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Article

Germination Differences Between Clodinafop-Propargyl-Resistant and -Susceptible Alopecurus japonicus Steud. Populations Under Multiple Abiotic Stresses

by
Rui Cheng
1,
Xiaoshen Song
1,
Lilei Zhang
1,
Weitang Liu
2,
Zhiwen Wu
3,* and
Yaling Bi
3,4,*
1
College of Resource and Environment, Anhui Science and Technology University, Chuzhou 233100, China
2
College of Plant Protection, Shandong Agricultural University, Tai’an 271018, China
3
College of Agriculture, Anhui Science and Technology University, Chuzhou 233100, China
4
Anhui Engineering Research Center for Smart Crop Planting and Process in Technology, Anhui Science and Technology University, Chuzhou 233100, China
*
Authors to whom correspondence should be addressed.
Agronomy 2026, 16(14), 1381; https://doi.org/10.3390/agronomy16141381
Submission received: 21 June 2026 / Revised: 12 July 2026 / Accepted: 17 July 2026 / Published: 21 July 2026
(This article belongs to the Section Weed Science and Weed Management)
Browse Figures
Versions Notes

Abstract

Clodinafop-propargyl-resistant Alopecurus japonicus Steud. has severely threatened wheat production, while its fitness and stress adaptability have not been systematically clarified. This study compared seed germination and seedling emergence of resistant AHHN-6 and susceptible HNLH-1 under multiple abiotic stress treatments including temperature, pH, water potential, soil moisture, salt and burial depth. Both biotypes exhibited >95% germination under optimal temperature and moisture conditions, indicating the highly resistant biotype AHHN-6 bears no germination-related fitness cost; however, fitness costs were detected in several other resistant populations across the sampling regions. The resistant population displayed markedly higher tolerance to adverse conditions: its 50% inhibitory water potential and salt concentration were −0.43 MPa and 124.22 mmol·L−1 versus −0.35 MPa and 56.25 mmol·L−1 for the susceptible population, and it could emerge normally from deeper soil layers. Collectively, resistance to clodinafop-propargyl does not reduce performance under benign environments but confers enhanced abiotic stress resistance, promoting the long-term survival and spread of resistant A. japonicus in farmlands.

1. Introduction

Alopecurus japonicus Steud. as a major troublesome or harmful grass weed in the main wheat-producing regions of the Huang Huai Hai and the middle and lower reaches of the Yangtze River in China, severely affects wheat yield formation and quality improvement due to its highly competitive growth ability [1].
Currently, chemical control remains the main tool for weed management in wheat field systems. Among the herbicides, acetyl-CoA carboxylase (ACCase) and acetolactate synthase (ALS) inhibitors (such as clodinafop-propargyl and mesosulfuron-methyl) are the main active ingredients applied in post-emergence for controlling A. japonicus. However, high-intensity herbicide application with the same mode action in a repeated application of herbicides with identical modes of action has led to intense selection pressure on A. japonicus, with several cases of resistance to the aforementioned herbicides [2], becoming a significant biological factor threatening sustainable wheat production in this region [3].
The evolution of resistance not only directly affects chemical control efficacy but also profoundly alters the adaptive strategies of the weed populations themselves. Notably, herbicide-resistant populations often develop distinct biological traits compared with their susceptible counterparts, especially in seed germination performance and stress tolerance capacity. Specifically, the survival and proliferation of weeds in farmland require adaptation to diverse interspecific and intraspecific competitions as well as responses to changing environments and intense artificial selection on the other hand, thereby shaping their unique biological characteristics. Among these, seed germination traits, as a key stage determining weed ecological adaptability and population establishment success, significantly influence this weed competitive process with crops. In particular, significant differences in germination characteristics and stress tolerance between ACCase herbicide-resistant and -susceptible populations of A. japonicus have been demonstrated in previous studies [4]. Environmental factors affecting seed germination are complex and diverse, typically including burial depth, moisture, light, temperature, pH, oxygen, and salinity [5,6,7]. Although previous studies have touched upon the biological characteristics of A. japonicus, in the context of increasingly prevalent herbicide resistance and ongoing changes in farming systems, re-examining the effects of environmental factors on the seed germination characteristics of A. japonicus is particularly urgent for revealing its adaptation mechanisms and formulating sustainable management strategies.
Based on the above background, this study sets the following objectives: preliminary herbicide screening to determine the sensitivity of A. japonicus populations to clodinafop-propargyl; evaluation of a comparative analysis of seed germination differences between a resistant population (AHHN-6) and a susceptible population (HNLH-1) under the influence of various stress factors.

2. Materials and Methods

2.1. Experimental Materials

Weeds: Seeds of the tested A. japonicus populations were collected from wheat fields in Anhui, Henan, and Jiangsu provinces between 2015 and 2023 (Table A1 and Figure 1). Seeds collected from non-cropland plots where herbicides had not been applied were used as a control. All seeds were air-dried and subsequently stored in a cold storage room at 0–5 °C until use.
Herbicide: 15% clodinafop-propargyl EC was purchased from Zhengzhou Da Nong Pesticide Co., Ltd., Zhengzhou, China.

2.2. Screening Between Clodinafop-Propargyl-Resistant and -Susceptible A. japonicus Populations Using the Field-Recommended Dose

To determine the susceptibility of 28 A. japonicus populations to clodinafop-propargyl, seeds were sown in 9 cm diameter plastic pots filled with air-dried, ground, and sieved sandy loam soil (pH 7.0, organic matter content 1.7%). Soil moisture was brought to saturation via sub-irrigation. Fifteen seeds were sown uniformly per pot and covered with a 0.5–1.0 cm layer of soil. After sowing, pots were transferred to a growth chamber set at a 16/8 h (light/dark) photoperiod and 20 ± 5 °C to promote robust growth under controlled conditions.
Plant growth was monitored regularly. At the two-leaf stage, seedlings were thinned to retain 12 uniform plants per pot, ensuring biological consistency across replicates. When plants reached the third true-leaf stage, foliar spray application was performed using an HCL-2000 moving spray tower. Clodinafop-propargyl was applied at a dose of 67.50 g a.i. ha−1 (the recommended field rate). Applications used a flat fan nozzle at a pressure of 275 kPa, with the nozzle maintained 50 cm above the plant canopy, delivering a spray volume of 450 L ha−1. A water-treated control was included. Above-ground fresh weight of surviving plants was recorded 21 days after treatment. All treatments consisted of four replicates.
The Moss Resistance Rating System (“3R” system) [8] was used to categorize resistance levels. SS (fully susceptible standard, 88.05%) represents the fresh weight reduction in the fully susceptible population HNLH-1 treated with clodinafop-propargyl at a discriminating dose of 56.25 g a.i. ha−1. RRR (highly resistant) was defined by a fresh weight inhibition rate range of 0% to 35.22%; RR (moderately resistant) was defined by a range of 35.22% to 70.44%; R? (potentially resistant) was defined by a range of 70.44% to 79.25%; and S (susceptible) was defined by a range of 79.25% to 100% [9].

