Susceptible Biotypes Research Articles

Growth form variations of Amaranthus hybridus L. biotypes with EPSPS mutations

AbstractSeveral Amaranthus hybridus L. biotypes present single and triple amino acid substitutions in EPSPS (5‐enolypyruvylshikimate‐3‐phosphate synthase). In resistant and tolerant species to glyphosate, differential susceptibility and alterations in the EPSPS sequence could cause modifications in their morphological–structural characteristics, an issue that is unknown for biotypes of A. hybridus. The aim of the work was to determine the susceptibility to glyphosate, the presence of mutations in EPSPS and the growth form in four biotypes of this weed from north‐central Argentina. To carry out this, a dose–response assay was conducted, to determine the presence of mutations in the EPSPS, DNA was extracted, amplified and sequenced, and finally, to evaluate the morphological–structural variations, the growth form was analysed. Our findings revealed that Ah03, Ah07 and Ah36 biotypes had resistance factors of 22 to 118. The EPSPS sequence remains unaltered in the Ah39 biotype, leading it to be considered a susceptible biotype. Biotypes Ah03 and Ah36 had heterozygous changes in the DNA sequence resulting in amino acid substitutions at positions 102, 103 and 106 being considered resistant biotypes, whereas in Ah07 some individuals showed unaltered DNA sequences and others exhibited heterozygous changes. The growth form was quantitatively different between biotypes, standing the most susceptible biotype that produced more seeds and required less thermal time for the appearance of the terminal inflorescence. The present investigation provides new evidence that resistant biotypes with the triple DNA mutation exhibit variations in the growth form compared to susceptible biotypes of this weed.

Evaluation of ALS-Resistant Yellow Nutsedge (Cyperus esculentus) in Georgia Peanut

Abstract Accounting for 53% of United States peanuts (Arachis hypogaea L.), Georgia is the top peanut-producing state with approximately 1.42 billion kg produced in 2023. Peanut producers often use the ALS imidazolinone herbicide imazapic but reduced yellow nutsedge (Cyperus esculentus L.) control was reported in Georgia peanuts after four-years of continuous imazapic use. This study aimed to determine the level of resistance (LD50, I50, and GR50), potential cross-resistance for the suspected resistant population, and identify the associated genetic mutations conferring resistance. A susceptible biotype was treated with 0, 0.0088, 0.0175, 0.035, 0.07, 0.14, 0.28, and 0.56 kg ai ha-1, and a resistant biotype was sprayed with 0, 0.07, 0.14, 0.28, 0.56, 1.13, 2.26, and 4.5 kg ai ha-1 of imazapic. To determine if the suspected resistant biotype was cross-resistant to halosulfuron-methyl, an ALS herbicide used to control nutsedge spp., both biotypes were treated with 0, 0.0117, 0.0233, 0.0466, 0.0933, 0.187, 0.373, and 0.746 g ai ha-1 of halosulfuron-methyl. Plants were rated for injury 7, 14, and 28 days after treatment (DAT), and above-ground biomass harvested at 28 DAT. For imazapic, LD50 was 0.041 and 1.503 kg ai ha-1 and the GR50 was estimated to be 0.0128 and 1.853 kg ai ha-1 for Sus and Res biotypes, respectively, indicating 36 and 145-fold increase in resistance of the Res biotype for I50 and GR50, respectively. Both biotypes responded similarly to applications of halosulfuron-methyl, with biomass reductionat rates greater than 0.023 kg ai ha-1. Transcriptome profiles revealed a mutation in the target-site gene of the resistant biotype, causing an amino acid substitution from Alanine to Valine at position 205 (Ala205Val). Growers should continue to rotate chemistries and implement integrated weed management approaches for control of C. esculentus as the use of imazapic over consecutive years has led to resistance in C. esculentus.

