Academic literature on the topic 'Auxinic herbicide resistance'

Auxinic herbicides are widely used for control of broadleaf weeds in cereal crops and turfgrass. These herbicides are structurally similar to the natural plant hormone auxin, and induce several of the same physiological and biochemical responses at low concentrations. After several decades of research to understand the auxin signal transduction pathway, the receptors for auxin binding and resultant biochemical and physiological responses have recently been discovered in plants. However, the precise mode of action for the auxinic herbicides is not completely understood despite their extensive use in agriculture for over six decades. Auxinic herbicide-resistant weed biotypes offer excellent model species for uncovering the mode of action as well as resistance to these compounds. Compared with other herbicide families, the incidence of resistance to auxinic herbicides is relatively low, with only 29 auxinic herbicide-resistant weed species discovered to date. The relatively low incidence of resistance to auxinic herbicides has been attributed to the presence of rare alleles imparting resistance in natural weed populations, the potential for fitness penalties due to mutations conferring resistance in weeds, and the complex mode of action of auxinic herbicides in sensitive dicot plants. This review discusses recent advances in the auxin signal transduction pathway and its relation to auxinic herbicide mode of action. Furthermore, comprehensive information about the genetics and inheritance of auxinic herbicide resistance and case studies examining mechanisms of resistance in auxinic herbicide-resistant broadleaf weed biotypes are provided. Within the context of recent findings pertaining to auxin biology and mechanisms of resistance to auxinic herbicides, agronomic implications of the evolution of resistance to these herbicides are discussed in light of new auxinic herbicide-resistant crops that will be commercialized in the near future.

The primary goal of this research was to determine the inheritance of cross-resistance to several groups of auxinic herbicides through classical genetic approaches using auxinic herbicide–resistant (R) and –susceptible (S) wild mustard biotypes obtained from western Canada. F1 progeny were raised from crosses between homozygous auxinic herbicide–R and –S wild mustard parental lines. The F1 and F2 populations were assessed for picloram (pyridine group) and 2,4-D (phenoxyalkanoic group) resistance or susceptibility. Analyses of the F1 as well as the F2 progeny indicate that a single dominant gene confers the resistance to picloram and 2,4-D similar to an earlier report of dicamba-based (benzoic acid group) resistance in this wild mustard biotype. Furthermore, analyses of backcross progeny in this species indicate that resistance to all three auxinic herbicides, i.e., picloram, dicamba, and 2,4-D, is determined by closely linked genetic loci. With this information on inheritance of resistance to several auxinic herbicide families, the R biotype of wild mustard offers an excellent system to isolate and characterize the auxinic herbicide–resistance gene.

A population of oriental mustard from Port Broughton in South Australia was reported as not being controlled by 2,4-D. Dose response experiments determined this population was resistant to both 2,4-D and MCPA, requiring greater than 20 times more herbicide for equivalent control compared to a known susceptible population (from Roseworthy, South Australia) and a population resistant only to the acetohydroxyacid synthase (AHAS)-inhibiting herbicides (from Tumby Bay, South Australia). The Port Broughton population was also found to be resistant to three chemical groups that inhibit AHAS; however, the level of resistance was lower than the known acetolactate synthase–resistant population from Tumby Bay. Herbicides from other modes of action were able to control the Port Broughton population. Assays of isolated AHAS from the Port Broughton population showed high levels of resistance to the sulfonylurea and sulfonamide herbicide groups, but not to the imidazolinone herbicides. A single nucleotide change in the AHAS gene that predicted a Pro to Ser substitution at position 197 in the protein was identified in the Port Broughton population. This population of oriental mustard has evolved multiple resistance to AHAS-inhibiting herbicides (AHAS inhibitors) and auxinic herbicides, through a mutation in AHAS and a second nontarget-site mechanism. Whether the same mechanism provides resistance to both AHAS inhibitors and auxinic herbicides remains to be determined. Multiple resistance to auxinic herbicides and AHAS inhibitors in the Port Broughton population will make control of this population more difficult.