2.3. Whole-Plant Bioassay for Determining the GR50 of Clodinafop-Propargyl Against Field Populations of A. japonicus

To accurately evaluate the susceptibility of A. japonicus to clodinafop-propargyl, a whole plant bioassay was conducted strictly following the “Guidelines for Bioassay Tests of Pesticides” (NY/T 1155.4—2006) [10]. The specific procedure was as follows:
  • Material Preparation and Sowing
Test seeds were sown in 9 cm diameter plastic pots filled with air-dried, ground, and sieved sandy loam soil (pH 7.0, organic matter content 1.7%). Soil moisture was brought to saturation via sub-irrigation. Fifteen seeds were sown uniformly per pot and covered with a 0.5–1.0 cm layer of soil.
2.
Plant Cultivation
After sowing, the plants were transferred to a climate-controlled greenhouse (photoperiod: 12 h light/12 h dark; temperature: 20 °C). Routine management was carried out to ensure healthy plant development until the three-true-leaf stage.
3.
Herbicide Treatment
Post-emergence applications were made using an HCL-2000 cabinet sprayer (Kunshan Hengchuangli Technology Co., Ltd., Suzhou, China; Nozzle type: flat-fan; Pressure: 275 kPa; Nozzle-to-canopy height: 50 cm; Spray volume: 450 L ha−1). A series of graded herbicide doses were applied (Table 1). A water-treated control was included for comparison. Each treatment consisted of four replicates, and the entire experiment was independently conducted twice.

2.4. Effect of Temperature on Seed Germination

Six constant temperature treatments (5, 10, 15, 20, 25, 30 °C) and five alternating temperature treatments (10/5, 15/10, 20/15, 25/20, 30/25 °C; 12 h/12 h light/dark cycle in each) were selected to study their effects on seed germination of A. japonicus [4]. Each treatment consisted of four replicates, incubated in growth chambers with a 12 h/12 h (L/D) photoperiod. Germinated seeds were observed and counted daily for 14 days.

2.5. Effect of Light on Seed Germination

Five photoperiod treatments 24/0, 16/8, 12/12, 8/16, and 0/24 h (L/D) were established. Each treatment had four replicates and was maintained in a growth chamber at 20 °C [11]. Germination was monitored and recorded daily over 14 days. (Note: Petri dishes for the 0/24 h treatment were wrapped with two layers of aluminum foil to ensure complete darkness.)

2.6. Seed Germination Tests Under Different pH Environments

Buffer solutions with pH values of 4, 5, 6, 7, 8, 9, and 10 were prepared according to the method of Chachalis & Reddy [12] with minor modifications. These solutions were added to Petri dishes containing seeds of A. japonicus, using distilled water (pH 7.2) as the control.

2.7. Effect of Soil Moisture Content on Seed Germination

Fifty grams of sterilized soil was placed into each Petri dish. Different volumes of distilled water—5, 10, 15, 20, 25, 30, 35, 40, and 45 mL—were added to create soil moisture content gradients of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%, respectively. Dishes were weighed daily, and evaporated water was replenished. Incubation conditions and investigation methods were the same as in Section 2.4.

2.8. Seed Germination Assays with Gradient Salt Treatments

Six salinity levels (0, 50, 100, 150, 200, 250, 300 mmol·L−1 NaCl), each with four replicates, were set to investigate the effects of salt stress on seed germination. Sodium chloride (NaCl, analytical grade, purity ≥ 99.5%, Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) was dissolved in distilled water to prepare gradient salt solutions. The 0 mmol·L−1 NaCl treatment (pure distilled water) was regarded as the control group. The incubation temperature was kept at 20 °C, and all other incubation conditions remained uniform across treatments.

2.9. Experimental Treatments of Water Potential for Seed Germination Detection

Five water potential treatments (−0.3, −0.6, −0.9, −1.2, −1.5 MPa) were selected to study the effect of water potential stress on the germination of two A. japonicus populations. Polyethylene Glycol 6000 (PEG 6000, purity ≥ 99%, purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) was used to prepare the solutions according to Formula (1) [13], with distilled water as the control. Petri dishes were placed in a constant temperature chamber at 20 °C, with other conditions unchanged.
Water potential = −(1.18 × 10−2)C − (1.18 × 10−4)C2 + (2.67 × 10−4)CT + (8.39 × 10−7)C2T
where C is the concentration of PEG (g L−1) at temperature T (°C).

2.10. Effect of Burial Depth on Seed Germination

The effects of seed burial depth on germination and seedling emergence dynamics were evaluated using a pot experiment. Plastic pots (12 cm × 9 cm) with drainage holes were filled with the experimental soil. Soil moisture was standardized across all treatments using sub-irrigation until saturated. Fifteen seeds were sown in each pot at burial depths of 0, 2, 4, 6, 8, and 10 cm, with four replicates per treatment. Soil moisture was maintained by daily sub-irrigation to fully saturate the soil in each pot; no fixed daily water depth was used, which ensured uniform moisture across all treatments. All other environmental parameters followed the standard seed germination protocol. Seedling emergence was recorded daily for 21 days.

2.11. Constant Temperature Germination Experiment

To explore the effects of constant temperature on seed germination of A. japonicus, seeds of all 28 populations were subjected to a series of constant temperature treatments. Uniformly sized, healthy seeds were surface-sterilized and placed on moist filter paper in Petri dishes. Each treatment contained three biological replicates with 30 seeds per replicate. Petri dishes were incubated in constant temperature light incubators with a 12 h light/12 h dark photoperiod. The germination number was recorded daily, and the final germination rate was calculated after 14 days of incubation.

2.12. Data Analysis

At 21 days post-sowing, seedling survival count was recorded, and the above-ground shoots were separated and weighed to determine shoot fresh weight for each replicate pot. Cumulative shoot fresh weight data were fitted with a non-linear logistic regression model to estimate the fresh weight 50% inhibitory dose (GR50). The resistance index (RI) was subsequently calculated by dividing the GR50 value of resistant populations by that of susceptible populations to compare inter-biotype stress tolerance differences. All model fitting procedures were performed via SigmaPlot 15.0 statistical software. The Resistance Index (RI) was calculated using Formula (2), and the Fresh Weight Inhibition Rate was calculated using Formula (3).
RI = GR50 (resistant population)/GR50 (susceptible population)
Fresh Weight Inhibition Rate (%) = [(Fresh weight of control weeds − Fresh weight of treated weeds)/Fresh
weight of control weeds ] × 100%
The resistance level was classified according to the following criteria: RI < 2 are classified as Susceptible (S); those with 2 ≤ RI < 5 are classified as low-level resistance (LR); those with 5 ≤ RI < 10 are classified as medium-level resistance (MR); and those with RI ≥ 10 are classified as high-level resistance (HR).
Experimental data were plotted using SigmaPlot 15.0 and Origin 2024. Significance testing was performed using DPS 7.05 software.
One-way analysis of variance (ANOVA) was performed to detect inter-biotype and treatment differences in germination rates. Tukey’s honest significant difference (HSD) test was adopted for multiple comparisons at the p < 0.05 significance level. Non-linear logistic regression was fitted to calculate GR50 values for herbicide, salt, water potential, and burial depth treatments using SigmaPlot 15.0. All statistical analyses were conducted via DPS 7.05 software.