Comparative analysis of bacterial populations in sulfonylurea-sensitive and -resistant weeds: insights into community composition and catabolic gene dynamics

This study aimed to compare the impact of iodosulfuron-methyl-sodium and an iodosulfuron-based herbicidal ionic liquid (HIL) on the microbiomes constituting the epiphytes and endophytes of cornflower (Centaurea cyanus L.). The experiment involved biotypes of cornflower susceptible and resistant to acetolactate synthase inhibition, examining potential bacterial involvement in sulfonylurea herbicide detoxification. We focused on microbial communities present on the surface and in the plant tissues of roots and shoots. The research included the synthesis and physicochemical analysis of a novel HIL, evaluation of shifts in bacterial community composition, analysis of the presence of catabolic genes associated with sulfonylurea herbicide degradation and determination of their abundance in all experimental variants. Overall, for the susceptible biotype, the biodiversity of the root microbiome was higher compared to shoot microbiome; however, both decreased notably after herbicide or HIL applications. The herbicide-resistant biotype showed lower degree of biodiversity changes, but shifts in community composition occurred, particularly in case of HIL treatment.Graphical

Revisiting the origins of glyphosate-resistant giant ragweed (Ambrosia trifida L.) in Canada

Glyphosate-resistant giant ragweed ( Ambrosia trifida L.) was first identified in Canada in 2008. Although early studies attributed resistance in this species solely to non-target site mechanisms, the presence of a proline (P) to serine (S) mutation at position 106 of EPSPS2 in common and giant ragweed has recently been reported. The objective of this research was (i) to determine whether a P106S mutation is present in historical samples of giant ragweed seed collected from the site of the first report of glyphosate resistance, and (ii) to determine the frequency and distribution of P106S in resistant and susceptible biotypes collected as part of historical surveys throughout southwestern Ontario.

Glyphosate hormesis effects on the vegetative and reproductive development of glyphosate-susceptible and -resistant Conyza sumatrensis biotypes

Low glyphosate doses that produce hormesis may alter the susceptibility to herbicides of weeds or enhance their propagation and dispersal. The objective of this work was to evaluate the hormetic effects of glyphosate on the vegetative, phenological and reproductive development in resistant (R) and susceptible (S) Conyza sumatrensis biotypes. The glyphosate resistance level of biotype R was 11.2-fold compared to the S biotype. Glyphosate doses <11.25 g ae ha−1 induced temporary and permanent hormetic effects for the number of leaves, plant height and dry mass accumulation up to 28 d after application in both R and S biotypes. The S biotype required 15–19% fewer thermal units at 1.4 and 2.8 g ae ha−1 glyphosate than untreated plants to reach the bolting stage. Also, this biotype had less thermal units associated with the appearance (1225 vs 1408 units) and opening (1520 vs 1765 units) of the first capitulum than the R biotype. In addition, glyphosate affected reproductive traits of both biotypes compared to their controls, increasing the number of capitulum's and seeds per plant up to 37 and 41% (at 2.8 and 0.7 g ae h−1, respectively) in the S biotype, and by 48 and 114% (both at 5.6 g ae ha−1) in the R biotype. Depending on environmental parameters, glyphosate may or may not cause hormetic effects on the vegetative and phenological development of C. sumatrenis biotypes; however, this herbicide increases the speed and fecundity of reproduction, regardless of the glyphosate susceptibility level, which can alter the population dynamics and glyphosate susceptibility of future generations.

Early growth, development and allometry of glyphosate-resistant and susceptible Amaranthus palmeri in response to current and elevated temperature and CO2