Herbicide-resistance traits are the most widely used agriculture biotechnology products. Yet, to maintain their effectiveness and to mitigate selection of herbicide-resistant weeds, the discovery of new resistance traits that use different chemical modes of action is essential. In plants, the Gretchen Hagen 3 (GH3) acyl acid amido synthetases catalyze the conjugation of amino acids to jasmonate and auxin phytohormones. This reaction chemistry has not been explored as a possible approach for herbicide modification and inactivation. Here, we examined a set of Arabidopsis GH3 proteins that use the auxins indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) as substrates along with the corresponding auxinic phenoxyalkanoic acid herbicides 2,4-dichlorophenoxylacetic acid (2,4-D) and 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB). The IBA-specific AtGH3.15 protein displayed high catalytic activity with 2,4-DB, which was comparable to its activity with IBA. Screening of phenoxyalkanoic and phenylalkyl acids indicated that side-chain length of alkanoic and alkyl acids is a key feature of AtGH3.15's substrate preference. The X-ray crystal structure of the AtGH3.15·2,4-DB complex revealed how the herbicide binds in the active site. In root elongation assays, Arabidopsis AtGH3.15-knockout and -overexpression lines grown in the presence of 2,4-DB exhibited hypersensitivity and tolerance, respectively, indicating that the AtGH3.15-catalyzed modification inactivates 2,4-DB. These findings suggest a potential use for AtGH3.15, and perhaps other GH3 proteins, as herbicide-modifying enzymes that employ a mode of action different from those of currently available herbicide-resistance traits.

In many countries, Amaranthus hybridus is a widespread weed in agricultural systems. The high prolificacy and invasive capacity as well as the resistance of some biotypes to herbicides are among the complications of handling this weed. This paper reports on the first A. hybridus biotypes with resistance to auxinic herbicides and multiple resistance to auxinic herbicides and the EPSPs inhibitor, glyphosate. Several dose response assays were carried out to determine and compare sensitivity of six population of A. hybridus to glyphosate, 2,4-D, and dicamba. In addition, shikimic acid accumulation and piperonil butoxide effects on 2,4-D and dicamba metabolism were tested in the same populations. The results showed four populations were resistant to dicamba and three of these were also resistant to 2,4-D, while only one population was resistant to glyphosate. The glyphosate-resistant population also showed multiple resistance to auxinic herbicides. Pretreatment with piperonil butoxide (PBO) followed by 2,4-D or dicamba resulted in the death of all individual weeds independent of herbicide or population.

AbstractApplication timing and environmental factors reportedly influence the efficacy of auxinic herbicides. In resistance-prone weed species such as Palmer amaranth (Amaranthus palmeri S. Watson), efficacy of auxinic herbicides recently adopted for use in resistant crops is of utmost importance to reduce selection pressure for herbicide-resistance traits. Growth chamber experiments were conducted comparing the interaction of different environmental effects with application time to determine the influence of these factors on visible phytotoxicity and hydrogen peroxide (H2O2) formation in A. palmeri. Temperature displayed a high degree of influence on 2,4-D and dicamba efficacy in general, with applications at the low-temperature treatment (31/20 C day/night) resulting in an increase in phytotoxicity compared with high-temperature treatments (41/30 C day/night). Application time across temperature treatments significantly affected 2,4-D–induced phytotoxicity, resulting in a ≥30% increase across rates with treatments at 4:00 PM compared with 8:00 AM. Temperature differential had a significant influence on dicamba efficacy based on visible phytotoxicity data, with a ≥46% increase with a high (37/20 C day/night) compared with a low differential (41/30 C day/night). Concentration of H2O2 in herbicide-treated plants was 34% higher under a high temperature differential compared with the low differential. Humidity treatments and application time interactions displayed undetected or inconsistent effects on visible phytotoxicity and H2O2 production. Overall, temperature-related influences seem to have the largest environmental effect on auxinic herbicides within conditions evaluated in this study. Leaf concentration of H2O2 appears to be generally correlated with phytotoxicity, providing a potentially useful tool in determining efficacy of auxinic herbicides in field settings.

