Resumo em Inglês:

Abstract: Background: Soybean cultivars show a positive response to low doses of glyphosate, called glyphosate hormesis, though the genetic and biochemical mechanisms are not fully understood. Objective: This study aimed to identify the pathways and differentially expressed genes (DEGs) related to glyphosate hormesis, along with their association with lignin and P content, and the shikimic acid pathway in glyphosate-resistant cultivars (RR and RR2) compared to a non-resistant cultivar (NR). It also evaluated how glyphosate hormesis impacted the electron transport rate (ETR) and biomass accumulation. Results: With 90% of reads matching the soybean reference genome, 31,515 genes were identified, including 587 DEGs. The DEGs enriched by glyphosate application in the NR cultivar were associated with flavone metabolism and auxin signaling, indicating impacts on phenylalanine-derived metabolites and developmental processes. In contrast, the RR cultivar showed enrichment in pathways related to stress response and fatty acid metabolism, while the RR2 cultivar exhibited enrichment in various metabolic pathways, notably lignin catabolism and auxin activity. Glyphosate treatments influenced electron transport rate (ETR), lignin, and P content, as well as components of the shikimic acid pathway and amino acid contents in soybean plants, with differential responses observed among cultivars and glyphosate doses. Overall, glyphosate hormesis led to increased dry biomass production across all cultivars. Conclusion: These findings provide insights into the molecular and physiological responses of soybean cultivars to glyphosate hormesis, highlighting the complex regulatory mechanisms that enable unique adaptations in each cultivar to the stress imposed by low herbicide doses.

Resumo em Inglês:

Abstract: Background: Triticum monococcum subsp. aegilopoides (wild einkorn wheat) is a problematic weed in the Mediterranean and Middle Eastern winter cereal crops. Objective: A process-based niche model for this species was developed using CLIMEX to evaluate its potential global distribution. Methods: Records from Iran were utilized in the model, and the prediction was applied under the current climate and two climate change scenarios (A1B, A2). Both scenarios represent contrasting temporal patterns of economic development and carbon dioxide (CO2) emissions. Results: The results showed that Europe and Africa continent were the most and least vulnerable regions, respectively, to wild einkorn wheat infestation. Under climate change scenarios A1B and A2, the average Climate Matching Index (CMI) showed significant increases of 4.7% and 5.6% in Europe and North America, respectively, compared to the current conditions. In contrast, Oceania, Asia, and Africa experienced notable decreases of 6.9%, 5.7%, and 4.7%, respectively. In the Northern Hemisphere, 97% of the areas with a CMI's greater than 0.75 were located within the 30° to 48° latitude range. Conclusions: These findings can serve as a foundation for ongoing monitoring efforts to prevent the further spread of this species, as well as to develop effective quarantine regulations and preventive measures aimed at minimizing its negative impact on wheat yields and appropriate management options.

Resumo em Inglês:

Abstract: Background: Phalaris minor Retz. is a major weed of rice-wheat cropping systems in South Asia, where its variable dormancy and germination behavior hinder effective control and often lead to heavy reliance on herbicides. Population-based threshold models offer a useful approach for predicting weed emergence, allowing for better management interventions and potentially reducing dependence on chemical control. Objective: The study aims to predict the germination and emergence behavior of Phalaris minor seeds in rice-wheat cropping systems by predicting key ecological drivers, particularly temperature and soil moisture regimes. Methods: Seeds were tested across a wide range of environmental factors, including temperature, soil moisture levels, light availability, and different sowing depths. Results: P. minor germination is highly temperature-dependent, with a base temperature of approximately 3.5°C and a ceiling temperature of 35.3°C, and a base water potential of −0.6 MPa. The highest germination occurred at temperatures between 20–25°C and at water potentials ranging from 0 to −0.3 MPa. Seeds kept in continuous darkness showed reduced germination compared to those exposed to a 12-hour light cycle. Seedling emergence was highest when seeds were sown on the soil surface, gradually decreased as sowing depth increased, and was completely inhibited at a depth of 6 cm. Conclusion: Understanding these patterns can help optimize weed management strategies by aligning control measures with key germination windows, reducing weed pressure in wheat fields. Further research should focus on validating the model in diverse agro-ecological conditions to improve its applicability in sustainable weed control.