3. Results

3.1. Screening of Resistant and Susceptible Populations Under Clodinafop-Propargyl Treatment

This study determined the susceptibility of 28 A. japonicus populations to clodinafop-propargyl via whole-plant bioassays under greenhouse pot culture conditions, with results shown in Table 2. The results indicate that clearly moderately resistant (RR) populations constituted the overwhelming majority, totaling 20 (71.4%), reflecting the widespread prevalence of resistance issues in the sampling areas. A further five populations (17.9%) were potentially resistant (R?), classifying them as high-risk groups for resistance development that require focused attention. In contrast, only three populations (10.7%) remained susceptible (S/SS), representing a very low proportion, which further illustrates the current severity of the resistance situation.

3.2. Further Confirmation of Susceptibility to Clodinafop-Propargyl

A whole-plant bioassay was further conducted to evaluate the sensitivity of 28 A. japonicus populations to clodinafop-propargyl (as shown in Table 3 and Figure 2). The results revealed obvious differences in resistance to clodinafop-propargyl among A. japonicus populations collected in different years, with populations from later sampling years exhibiting higher resistance levels. Under continuous herbicide selection pressure, the population structure underwent significant shifts: early populations (e.g., 2015) were predominantly susceptible (GR50 ≤ 20 g a.i. ha−1), whereas by 2021 and later, most populations had evolved toward moderate to high resistance levels (GR50 ≥ 57.43 g a.i. ha−1). Among them, the AHHN-6 population collected in 2021 exhibited the highest resistance index of 45.88, indicating that resistant populations have established a stable dominance in the field. Based on these findings, HNLH-1 (2015) was identified as the susceptible population and AHHN-6 (2021) as the resistant population, both serving as test materials for subsequent comparative studies on ecological adaptability.

3.3. Effect of Constant Temperature on Seed Germination

Comparison of germination rates between the resistant and susceptible populations at the same temperature showed that there was a significant difference (p < 0.05) between the seed germination rates of the resistant population AHHN-6 and susceptible population HNLH-1 at 10 °C and 15 °C, with the germination rate of HNLH-1 being significantly lower than that of AHHN-6. No significant differences were observed at other temperatures (Figure 3A).
Results comparing the significance of differences in germination rates between the resistant and susceptible populations under different temperature conditions showed that for the susceptible population HNLH-1, there was no significant difference in germination rate between 20 °C and 25 °C, and both were significantly higher than those at other temperatures. For the resistant population AHHN-6, there was no significant difference in germination rate between 15 °C and 20 °C, but both were significantly higher than those at other temperatures (Figure 3B).
In summary, under the 20 °C condition, there was no significant difference in germination rate between the resistant population AHHN-6 and susceptible population HNLH-1, and both maintained a high germination level.

3.4. Effect of Alternating Temperatures on Seed Germination

Within each tested alternating temperature regime, there were no significant differences in germination rate between resistant and susceptible populations of A. japonicus (Figure 3C). However, comparisons within the same population type under different alternating temperature regimes revealed (Figure 3D) that germination rates for both the resistant population AHHN-6 and susceptible population HNLH-1 under 20/15 °C and 25/20 °C regimes were significantly higher than those under other temperature conditions.

3.5. Effect of Photoperiod on Seed Germination

Comparison of germination rates between the susceptible and resistant populations under identical photoperiod conditions revealed no significant differences between the resistant population AHHN-6 and susceptible population HNLH-1 across the various photoperiod treatments (Figure 3E). Analysis of the differences in germination rates under different photoperiod conditions showed that for the susceptible population HNLH-1, germination rates under the 12/12 h and 8/16 h photoperiods were significantly higher than under other conditions. For the resistant population AHHN-6, germination rates under the 12/12 h, 24/0 h, and 8/16 h photoperiods were significantly higher than under other photoperiod conditions (Figure 3F). In summary, under both the 12/12 h and 8/16 h photoperiod conditions, no significant difference in germination rate was observed between the resistant population AHHN-6 and susceptible population HNLH-1, with both populations maintaining a high germination level.

3.6. Effect of pH on Seed Germination

Comparison of germination rates between the susceptible and resistant populations under identical pH conditions revealed no significant differences between the resistant population AHHN-6 and susceptible population HNLH-1 across the various pH treatments when compared to the control (Figure 4A). Analysis of germination rates under different pH conditions showed that, compared to the control, the susceptible population HNLH-1 exhibited no significant difference in germination between pH 9 and 10, but both were significantly higher than those at pH 4, pH 6, pH 7 and pH 8 (p < 0.05). In contrast, no significant differences in germination rate of the resistant population AHHN-6 were observed across all pH treatments. (Figure 4B).
In summary, under both pH 9 and pH 10 conditions, no significant difference in germination rate was observed between the resistant population AHHN-6 and the susceptible population HNLH-1, with both populations maintaining a high germination level.

3.7. Effect of Water Content on Seed Germination

Comparisons between resistant and susceptible populations under identical water content treatments revealed that AHHN-6 had a significantly higher germination rate than HNLH-1 at the 50% water content level. No significant differences were observed between the two populations under other water content conditions (Figure 4C). Comparisons within the same population type (resistant or susceptible) across different water content levels revealed that the germination rate of the resistant population AHHN-6 at 50%, 40%, and 30% water content was significantly higher than that under other water content levels. For the susceptible population HNLH-1, the germination rate at 40% water content was significantly higher than that under other conditions (Figure 4D). In summary, at 40% water content, no significant difference in germination rate was observed between the resistant population AHHN-6 and the susceptible population HNLH-1, with both populations maintaining a high germination level.

3.8. Effect of Salt Stress on Seed Germination

Increasing salt stress concentrations gradually reduced the germination rates of both resistant AHHN-6 and susceptible HNLH-1 populations of A. japonicus. The measured half-maximal inhibitory concentration for germination was 124.22 mmol·L−1 for the resistant population AHHN-6 and 56.25 mmol·L−1 for the susceptible population HNLH-1 (Figure 5A). This indicates that the resistant population AHHN-6 possesses a stronger salt tolerance capability compared to the susceptible population HNLH-1.

3.9. Effect of Water Potential on Seed Germination

The results regarding the effect of water potential on seed germination demonstrated that the germination rates of both the resistant A. japonicus population AHHN-6 and the susceptible population HNLH-1 gradually decreased with increasing water potential stress. The water potential required for half-maximal inhibition of germination (GR50) was −0.43 MPa for the resistant population AHHN-6 and −0.35 MPa for the susceptible population HNLH-1 (Figure 5B), indicating that the resistant population AHHN-6 possesses a stronger tolerance to low water potential during the seed germination stage.

