of Kochia Scoparia : Evidence of Herbicide Antagonism.” Scientific Reports 8, no. 1 (March 28, 2018): 1–11. https://doi.org/10.1038/s41598-018-23742-3.Kochia scoparia is a troublesome weed across the Great Plains of North America. Glyphosate and dicamba have been used for decades to control K. scoparia. Due to extensive selection, glyphosate- and dicamba-resistant (GDR) K. scoparia have evolved in the USA. Herbicide mixtures are routinely used to improve weed control. Herbicide interactions if result in an antagonistic effect can significantly affect the management of weeds, such as K. scoparia. To uncover the interaction of glyphosate and dicamba when applied in combination in K. scoparia management the efficacies of different doses of glyphosate plus dicamba were evaluated under greenhouse and field conditions using GDR and a known glyphosate- and dicamba-susceptible (GDS) K. scoparia. The results of greenhouse and field studies suggest that the combination of glyphosate and dicamba application controlled GDS, but glyphosate alone provided a better control of GDR K. scoparia compared to glyphosate plus dicamba combinations. Furthermore, investigation of the basis of this response suggested glyphosate and dicamba interact antagonistically and consequently, the translocation of both herbicides was significantly reduced resulting in poor control of K. scoparia. Therefore, a combination of glyphosate plus dicamba may not be a viable option to control GDR K. scoparia

Transfer of Dicamba Tolerance from Sinapis arvensis to Brassica napus via Embryo Rescue and Recurrent Backcross Breeding

Citation: Jugulam M, Ziauddin A, So KKY, Chen S, Hall JC (2015) Transfer of Dicamba Tolerance from Sinapis arvensis to Brassica napus via Embryo Rescue and Recurrent Backcross Breeding. PLoS ONE 10(11): e0141418. https://doi.org/10.1371/journal.pone.0141418Auxinic herbicides (e.g. dicamba) are extensively used in agriculture to selectively control broadleaf weeds. Although cultivated species of Brassicaceae (e.g. Canola) are susceptible to auxinic herbicides, some biotypes of Sinapis arvensis (wild mustard) were found dicamba resistant in Canada. In this research, dicamba tolerance from wild mustard was introgressed into canola through embryo rescue followed by conventional breeding. Intergeneric hybrids between S. arvensis (2n = 18) and B. napus (2n = 38) were produced through embryo rescue. Embryo formation and hybrid plant regeneration was achieved. Transfer of dicamba tolerance from S. arvensis into the hybrid plants was determined by molecular analysis and at the whole plant level. Dicamba tolerance was introgressed into B. napus by backcrossing for seven generations. Homozygous dicamba-tolerant B. napus lines were identified. The ploidy of the hybrid progeny was assessed by flow cytometry. Finally, introgression of the piece of DNA possibly containing the dicamba tolerance gene into B. napus was confirmed using florescence in situ hybridization (FISH). This research demonstrates for the first time stable introgression of dicamba tolerance from S. arvensis into B. napus via in vitro embryo rescue followed by repeated backcross breeding. Creation of dicamba-tolerant B. napus varieties by this approach may have potential to provide options to growers to choose a desirable herbicide-tolerant technology. Furthermore, adoption of such technology facilitates effective weed control, less tillage, and possibly minimize evolution of herbicide resistant weeds

Research Report: Prevalence and Mechanism of Atrazine Resistance in Waterhemp from Nebraska

Waterhemp is a troublesome summer annual broadleaf weed species that has evolved resistance to glyphosate and other herbicide sites of action (SOA) in Nebraska, including to groups 2 (i.e., Classic, Pursuit, FirstRate), 4 (i.e., 2, 4-D), 5(i.e., atrazine) and 27 (e.g., Callisto, Laudis). The overall objectives of this study were to Evaluate the eficay of PRE applied atrazine, metribuzin and sulfentrazone to control Nebraska waterhemp populations; Evaluate the efficacy of POST applied atrazine to control Nebraska waterhemp populations; and Determine the mechanism of atrazine resistance in Nebraska waterhemp populations

Physiological and Molecular Mechanisms of Differential Sensitivity of Palmer Amaranth (Amaranthus palmeri) to Mesotrione at Varying Growth Temperatures

Citation: Godar, A. S., Varanasi, V. K., Nakka, S., Prasad, P. V. V., Thompson, C. R., & Mithila, J. (2015). Physiological and Molecular Mechanisms of Differential Sensitivity of Palmer Amaranth (Amaranthus palmeri) to Mesotrione at Varying Growth Temperatures. Plos One, 10(5), 17. doi:10.1371/journal.pone.0126731Herbicide efficacy is known to be influenced by temperature, however, underlying mechanism(s) are poorly understood. A marked alteration in mesotrione [a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor] efficacy on Palmer amaranth (Amaranthus palmeri S. Watson) was observed when grown under low- (LT, 25/15 degrees C, day/night temperatures) and high (HT, 40/30 degrees C) temperature compared to optimum (OT, 32.5/22.5 degrees C) temperature. Based on plant height, injury, and mortality, Palmer amaranth was more sensitive to mesotrione at LT and less sensitive at HT compared to OT (ED50 for mortality; 18.5, 52.3, and 63.7 g ai ha(-1), respectively). Similar responses were observed for leaf chlorophyll index and photochemical efficiency of PSII (F-v/F-m). Furthermore, mesotrione translocation and metabolism, and HPPD expression data strongly supported such variation. Relatively more mesotrione was translocated to meristematic regions at LT or OT than at HT. Based on T-50 values (time required to metabolize 50% of the C-14 mesotrione), plants at HT metabolized mesotrione faster than those at LT or OT (T-50; 13, 21, and 16.5 h, respectively). The relative HPPD: CPS (carbamoyl phosphate synthetase) or HPPD:beta-tubulin expression in mesotrione-treated plants increased over time in all temperature regimes; however, at 48 HAT, the HPPD:beta-tubulin expression was exceedingly higher at HT compared to LT or OT (18.4-, 3.1-, and 3.5-fold relative to untreated plants, respectively). These findings together with an integrated understanding of other interacting key environmental factors will have important implications for a predictable approach for effective weed management

