Insulinoma: Metastatic Recurrence 38 Years Following Initial Diagnosis in Pregnancy.

A case of recurrent insulinoma spanning 4 decades is described. Following a delayed diagnosis, hyperinsulinemic hypoglycemia was confirmed in a 24-year-old woman during early pregnancy. Initial surgery, culminating in subtotal pancreatectomy, was noncurative. A 1-cm insulinoma was subsequently resected from the head of the pancreas postpartum, with postoperative resolution of hypoglycemia. However, 32 years later, the patient experienced a recurrence of hypoglycemic symptoms. Eventually, a subcentimeter extrapancreatic lesion was identified anterior to the pancreatic head on gallium-68 DOTA-Exendin-4 positron emission tomography/computed tomography. In 2022, a third operation was performed, with excision of a 4 × 3 mm tumor adjacent to the pancreatic head, and histology confirming insulinoma. She was again cured of symptoms.

Point mutations including a novel Pro-197-Phe mutation confer cross-resistance to acetolactate synthase (ALS) inhibiting herbicides in Lactuca serriola in Australia.

BACKGROUND: Control of prickly lettuce has become increasingly difficult for lentil growers in southern Australia because of widespread resistance to common herbicides, a lack of alternative herbicide options and the prolific production of highly mobile seed. This study aimed to quantify acetolactate synthase (ALS)-inhibiting herbicide resistance in the Mid North (MN) and Yorke Peninsula (YP) of South Australia, characterize the resistance mutations present and investigate population structure and gene flow in this species. RESULTS: Resistance was identified in all populations tested, with average survival of 92% to chlorsulfuron and 95% to imazamox + imazapyr. Five different amino acid substitutions were identified at proline 197 of the ALS gene. There was no significant difference in the median lethal dose (LD50 ) between plants with these five different substitutions when treated with metsulfuron-methyl; however, the imidazolinone resistance level was higher in plants with a phenylalanine substitution and lower in plants with a serine. Population structure based on 701 single nucleotide polymorphisms and 271 individuals provided evidence for both independent evolution of the same mutation in different populations, as well as frequent short- to medium-distance dispersal accompanied by occasional long-distance dispersal events. The overall inbreeding coefficient (FIS ) was calculated at 0.5174, indicating an intermediate level of outcrossing despite the cross-pollination experiment showing only low outcrossing. In the structure analyses, most individuals from YP were assigned to a single cluster, whereas most individuals from MN were assigned 50% to each of two clusters, indicating some genetic differences between these two regions, but also evidence for dispersal between them. CONCLUSIONS: Use of imidazolinone herbicides has selected for mutations conferring higher levels of resistance, such as the Pro-197-Phe mutation, and resulted in further spread of resistance in this species. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Population structure of ALS-inhibiting herbicide-resistant Sonchus oleraceus in South Australia.

BACKGROUND: Annual sowthistle is a weed that is difficult to control in lentil crops in southern Australia due to a lack of herbicide options, widespread herbicide resistance and prolific production of highly mobile seed. This study investigates herbicide resistance in annual sowthistle in the Mid-North (MN) and Yorke Peninsula (YP) regions of South Australia, identifies and characterizes the mechanisms of acetolactate-synthase (ALS)-inhibitor resistance in this amphidiploid species, and combines this with analyses of population structure and gene flow. RESULTS: ALS-inhibitor-resistant annual sowthistle is widespread across the YP and MN of South Australia and is associated with a variety of Proline-197 mutations of the ALS gene, including leucine, alanine, arginine, serine, threonine and histidine. These mutations were found in different combinations on either of the two copies of the ALS gene. An additional 200 tissue samples were collected from across a single field on the YP and the ALS gene was sequenced for all these individuals. Different ALS-inhibitor resistance profiles were evident between mutation combinations and within mutation combinations, possibly mediated by differing subgenome assortment of the mutations, or altered gene experession of the two ALS homeologs. Population genetics analysis showed evidence of long-distance dispersal, resulting in highly mobile resistance genes, and multiple instances of resistance mutation evolution. CONCLUSIONS: Continuing selection of Sonchus oleraceus populations with ALS-inhibiting herbicides has resulted in the accumulation of additional mutations within the ALS gene. New practices to control herbicide-resistant S. oleraceus should be examined, and control should focus on reducing seed set and dispersal to prevent the spread of emerging cases of resistance. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

An in-frame deletion mutation in the degron tail of auxin coreceptor IAA2 confers resistance to the herbicide 2,4-D in Sisymbrium orientale.