3.10. Effect of Soil Burial Depth on Seed Germination

Results on the effect of soil burial depth on seed germination showed that the germination rates of both the resistant A. japonicus population AHHN-6 and the susceptible population HNLH-1 gradually decreased with increasing burial depth. The measured burial depth for half-maximal emergence inhibition was 8.086 cm for the resistant population AHHN-6 and 5.664 cm for the susceptible population HNLH-1 (Figure 5C). The seed germination rate of the resistant population AHHN-6 was significantly higher than that of the susceptible population HNLH-1, indicating that the resistant population exhibits relatively broader adaptability to soil burial depth.

3.11. Effect of Constant Temperature on Seed Germination of 28 A. japonicus Populations

Following the initial sensitivity screening that identified two distinct populations for comparative fitness assessment under various stress conditions—which revealed that the resistant population exhibited higher fitness—this study further investigated the generality of this phenomenon. All 28 populations were re-evaluated under constant temperature conditions to determine the effect of temperature on their seed germination. The experimental results showed that populations AHHN-3, AHCZ-2, HNZMD-1, AHCZ-4, and AHLA-1 exhibited significant fitness costs, as their germination rates were lower than those of the susceptible population across multiple temperature conditions. Notably, the germination rate of AHHN-3 remained below 40% across three temperature gradients, indicating a substantial negative impact of the resistance trait on fundamental physiological functions (Figure 6 and Figure 7). In contrast, populations such as JSTZ-1, AHHN-4, AHCZ-3, AHFY-1, AHBB-2, AHHN-5, and AHHN-6 showed no apparent fitness costs, maintaining germination rates above 80% across all temperature gradients (Figure A1 and Figure A2). This variation in the distribution of fitness costs confirms the diversity of evolutionary trajectories in resistance development. It demonstrates that the acquisition of herbicide resistance does not inevitably incur fitness costs and that the resulting phenotypic outcome depends on the specific genetic background and physiological integration capacity of each population.