Resumo em Inglês:

Abstract Background: Weed interference is one of the factors that reduces the productivity of citrus orchards, as it limits the availability of resources for plants. Objective: Evaluate the influence of weed control area width on the development, productivity, and quality of the ‘Pera Rio’ orange tree. Methods: The experiment was conducted in a commercial ‘Pera Rio’ orange orchard. A randomized block design was used, with 12 treatments and three replications, evaluating different weed control widths: manual crowning in radii of 0.5 m, 1 m, and according to the projection of the canopy; clean and infested strips of 1 m, 2 m, and 3 m; as well as two controls (with and without management). Vegetative development (height, crown diameter, branch length, and chlorophyll content) was assessed at 0, 12, and 18 months, and fruit yield and quality (mass, diameter, juice yield, soluble solids, acidity, and ratio) at two harvests. Weeds were controlled through weeding or the use of glyphosate herbicide and monitored after seven applications. Results: The presence of weeds reduced vegetative growth (except height), productivity, and fruit quality of the ‘Pera Rio’ orange tree. The highest yields were observed in the control group, in the 1 m radius crowning, and in the 1 and 3 m clean strips. These same conditions also favored fruit with greater mass, diameter, and juice yield. Continuous coexistence with weeds resulted in yield losses of up to 60%. Conclusions: The control area directly influences vegetative growth, productivity, fruit quality, and the industrial yield of ‘Pera Rio’ orange juice.

Resumo em Inglês:

Abstract Background: Buttonweed (genera Borreria and Mitracarpus) is an emerging, difficult to control weed increasingly prevalent in agricultural areas of Brazil, particularly in the Cerrado biome. Objective: Identify four buttonweed accessions, common in agricultural areas of the Brazilian Cerrado, in addition to separate and group the species based on molecular analysis. Methods: Seeds were collected, sown in pots, and plants cultivated under greenhouse and field conditions. At the time of field transplantation, part of the plants from each accession was sent to the laboratory for molecular analysis. The species of the four accessions were determined based on vegetative and reproductive morphological characteristics, using identification keys for Borreria and Mitracarpus species. In the laboratory, samples were processed, and DNA was extracted for subsequent PCR amplification, Sanger sequencing, sequence alignment, and phylogenetic analysis. Results: The accessions were identified as Borreria diacrodonta L.M. Miguel & E.L. Cabral, Borreria spinosa Cham. & Schltdl. ex DC, Borreria verticillata (L.) G. Mey., and Mitracarpus hirtus (L.) DC, corresponding to accessions PA-01, PA-02, PA-03, and PA-04, respectively. The phylogenetic analysis showed that the PA-01 accession grouped with B. diacrodonta, the PA-02 accession grouped with B. spinosa, the PA-03 accession grouped with B. verticillata and the PA-04 accession grouped with M. hirtus. Conclusions: Three species of Borreria and Mitracarpus hirtus were identified, and confirmed by molecular analysis. Borreria diacrodonta was reported for the first time as a weed in Brazil. This study provided additional morphological and molecular information to correctly identify the buttonweed species in Brazil.

Resumo em Inglês:

Abstract Background: Growing public concerns about the health and environmental hazards associated with synthetic herbicides have necessitated the pursuit of sustainable weed management alternatives. Allelopathic plant extracts present a potential solution for environmentally friendly weed control. However, little is known about the bioherbicidal potential of allelopathic plant species native to Ghana. Objective: This study screened aqueous and ethanol extracts from allelopathic plants in Ghana, to examine their potential as bio-herbicides for sustainable weed management, and also identified the allelocompounds present. Method: Laboratory experiments evaluated 27 plant extracts plus a control using a completely randomized design with three replications. Both aqueous and ethanol extraction methods were applied to different plant organs (leaves, roots, bark, stems). Daily emergence of monocot and dicot weeds was monitored over 21 days and analyzed using Generalized Linear Models with control as reference. Using GC-MS analysis, promising extracts were analyzed for bioactive compounds responsible for herbicidal activity. Results: Multiple extracts suppressed (p<0.05) cumulative monocot weed emergence over the 21 days compared to the control. Effective aqueous extracts included Chromolaena odorata leaves (ChLE), Gliricidia sepium bark (GBE), Azadirachta indica leaves (NLE), Moringa oleifera leaves (MLE), among others. Ethanol extracts of Senna siamea bark (CBE), Callophyllum inophyllum leaf (CiLE), and Leucaena leucocephala root (LeRE) demonstrated superior performance with sustained suppression effects. GC-MS analysis identified phenolic compounds, alkaloids, and terpenoids, including I-[-]-4-Hydroxy-1-methylproline, 5-Hydroxypipecolic acid, as major bioactive compounds showing potential for commercial bioherbicide development. Conclusion: The study identified plant extracts with bioherbicidal activities, with specific plant-solvent combinations showing potential for commercial bioherbicide development.