This study aimed to evaluate the influence of CO2 and temperature on glyphosate-resistant and susceptible biotypes of Amaranthus palmeri (Palmer amaranth) in terms of morphological development. Height (cm), stem diameter (cm), leaf area (cm2), number of leaves, leaf, stem, and root dry matter, plant volume (m3), as well as shoot-to-root allometry were evaluated. The Palmer amaranth biotypes were grown under four different scenarios: 1—low temperature (23/33 °C) and CO2 (410 ± 25 ppm); 2—low temperature (23/33 °C) and high CO2 (750 ± 25 ppm); 3—high temperature (26/36 °C) and low CO2 (410 ± 25 ppm); and 4—high temperature (26/36 °C) and CO2 (750 ± 25 ppm). Between CO2 and temperature, the majority of differences observed were driven by CO2 levels. Palmer amaranth grown under 750 ppm of CO2 was 15.5% taller, displayed 10% more leaf area (cm2), 18% more stem dry matter, and had a 28.4% increase in volume (m3) compared to 410 ppm of CO2. GA2017 and GA2020 were 18% and 15.5% shorter, respectively. The number of leaves was 27% greater for GA2005. Plant volume decreased in GA2017 (35.6%) and GA2020 (23.8%). The shoot-to-root ratio was isomeric, except at 14 and 21 DAT, where an allometric growth towards shoot development was significant. Palmer amaranth biotypes responded differently to elevated CO2, and the impacts of temperature need further investigation on weed physiology. Thus, environmental and genetic background may affect the response of glyphosate-resistant and susceptible populations to climate change scenarios.

Herbicide resistance status impacts the profile of non-anthocyanin polyphenolics and some phytomedical properties of edible cornflower (Centaureacyanus L.) flowers

To ensure sufficient food supply worldwide, plants are treated with pesticides to provide protection against pathogens and pests. Herbicides are the most commonly utilised pesticides, used to reduce the growth of weeds. However, their long-term use has resulted in the emergence of herbicide-resistant biotypes in many weed species. Cornflower (Centaureacyanus L., Asteraceae) is one of these plants, whose biotypes resistant to herbicides from the group of acetolactate synthase (ALS) inhibitors have begun to emerge in recent years. Some plants, although undesirable in crops and considered as weeds, are of great importance in phytomedicine and food production, and characterised by a high content of health-promoting substances, including antioxidants. Our study aimed to investigate how the acquisition of herbicide resistance affects the health-promoting properties of plants on the example of cornflower, as well as how they are affected by herbicide treatment. To this end, we analysed non-anthocyanin polyphenols and antioxidant capacity in flowers of C.cyanus from herbicide-resistant and susceptible biotypes. Our results indicated significant compositional changes associated with an increase in the content of substances and activities that have health-promoting properties. High antioxidant activity and higher total phenolic and flavonoid compounds as well as reducing power were observed in resistant biotypes. The latter one increased additionally after herbicide treatment which might also suggest their role in the resistance acquisition mechanism. Overall, these results show that the herbicide resistance development, although unfavourable to crop production, may paradoxically have very positive effects for medicinal plants such as cornflower.

Application of ALS inhibitors at pre-emergence is effective in controlling resistant barnyardgrass biotypes depending on the mechanism of resistance

Echinochloa species are one of the most troublesome weeds in rice crops, and their control is hampered due to herbicide resistance. The aim of this study was to identify the cross-resistance pattern and the differential resistance level for pre- and post-emergence applications of imazethapyr and penoxsulam in populations of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] with different ALS gene mutations. Of 26 biotypes, 23 were imazethapyr-resistant, and 10 were cross-resistant to penoxsulam. The resistance index (RI) to imazethapyr was 5.7–19.5 for Ser653Asn, 26.7–68.3 for Ala122Thr and Ala205Asn, and 70.9–252.9 for Trp574Leu. Only Trp574Leu also resulted in resistance to penoxsulam. The double ALS mutation Ala122Asn + Trp574Leu resulted in a RI for imazethapyr and penoxsulam higher than 2800. The ED50 for penoxsulam applied at pre-emergence was three and six times lower than at post-emergence for the susceptible and resistant biotypes, respectively. The application of imazethapyr at pre-emergence was more effective than at post-emergence only for the biotypes with low resistance level mutation Ser653Asn. The efficacy of the herbicide quinclorac was similar for the application at pre- and post-emergence for susceptible and resistant biotypes. The ALS mutations Ala205Asn and Ala122Asn + Trp574Leu are reported for the first time in barnyardgrass. The use of ALS inhibitors at pre-emergence should be prioritized over post-emergence in fields with resistant barnyardgrass and in need of using these products to control other non-resistant weeds.

