Changes in the herbicide sensitivity and competitive ability of Abutilon theophrasti over 28 years: Implications for hormesis and weed evolution

BACKGROUND

The potential of weed species to respond to selection forces affecting the evolution of weedy traits such as competitive ability is poorly understood. This research characterized evolutionary growth changes in a single Abutilon theophrasti Medik. population comparing multiple generations collected from 1988 to 2016. A competition study was performed to understand changes in competitive ability, and a herbicide dose–response study was carried out to assess changes in sensitivity to acetolactate synthase-inhibiting herbicides and glyphosate over time.

RESULTS

When grown in monoculture, A. theophrasti biomass production per plant increased steadily across year-lines while leaf number decreased. In replacement experiments, A. theophrasti plants from newer year-lines were more competitive and produced more biomass and leaf area than the oldest year-line. No clear differences in sensitivity to imazamox were observed among year-lines. However, starting in 1995, this A. theophrasti population exhibited a progressive increase in growth in response to a sublethal dose of glyphosate (52 g a.e. ha⁻¹), with the 2009 and 2016 year-lines having more than 50% higher biomass than the nontreated control.

CONCLUSION

This study demonstrates that weeds can rapidly evolve increased competitive ability. Furthermore, the results indicate the possibility of changes in glyphosate hormesis over time. These results highlight the importance of the role that rapid (i.e., subdecadal) evolution of growth traits might have on the sustainability of weed management strategies. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

The effect of salinity on corn yield using the CERES-maize model

In most cases, when calculating soil water availability, only thewater content is considered. The effect of salinity on the wiltingpoint is neglected. The objective of this work is to use asimulation model (CERES-maize) in order to predict cornyields as a function of water salinity under severalenvironmental, agrotechnical, and plant characteristics. A modelis presented in which the wilting point is a function of the soilsalt content. At high salinity, the water content at wilting pointis higher than at low salinity, resulting in an insufficient amountof available water and, therefore, a reduced yield. The modelwas used to simulate several theoretical and experimentalsituations for forage corn and grain corn. Simulation resultsshowed that nitrogen fertilization increases the salinity thresholdvalue and the yield sensitivity (rate of yield reduction per unitof salinity). The also showed that forage corn is more sensitiveto salinity than grain corn. If the soil is not leached, a heaviersoil texture has a higher salinity threshold value. On the otherhand, if the soil is leached, the soil texture has no influence onthe salinity threshold value and the yield is less sensitive tosalinity in sandy soils. The determination coefficient (r²= 0.75) indicated that the results of the simulations were in goodagreement with the field data.     

Simulated water and solute distribution from a crossed triple line-source

Summary Multivariable irrigation experiments are usually expensive and seldom cover the whole range of desired values. The crossed triple line-source (CTLS) was designed to provide a relatively simple and inexpensive irrigation system for creating continuous gradients of more than one variable. A computer model was developed to assist in evaluating the continuously changing multivariable levels, produced by the CTLS, given various inputs. A single sprinkler's distribution function was used in the model's development. The results of the overlapping sprinkling patterns are calculated throughout the experimental area for water depth, salinity level, and Nitrogen concentration. Measured values of irrigation water electrical conductivity (EC_i) and Nitrogen concentration were in good agreement with predicted values.     

Effect of background serum lithium concentrations on the accuracy of lithium dilution cardiac output determination in dogs

OBJECTIVES: To assess the effect of increasing serum lithium concentrations on lithium dilution cardiac output (LiDCO) determination and to determine the ability to predict the serum lithium concentration from the cumulative lithium chloride dosage. ANIMALS: 10 dogs (7 males, 3 females). PROCEDURE: Cardiac output (CO) was determined in anesthetized dogs by measuring LiDCO and thermodilution cardiac output (TDCO). The effect of the serum lithium concentration on LiDCO was assessed by observing the agreement between TDCO and LiDCO at various serum lithium concentrations. Also, cumulative lithium chloride dosage was compared with the corresponding serum lithium concentrations. RESULTS: 44 paired observations were used. The linear regression analysis for the effect of the serum lithium concentration on the agreement between TDCO and LiDCO revealed a slope of -1.530 (95% confidence interval [CI], -2.388 to -0.671) and a y-intercept of 0.011 (r2 = 0.235). The linear regression analysis for the effect of the cumulative lithium chloride dosage on the serum lithium concentration revealed a slope of 2.291 (95% CI, 2.153 to 2.429) and a y-intercept of 0.008 (r2 = 0.969). CONCLUSIONS AND CLINICAL RELEVANCE: The LiDCO measurement increased slightly as the serum lithium concentration increased. This error was not clinically relevant and was minimal at a serum lithium concentration of 0.1 mmol/L and modest at a concentration of 0.4 mmol/L. The serum lithium concentration can be reliably predicted from the cumulative lithium dosage if lithium chloride is administered often within a short period.     