4. Discussion

With the increasing application of acetyl-CoA carboxylase (ACCase) inhibiting herbicides, major grass weeds in global grain cropping systems have evolved resistance [14]. Species such as Beckmannia syzigachne [15], A. japonicus [16], and Lolium multiflorum [17] have developed significant resistance to fenoxaprop-P-ethyl. A. japonicus is an important grass weed in Chinese wheat fields. The preliminary susceptibility screening in this study revealed that clearly resistant and potentially resistant populations accounted for 89.29% of the 28 A. japonicus populations tested, indicating a severe resistance problem to clodinafop-propargyl in field populations.
All field populations in this study were sampled, processed and preserved with unified standard protocols; as Rafiq [18] highlighted in their crop resistance screening framework, such standardization guarantees valid cross-population comparisons of germination and stress tolerance phenotypes. Intact mature wheat seeds were randomly gathered from independent plots with full records of location, soil traits, herbicide use and tillage types, with hollow, damaged and pest-infected grains manually removed. Purified seeds were shade air-dried to 12–15% balanced moisture, sealed in aluminum foil bags and stored dark at constant 4 °C prior to germination assays. Irregular seed pretreatment disrupts seed dormancy, viability and stress reactivity and yields unmatched phenotypic data between resistant and susceptible biotypes, while our unified pretreatment removes confounding variables and supplies replicable guidelines for future multi-population co-screening of grass weed resistance and abiotic stress tolerance.
Various environmental stresses affect normal plant growth and development throughout its life cycle. The biological characteristics of seeds from resistant and susceptible A. japonicus populations determine their respective survival capabilities in the soil. Fitness differences between them directly influence their invasion potential and damage severity. Therefore, identifying the key environmental factors affecting their germination and emergence is crucial for mitigating the harm caused by this weed to agricultural production through the regulation of seed germination behavior. The mechanisms influencing weed seed germination and emergence are not yet fully understood. It is generally accepted that seed germination results from the interaction of internal factors and the external environment. Internal factors primarily include seed viability, maturity, dormancy characteristics, and genotype; external factors encompass temperature, light, salinity, moisture, and water potential, among others. Based on this, our study systematically investigated the effects of environmental stress factors—including temperature, light, pH, soil water content, salt stress, water potential, and burial depth—on the seed germination of the clodinafop-propargyl-resistant population AHHN-6 and the susceptible population HNLH-1 of A. japonicus.
All abiotic stress gradients in laboratory assays match the actual stress range of winter wheat agroecosystems in the middle and lower Yangtze River reaches. Diverse agronomic measures (no-tillage, deep plowing, straw mulching, crop rotation) drastically alter soil microhabitats and adjust field stress levels, imposing differential selection pressure on resistant and susceptible weed biotypes [19]. Long-term no-tillage promotes the accumulation of A. japonicus seeds in the 0–10 cm topsoil, while surface straw mulching stabilizes soil temperature and moisture to support consistent seed germination. By contrast, yearly deep plowing buries most seeds deeper than 10 cm and strongly inhibits seedling emergence. Agronomic regulation of abiotic stress strengthens the multi-stress adaptability of resistant biotypes recorded in lab trials, partially accounting for their fast prevalence in farmlands under long-term herbicide screening.
In terms of temperature and light adaptation, both susceptible and resistant A. japonicus populations were tolerant of a broad range of temperatures, and their seed germination was generally more vigorous under light conditions than in darkness. This conclusion is supported by findings that germination rates for both populations surpassed 80% under most temperature regimes with a 12 h light/12 h dark cycle, showing no significant inter-biotypic difference. In contrast, no seed germination occurred under complete darkness at 5 °C, 10/5 °C, and 30/25 °C. The resistant population did not exhibit a germination disadvantage at low temperatures; instead, its germination rate was somewhat higher than that of the susceptible population, aligning with the results of Kee Woong Park [20], who found that seeds of A. japonicus resistant to haloxyfop-P-methyl had higher germination rates at both 5 °C and 30 °C compared to the susceptible population. This inter-biotype divergence in germination performance is closely associated with rising global temperatures and ongoing climate change. As reported by Oveisi [21], rising soil temperatures under climate warming consistently promote seed germination across weed species, yet substantial intraspecific differences in germination performance exist among populations under elevated thermal conditions, implying warming will reshape the competitive balance between resistant and susceptible weed biotypes. The strong germination performance of resistant biotypes across various temperatures may offer potential competitive advantages amid ongoing climate warming in agricultural fields.
Beyond temperature and light, salt stress also exerts multiple inhibitory effects on plant growth. Sodium ions can directly cause toxicity to plants and can also displace calcium and magnesium ions in the soil, disrupting soil structure and inducing water and nutrient deficiencies [22]. The ability of weed seeds to germinate under high salinity is crucial for their successful invasion of farmland and population establishment. Our results indicated that the resistant population AHHN-6 still maintained stronger salt stress tolerance in terms of seed germination rate compared to the susceptible population, enabling it to occur and reproduce in high-salinity areas such as coastal regions.
Imbibition, essential for plant seeds, requires sufficient water. Moderate water potential stress can promote seed germination, whereas severe water potential stress inhibits the process [23,24]. Following the PEG-6000 simulation method reported in earlier reports, we set a series of water potential treatments to evaluate drought effects on A. japonicus seed germination [25]. The results showed that the water potential values inhibiting 50% of seed germination (GR50) were −0.43 MPa for the resistant population AHHN-6 and −0.35 MPa for the susceptible population HNLH-1, indicating that resistant individuals possess a greater tolerance for germination under low-water-potential environments. This finding is consistent with the conclusion of Kee Woong Park [20] who observed that resistant populations still exhibited superior growth vigor at the seedling stage under relatively high water potential stress (−0.6 MPa). The variation in stress resistance between germination and growth stages might be related to the different resistance mechanisms employed by A. japonicus at various developmental stages, the specifics of which require further research.
Numerous domestic and international studies have reported that seeds can germinate over a relatively wide range of soil pH levels, with various weed seeds capable of germinating within a soil pH range of 4 to 10 [12,26]. The soil pH in the middle and lower reaches of the Yangtze River in China ranges between 5.0 and 10.0 [24]. Our experiment found that A. japonicus seeds could germinate within the pH range of 4 to 10, with germination rates all exceeding 80%, demonstrating broad adaptability to pH. This also explains why A. japonicus is widely distributed in the middle and lower reaches of the Yangtze River.
Furthermore, the large seeds of A. japonicus accumulate abundant energy reserves, which promote germination and seedling emergence even in deep soil layers [4]. Sufficient nutrient storage allows susceptible populations to retain acceptable emergence rates at a burial depth of 8 cm. Even under a 10 cm organic matter cover, resistant individuals could emerge, with an emergence rate of 13.3%, demonstrating strong soil penetration ability and emergence adaptability. This also constitutes a significant ecological advantage contributing to the continued spread of resistant populations in the field.
This study revealed that the superior multi-stress germination performance of clodinafop-propargyl-resistant A. japonicus is intrinsically determined by herbicide resistance molecular pathways, which explains the heterogeneous fitness costs among geographically distinct field populations. ACCase-resistant grass weeds mainly exhibit two resistance mechanisms, namely target-site resistance (TSR) and metabolic resistance. TSR, caused by amino acid substitutions in the ACCase enzyme, alters enzyme spatial conformation and enhances cross-tolerance to cold, drought and salinity without obvious germination fitness penalties. In contrast, metabolic resistance mediated by the overexpression of cytochrome P450s and GSTs proteins requires continuous energy consumption for xenobiotic detoxification, resulting in apparent fitness trade-offs, reduced germination rate and seedling vigor in certain resistant populations. Assays of 28 A. japonicus populations confirmed that biotypes with single mild TSR mutations show negligible germination defects, whereas multi-site TSR mutants and metabolic-resistant biotypes display poor adaptability under abiotic stresses. Long-term dual selection pressure imposed by herbicide application and field environmental conditions further promotes population divergence: resistant genotypes with high fitness costs are eliminated in harsh farmland habitats, while resistant biotypes with prominent fitness deficits are retained in stable and mild inland fields. These findings demonstrate that the fitness cost of herbicide resistance is not a fixed inherent trait, but a context-dependent phenotype shaped by mutation type and local agroclimatic conditions. Consistently, Riaz [19] illustrated that biological stress adaptability is co-determined by resistance genetics and long-term field agronomic selection.
Regional A. japonicus populations carry both high-frequency herbicide resistance and strong broad-spectrum abiotic stress adaptability, posing dual risks to winter wheat yield. Rafiq [18] put forward integrated monitoring and weed management frameworks targeting chemical selection pressure and field abiotic stresses for crop multi-stress resistance surveillance. Traditional resistance screening merely performs single-dose herbicide bioassays while ignoring multi-stress germination phenotyping, leading to severe underestimation of invasion and breakout risks of resistant biotypes with cross abiotic tolerance. We thus recommend embedding standardized seed germination tests under simulated drought, salinity and temperature gradients into regular regional weed resistance surveys to forecast the dispersal risk of resistant populations amid climate change and heterogeneous field microenvironments. Exclusive use of ACCase-inhibiting herbicides will expedite resistance evolution and facilitate the dominance of stress-hardy resistant biotypes in weed assemblages. Coordinated integrated agronomic and chemical interventions are required: alternating herbicides with distinct mechanisms of action, deep tillage to reduce deep seedling emergence, adjusting straw mulch thickness to alter soil temperature and moisture conditions, and cultivating competitive high-yield wheat varieties to shrink the ecological niche of A. japonicus. Such combined control practices mitigate the overall competitive edge of resistant populations and relieve the dual threats of herbicide resistance and abiotic stress adaptation in wheat fields, aligning with the molecular–agronomy coupled sustainable stress alleviation system established by Riaz [19].
Although the extensive literature confirms that herbicide resistance is often accompanied by fitness costs related to germination, growth, or reproduction, our study found that some A. japonicus populations did not exhibit significant fitness defects despite having evolved high levels of herbicide resistance. To deeply analyze the success mechanisms of these resistant populations lacking fitness costs, we further selected representative non-cost resistant populations and susceptible populations for comparison. This aims to elucidate the internal mechanisms allowing them to maintain high resistance without sacrificing ecological adaptability through systematic physiological, biochemical, and molecular studies.
In summary, resistant A. japonicus populations exhibit strong adaptive capacities to temperature, water potential, salinity, and seed burial depth. In recent years, A. japonicus has gradually spread and become a severe malignant weed in Chinese farmland. To prevent its further escalation, monitoring of this weed should be strengthened, its occurrence and damage characteristics further clarified, and integrated management strategies employing multiple measures should be implemented for its comprehensive control [27].
This study only evaluated seed germination responses under controlled indoor laboratory conditions, which cannot fully simulate complex interactive multiple abiotic stresses in actual wheat field ecosystems. In addition, fitness performance was merely assessed at the germination stage; growth, biomass accumulation, and seed fecundity of resistant and susceptible biotypes under field conditions remain uncharacterized. Subsequent research will focus on: (1) clarifying the molecular physiological mechanisms underlying enhanced abiotic stress tolerance of resistant A. japonicus; (2) conducting multi-year field positioning trials to quantify population dynamics of resistant biotypes under different tillage and herbicide rotation regimes; (3) developing targeted agronomic control technologies based on the germination ecological characteristics identified in this study.

5. Conclusions

Widespread resistance to clodinafop-propargyl has evolved in A. japonicus populations inhabiting wheat fields across Anhui, Henan and Jiangsu provinces. Among the 28 tested populations, resistant and potentially resistant biotypes accounted for 89.29%, with their resistance levels progressively increasing with years of herbicide application.
The highly resistant biotype AHHN-6 exhibited no germination fitness cost under optimal growth conditions. Relative to the susceptible biotype HNLH-1, AHHN-6 showed stronger tolerance to low temperature, salt stress, osmotic drought and deep soil burial, alongside a wider soil pH adaptation range (pH 4–10). Notably, its seeds could emerge successfully from 10 cm deep soil with an emergence rate of 13.3%, conferring it a distinct ecological competitive edge in farmland ecosystems.
Fitness costs varied substantially among resistant A. japonicus populations, indicating that herbicide resistance evolution does not necessarily bring ecological disadvantages, as such traits are determined by the genetic background of individual populations. The improved adaptability to abiotic stresses enables resistant A. japonicus to achieve long-term survival and continuous field expansion. To constrain further resistance evolution, sole chemical weed control should be phased out. To address the escalating resistance, an integrated management strategy is recommended, focusing on the rotation of herbicides with different modes of action combined with agro-ecological measures, to establish a sustainable weed resistance control system. Specifically, targeted tactics including deep tillage, cultivation of competitive wheat varieties, and rotation of herbicides with different target sites can be adopted to facilitate the sustainable field management of resistant A. japonicus.