Nontarget-site resistance due to rapid physiological response in 2,4-D resistant Conyza sumatrensis: reduced 2,4-D translocation and auxin-induced gene expression.

Resistance to 2,4-Dichlorophenoxyacetic acid (2,4-D) has been reported in several weed species since the 1950s; however, a biotype of Conyza sumatrensis showing a novel physiology of the rapid response minutes after herbicide application was reported in 2017. The objective of this research was to investigate the mechanisms of resistance and identify transcripts associated with the rapid physiological response of C. sumatrensis to 2,4-D herbicide. Differences were found in 2,4-D absorption between the resistant and susceptible biotypes. Herbicide translocation was reduced in the resistant biotype compared to the susceptible. In resistant plants 98.8% of [14 C] 2,4-D was found in the treated leaf, whereas ≈13% translocated to other plant parts in the susceptible biotype at 96 h after treatment. Resistant plants did not metabolize [14 C] 2,4-D and had only intact [14 C] 2,4-D at 96 h after application, whereas susceptible plants metabolized [14 C] 2,4-D into four detected metabolites, consistent with reversible conjugation metabolites found in other 2,4-D sensitive plant species. Pre-treatment with the cytochrome P450 inhibitor malathion did not enhance 2,4-D sensitivity in either biotype. Following treatment with 2,4-D, resistant plants showed increased expression of transcripts within plant defense response and hypersensitivity pathways, whereas both sensitive and resistant plants showed increased expression of auxin-response transcripts. Our results demonstrate that reduced 2,4-D translocation contributes to resistance in the C. sumatrensis biotype. The reduction in 2,4-D transport is likely to be a consequence of the rapid physiological response to 2,4-D in resistant C. sumatrensis. Resistant plants had increased expression of auxin-responsive transcripts, indicating that a target-site mechanism is unlikely. © 2023 Society of Chemical Industry.

Growth rate and competitive ability of susceptible and multiple-resistant late watergrass (Echinochloa phyllopogon) biotypes to rice

Abstract Late watergrass [Echinochloa phyllopogon (Stapf) Koss.] has evolved multiple-resistance (MR) to herbicides in many areas worldwide and scientists wonder if this resistance has imposed fitness cost or advantage on the resistant (MR) biotypes. As multiple-resistance of this weed has also been recorded in Greece, one susceptible (S), one with multiple-resistance to ALS (penoxsulam, bispyribac, imazamox and nicosulfuron + rimsulfuron) and ACCase-cyhalofop (MRAC) and two with multiple-resistance to ALS and synthetic auxin-quinclorac (MRAQ1, MRAQ2) late watergrass biotypes collected from rice fields (northern Greece) were studied for their growth rate and competitive ability (regarding stem number and fresh weight) in the absence and presence of rice. Also, the competition indices relative yield (RY), competitive ratio (CR) and aggressiveness (AI) were evaluated. The S and the three MR biotypes grown in absence of competition (one plant/pot) showed different shoot number but similar fresh weight growth rates. In contrast, grown under intra-specific competition (one, two, four and six plants/pot), the S late watergrass biotype produced similar fresh weight with that of MRAQ1 but lower than that of the MRAC and MRAQ2 biotypes. However, grown under inter-specific competition (one, two, four and six plants of late watergrass/pot in competition with six rice plants/pot), the MRAQ2 late watergrass biotype produced more shoot number and fresh weight than the other biotypes at all weed densities, but the rice shoot number and fresh weight reduction were not followed the opposite trend of the late watergrass biotypes. Also, the competition indices of the MR biotypes (based on both intra- and inter-specific completion data) were found similar in most cases to that of the S biotype. These findings strongly suggest that there is no clear association between the growth rate and competitive ability of the late watergrass biotypes and their herbicide resistance.