Effects of cryptic mortality and the hidden costs of using length limits in fishery management

Fishery collapses cause substantial economic and ecological harm, but common management actions often fail to prevent overfishing. Minimum length limits are perhaps the most common fishing regulation used in both commercial and recreational fisheries, but their conservation benefits can be influenced by discard mortality of fish caught and released below the legal length. We constructed a computer model to evaluate how discard mortality could influence the conservation utility of minimum length regulations. We evaluated policy performance across two disparate fish life‐history types: short‐lived high‐productivity (SLHP) and long‐lived low‐productivity (LLLP) species. For the life‐history types, fishing mortality rates and minimum length limits that we examined, length limits alone generally failed to achieve sustainability when discard mortality rate exceeded about 0.2 for SLHP species and 0.05 for LLLP species. At these levels of discard mortality, reductions in overall fishing mortality (e.g. lower fishing effort) were required to prevent recruitment overfishing if fishing mortality was high. Similarly, relatively low discard mortality rates (>0.05) rendered maximum yield unobtainable and caused a substantial shift in the shape of the yield response surfaces. An analysis of fishery efficiency showed that length limits caused the simulated fisheries to be much less efficient, potentially exposing the target species and ecosystem to increased negative effects of the fishing process. Our findings suggest that for overexploited fisheries with moderate‐to‐high discard mortality rates, reductions in fishing mortality will be required to meet management goals. Resource managers should carefully consider impacts of cryptic mortality sources (e.g. discard mortality) on fishery sustainability, especially in recreational fisheries where release rates are high and effort is increasing in many areas of the world.     

Creutzfeldt-Jakob disease (spongiform encephalopathy): transmission to the chimpanzee

Biopsy material taken from the brain of a patient with CreutzfeldtJakob disease with status spongiosus induced a similar fatal encephalopathy in a chimpanzee 13 months after inoculation.     

Evaluation of spectrophotometric and HPLC methods for shikimic acid determination in plants: models in glyphosate-resistant and -susceptible crops

Endogenous shikimic acid determinations are routinely used to assess the efficacy of glyphosate in plants. Numerous analytical methods exist in the public domain for the detection of shikimic acid, yet the most commonly cited comprise spectrophotometric and high-pressure liquid chromatography (HPLC) methods. This paper compares an HPLC and two spectrophotometric methods (Spec 1 and Spec 2) and assesses the effectiveness in the detection of shikimic acid in the tissues of glyphosate-treated plants. Furthermore, the study evaluates the versatility of two acid-based shikimic acid extraction methods and assesses the longevity of plant extract samples under different storage conditions. Finally, Spec 1 and Spec 2 are further characterized with respect to (1) the capacity to discern between shikimic acid and chemically related alicyclic hydroxy acids, (2) the stability of the chromophore (t1/2), (3) the detection limits, and (4) the cost and simplicity of undertaking the analytical procedure. Overall, spectrophotometric methods were more cost-effective and simpler to execute yet provided a narrower detection limit compared to HPLC. All three methods were specific to shikimic acid and detected the compound in the tissues of glyphosate-susceptible crops, increasing exponentially in concentration within 24 h of glyphosate application and plateauing at approximately 72 h. Spec 1 estimated more shikimic acid in identical plant extract samples compared to Spec 2 and, likewise, HPLC detection was more effective than spectrophotometric determinations. Given the unprecedented global adoption of glyphosate-resistant crops and concomitant use of glyphosate, an effective and accurate assessment of glyphosate efficacy is important. Endogenous shikimic acid determinations are instrumental in corroborating the efficacy of glyphosate and therefore have numerous applications in herbicide research and related areas of science as well as resolving many commercial issues as a consequence of glyphosate utilization.     

Benchmark study on glyphosate-resistant crop systems in the United States. Part 2: Perspectives

A six-state, 5 year field project was initiated in 2006 to study weed management methods that foster the sustainability of genetically engineered (GE) glyphosate-resistant (GR) crop systems. The benchmark study field-scale experiments were initiated following a survey, conducted in the winter of 2005-2006, of farmer opinions on weed management practices and their views on GR weeds and management tactics. The main survey findings supported the premise that growers were generally less aware of the significance of evolved herbicide resistance and did not have a high recognition of the strong selection pressure from herbicides on the evolution of herbicide-resistant (HR) weeds. The results of the benchmark study survey indicated that there are educational challenges to implement sustainable GR-based crop systems and helped guide the development of the field-scale benchmark study. Paramount is the need to develop consistent and clearly articulated science-based management recommendations that enable farmers to reduce the potential for HR weeds. This paper provides background perspectives about the use of GR crops, the impact of these crops and an overview of different opinions about the use of GR crops on agriculture and society, as well as defining how the benchmark study will address these issues.