Resumo em Inglês:

Abstract Background: Eragrostis plana Nees is the main invasive plant species in the grasslands of the Pampa Biome, southern Brazil. Crop-livestock integration has been used as a management strategy through the cultivation of soybean tolerant to glyphosate herbicide. However, in recent years, farmers have reported failures in the control of E. plana. Objective: To evaluate the response of two E. plana biotypes to glyphosate (S - susceptible and R – resistant plants with suspected failure of control by the herbicide), as well as to investigate the mechanism involved in the differential response to the herbicide. Methods: Dose-response assays were performed to estimate ED50 and GR50, based on seeds and clonal plants. The partial sequencing of the EPSPS gene was analysed. The gene expression of EPSPS, AKR, ABC-MRP8 and ABC-MRP10 were investigated, when the biotypes grown at 20/15ºC or 35/30ºC day/night temperature conditions. Results: The ED50 values of R biotype were 6634.18 and 4479.79 g ae. ha–1 glyphosate in 2024 and 2025, respectively compared with S biotype (591.20 and 589.08 g ae. ha–1). The GR50 values were 103.71 and 1118.08 g ae. ha–1 glyphosate for S and R, respectively. Dose-response assays using seedderived plants (not clonal plants) showed considerable genetic variability, reflecting the natural condition in the field. Partial EPSPS gene sequencing revealed a heterozygous mutation at the Pro106Leu position. Conclusions: The results contribute to the understanding of glyphosate performance variability in E. plana populations, confirming the evolution for glyphosate resistance, and underscore the necessity of adopting integrated weed management strategies.

Resumo em Inglês:

Abstract Background: Weeds are among the most limiting factors in sugar beet (Beta vulgaris L.) production, as they compete for resources, reduce crop growth and yield and increase production costs. Therefore, effective and sustainable weed management strategies are essential to ensure stable and profitable sugar beet production. Objective: This study aimed to evaluate the effectiveness of different herbicide active ingredients, their mixtures, and mechanical control practices on weed suppression, crop growth, and yield in sugar beet. Methods: Field experiments were conducted during the 2023 and 2024 growing seasons using a randomized complete block design. Pre-emergence applications included 1575 g a.i. ha–¹ metamitron + 120 g a.i. ha–¹ quinmerac (MQ), while post-emergence treatments consisted of 1200 g a.i. ha–¹ metamitron + 165 g a.i. ha–¹ ethofumesate + 105 g a.i. ha–¹ phenmedipham (MEP) and 37.5–50 g a.i. ha–¹ quizalofop-p-ethyl (Q). Herbicides were applied alone and in combination with mechanical hoeing. Weed dry weight, herbicide efficacy, yield components, and root yield were measured, and treatment effects were assessed at regular intervals. Results: Single herbicide applications provided limited weed suppression, whereas combined treatments resulted in significantly higher and more persistent control. Weed suppression peaked at 40 days after application and remained high until 150 days. The MQ + weed-free treatment achieved 100% control, followed by MQ + MEP + Q with 94.38%. Yield increased by 136% and 135% in MQ + weed-free and weed-free controls compared to weedy controls. A 1% increase in weed control corresponded to a 0.0035 t ha–¹ increase in yield. Weed density was identified as the most influential factor affecting yield. Conclusions: Integrating herbicides with mechanical control provided superior and long-lasting weed management compared with single treatments and significantly enhanced sugar beet yield. Effective weed management should therefore prioritize maintaining low weed density to ensure sustainable production.