Recurrent Selection of Echinochloa crus-galli with a Herbicide Mixture Reduces Progeny Sensitivity.

Herbicide mixtures are used to increase the spectrum of weed control and to manage weeds with target-site resistance to some herbicides. However, the effect of mixtures on the evolution of herbicide resistance caused by enhanced metabolism is unknown. This study evaluated the effect of a fenoxaprop-p-ethyl and imazethapyr mixture on the evolution of herbicide resistance in Echinochloa crus-galli using recurrent selection at sublethal doses. The progeny from second generations selected with the mixture had lower control than parental plants or the unselected progeny. GR50 increased 1.6- and 2.6-fold after two selection cycles with the mixture in susceptible (POP1-S) and imazethapyr-resistant (POP2-IR) biotypes, respectively. There was evidence that recurrent selection with this sublethal mixture had the potential to evolve cross-resistance to diclofop, cyhalofop, sethoxydim, and quinclorac. Mixture selection did not cause increased relative expression for a set of analyzed genes (CYP71AK2, CYP72A122, CYP72A258, CYP81A12, CYP81A14, CYP81A21, CYP81A22, and GST1). Fenoxaprop, rather than imazethapyr, is the main contributor to the decreased control in the progenies after recurrent selection with the mixture in low doses. This is the first study reporting the effect of a herbicide mixture at low doses on herbicide resistance evolution. The lack of control using the mixture may result in decreased herbicide sensitivity of the weed progenies. Using mixtures may select important detoxifying genes that have the potential to metabolize herbicides in patterns that cannot currently be predicted. The use of fully recommended herbicide rates in herbicide mixtures is recommended to reduce the risk of this type of resistance evolution.

Metabolic Exploration for Cyhalofop-Butyl Antagonism in Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] Following Pretreatment of Malathion.

The present study investigated the effects of broad-spectrum metabolic inhibitors malathion (cytochrome P450 inhibitor) and/or 4-chloro-7-nitrobenzofurazan (NBD-Cl; glutathione S-transferase inhibitor) on the metabolism of cyhalofop-butyl (CyB) in barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] biotypes confirmed previously with multiple resistance to two herbicides CyB and florpyrauxifen-benzyl. The metabolic inhibitors were not effective at recovering the sensitivity of resistant barnyardgrass biotypes to CyB treated at the labeled rate (313 g ai ha-1). Rather, treatment with malathion followed by CyB caused antagonism, reducing the efficacy of CyB and promoting the growth of resistant biotypes. Pretreatment with malathion did not influence absorption/translocation of the applied form CyB and its conversion to the active herbicide form cyhalofop-acid (CyA), in both susceptible and resistant biotypes. In contrast, metabolism of the applied form (CyB) decreased 1.5 to 10.5 times by the malathion pretreatment. Taken together, the maintained CyA production against the reduced CyB metabolism could be the mechanism to account for the cause of CyB antagonism observed in barnyardgrass following malathion pretreatment. Additionally, the evolution of CyB resistance in barnyardgrass might be associated with reduced production of CyA in resistant biotypes, independent of activities of cytochrome P450 or GST enzymes.

Conyza Species in Citrus Orchards and Vineyards of Turkey and Their Management with Glyphosate