Author Contributions

Conceptualization, R.C. and Y.B.; methodology, R.C. and Y.B.; software, L.Z. and X.S.; validation, R.C. and L.Z.; formal analysis, R.C. and X.S.; investigation, R.C. and L.Z.; resources, Z.W. and Y.B.; data curation, R.C. and X.S.; writing—original draft preparation, R.C. and W.L.; writing—review and editing, R.C., W.L., Z.W. and Y.B.; visualization, R.C. and L.Z.; supervision, W.L., Z.W. and Y.B.; project administration, R.C.; funding acquisition, Y.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Key Research and Development Program of China (Grant No. 2023YFD1400501), the Anhui Provincial Academician Workstation (Filing Document No. WKCM [2024] 369; Cooperative Academician: PAN Canping, Russian Academy of Engineering), the Fengyang County Science and Technology Planning Program (Grant No. 2025YS-01), and the Key Discipline Construction Funds for Crop Science of Anhui Science and Technology University (Grant No. XK-XJGF001).

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

Acknowledgments

The authors sincerely thank the laboratory members for their assistance in seed collection, greenhouse bioassays, and data sorting. Gratitude is extended to the academic editors and anonymous reviewers for their constructive comments that substantially improved the quality of this manuscript. We also appreciate the technical support provided by Anhui Science and Technology University for the constant temperature incubator and spray tower equipment.

Conflicts of Interest

The authors declare no conflicts of interest.