AbstractWild radish (Raphanus raphanistrum L.) is a problematic and economically damaging dicotyledonous weed infesting crops in many regions of the world. Resistance to the auxinic herbicides 2,4-D and dicamba is widespread in Western Australian R. raphanistrum populations, with the resistance mechanism appearing to involve alterations in the physiological response to synthetic auxins and in plant defense. This study aimed to determine whether these alterations cause inhibition in plant growth or reproduction that could potentially be exploited to manage 2,4-D–resistant populations in cropping areas. Therefore, the morphology and seed production of resistant and susceptible populations were compared in an outdoor pot study, with plants grown in the presence and absence of competition by wheat (Triticum aestivum L.). The susceptible and resistant R. raphanistrum populations were equally suppressed by wheat competition, with plant growth and seed production being decreased by approximately 50%. Although resistant populations produced less vegetative biomass than susceptible populations, there was no negative association between resistance and seed production. Therefore, it is unlikely that any nonherbicidal management practices will be more efficacious on 2,4-D–resistant than 2,4-D–susceptible R. raphanistrum populations.

This article reviews, focusing on maize and soybean, previous efforts to develop nontransgenic herbicide-resistant crops (HRCs), currently available transgenic HRC traits and technologies, as well as future chemical weed management options over the horizon. Since the mid twentieth century, herbicides rapidly replaced all other means of weed management. Overreliance on ‘herbicide-only’ weed control strategies hastened evolution of HR weed species. Glyphosate-resistant (GR) crop technology revolutionized weed management in agronomic crops, but GR weeds, led by Palmer amaranth, severely reduced returns from various cropping systems and affected the bottom line of growers across the world. An additional problem was the lack of commercialization of a new herbicide mode of action since the 1990s. Auxinic HRCs offer a short-term alternative for management of GR Palmer amaranth and other weed species. New HRCs stacked with multiple herbicide resistance traits and at least two new herbicide modes of action expected to be available in the mid-2020s provide new chemical options for weed management in row crops in the next decade.

Herbicide-resistantAmaranthusspp. continue to cause management difficulties in soybean. New soybean technologies under development, including resistance to various combinations of glyphosate, glufosinate, dicamba, 2,4-D, isoxaflutole, and mesotrione, will make possible the use of additional herbicide sites of action in soybean than is currently available. When this research was conducted, these soybean traits were still regulated and testing herbicide programs with the appropriate soybean genetics in a single experiment was not feasible. Therefore, the effectiveness of various herbicide programs (PRE herbicides followed by POST herbicides) was evaluated in bare-ground experiments on glyphosate-resistant Palmer amaranth and glyphosate-resistant waterhemp (both tall and common) at locations in Arkansas, Illinois, Indiana, Missouri, Nebraska, and Tennessee. Twenty-five herbicide programs were evaluated; 5 of which were PRE herbicides only, 10 were PRE herbicides followed by POST herbicides 3 to 4 wks after (WA) the PRE application (EPOST), and 10 were PRE herbicides followed by POST herbicides 6 to 7 WA the PRE application (LPOST). Programs with EPOST herbicides provided 94% or greater control of Palmer amaranth and waterhemp at 3 to 4 WA the EPOST. Overall, programs with LPOST herbicides resulted in a period of weed emergence in which weeds would typically compete with a crop. Weeds were not completely controlled with the LPOST herbicides because weed sizes were larger (≥ 15 cm) compared with their sizes at the EPOST application (≤ 7 cm). Most programs with LPOST herbicides provided 80 to 95% control at 3 to 4 WA applied LPOST. Based on an orthogonal contrast, using a synthetic-auxin herbicide LPOST improves control of Palmer amaranth and waterhemp over programs not containing a synthetic-auxin LPOST. These results show herbicides that can be used in soybean and that contain auxinic- or HPPD-resistant traits will provide growers with an opportunity for better control of glyphosate-resistant Palmer amaranth and waterhemp over a wide range of geographies and environments.