Conyza species are considered one of the most aggressive weeds in the Aegean and Mediterranean regions of Turkey in terms of their invasive character and their ability to spread to agricultural and nonagricultural areas, including citrus orchards and vineyards. This study was conducted to determine the distribution of Conyza species in citrus orchards and vineyards in these regions and the efficacy of glyphosate when used at different growth stages. The majority of citrus fields and nearly half of the vineyard fields of Turkey were visited in 2015. Due to their similar appearance, the identification of Conyza species at the early stages of growth cannot straightforward; therefore, the species C. canadensis, C. bonariensis, and C. sumatrensis were identified by using PCR and DNA sequence analysis. A total of 252 citrus orchards (131) and vineyards (121) were included in the field survey conducted in the Aegean and Mediterranean regions, and 203 Conyza species were collected. The molecular data revealed that C. bonariensis was the most common Conyza species in nearly half of the citrus orchards, followed by C. canadensis at 33%. C. canadensis was the most dominant Conyza species in more than half of the vineyards, while C. bonariensis and C. sumatrensis were found in 36 and 13 vineyards, respectively. Sequence information of Conyza species was submitted to NCBI with GenBank accession numbers (Conyza (Erigeron) canadensis accession number: OM302550.1, C. bonarensis accession number: OM302551.1, C. sumatrensis accession number: OM302548.1). Glyphosate was more effective when it was applied at the earlier rosette stages for both susceptible and resistant biotypes. Therefore, late treatments could be the main reason for glyphosate having low efficacy against non-resistant populations of Conyza spp.&#x0D; &#x0D; Keywords: Citrus orchard, DNA sequence analysis, Glyphosate, Horseweed, Vineyard

First report on ALS herbicide resistance in barnyardgrass (Echinochloa crus-galli) from rice fields of India

AbstractBispyribac-sodium, a herbicide that inhibits acetolactate synthase (ALS), is frequently used in rice fields in India to control weeds, including the most common noxious weed, barnyardgrass. However, rice growers have recently reported reduced control of barnyardgrass with bispyribac-sodium. Hence, a large-scale survey was carried out to assess bispyribac-sodium resistance in Chhattisgarh and Kerala, two rice-growing states. Open-field pot experiments were conducted for 2 yr to confirm resistance to bispyribac-sodium. Of the 37 biotypes tested, 30% (11) survived the recommended label rate of bispyribac-sodium (25 g ai ha−1). The effective rate of bispyribac-sodium required to achieve 50% control (ED50) of putative resistant biotypes ranged from 18 to 41 g ha−1, whereas it was about 10 g ha−1 for susceptible biotypes. This suggests that putative biotypes were two to four times more resistant to bispyribac-sodium. At 6 d after herbicide application, an in vitro enzyme assay demonstrated higher ALS enzyme activity in putative resistant biotypes (66% to 75%) compared with susceptible biotypes (48% to 52%). This indicates the presence of an insensitive ALS enzyme in those biotypes and a target site mutation as a possible mechanism for resistance. Whole-plant bioassays also suggested that the resistance problem is more widespread in Chhattisgarh than in Kerala. This study confirmed the first case of evolved resistance in barnyardgrass to bispyribac-sodium in rice fields of India.

Kin Recognition in an Herbicide-Resistant Barnyardgrass (Echinochloa crus-galli L.) Biotype.

Despite increasing evidence of kin recognition in natural and crop plants, there is a lack of knowledge of kin recognition in herbicide-resistant weeds that are escalating in cropping systems. Here, we identified a penoxsulam-resistant barnyardgrass biotype with the ability for kin recognition from two biotypes of penoxsulam-susceptible barnyardgrass and normal barnyardgrass at different levels of relatedness. When grown with closely related penoxsulam-susceptible barnyardgrass, penoxsulam-resistant barnyardgrass reduced root growth and distribution, lowering belowground competition, and advanced flowering and increased seed production, enhancing reproductive effectiveness. However, such kin recognition responses were not occurred in the presence of distantly related normal barnyardgrass. Root segregation, soil activated carbon amendment, and root exudates incubation indicated chemically-mediated kin recognition among barnyardgrass biotypes. Interestingly, penoxsulam-resistant barnyardgrass significantly reduced a putative signaling (-)-loliolide production in the presence of closely related biotype but increased production when growing with distantly related biotype and more distantly related interspecific allelopathic rice cultivar. Importantly, genetically identical penoxsulam-resistant and -susceptible barnyardgrass biotypes synergistically interact to influence the action of allelopathic rice cultivar. Therefore, kin recognition in plants could also occur at the herbicide-resistant barnyardgrass biotype level, and intraspecific kin recognition may facilitate cooperation between genetically related biotypes to compete with interspecific rice, offering many potential implications and applications in paddy systems.