Resumo em Inglês:

Abstract: Background: Johnsongrass (Sorghum halepense) is an important weed in summer crops of Argentina. In 2005, the first population resistant to glyphosate was identified and in 2015 one multiple resistant to glyphosate and haloxyfop methyl was registered. Another population with multiple resistance to glyphosate, haloxyfop methyl and clethodim was also identified in 2020. This study represents the first complete survey of herbicide resistant populations of johnsongrass in Argentina. Objective: The objective was to quantify the presence and distribution of ACCase and glyphosate resistant johnsongrass populations. In addition, the resistance factor (RF) was estimated for some populations, and the target site resistance mechanism was also studied. Methodology: From 2014 to 2023, a set of experiments was performed with the aim of studying the responses of 392 populations of johnsongrass to glyphosate, clethodim and haloxyfop-methyl. Survival was assessed 30 days after herbicide applications. One population known as susceptible to each herbicide was included. The applications were made with a CO2- powered backpack sprayer when seedling plants had four to six expanded leaves. Results: Glyphosate resistance was prevalent (70%). The frequency of populations showing survival with haloxyfop-methyl (15%) was greater than that with clethodim (7%). Eight percent were cross resistant (haloxyfop-methyl + clethodim), and 19% multiple resistance to glyphosate + ACCase inhibitors. Mutation W2027C was identified in one population resistant to haloxyfop methyl and glyphosate. Mutation W1999G was identified in a population with multiple resistance to haloxyfop-methyl, clethodim and glyphosate from Santa Fe, and mutations W2027C and G2096A occurred in another population from Córdoba.

Resumo em Inglês:

Abstract: Background: Hairy fleabane (Conyza bonariensis L.) is a difficult weed to control in soybean production systems as it presents resistance to some herbicides; thus, leading to substantial grain yield losses. Objective: The objective of this study was to evaluate the efficacy and selectivity of herbicides applied before and after soybean planting on glyphosate-resistant C. bonariensis. Methods: Field experiments were conducted over two soybean growing seasons in 2021/22 and 2022/23 near Erechim, Rio Grande do Sul, Brazil. Early weed management treatments included terbuthilazine (1,500 g ha−1), mesotrione+atrazine (120+1,200 g ha−1), metsulfuron-methyl (6 g ha−1), dicamba (720 g ha−1), 2,4-D amine (1,612 g ha−1), flumioxazin (50 g ha−1), diclosulam (35.28 g ha−1) and atrazine+simazine (1,500+1,500 g ha−1) applied 60 days before soybean planting. For pre-plant burndown, diquat + saflufenacil (600+70 g ha−1) were applied three days before soybean planting. For post-emergence weed control, 2,4-D choline+glyphosate (971.28+1232.65 g ha−1) were applied at the V3 to V4 soybean growth stage. The C. bonariensis plants present in the experimental area were resistant to the herbicide glyphosate. Results: The best early hairy fleabane control was achieved with mesotrione+atrazine, dicamba, and 2,4-D amine, providing more than 90% efficacy. Diquat+saflufenacil applied pre-plant burndown provided excellent level of control, particularly following dicamba in early management, reaching 100% control. Post-emergence application of 2,4-D choline+glyphosate after early treatments with mesotrione+atrazine or dicamba resulted in 100% control. Conclusions: The combination of atrazine + simazine for early management, diquat + saflufenacil for pre-plant burndown, and 2,4-D choline+glyphosate post-emergence effectively controlled hairy fleabane and contributed to higher grain yield.

Resumo em Inglês:

Abstract Background: In banana greenhouses in Türkiye, extensive herbicide use and high irrigation demand create environmental and management challenges. However, the effects of herbicide application frequency and irrigation on weed control strategies and their effectiveness remain unclear. Objective: The research, conducted in Mersin in 2022–2024, evaluated the effects of alternative weed control methods (mowing and geotextile mulching) and sequential herbicide treatment programs (oxyfluorfen, pendimethalin, indaziflam, glyphosate, diquat) under full (100%) and deficit (50%) irrigation. Methods: The experiment was established using split-plot design, with irrigation levels assigned to the main plots and randomized subplots arranged in three replications. Control for coverage (% population thresholds), weed density (plant m-2), and end-of-experiment dry biomass (g m-2) were measured. Results: Weed community changes were evaluated using Shannon-Wiener and Simpson indices, and treatment–species relationships were analyzed by canonical discriminant analysis (CDA). Herbicide treatments (especially indaziflam+diquat; 1.00 plant m-2; 7.92 g m-2) reduced weed populations compared to the weedy control. Mulching (0.00 plant m-2; 0.00 g m-2) was the most effective. Mowing demonstrated partial effectiveness, achieving only limited weed suppression (41.09 plant m-2; 125.00 g m-2). Irrigation levels did not significantly affect weed density or biomass, whereas control methods significantly altered weed composition, species abundance, and diversity. Setaria viridis decreased depending on treatments, while Cardamine occulta, Oxalis spp., Urtica urens, and Amaranthus viridis increased. CDA revealed that weed treatments significantly influenced species composition. Conclusions: Integrating alternative and chemical control programs, and minimizing chemical use, are vital for sustainable banana production and for maintaining ecological balance.