Appendix A

Table A1. Collection sites and distribution of different Alopecurus japonicus Steud. populations.
Table A1. Collection sites and distribution of different Alopecurus japonicus Steud. populations.
Population CodeCollection LocationYearsLatitude and Longitude
AHHN-1Wanxu Village, Yankou Town, Shou County, Huainan City, Anhui Province2015N: 32.396; E: 116.794
AHHN-2Gebei Village, Anfengtang Subdistrict, Shou County, Huainan City, Anhui Province2016N: 32.343; E: 116.675
AHHN-3Gulou Village, Xiaodian Town, Shou County, Huainan City, Anhui Province2016N: 32.176; E: 116.999
AHHN-4Xiaji Town, Fengtai County, Huainan City, Anhui Province2017N: 32.654; E: 116.556
AHHN-5X018, Panji Town, Panji District, Huainan City, Anhui Province2021N: 32.837; E: 116.789
AHHN-6Zhangzhuang, Panji Town, Panji District, Huainan City, Anhui Province2021N: 32.881; E: 116.826
AHCZ-1Walu Village, Shiba Town, Mingguang City, Anhui Province2015N: 32.802; E: 118.186
AHCZ-2Plantation Garden, Anhui Science and Technology University, Fengyang County, Chuzhou City, Anhui Province2021N: 32.875; E: 117.564
AHCZ-3Wu gang, Shuangyuan Village, Xinjie Town, Tianchang City, Chuzhou City, Anhui Province2019N: 32.670; E: 118.818
AHCZ-4Longpan Avenue, Fengyang County, Chuzhou City, Anhui Province2021N: 32.839; E: 117.550
AHCZ-5Qianlouzi, Guantang, Fengyang County, Chuzhou City, Anhui Province2022N: 32.678; E: 117.215
AHXC-1Songkeli, Chen Village, Xuanzhou District, Xuancheng City, Anhui Province2019N: 30.915; E: 118.810
AHLA-1Huaitaizi, Wangjieliu Township, Huoqiu County, Lu’an City, Anhui Province2023N: 32.538; E: 116.042
AHBB-1Huaiyuan County, Bengbu City, Anhui Province2019N: 32.955; E: 117.200
AHBB-2Maqiao Village, Xinji Town, Wuhe County, Bengbu City, Anhui Province2021N: 33.091; E: 117.714
AHFY-1Runhe Town, Yingshang County, Fuyang City, Anhui Province2021N: 32.537; E: 116.106
HNLH-1Yancheng District, Luohe City, Henan Province2015N: 33.585; E: 114.007
HNLH-2Qingmingli Village, Zhaoling District, Luohe City, Henan Province2015N: 33.533; E: 114.059
HNXY-1Changtaikou, Gangan Town, Pingqiao District, Xinyang City, Henan Province2015N: 32.279; E: 114.030
HNXY-2Fanlou Village, Sunmiao Township, Xi County, Xinyang City, Henan Province2019N: 32.319; E: 114.667
HNZMD-1Hexiao Town, Runan County, Zhumadian City, Henan Province2015N: 32.727; E: 114.285
HNSQ-1Daxinzhuang, Yucheng County, Shangqiu City, Henan Province2015N: 34.185; E: 115.831
HNNY-1East Station, Jinhe Town, Xichuan County, Nanyang City, Henan Province2016N: 33.129; E: 111.470
JSTZ-1Jiangyan District, Taizhou City, Jiangsu Province2016N: 32.505; E: 120.105
JSTZ-2Xijiao Town, Xinghua City, Taizhou City, Jiangsu Province2016N: 32.961; E: 119.756
JSHA-1Shiqiao Village, Maba Town, Xuyi County, Huai’an City, Jiangsu Province2016N: 32.991; E: 118.770
JSYZ-1Tangtou Village, Guocun Town, Jiangdu District, Yangzhou City, Jiangsu Province2016N: 32.499; E: 119.810
JSYC-1Dongqiao Village, Liangenglianzhong Demonstration Village, Qingfeng Village, Jianhu County, Yancheng City, Jiangsu Province2019N: 33.294; E: 119.822
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Figure A1. Seed germination phenotypes of susceptible (S) and low-resistant (LR) A. japonicus populations incubated at 15, 20, and 25 °C constant temperatures.
Figure A1. Seed germination phenotypes of susceptible (S) and low-resistant (LR) A. japonicus populations incubated at 15, 20, and 25 °C constant temperatures.
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Figure A2. Germination performance of low-, medium-, and high-resistant A. japonicus biotypes under 15, 20, and 25 °C constant temperature regimes. Note: LR, low-level resistant population; MR, moderately resistant population; HR, highly resistant population; S, susceptible population.
Figure A2. Germination performance of low-, medium-, and high-resistant A. japonicus biotypes under 15, 20, and 25 °C constant temperature regimes. Note: LR, low-level resistant population; MR, moderately resistant population; HR, highly resistant population; S, susceptible population.
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Figure 1. Point distribution map of collection information for different populations of Alopecurus japonicus Steud.
Figure 1. Point distribution map of collection information for different populations of Alopecurus japonicus Steud.
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Figure 2. Screening for resistance levels to clodinafop-propargyl and inter-annual sensitivity analysis in 28 populations of A. japonicus. (A) Quantification of resistance levels to clodinafop-propargyl in A. japonicus. (B) Sensitivity to clodinafop-propargyl across different years in 28 A. japonicus populations. Note: Abbreviations and symbols for (A): Different shapes and colors indicate distinct resistance levels. Blue five-pointed star = susceptible; red square = low resistance; green circle = moderate resistance; purple triangle = high resistance.
Figure 2. Screening for resistance levels to clodinafop-propargyl and inter-annual sensitivity analysis in 28 populations of A. japonicus. (A) Quantification of resistance levels to clodinafop-propargyl in A. japonicus. (B) Sensitivity to clodinafop-propargyl across different years in 28 A. japonicus populations. Note: Abbreviations and symbols for (A): Different shapes and colors indicate distinct resistance levels. Blue five-pointed star = susceptible; red square = low resistance; green circle = moderate resistance; purple triangle = high resistance.
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Figure 3. Effects of constant temperature, fluctuating temperature, and photoperiod on seed germination of resistant and susceptible A. japonicus populations. (A) Significant difference comparison between populations under the same constant temperature. (B) Significant difference comparison within populations across different constant temperatures. (C) Significant difference comparison between populations under the same fluctuating temperature regime. (D) Significant difference comparison within populations across different fluctuating temperature regimes. (E) Significant difference comparison between populations under the same photoperiod. (F) Significant difference comparison within populations across different photoperiods.
Figure 3. Effects of constant temperature, fluctuating temperature, and photoperiod on seed germination of resistant and susceptible A. japonicus populations. (A) Significant difference comparison between populations under the same constant temperature. (B) Significant difference comparison within populations across different constant temperatures. (C) Significant difference comparison between populations under the same fluctuating temperature regime. (D) Significant difference comparison within populations across different fluctuating temperature regimes. (E) Significant difference comparison between populations under the same photoperiod. (F) Significant difference comparison within populations across different photoperiods.
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Figure 4. Effects of soil moisture and pH on seed germination of clodinafop-propargyl-resistant and -susceptible A. japonicus populations. (A) Significant difference comparison between R and S populations under the same pH. (B) Significant difference comparison within R and within S populations across different pH levels. (C) Significant difference comparison between R and S populations under the same soil moisture level. (D) Significant difference comparison within R and within S populations across different soil moisture levels.
Figure 4. Effects of soil moisture and pH on seed germination of clodinafop-propargyl-resistant and -susceptible A. japonicus populations. (A) Significant difference comparison between R and S populations under the same pH. (B) Significant difference comparison within R and within S populations across different pH levels. (C) Significant difference comparison between R and S populations under the same soil moisture level. (D) Significant difference comparison within R and within S populations across different soil moisture levels.
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Figure 5. Effects of individual stress factors on seed germination of clodinafop-propargyl-resistant and -susceptible A. japonicus populations. (A) Effects of salt stress on seed germination. (B) Effects of water potential on seed germination. (C) Effects of burial depth on seed germination. Note: Blue lines represent the susceptible population HNLH-1, and red lines represent the resistant population AHHN-6. Red arrows indicate the environmental factor value that inhibits 50% seed germination of HNLH-1, while green arrows indicate the environmental factor value that inhibits 50% seed germination of AHHN-6.