Assessment of ACC and P450 Genes Expression in Wild Oat (Avena ludoviciana) in Different Tissues Under Herbicide Application.

Target-site resistance (TSR) and non-target-site resistance (NTSR) to herbicides in arable weeds are increasing rapidly all over the world and threatening universal food safety. Resistance to herbicides that inhibit ACCase activity has been identified in wild oat. In this study, expression of ACC1, ACC2, CYP71R4 and CYP81B1 genes under herbicide stress conditions were studied in two TSR (resistant in the residue Ile1781-Leu and Ile2041-Asn of ACCase) biotypes, two NTSR biotypes and one susceptible biotype of A. ludoviciana for the first time. Treated and untreated biotypes with ACCase-inhibitor clodinafop propargyl herbicide were sampled from the stem and leaf tissues at 24h after treatment. Our results showed an increase in gene expression levels in different tissues of both types of resistance biotypes that occurred under herbicide treatment compared with non-herbicide treatment. In all samples, the expression levels of leaf tissue in all studied genes were higher than in stem tissue. The results of ACC gene expression showed that the expression level of ACC1 was significantly higher than that of ACC2. Also, expression levels of TSR biotypes were higher than NTSR biotypes for the ACC1 gene. For both CYP71R4 and CYP81B1 genes, the expression ratio increased significantly in TSR and NTSR biotypes in different tissues after herbicide treatment. In contrast, the expression levels of CYP genes in NTSR biotypes were higher than in TSR biotypes. Our results support the hypothesis that the reaction of plants to herbicide is carried out through a different regulation of genes, which can be the result of the interaction of resistance type in the target or non-target-site.

Quick bioassay test from tillers for detecting ALS herbicide resistance of weedy rice and barnyardgrass

Resistance to acetolactate synthase (ALS) inhibitors have increased recently in South Brazil where the major weeds of flooded rice (barnyardgrass and weedy rice) have evolved resistance to imazapyr+imazapic. The aim of this research was to evaluate a growth medium for tissue regeneration of tillers in barnyardgrass, as well as an agar-based bioassays test (also from tillers) to detect susceptible and resistant biotypes of weedy rice and barnyardgrass to imazapyr+imazapic in vitro. Greenhouse experiments were conducted to detect ALS-resistant (R) and susceptible (S) weedy rice and barnyardgrass biotypes, and bioassays were carried out to evaluate an adequate growth medium for barnyardgrass tiller regeneration and determine the concentration of herbicide to distinguish R and S plants. The culture medium that provided a suitable barnyardgrass growth was MS 50% with the addition of benzylamino-purine. The tissue regeneration in vitro with the growth medium containing imazapyr+imazapic allowed to discriminate between R and S barnyardgrass and weedy rice plants. The concentration required for satisfactory control of susceptible barnyardgrass and weedy rice explants grown in vitro was 0.9 μM and 1.3 μM of imazapyr+imazapic herbicide, respectively. The bioassay in vitro using tiller regeneration provides an opportunity to predict effectively imazapyr+imazapic resistance in barnyardgrass and weedy rice.

Proteomic Analysis Comparison on the Ecological Adaptability of Quinclorac-Resistant Echinochloa crus-galli.