Resumo em Inglês:

Abstract: Background: Weeds remain a key constraint in cotton systems of Southeastern Anatolia, and agronomic practices, including crop rotation and conservation tillage, may alter weed communities and pressure. Objective: The primary objective was to quantify the effects of crop rotation and tillage on weed flora (density/diversity, and key species) and cotton yield. Methods: Field studies were conducted at Harran University (Şanlıurfa, Türkiye) during 2021–2024 using three tillage methods [conventional tillage (CT), reduced tillage (RT), no tillage (NT)] and three cropping systems (cotton/cotton; cover crop [vetch + triticale]/cotton; wheat/maize/cotton). Weed species, their densities/diversity, and cotton yield were recorded. Results: A total of 69 weed species (23 families) were recorded. Amaranthus palmeri, Sorghum halepense, and Physalis angulata were the dominant weeds. Weed density/diversity was highest under cotton/cotton (≈50–120 plants m−2) and lowest under wheat/maize/cotton (≈20–60 plants m−2). Weed density was significantly altered by tillage practices, and the highest (≈60–140 plants m−2) and the lowest (≈20–70 plants m−2) densities were recorded for NT and CT, respectively. The highest cotton yield (≈5,940–6,670 kg ha−1) was recorded for cover crop/cotton, whereas cotton/cotton resulted in the lowest yield (≈4,070–4,260 kg ha−1). Conclusions: Crop diversification reduced weed pressure compared with continuous cotton, and CT generally minimized weed density relative to NT. However, crop rotation or tillage alone was insufficient for weed control. The findings support integrated weed management that combines cultural practices and herbicide programs. Nevertheless, longer-term trials (≥5 years) are needed to confirm the results.

Resumo em Inglês:

Abstract: Background: Weed infestation significantly threatens groundnut productivity, particularly during the later stages of growth. productivity. Objectives: To address this, a field experiment was conducted at two distinct locations under rainfed conditions in Nigeria's Southern Guinea Savanna to evaluate the effects of pre-emergence and post-emergence herbicides, combined with hand-weeding, on weed suppression, yield, and seed quality in two groundnut varieties. Methods: A split-plot field trial tested two groundnut varieties (SAMNUT 23, 26; main-plot) and eight weed-control regimes (sub-plot). Results: Tridax procumbens L., Andropogon tectorum Schumach, and Mitracarpus villosus (Sw.) DC. were the dominant weeds. Two hand-weeding events at 20 and 40 days after treatment (DAT) resulted in the lowest weed density and biomass, while the integrated treatment of butachlor at 1.0 kg a.i. ha−1 + supplementary hoe weeding (SHW) at 40 DAT achieved comparable suppression. These treatments also produced the highest pod yields (2195.20 and 1985.40 kg ha−1, respectively) compared to the weedy check (280.79 kg ha−1). SAMNUT 26 demonstrated superior yield and nutritional profile compared to SAMNUT 23. Mineral analysis revealed high potassium and low iron concentrations across treatments. Conclusions: We conclude that butachlor at 1.0 kg a.i. ha−1 + SHW at 40 DAT provides an effective, labour-saving alternative to two hand-weedings and is recommended for adoption by farmers in the Southern Guinea Savanna.

Resumo em Inglês:

Abstract Background: Turkiye accounts for a large share of global apricot production, and weed infestations negatively affect yield and quality. Understanding seed bank composition and distribution of weed species are essential for effective weed management. Objective: This study evaluated weed flora and soil seed bank dynamics in apricot orchards and investigated the impact of different orchard management practices, particularly tillage, on weed species composition and distribution. Methods: Soil samples were collected from 25 orchards at two soil depths (0–7.5 and 7.5–15 cm) to determine seed bank composition. Field surveys were conducted in spring and summer of 2024 to record weed species density and frequency of occurrence. The relationship between weed distribution and orchard management practices was analyzed using principal component analysis (PCA). Results: The soil seed bank contained 43 weed species across 20 families, with annual species accounting for 75% of the total. Field surveys identified 85 weed species in spring and 30 in summer (57 and 2 species unique in each season, respectively), with Poaceae and Asteraceae as the dominant families. PCA indicated that weed species distribution varied among orchards according to the management practices employed, with shallower tillage associated with higher weed species diversity. Conclusions: Weed species composition and seed bank were significantly influenced by orchard management practices. The results are preliminary, and long–term studies, along with extensive sampling, are needed to further substantiate the claims.