The natural auxin indole-3-acetic acid (IAA) is a key regulator of many aspects of plant growth and development. Synthetic auxin herbicides such as 2,4-D mimic the effects of IAA by inducing strong auxinic-signaling responses in plants. To determine the mechanism of 2,4-D resistance in a Sisymbrium orientale (Indian hedge mustard) weed population, we performed a transcriptome analysis of 2,4-D-resistant (R) and -susceptible (S) genotypes that revealed an in-frame 27-nucleotide deletion removing nine amino acids in the degron tail (DT) of the auxin coreceptor Aux/IAA2 (SoIAA2). The deletion allele cosegregated with 2,4-D resistance in recombinant inbred lines. Further, this deletion was also detected in several 2,4-D-resistant field populations of this species. Arabidopsis transgenic lines expressing the SoIAA2 mutant allele were resistant to 2,4-D and dicamba. The IAA2-DT deletion reduced binding to TIR1 in vitro with both natural and synthetic auxins, causing reduced association and increased dissociation rates. This mechanism of synthetic auxin herbicide resistance assigns an in planta function to the DT region of this Aux/IAA coreceptor for its role in synthetic auxin binding kinetics and reveals a potential biotechnological approach to produce synthetic auxin-resistant crops using gene-editing.

Inheritance and mechanism of glyphosate resistance in annual bluegrass (Poa annua L.).

BACKGROUND: In initial screening, glyphosate was ineffective in controlling five Poa annua populations. These populations were tested for resistance, and studies undertaken to determine resistance mechanisms and inheritance pattern. RESULTS: Dose-response studies conducted at 16/12°C and 27/20°C on the five putative resistant populations showed low-level resistance (1.4- to 2.5-fold) to glyphosate. Shikimic acid accumulation in response to glyphosate confirmed differences among the populations, with greater shikimic acid accumulation in the susceptible population. The EPSPS gene copy number was 0.5- to 5.2-fold greater in one resistant population (HT) than in the susceptible (S) population, but not in the others. EPSPS gene expression was five- to tenfold higher in HT compared with the susceptible population. Target site mutations, differences in glyphosate absorption or translocation or altered expression of aldo-keto reductase (AKR) were not identified in any of the resistant populations. Crosses were successful between one resistant population and the susceptible population (P262-16♂ ✕ S♀) and inheritance of glyphosate resistance appears to be controlled by a single, nuclear dominant gene in this population. CONCLUSION: Our study identified EPSPS gene amplification in a South Australian glyphosate-resistant P. annua population (HT). This mechanism of resistance was not identified in the other four glyphosate-resistant populations, and other common mechanisms were excluded. Although the resistance mechanism in some P. annua populations remains unknown, inheritance studies with one population suggest the involvement of a single dominant gene. © 2021 Society of Chemical Industry.

Evidence for the Application of Emerging Technologies to Accelerate Crop Improvement - A Collaborative Pipeline to Introgress Herbicide Tolerance Into Chickpea.