Barnyardgrass (Echinochloa crus-galli L.) is the most serious weed threatening rice production, and its effects are aggravated by resistance to the quinclorac herbicide in the Chinese rice fields. This study conducted a comparative proteomic characterization of the quinclorac-treated and non-treated resistant and susceptible E. crus-galli using isobaric tags for relative and absolute quantification (iTRAQ). The results indicated that the quinclorac-resistant E. crus-galli had weaker photosynthesis and a weaker capacity to mitigate abiotic stress, which suggested its lower environmental adaptability. Quinclorac treatment significantly increased the number and expression of the photosynthesis-related proteins in the resistant E. crus-galli and elevated its photosynthetic parameters, indicating a higher photosynthetic rate compared to those of the susceptible E. crus-galli. The improved adaptability of the resistant E. crus-galli to quinclorac stress could be attributed to the observed up-regulated expression of eight herbicide resistance-related proteins and the down-regulation of two proteins associated with abscisic acid biosynthesis. In addition, high photosynthetic parameters and low glutathione thiotransferase (GST) activity were observed in the quinclorac-resistant E. crus-galli compared with the susceptible biotype, which was consistent with the proteomic sequencing results. Overall, this study demonstrated that the resistant E. crus-galli enhanced its adaptability to quinclorac by improving the photosynthetic efficiency and GST activity.

Investigations into differential glyphosate sensitivity between two horseweed (Conyza canadensis) growth types

AbstractHorseweed [Conyza canadensis (L.) Cronquist] grows in one of two distinct growth phenotypes, “rosette” and “upright” growth types, and they have recently been observed co-occurring in Michigan fields. Previous research found that upright plants from two glyphosate-resistant populations were 3- and 4-fold less sensitive to glyphosate than their rosette siblings. Further experiments were conducted to investigate whether differential glyphosate sensitivity of the growth types was due to glyphosate retention, absorption, or translocation. The total amount of glyphosate retained on the C. canadensis leaf surface was similar for both growth types; however, on a per-weight and per-area bases, the upright growth type retained 21% and 18% less glyphosate, respectively. Glyphosate absorption was up to 85% at 168 h after treatment (HAT), and was not different between the rosette and upright growth types or between the susceptible (S) and resistant (R) biotypes. Additionally, there was no difference in translocation between the two growth types within each biotype at any time point. Interestingly, at 168 HAT, [14C]glyphosate translocation was higher in the S rosette compared with the two growth types from the R biotype; however, the S upright type was similar to both R growth types. Thus, glyphosate resistance in the R biotype may be due to an alternative mechanism rather than impaired translocation, which has been cited as the primary mechanism of glyphosate resistance in C. canadensis. These results suggest that reduced glyphosate retention on a per-weight and per-area bases of the upright growth type may contribute to increased glyphosate tolerance due to a diluted concentration of glyphosate in the plant. However, another factor is likely related to the mechanism of resistance within the R biotype, which is contributing to a 3-fold difference in glyphosate sensitivity between the two growth types, such as alterations in EPSPS gene expression or changes in undescribed metabolism genes.

Seed Meals from Allelopathic Crops as a Potential Bio-Based Herbicide on Herbicide-Susceptible and -Resistant Biotypes of Wild Oat (Avena fatua L.)

Wild oat is a nuisance monocot weed mainly in cereal canopies. The increasing problem of herbicide resistance and the implementation of integrated pest management includes the use of seed meals from species with allelopathic potential. This study aimed to assess the efficacy of seed meals as an environmentally friendly alternative for the control of herbicide-susceptible (S) and -resistant (R) wild oat biotypes. A pot experiment was carried out under greenhouse conditions at the Swojczyce Research and Training Station in Wrocław (Poland) to determine the impact of seed meals from Fagopyrum esculentum, Lupinus luteus, Ornithopus sativus, Phacelia tanacetifolia, Raphanus sativus var. oleiformis and Sinapis alba at two concentrations—1 and 3%. The lowest percentage of seedling emergence was recorded after the application of S. alba seed meal. Seed meals from S. alba reduced the emergence of both S and R biotypes by approximately 82 and 61 percentage points, respectively, and limited the initial growth of both biotypes. F. esculentum, O. sativus and R. sativus seed meals generally did not decrease the number of seedlings. Almost all the seed meals inhibited the growth of the aboveground parts of the susceptible biotype of wild oat to a greater extent than the herbicide treatment.