Resumo em Inglês:

Abstract Background: Paspalum urvillei Steud. (vaseygrass) is an important Poaceae species in several countries. This species is native to Brazil; however, it has become a troublesome weed, especially in pasture areas in Florida, USA. Vaseygrass is botanically similar to forage species in Brazil, including Paspalum notatum, Paspalum dilatatum, and Urochloa brizantha. Therefore, herbicide options to control vaseygrass are limited. Also, polyploid grasses often possess enhanced herbicide detoxification capacity, which can affect control of this species. Objective: Determine the ploidy level and evaluate chemical control of two populations of vaseygrass historically exposed to herbicide selection pressure. Methods: The ploidy level was evaluated using flow cytometry, and the chemical control was assessed using five herbicide treatments in two experiments: Control, imazapic, nicosulfuron, glyphosate, and nicosulfuron + glyphosate. Visible injury, plant height, culm diameter, number of leaves, total relative chlorophyll content, number of tillers, and dry matter were evaluated. Results: The ploidy analysis revealed that both populations had similar DNA content and were classified as tetraploids. The average DNA content in accessions of vaseygrass was 2.31 pg for Fence and 2.25 pg for Pasture. Considering visible injury, glyphosate and nicosulfuron + glyphosate caused 65% at 7 days after treatment. Conclusions: The two populations P. urvillei are tetraploids. Glyphosate alone or mixed with nicosulfuron are the best herbicide options to control P. urvillei.

Resumo em Inglês:

Abstract: Background: ProvisiaTM rice was developed as an alternative to Clearfield® rice technology. However, the ProvisiaTM system's long-term efficacy may be quickly reduced by gene flow from crop to weedy rice. Objective: This study aimed to assess the pollen-mediated gene flow from ProvisiaTM to weedy rice. Methods: Two field experiments were conducted in rectangular design. The pollen donor (ProvisiaTM) was sown upwind of the predominant wind direction and the pollen acceptor (quizalofop-p-ethyl (QPE)-susceptible weedy rice) was placed downwind at 0, 0.5 and 1m from donor. Weedy rice seeds from putative hybrids were sown on Germitest® paper containing QPE solution (1.6 mg ai L−1). The surviving seedlings were transplanted into pots and at V3, seedlings were treated with QPE (120 g ai ha−1). The survivors (putative F1 crosses) were cultured. Seeds (F2) were harvested and used in QPE dose-response assay. Genomic DNA was extracted from ProvisiaTM, QPE-susceptible weedy rice and F1 for analysis of the presence or absence of the Ile1781Leu mutation in ACCase. Results: A few (0.07%) survived the QPE treatment and no difference between the distances was observed. All F1 survivors carried the same ACCase mutation (Ile1781Leu) present in ProvisiaTM. Dose-response assay showed that all F2 were resistant to QPE. Conclusions: QPE-resistant weedy rice arose from crop-to-weed pollen-mediated gene flow. It is recommended to avoid weedy rice escapes from ProvisiaTM rice fields.

Resumo em Inglês:

Abstract Background: Common ragweed (Ambrosia artemisiifolia) is an aggressive weed with tolerance and resistance to multiple herbicides, hindering chemical control and raising concerns among soybean growers due to its growth and stature. Nevertheless, studies defining a critical interference threshold and a elucidating how this weed impacts soybean yield formation are lacking. Objective: To determine the critical interference threshold of common ragweed on soybean yield and to characterize the agronomic mechanisms involved. Methods: Experiments were conducted at four fields with seven weed densities (ranging from 0 to 32 plants m-2), arranged in a completely randomized design with five replicates. Weed growth traits and soybean yield components were analyzed. A regression analysis was performed to identify the critical threshold, and agronomic mechanisms were analyzed through multiple regression and principal component analysis. Results: Regression analysis, using pooled data from the four fields, identified a breakpoint in soybean yield loss at 2.47 ± 0.52 plants m-2. Below this threshold, each additional common ragweed plant reduced soybean yield by 10.72%, whereas above this density, yield loss was reduced to 1.45% per additional plant, indicating asymptotic competition. At the critical threshold (2.47 plants m-2), soybean yield loss reached ≈26.5%. Conclusions: Our findings indicate that there is non detrimental infestation density for this species, as the presence of one plant per square meter can result in yield reductions exceeding 10%. These results highlight the need for early preventive weed management strategies in soybean fields.