Accelerating genetic gain in crop improvement is required to ensure improved yield and yield stability under increasingly challenging climatic conditions. This case study demonstrates the effective confluence of innovative breeding technologies within a collaborative breeding framework to develop and rapidly introgress imidazolinone Group 2 herbicide tolerance into an adapted Australian chickpea genetic background. A well-adapted, high-yielding desi cultivar PBA HatTrick was treated with ethyl methanesulfonate to generate mutations in the ACETOHYDROXYACID SYNTHASE 1 (CaAHAS1) gene. After 2 years of field screening with imidazolinone herbicide across >20 ha and controlled environment progeny screening, two selections were identified which exhibited putative herbicide tolerance. Both selections contained the same single amino acid substitution, from alanine to valine at position 205 (A205V) in the AHAS1 protein, and KASP™ markers were developed to discriminate between tolerant and intolerant genotypes. A pipeline combining conventional crossing and F2 production with accelerated single seed descent from F2:4 and marker-assisted selection at F2 rapidly introgressed the herbicide tolerance trait from one of the mutant selections, D15PAHI002, into PBA Seamer, a desi cultivar adapted to Australian cropping areas. Field evaluation of the derivatives of the D15PAHI002 × PBA Seamer cross was analyzed using a factor analytic mixed model statistical approach designed to accommodate low seed numbers resulting from accelerated single seed descent. To further accelerate trait introgression, field evaluation trials were undertaken concurrent with crop safety testing trials. In 2020, 4 years after the initial cross, an advanced line selection CBA2061, bearing acetohydroxyacid synthase (AHAS) inhibitor tolerance and agronomic and disease resistance traits comparable to parent PBA Seamer, was entered into Australian National Variety Trials as a precursor to cultivar registration. The combination of cross-institutional collaboration and the application of novel pre-breeding platforms and statistical technologies facilitated a 3-year saving compared to a traditional breeding approach. This breeding pipeline can be used as a model to accelerate genetic gain in other self-pollinating species, particularly food legumes.

Non-Mendelian inheritance of gene amplification-based resistance to glyphosate in Hordeum glaucum (barley grass) from South Australia.

BACKGROUND: Hordeum glaucum Steud. is an important grass weed species in South Australia that has evolved resistance to glyphosate. This study investigated the mode of inheritance of glyphosate resistance in this species. RESULTS: Hand-pollination of glyphosate susceptible and resistant populations generated two F1 individuals, selfed to yield F2 progenies. In dose-response experiments, the F2 progenies showed intermediate response between the two parent populations. High variation in EPSPS gene copies was observed among F2 individuals, with some individuals possessing more gene copies than the resistant parent population. No evidence of a Mendelian single-gene pattern of inheritance was observed. CONCLUSION: Inheritance of gene amplification in H. glaucum is non-Mendelian. © 2021 Society of Chemical Industry.

Increasing the value and efficiency of herbicide resistance surveys.

The scale of herbicide resistance within a cropping region can be estimated and monitored using surveys of weed populations. The current approach to herbicide resistance surveys is time-consuming, logistically challenging and costly. Here we review past and current approaches used in herbicide resistance surveys with the aims of (i) defining effective survey methodologies, (ii) highlighting opportunities for improving efficiencies through the use of new technologies and (iii) identifying the value of repeated region-wide herbicide resistance surveys. One of the most extensively surveyed areas of the world's cropping regions is the Australian grain production region, with >2900 fields randomly surveyed in each of three surveys conducted over the past 15 years. Consequently, recommended methodologies are based on what has been learned from the Australian experience. Traditional seedling-based herbicide screening assays remain the most reliable and widely applicable method for characterizing resistance in weed populations. The use of satellite or aerial imagery to plan collections and image analysis to rapidly quantify screening results could complement traditional resistance assays by increasing survey efficiency and sampling accuracy. Global management of herbicide-resistant weeds would benefit from repeated and standardized surveys that track herbicide resistance evolution within and across cropping regions. © 2021 Society of Chemical Industry.

Stability of EPSPS gene copy number in Hordeum glaucum Steud (barley grass) in the presence and absence of glyphosate selection.