The objective of this Ph.D. research was to identify new and novel mechanisms of wild radish (Raphanus raphanistrum L.) resistance to photosystem II (PSII) inhibitors, auxinics, and acetohydroxyacid synthase (AHAS) inhibitors. PSIIinhibitor resistance was demonstrated to be target-site based, and conferred by a Ser264 to Gly substitution of the D1 protein. Auxinic resistance was associated with reduced herbicide translocation to the meristematic regions of resistant wild radish plants. Two new resistance mutations of wild radish AHAS were discovered, including one encoding the globally rare Asp376 to Glu substitution, and another encoding an Ala122 to Tyr substitution, which has never been identified or assessed for resistance in plants previously. Characterization of the frequency and distribution of AHAS resistance mutations in wild radish from the WA wheatbelt revealed that Glu376 was widespread, and that some mutations of AHAS are more common than others. Computer simulation was used to examine the molecular basis of resistance-endowing AHAS target-site mutations. Furthermore, through the computer-aided analysis, residues were identified with the potential to confer resistance upon substitution, but which have not previously been assessed for this possibility. Results from this Ph.D. research demonstrate that diverse, unrelated mechanisms of resistance to PSII inhibitors, auxinics, and AHAS inhibitors have evolved in wild radish of the WA wheatbelt, and that these mechanisms have accumulated in some populations.