Resumo em Inglês:

Abstract: Background: Multiple-herbicide-resistant (R) Echinochloa spp. are increasingly challenging global rice production. The adaptive mechanisms for herbicide resistance in Echinochloa populations remain poorly understood. Objective: This study aimed to characterize the resistance profile of five Echinochloa accessions to propanil and quinclorac and investigate the expression patterns of candidate genes potentially associated with resistance. Methods: Whole-plant dose-response assays were conducted to quantify resistance levels, while the expression of four cytochrome P450s and one glycosyl transferase was measured 12 h after herbicide treatment using quantitative PCR. Results: Resistance profiles varied among accessions with resistance factors ranging from 6.4 to 12.0-fold for propanil and 8.0- to >309-fold for quinclorac. Differential induction of candidate genes was observed across resistant accessions. CYP709B1 was significantly upregulated by both herbicides in most R accessions indicating its involvement in multiple resistance. UGT75D1 was consistently induced by quinclorac in all resistant accessions and by propanil in all, except ECO-45. CYP709B2 and CYP72A14 were induced by quinclorac in four and five resistant accessions, respectively. CYP72A15 was notably induced only in ECO-45 by both herbicides suggesting a different metabolic process in this accession. Conclusions: Phase 1 metabolism genes CYP709B1 and CYP709B2 and the conjugation gene UGT75D1 are associated with multiple resistance to propanil and quinclorac in E. colona. The coordinated and differential induction of Phase I and Phase II metabolic genes contributes to varying levels of multiple herbicide resistance across E. colona populations.

Resumo em Inglês:

Abstract: Background: Sagittaria montevidensis is one of the main weeds in paddy rice, especially in the water-seeded system. The incorrect use of herbicides allowed the selection of populations resistant to the main herbicides labeled for rice. Objective: The objective of the experiment was to evaluate the mechanisms involved in resistance to ALS- and PSII-inhibiting (i.ALS and i.PSII) herbicides in SAGMO 32 and SAGMO 10. Methods: The accessions SAGMO 35 (susceptible), SAGMO 32 (resistant i.ALS and PSII), and SAGMO 10 (resistant i.ALS) were used in the greenhouse experiments. The first study evaluated the effect of CYP450 inhibitors on the activity of the herbicides penoxsulam, bispyribac-sodium, and bentazon. The second study was an in vitro analysis of ALS enzyme activity with imazethapyr and metsulfuron-methyl herbicides. The third study was sequencing the ALS and psbA genes to detect resistance-conferring mutations. Results: CYP450 inhibitors did not alter the efficiency of any of the herbicides tested. SAGMO 32 and SAGMO 10 showed RF (enzyme inhibition) of >600 and >13 for metsulfuron-methyl and imazethapyr. The ALS mutation Trp574Leu was detected in SAGMO, which confers resistance to imazethapyr and metsulfuron-methyl. The psbA sequence did not reveal any resistance-conferring mutations. Conclusions: The resistance mechanism of Sagittaria montevidensis (SAGMO 32 and SAGMO 10) to the ALS-inhibiting herbicides is due to target-site mutation, Trp574Leu. The mechanism of resistance to the herbicide bentazon remains unidentified.

Resumo em Inglês:

Abstract: Weeds are a problem for the development of agricultural crops, mainly due to the acquired resistance to herbicides. One approach to weed control is based on the chemical method, using herbicides in a mixture. However, herbicide combinations are complex and may lead to synergistic, antagonistic, or additive effects. One way of evaluating this effect is by means of isobolograms, the doses of which have previously been defined using dose response curve studies. The determination of doses for isobologram construction can be based on the relative potency of the ED50 values, defined as the ratio between the doses of the two herbicides that produce a 50% effect. Nevertheless, calculating these doses manually or using spreadsheets carries a risk of operational errors, potentially leading to incorrect decisions. The aim of this study was to present a computational routine in the R software to help define doses for isobologram studies. To do this, data from four dose-response curve experiments conducted in a completely randomized design under greenhouse conditions were used to obtain the necessary doses. In the same time, doses obtained using Microsoft Excel to validate the proposed methodology. The same results were obtained using the spreadsheet and the proposed routine, but in R it was with more agility, practicality and with the work centralized in the same software.