BACKGROUND: Gene amplification has been shown to provide resistance to glyphosate in several weed species, including Hordeum glaucum populations in South Australia. The stability of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copies in resistant populations in the presence or absence of glyphosate selection has not been determined. RESULTS: Applying glyphosate to a cloned plant resulted in an increase in resistance and EPSPS copy number in the progeny of that plant compared to the untreated clone. The LD50 (herbicide concentration required for 50% mortality) increased by 75% to 79% in the progeny of the treated clones compared to the untreated in both populations (YP-17 and YP-16). EPSPS copy number estimates were higher in treated individuals compared to untreated individuals with an average of seven copies compared to six in YP-16 and 11 compared to six in YP-17. There was a positive correlation (R2  = 0.78) between EPSPS copy number and LD50 of all populations. CONCLUSION: EPSPS gene copy number and resistance to glyphosate increased in H. glaucum populations under glyphosate selection, suggesting the number of EPSPS gene copies present is dependent on glyphosate selection. © 2021 Society of Chemical Industry.

Review: evolutionary drivers of agricultural adaptation in Lolium spp.

The genus Lolium comprises many species, of which L. perenne ssp. multiflorum, L. perenne ssp. perenne, and L. rigidum are of worldwide agricultural importance as both pasture crops and as weeds. These three species are inter-fertile, obligate out-crossers with a self-incompatible reproduction system. This combination contributes to high genetic diversity that supplies new variants during expansion to new natural areas and agricultural environments. Human dispersal, de-domestication and crop-weed hybridization events between Lolium spp., or with others such as Festuca spp., are likely associated with their distinct weediness abilities. Furthermore, new introductions followed by introgression may hasten adaptation to new environments. Most Lolium-related weed science studies have focused on adaptation leading to herbicide resistance, but other forms of adaptation may also occur. In this review, we explore how the wide genetic variation among Lolium species and hybridization with other species may contribute to range expansion, and adaptation to both new agricultural practices and future predicted climate change scenarios. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Synthetic auxin herbicides: finding the lock and key to weed resistance.

Synthetic auxin herbicides are designed to mimic indole-3-acetic acid (IAA), an integral plant hormone affecting cell growth, development, and tropism. In this review, we explore target site genes in the auxin signaling pathway including SCFTIR1/AFB, Aux/IAA, and ARFs that are confirmed or proposed mechanisms for weed resistance to synthetic auxin herbicides. Resistance to auxin herbicides by metabolism, either by enhanced cytochrome P450 detoxification or by loss of pro-herbicide activation, is a major non-target-site resistance pathway. We speculate about potential fitness costs of resistance due to effects of resistance-conferring mutations, provide insight into the role of polyploidy in synthetic auxin resistance evolution, and address the genetic resources available for weeds. This knowledge will be the key to unlock the long-standing questions as to which components of the auxin signaling pathway are most likely to have a role in resistance evolution. We propose that an ambitious research effort into synthetic auxin herbicide/target site interactions is needed to 1) explain why some synthetic auxin chemical families have activity on certain dicot plant families but not others and 2) fully elucidate target-site cross-resistance patterns among synthetic auxin chemical families to guide best practices for resistance management.

Loss of trifluralin metabolic resistance in Lolium rigidum plants exposed to prosulfocarb recurrent selection.