Physiological and Molecular Characterization of Hydroxyphenylpyruvate Dioxygenase (HPPD)-inhibitor Resistance in Palmer Amaranth (Amaranthus palmeri S. Wats.)

Citation: Nakka, S., Godar, A. S., Wani, P. S., Thompson, C. R., Peterson, D. E., Roelofs, J., & Jugulam, M. (2017). Physiological and Molecular Characterization of Hydroxyphenylpyruvate Dioxygenase (HPPD)-inhibitor Resistance in Palmer Amaranth (Amaranthus palmeri S. Wats.). Frontiers in Plant Science, 8, 12. doi:10.3389/fpls.2017.00555Herbicides that inhibit hydroxyphenylpyruvate dioxygenase (HPPD) such as mesotrione are widely used to control a broad spectrum of weeds in agriculture. Amaranthus palmeri is an economically troublesome weed throughout the United States. The first case of evolution of resistance to HPPD-inhibiting herbicides in A. palmeri was documented in Kansas (KS) and later in Nebraska (NE). The objective of this study was to investigate the mechansim of HPPD-inhibitor (mesotrione) resistance in A. palmeri. Dose response analysis revealed that this population (KSR) was 10-18 times more resistant than their sensitive counterparts (MSS or KSS). Absorbtion and translocation analysis of [C-14] mesotrione suggested that these mechanisms were not involved in the resistance in A. palmeri. Importantly, mesotrione (>90%) was detoxified markedly faster in the resistant populations (KSR and NER), within 24 hours after treatment (HAT) compared to sensitive plants (MSS, KSS, or NER). However, at 48 HAT all populations metabolized the mesotrione, suggesting additional factors may contribute to this resistance. Further evaluation of mesotrione-resistant A. palmeri did not reveal any specific resistance-conferring mutations nor amplification of HPPD gene, the molecular target of mesotrione. However, the resistant populations showed 4- to 12-fold increase in HPPD gene expression. This increase in HPPD transcript levels was accompanied by increased HPPD protein expression. The significant aspects of this research include: the mesotrione resistance in A. palmeri is conferred primarily by rapid detoxification (non-target-site based) of mesotrione; additionally, increased HPPD gene expression (target-site based) also contributes to the resistance mechanism in the evolution of herbicide resistance in this naturally occurring weed species

Weed resistance to synthetic auxin herbicides

Herbicides classified as synthetic auxins have been most commonly used to control broadleaf weeds in a variety of crops and in non-cropland areas since the first synthetic auxin herbicide (SAH), 2,4-D, was introduced to the market in the mid-1940s. The incidence of weed species resistant to SAHs is relatively low considering their long-term global application with 29 broadleaf weed species confirmed resistant to date. An understanding of the context and mechanisms of SAH resistance evolution can inform management practices to sustain the longevity and utility of this important class of herbicides. A symposium was convened during the 2nd Global Herbicide Resistance Challenge (May 2017 in Denver, CO, USA) to provide an overview of the current state of knowledge of SAH resistance mechanisms including case studies of weed species resistant to SAHs and perspectives on mitigating resistance development in SAH-tolerant crops

Metabolism of 2,4-dichlorophenoxyacetic acid contributes to resistance in a common waterhemp (\u3ci\u3eAmaranthus tuberculatus\u3c/i\u3e) population

BACKGROUND: Synthetic auxins such as 2,4-D have been widely used for selective control of broadleaf weeds since the mid-1940s. In 2009, an Amaranthus tuberculatus (common waterhemp) population with 10-fold resistance to 2,4-D was found in Nebraska, USA. The 2,4-D resistance mechanism was examined by conducting [14C] 2,4-D absorption, translocation and metabolism experiments. RESULTS: No differences were found in 2,4-D absorption or translocation between the resistant and susceptible A. tuberculatus. Resistant plants metabolized [14C] 2,4-D more rapidly than did susceptible plants. The half-life of [14C] 2,4-D in susceptible plants was 105 h, compared to 22 h in resistant plants. Pre-treatment with the cytochrome P450 inhibitor malathion inhibited [14C] 2,4-D metabolism in resistant plants and reduced the 2,4-D dose required for 50% growth inhibition (GR50) of resistant plants by 7-fold to 27 g ha-1, similar to the GR50 for susceptible plants in the absence of malathion. CONCLUSIONS: Our results demonstrate that rapid 2,4-D metabolism is a contributing factor to resistance in A. tuberculatus, potentially mediated by cytochrome P450. Metabolism-based resistance to 2,4-D could pose a serious challenge for A. tuberculatus control due to the potential for cross-resistance to other herbicides