Palmer amaranth (Amaranthus palmeri) and common ragweed (Ambrosia artemisiifolia) are two of the most troublesome weeds in soybean. Both weeds possess widespread resistance to glyphosate and acetolactate synthase (ALS) inhibiting herbicides resulting in the use of protoporphyrinogen oxidase- (PPO) inhibitors to control these biotypes, although PPO-resistant biotypes are increasing. New soybean herbicide-resistant trait technologies enable novel herbicide combinations. Combinations of two herbicide sites-of-action (SOA) improved control 19 to 25% and 14 to 19% of Palmer amaranth and common ragweed, respectively, versus using one SOA (mesotrione, dicamba, 2,4-D, or glufosinate alone). Seed production of 5 to 10 cm Palmer amaranth and common ragweed was reduced greater than 76% by fomesafen, auxin (dicamba and 2,4-D), or glufosinate containing treatments. Some weeds survived and set seed even when treated at the proper size. As weed size increased from 10 to 30 cm, control diminished and fecundity increased, underscoring the importance of proper herbicide application timing. Effective preemergence herbicides reduced the number of weeds present at the postemergence application compared to no treatment, reducing the likelihood of herbicide resistance development. Dicamba, 2,4-D, or glufosinate applied alone or auxin + glufosinate combinations reduced Palmer amaranth seed production greater than 95% when applied at first visible female inflorescence; this first report, in addition to previous reports on individual herbicides, indicates this application timing may be useful for soil seed bank management. This research informs mitigation of herbicide resistance spread and development.
Master of Science in Life Sciences
Over 30 million hectares of soybeans were harvested in 2019 in the United States, totaling over $31 billion in value. Two of the most troublesome weeds in soybean, Palmer amaranth (Amaranthus palmeri) and common ragweed (Ambrosia artemisiifolia) can cause even greater yield reductions in soybean, up to 79 to 95%, respectively. Frequent, exclusive, and repeated use of a single herbicide has led to multiple herbicide-resistance in both of these weeds. Co-applying two effective herbicides reduces the likelihood of resistance development. New soybean varieties have been genetically modified for resistance to herbicides that were previously unusable, allowing new herbicide combinations. Research was established to investigate these herbicide options to control and reduce seed production of Palmer amaranth and common ragweed with the overarching goal of mitigating herbicide resistance, particularly resistance to protoporphyrinogen oxidase (PPO) inhibiting herbicides, which are a critical part of herbicide options in soybean production. Preemergence herbicides are vital tools in herbicide programs, reducing the number of weeds present at a postemergence application and thereby reducing the risk of herbicide resistance development to the postemergence herbicide. PPO herbicides (flumioxazin, sulfentrazone, or fomesafen) applied preemergence reduced Palmer amaranth and common ragweed density at the postemergence application 82 to 89% and 53 to 94%, respectively. The preemergence herbicide used did not affect control four weeks after the postemergence herbicides were applied. Postemergence herbicides were applied targeting three weed heights: 5 to 10 cm (ideal), 10 to 20 cm, and 20 to 30 cm. Control decreased as weed height increased and larger weeds had greater biomass and seed production, underscoring the importance of proper herbicide application timing. The single site-of-action treatments dicamba, 2,4-D, glufosinate, or fomesafen resulted in greater than 85 and 92% morality of 5 to 10 cm Palmer amaranth and common ragweed, respectively. Palmer amaranth and common ragweed control improved by 19 to 25% and 14 to 19%, respectively, when using two herbicide sites-of-action increased versus using one SOA (mesotrione, dicamba, 2,4-D, or glufosinate alone). The use of two herbicide sites of action resulted in maximum biomass reductions, depending on weed height, of 57 to 96% and 73 to 85% for Palmer amaranth and common ragweed, respectively. Dicamba, 2,4-D, glufosinate alone and in combination with fomesafen reduced seed production (relative to the nontreated) of 5 to 10 cm Palmer amaranth and common ragweed greater than 98 and 76%, respectively. Dicamba, 2,4-D, and glufosinate applied alone or auxin (dicamba and 2,4-D) and glufosinate combinations reduced Palmer amaranth seed production greater than 95% when applied at first visible female inflorescence. This indicates that these herbicides may be useful in soil weed seed bank management. This research reinforces the utility of PPO herbicides for preemergence control and their efficacy postemergence when combined with another effective herbicide, a practice known to reduce herbicide resistance development. This research also reinforces the potential for dicamba, 2,4-D, or glufosinate to reduce weed seed production when applied at a delayed timing. Future research should investigate the progeny of these weeds treated with herbicides at a delayed timing to evaluate the potential for this practice to reduce herbicide resistance development.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Os herbicidas são um dos fatores mais importantes que vem consideravelmente contribuindo no aumento na proteção das culturas, devido sua inovação no controle de plantas daninhas ao longo dos últimos 70 anos. O uso continuo de um mesmo ingrediente ativo ou modo de ação impõe uma alta pressão de seleção em uma população de plantas daninhas e a seleção de indivíduos resistentes a herbicidas pode ocorrer. A intensidade da seleção imposta pelos herbicidas e a frequência inicial de indivíduos resistentes a herbicidas dentro de uma população de plantas daninhas são fatores chave importantes no processo de evolução da resistência. Fluxo gênico via pólen, sementes e propágulos vegetativos são uma potencial fonte de distribuição de resistência a herbicidas, como previamente reportado em Conyza canadensis e Amaranthus ssp. Conyza canadensis e Amaranthus ssp são potencialmente capazes de transferir genes que conferem resistência a herbicidas via pólen e/ou sementes, por produzirem pólen que pode ser disseminado a longas distancia e grande número de sementes. Os objetivos gerais dos estudos realizados foram caracterizar o nível de resistência de duas espécies de plantas daninhas de Nebraska, Estados Unidos da América. Um primeiro estudo em casa de vegetação foi conduzido para caracterizar o nível de resistência a glyphosate de populações de buva coletadas em áreas não cultivadas foi conduzido. Experimentos de dose-resposta com 9 doses de glyphosate e 28 populações de buva foram avaliados. Um segundo estudo em casa de vegetação foi conduzido para caracterizar o nível de uma população de caruru resistente a 2,4-D a diferentes formulações de herbicidas fenóxicos. De acordo com o primeiro estudo de dose-resposta, menos de sete por cento das populações de Conyza canadensis em áreas de pastagem próximas a áreas de cultivo expressaram “resistência prática” a glyphosate (plantas sobreviventes a dose de glyphosate mais usual em Nebraska – 1,260 g ae ha-1). Baseado em nossos resultados, foi detectado baixa frequência de resistência a glyphosate em populações de Conyza canadensis em áreas de pastagem de Nebraska, indicando que indivíduos resistentes a glyphosate dispersos das áreas de cultivo não são o biótipo predominante nessas áreas. Os resultados do segundo estudo mostraram que a população de Amarantus tuberculatus resistente a 2,4-D foi significativamente mais suscetíveis às formulações dos herbicidas Dicamba DGA, Dicamba DMA, Corasil, 2,4-DP, e 2,4-DP-p, enquanto sobreviveram a altas doses dos herbicidas 2,4-D 2EHE, 2,4-D EE, 2,4-DB, MCPB, MCPA, MCPA 2EHE, CMPP e CMPP-p.
Herbicides are one of the most important factors that have contributed to protect crop yields. This is due to innovative weed control over the last 70 years. The over-reliance on a single herbicide active ingredient or mode of action impose a high selection pressure on a weed population and the selection of herbicide-resistant individual plants may occur. The intensity of selection imposed by herbicides and the initial frequency of herbicide resistant in a weed population play a major role in the herbicide resistance evolution. Gene flow by pollen, seed, and vegetative propagules have the potential to move herbicide-resistant weed species, as reported previous reported in Conyza canadensis and Amaranthus genus. Conyza canadensis and Amaranthus tuberculatus are potentially able to proliferate herbicide resistance by pollen and/or seeds due to be prolific seed producer and its pollen are capable to be disseminated for long distances. The general objectives of these studies were to characterize the herbicide resistance level of two weed species in Nebraska, United States. A greenhouse study was performed to characterize the fold of glyphosate resistance in horseweed populations from non-crop areas. Dose-response experiments with 28 horseweed populations were evaluated across nine glyphosate rates. A second greenhouse study was performed to characterize the level of a 2,4-D-resistant waterhemp population resistance to various auxinic herbicides. According to the first dose-response study, less than seven percent of the rangeland Conyza canadensis populations screened expressed “practical” resistance to glyphosate (plants surviving to most common glyphosate rate used in Nebraska of 1,260g ae ha-1). Therefore, low frequency of GR in horseweed populations was detected in Nebraska rangeland indicating that GR individuals dispersed from row crops into rangeland are not the predominant biotype in these non-row crop areas. For the second study, the results showed that 2,4-D-WR population were significantly more sensitive to Dicamba DGA, Dicamba DMA, Corasil, 2,4-DP, and 2,4-DP-p herbicides formulations, whereas survived to the higher doses of 2,4-D 2EHE, 2,4-D EE, 2,4-DB, MCPB, MCPA, MCPA 2EHE, CMPP and CMPP-p. The founds on this studied showed the 2,4-D-WR population exhibits cross-resistance to 2,4-D 2EHE, 2,4-D EE, 2,4-DB, MCPB, MCPA, MCPA 2EHE, CMPP and CMPP-p herbicides.
006860/2015-00