BACKGROUND: Resistance to the dinitroaniline herbicide trifluralin in Lolium rigidum (annual ryegrass) often is mediated by the enhanced capacity to metabolize the herbicide to less toxic polar conjugates and/or by functionally recessive target-site mutations in α-tubulin. RESULTS: In two L. rigidum populations possessing enhanced trifluralin metabolism, resistance was largely reversed by recurrent selection with the thiocarbamate herbicide prosulfocarb (i.e. plant survival was two- to >20-fold lower). Their ability to metabolize trifluralin was significantly decreased (by ≈2.3-fold) following recurrent prosulfocarb selection, to levels comparable to those observed in susceptible plants or when trifluralin metabolism was inhibited by treatment with the insecticide phorate. CONCLUSIONS: This study provides evidence that trait(s) enabling efficient trifluralin metabolism in L. rigidum are purged from the population under prosulfocarb recurrent selection. The level of trifluralin metabolism in vitro and its inhibition caused by phorate action on trifluralin-metabolizing enzyme(s) is equivalent to the effect produced by prosulfocarb selection. The hypothetical link between the two phenomena is that the putative monooxygenase(s) conferring trifluralin metabolic resistance also mediate the activation of prosulfocarb to its toxic sulfoxide. Thus, we speculate that survival to prosulfocarb via a lack of metabolic herbicide activation, and survival to trifluralin conferred by enhanced herbicide metabolism, are mutually exclusive. These findings not only open up a new research direction in terms of the interaction between different herbicide resistance mechanisms in L. rigidum, but also offer strategies for immediate management of the population dynamics of metabolism-based resistance in the field. © 2020 Society of Chemical Industry.

A novel insight into the mode of action of glufosinate: how reactive oxygen species are formed.

Glufosinate targets glutamine synthetase (GS), but its fast herbicidal action is triggered by reactive oxygen species (ROS). The relationship between GS inhibition and ROS accumulation was investigated in Amaranthus palmeri. Glufosinate's fast action is light-dependent with no visual symptoms or ROS formation in the dark. Inhibition of GS leads to accumulation of ammonia and metabolites of the photorespiration pathway, such as glycolate and glyoxylate, as well as depletion of other intermediates such as glycine, serine, hydroxypyruvate, and glycerate. Exogenous supply of glycolate to glufosinate-treated plants enhanced herbicidal activity and dramatically increased hydrogen peroxide accumulation (possibly from peroxisomal glycolate oxidase activity). Glufosinate affected the balance between ROS generation and scavenging. The activity of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase increased after glufosinate treatment in an attempt to quench the nascent ROS burst. Low doses of atrazine and dinoseb were used to investigate the sources of ROS by manipulating photosynthetic electron transport and oxygen (O2) evolution. ROS formation depended on electron flow and O2 evolution in photosystem II (PSII). Inhibition of GS disrupted photorespiration, carbon assimilation, and linear electron flow in the light reactions. Consequently, the antioxidant machinery and the water-water cycle are overwhelmed in the presence of light and glufosinate. The O2 generated by the splitting of water in PSII becomes the acceptor of electrons, generating ROS. The cascade of events leads to lipid peroxidation and forms the basis for the fast action of glufosinate.

Treatment Outcomes for Periprosthetic Femoral Fractures in Cementless Press-Fit Total Hip Replacement.

OBJECTIVE: The aim of this study was to report outcomes in dogs with periprosthetic femoral fractures associated with a press-fit cementless femoral total hip replacement implant. MATERIALS AND METHODS: Electronic medical records and digital radiographs were used to identify dogs with periprosthetic femoral fractures associated with press-fit cementless total hip replacement. Data collected included signalment, weight, time of fracture, cause of fracture, presence of intra-operative fissure, fracture type, repair technique, and clinical and radiographic outcomes. Long-term patient outcome was assessed by communication with owners or referring veterinarians. RESULTS: Twenty-eight dogs with femoral fracture repair associated with cementless press-fit total hip replacement were identified. Eight of the fractures occurred intraoperatively and 20 occurred at a median of 2 days postoperatively. An oblique or spiral configuration was noted in 19 cases and 15 occurred at the distal end of the femoral stem (type B), with thirteen type B1, one type B2 and one type B3 fractures. Fractures were repaired with non-locking (18/28) or locking-plate fixation (10/28). Cerclage wire was applied around the plate and proximal bone segment in 17/28 dogs. Major complications occurred in 7/28 cases (five deep infection, two mechanical failures). Bone healing was noted in 21/23 cases, for which follow-up radiographic interpretation was available. Return to function was complete in 17 cases, acceptable in 8 cases and unacceptable in 3 cases. CONCLUSIONS: While cementless total hip replacement periprosthetic femoral fractures can be successfully repaired with lateral plate fixation, the risk of infection appears to be high.

Physiological Factors Affecting Uptake and Translocation of Glufosinate.

Glufosinate is considered a contact herbicide because of its fast activity and limited translocation in plants. We used Palmer amaranth (Amaranthus palmeri S. Watson) as a model species to study plant-related factors affecting glufosinate uptake and translocation. Glufosinate uptake increased rapidly during the initial 24 h, achieving maximum uptake from this time on. The rate of uptake saturated with doses higher than 250 µM glufosinate, suggesting the involvement of a membrane transporter. When glufosinate concentrations were higher (>1 mM), uptake was a simple diffusion process in favor of a concentration gradient between the inside and the outside of the cells. Glufosinate uptake was inhibited by the presence of glutamine. The fast action of glufosinate did not limit its own translocation. Because glufosinate is highly water soluble, it translocates mostly through the apoplast or the xylem system. Consequently, old leaves tend to accumulate more herbicide than young meristematic leaves.

EPSPS gene amplification confers resistance to glyphosate resistant populations of Hordeum glaucum Stued (northern barley grass) in South Australia.

BACKGROUND: Glyphosate failed to control two populations of Hordeum glaucum (northern barley grass) along a fence line and around stockyards near Arthurton on the Yorke Peninsula, South Australia after more than a decade of regular use of glyphosate. These were investigated to confirm resistance and to determine resistance mechanisms. RESULTS: Dose-response experiments confirmed resistance of these populations to glyphosate with resistance levels of 2.8-6.6-fold compared with two susceptible populations. Shikimate assays confirmed resistance to glyphosate with less shikimate accumulation in the resistant populations compared with the susceptible populations. Quantitative PCR of genomic DNA showed increased gene copy number in the resistant populations with 9-11-fold more copies of EPSPS compared with the susceptible populations, suggesting resistance is likely conferred by gene amplification. CONCLUSION: This study identified the first examples of glyphosate resistance in the grass species H. glaucum with resistance associated with EPSPS gene amplification. © 2019 Society of Chemical Industry.

Diversity and extent of mutations endowing resistance to the acetolactate synthase (AHAS)-inhibiting herbicides in Indian hedge mustard (Sisymbrium orientale) populations in Australia.

Indian hedge mustard (Sisymbrium orientale) (IHM) is an important broadleaf weed across southern Australia. Resistance to sulfonylurea (SU) herbicides that inhibit acetohydroxyacid synthase (AHAS) is extensive in Australia, but resistance to imidazolinone (IMI) herbicides has only been reported recently. The AHAS-mutation profile of 65 IHM populations collected randomly from cropped fields was investigated to better understand the extent and types of resistance present. Resistance to SU herbicides was present in 40% of the populations and resistance to IMI herbicides in 11%. Mutations were identified in SoAHAS by sequence analysis, and included previously reported amino-acid substitutions at Pro197 and Trp574, but also new substitutions at Pro197 and Asp376 for this species. One population with possible non-target-site resistance was identified. Germination studies with fresh seed found no significant effect by mutations in SoAHAS on germination; however, population factors had a large effect on germination in S. orientale. Resistance to AHAS-inhibiting herbicides in populations of S. orientale is endowed by mutations in SoAHAS in all but one population examined. Mutations at Pro197 conferring resistance to SU herbicides were most common, while mutations at Trp574 that provide resistance to IMI herbicides are also present.

No apparent fitness costs associated with phytoene desaturase mutations conferred resistance to diflufenican and picolinafen in oriental mustard (Sisymbrium orientale L.).