Auxinic herbicide-resistant (i.e., resistant to 2,4-D and MCPA) wild radish (Raphanus raphanistrum L.) was discovered in the Western Australian wheatbelt, providing an opportunity to integrate auxinic herbicide resistance into cultivated radish (R. sativus L.) using conventional breeding methods. It was hypothesized that the inheritance of auxinic herbicide resistance in wild radish is conferred by a single, dominant nuclear gene and, therefore, will be relatively easy to introgress from wild radish to cultivated radish; and the mechanism of auxinic herbicide resistance in wild radish is through an altered target-site. Visual injury data of the F2 progeny suggested that resistance was conferred by a quantitative trait with the susceptible allele(s) exhibiting dominance with minor cytoplasmically inherited genes masking the susceptible trait. In conclusion, the resistance allele(s) were quantitative and, thus, make selection for resistance difficult. Therefore, the introgression of the resistance allele(s) was not successfully completed. To determine the mechanism of resistance, the wild radish plants resistant WARR6-26 (R) and susceptible WARR7-5 (S) were treated with radiolabeled MCPA. There was no difference in metabolism of [14C]MCPA between R and S plants. Based upon the decline in the total 14C recovered over 72 h in R and S it was clear that both were “losing” [14C]MCPA; however, R plants were losing MCPA more rapidly. It was hypothesized that because R plants exude 14C more rapidly from their roots than S plants, this accounted for the resistance of R plants.