Two mutations Leu498 and Glu425 in the PDS gene were identified as the main cause conferring resistance to diflufenican and picolinafen in two oriental mustard populations P3 and P40. As mutations are suspected to affect fitness, this study was designed to test this hypothesis using the F2 of two crosses P3.2 (P3♂ × S♀) and P40.5 (P40♂ × S♀) of oriental mustard. The F2 plants, which segregated for target-site point mutations of PDS gene (Leu498 and Glu425) grown in monoculture and under competition with wheat in pot-trials and evaluated for growth and fecundity. All F2 individuals were genotyped by using Cleaved Amplified Polymorphic Sequence (CAPS) technique. Regression analysis showed no fitness cost in the resistant plants because no significant difference was identified in seed and biomass production within RR, RS and SS individuals. The absence of measurable negative effects on fitness associated mutations suggests that the frequency of the PDS resistance alleles will not decline in the absence of selection pressure of PDS-inhibitors.

Reactive oxygen species trigger the fast action of glufosinate.

MAIN CONCLUSION: Glufosinate is primarily toxic to plants due to a massive light-dependent generation of reactive oxygen species rather than ammonia accumulation or carbon assimilation inhibition. Glutamine synthetase (GS) plays a key role in plant nitrogen metabolism and photorespiration. Glufosinate (C5H12NO4P) targets GS and causes catastrophic consequences leading to rapid plant cell death, and the causes for phytoxicity have been attributed to ammonia accumulation and carbon assimilation restriction. This study aimed to examine the biochemical and physiological consequences of GS inhibition to identify the actual cause for rapid phytotoxicity. Monocotyledonous and dicotyledonous species with different forms of carbon assimilation (C3 versus C4) were selected as model plants. Glufosinate sensitivity was proportional to the uptake of herbicide between species. Herbicide uptake also correlated with the level of GS inhibition and ammonia accumulation in planta even with all species having the same levels of enzyme sensitivity in vitro. Depletion of both glutamine and glutamate occurred in glufosinate-treated leaves; however, amino acid starvation would be expected to cause a slow plant response. Ammonia accumulation in response to GS inhibition, often reported as the driver of glufosinate phytotoxicity, occurred in all species, but did not correlate with either reductions in carbon assimilation or cell death. This is supported by the fact that plants can accumulate high levels of ammonia but show low inhibition of carbon assimilation and absence of phytotoxicity. Glufosinate-treated plants showed a massive light-dependent generation of reactive oxygen species, followed by malondialdehyde accumulation. Consequently, we propose that glufosinate is toxic to plants not because of ammonia accumulation nor carbon assimilation inhibition, but the production of reactive oxygen species driving the catastrophic lipid peroxidation of the cell membranes and rapid cell death.

Phenotypic and molecular characterisation of novel Vicia faba germplasm with tolerance to acetohydroxyacid synthase-inhibiting herbicides (AHAS) developed through mutagenesis techniques.

BACKGROUND: Faba bean (Vicia faba L.) is an important crop in Australian farming systems, however, weed control is a major constraint due to a lack of in-crop broadleaf herbicide options. To address this, we developed acetohydroxyacid synthase (AHAS) inhibitor herbicide tolerance in faba bean using mutagenesis techniques. Dose-response experiments, agronomic field evaluation and DNA sequencing of the AHAS gene were used to quantify and validate tolerance traits. RESULTS: Four M2 faba bean single-plant biotypes (IMI-1, IMI-2, IMI-3 and IMI-4) at a frequency of 3.63 × 10-6 were successfully recovered. Molecular characterisation of the AHAS gene identified two known target site mutations (resulting in protein substitutions Ala205Val and Ser653Asn) conferring tolerance. Phenotypic characterisation found that both mutations conferred high levels of tolerance to the imidazolinone herbicide imazapyr. However, although the Ala205Val substitution showed improved levels of cross-tolerance to a range of sulfonylurea chemistries, the Ser653Asn substitution did not. In the field, IMI-3 showed the highest level of agronomic tolerance across a range of imidazolinone herbicides. CONCLUSIONS: Mutagenesis techniques were successful in the development of tolerance to AHAS inhibitor herbicides in faba bean, and could facilitate the first safe in-crop broadleaf herbicide control option in Australian faba bean production. © 2019 Society of Chemical Industry.