Figure 5. Effects of individual stress factors on seed germination of clodinafop-propargyl-resistant and -susceptible A. japonicus populations. (A) Effects of salt stress on seed germination. (B) Effects of water potential on seed germination. (C) Effects of burial depth on seed germination. Note: Blue lines represent the susceptible population HNLH-1, and red lines represent the resistant population AHHN-6. Red arrows indicate the environmental factor value that inhibits 50% seed germination of HNLH-1, while green arrows indicate the environmental factor value that inhibits 50% seed germination of AHHN-6.
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Figure 6. Seed germination rates of 28 field-collected A. japonicus populations incubated under three constant temperature regimes (15, 20, and 25 °C), used to characterize germination-related fitness costs. Red circles indicate susceptible biotypes, and blue circles represent resistant biotypes. (A) Effects of 15 °C on seed germination of clodinafop-propargyl resistant and susceptible populations of A. japonicus; (B) Effects of 20 °C on seed germination of clodinafop-propargyl resistant and susceptible populations of A. japonicus; (C) Effects of 25 °C on seed germination of clodinafop-propargyl resistant and susceptible populations of A. japonicus.The horizontal black solid line denotes the mean germination rate of susceptible reference populations. Population abbreviations are consistent with those listed in Table A1.
Figure 6. Seed germination rates of 28 field-collected A. japonicus populations incubated under three constant temperature regimes (15, 20, and 25 °C), used to characterize germination-related fitness costs. Red circles indicate susceptible biotypes, and blue circles represent resistant biotypes. (A) Effects of 15 °C on seed germination of clodinafop-propargyl resistant and susceptible populations of A. japonicus; (B) Effects of 20 °C on seed germination of clodinafop-propargyl resistant and susceptible populations of A. japonicus; (C) Effects of 25 °C on seed germination of clodinafop-propargyl resistant and susceptible populations of A. japonicus.The horizontal black solid line denotes the mean germination rate of susceptible reference populations. Population abbreviations are consistent with those listed in Table A1.
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Figure 7. Visual comparison of seed germination performance among eight representative A. japonicus biotypes with different clodinafop-propargyl resistance levels under constant temperatures of 15, 20, and 25 °C. Biotypes are arranged from left to right as follows: HNLH-1 (S), AHHN-1 (S), HNSQ-1 (LR), JSTZ-1 (LR), AHHN-5 (MR), AHCZ-4 (MR), AHHN-6 (HR), AHCZ-3 (HR).
Figure 7. Visual comparison of seed germination performance among eight representative A. japonicus biotypes with different clodinafop-propargyl resistance levels under constant temperatures of 15, 20, and 25 °C. Biotypes are arranged from left to right as follows: HNLH-1 (S), AHHN-1 (S), HNSQ-1 (LR), JSTZ-1 (LR), AHHN-5 (MR), AHCZ-4 (MR), AHHN-6 (HR), AHCZ-3 (HR).
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Table 1. Tested herbicides and application rates.
Table 1. Tested herbicides and application rates.
Mechanism of ActionTested HerbicidesCategoryDose (g a.i. ha−1)
Acetyl-CoA carboxylase
inhibitor		15% clodinafop-propargyl ECAryloxyphenoxypropionates (APP)S: 0, 0.88, 1.76, 3.52, 7.03, 14.06, 28.13, 56.25
R: 0, 28.13, 56.25, 112.5, 225, 450, 900, 1800
Note: S denotes the susceptible population; R denotes the resistant population; the underlined dose indicates the field recommended dose; the unit g a.i. ha−1 means grams of active ingredient per hectare.
Table 2. Preliminary screening of 28 A. japonicus populations for response to clodinafop-propargyl.
Table 2. Preliminary screening of 28 A. japonicus populations for response to clodinafop-propargyl.
Population CodeFresh Weight Inhibition % ± SESusceptibility
HNLH-188.05 ± 0.01SS
AHHN-180.56 ± 0.01S
JSTZ-282.36 ± 0.04S
HNLH-274.60 ± 0.02R?
HNXY-176.29 ± 0.06R?
AHHN-270.91 ± 0.03R?
JSYC-172.78 ± 0.03R?
HNSQ-173.46 ± 0.02R?
AHCZ-178.76 ± 0.03R?
HNXY-262.14 ± 0.03RR
HNZMD-162.08 ± 0.02RR
HNNY-149.32 ± 0.04RR
AHHN-345.14 ± 0.05RR
AHHN-459.41 ± 0.03RR
AHHN-539.76 ± 0.02RR
AHHN-635.23 ± 0.01RR
AHCZ-253.82 ± 0.01RR
AHCZ-357.32 ± 0.03RR
AHCZ-437.02 ± 0.01RR
AHCZ-541.81 ± 0.04RR
ANBB-163.35 ± 0.05RR
AHBB-253.67 ± 0.03RR
AHXC-143.57 ± 0.02RR
AHLA-140.79 ± 0.03RR
AHFY-141.86 ± 0.08RR
JSTZ-160.04 ± 0.02RR
JSHA-140.11 ± 0.02RR
JSYZ-142.99 ± 0.02RR
Note: SS (fully susceptible standard, 88.05%) represents the fresh weight reduction in the fully susceptible population HNLH-1 treated with clodinafop-propargyl at a discriminating dose of 56.25 g a.i. ha−1; RRR, highly resistant (0%–35.22% inhibition); RR, moderately resistant (35.22%–70.44% inhibition); R?, potentially resistant (70.44%–79.25% inhibition); S, susceptible (79.25%–100% inhibition). Classification follows the Moss 3R resistance rating system.
Table 3. Resistance levels of different A. japonicus populations to clodinafop-propargyl.
Table 3. Resistance levels of different A. japonicus populations to clodinafop-propargyl.
Population CodeRegression Formula
(y = a + bx)		Correlation Coefficient (r)GR50
(g a.i. ha−1)		95% Confidence
Interval		Resistant Index
(RI)		Resistance Level
HNLH-1y = 3.6631 + 1.3465x0.99579.83848.3282~11.62251S
HNLH-2y = 3.4264 + 1.2173x0.993319.617316.9312~22.72961.99S
HNXY-1y = 3.2084 + 1.4239x0.996018.123416.1054~20.39431.84S
AHHN-1y = 3.7251 + 1.2122x0.994611.26489.4719~13.39711.14S
AHHN-2y = 3.3327 + 1.3027x0.978119.051914.4945~25.04221.94S
JSTZ-2y = 3.1425 + 1.5026x0.990517.227414.2899~20.76881.75S
JSYC-1y = 4.0597 + 0.7954x0.934615.21188.8303~26.20511.55S
HNXY-2y = 4.3490 + 0.4824x0.970622.365416.5994~30.13442.27LR
HNZMD-1y = 4.0137 + 0.7530x0.982820.409116.1442~25.80072.07LR
HNSQ-1y = 3.7306 + 0.9793x0.976319.776914.9451~25.80072.01LR
AHHN-4y = 3.5567 + 0.8935x0.983641.237533.5181~50.73484.19LR
AHCZ-1y = 3.0057 + 1.5298x0.995320.120517.8027~22.74002.05LR
AHCZ-2y = 2.0551 + 1.8289x0.974340.756831.1111~53.39304.14LR
ANBB-1y = 2.9824 + 1.2754x0.995638.193634.3958~42.41083.88LR
JSTZ-1y = 3.7807 + 0.7991x0.997833.567231.2008~36.11303.41LR
HNNY-1y = 3.3946 + 0.8924x0.969162.952145.0500~87.96816.40MR
AHHN-3y = 4.0567 + 0.4787x0.977493.461366.1024~132.14379.50MR
AHHN-5y = 3.0101 + 1.1312x0.992157.429748.9528~67.37455.84MR
AHCZ-4y = 3.5046 + 0.8906x0.959547.753133.8006~67.46494.85MR
AHHN-6y = 3.8486 + 0.4337x0.9826451.3621249.4490~816.710945.88HR
AHCZ-3y = 3.7691 + 0.8906x0.9632146.433483.8983~255.580014.88HR
AHCZ-5y = 3.5836 + 0.6190x0.9793194.1830121.4102~310.575419.74HR
AHBB-2y = 3.9519 + 0.4053x0.9906385.1882255.6725~580.312739.15HR
AHXC-1y = 3.7359 + 0.4849x0.9899404.5877262.2737~624.123541.12HR
AHLA-1y = 4.0993 + 0.3700x0.9689271.8470139.6466~529.198727.63HR
AHFY-1y = 4.1758 + 0.3388x0.9714270.8837143.3720~511.801427.53HR
JSHA-1y = 4.0398 + 0.3741x0.9859368.6088224.2826~605.809237.47HR
JSYZ-1y = 4.0638 + 0.3988x0.9670222.4553118.1062~418.998922.61HR
Note: Resistance levels were classified according to resistance index (RI): populations with RI < 2 were classified as susceptible (S); 2 ≤ RI < 5 as low-level resistant (LR); 5 ≤ RI < 10 as moderately resistant (MR); and RI ≥ 10 as highly resistant (HR).
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Cheng, R.; Song, X.; Zhang, L.; Liu, W.; Wu, Z.; Bi, Y. Germination Differences Between Clodinafop-Propargyl-Resistant and -Susceptible Alopecurus japonicus Steud. Populations Under Multiple Abiotic Stresses. Agronomy 2026, 16, 1381. https://doi.org/10.3390/agronomy16141381

AMA Style

Cheng R, Song X, Zhang L, Liu W, Wu Z, Bi Y. Germination Differences Between Clodinafop-Propargyl-Resistant and -Susceptible Alopecurus japonicus Steud. Populations Under Multiple Abiotic Stresses. Agronomy. 2026; 16(14):1381. https://doi.org/10.3390/agronomy16141381

Chicago/Turabian Style

Cheng, Rui, Xiaoshen Song, Lilei Zhang, Weitang Liu, Zhiwen Wu, and Yaling Bi. 2026. "Germination Differences Between Clodinafop-Propargyl-Resistant and -Susceptible Alopecurus japonicus Steud. Populations Under Multiple Abiotic Stresses" Agronomy 16, no. 14: 1381. https://doi.org/10.3390/agronomy16141381

APA Style

Cheng, R., Song, X., Zhang, L., Liu, W., Wu, Z., & Bi, Y. (2026). Germination Differences Between Clodinafop-Propargyl-Resistant and -Susceptible Alopecurus japonicus Steud. Populations Under Multiple Abiotic Stresses. Agronomy, 16(14), 1381. https://doi.org/10.3390/agronomy16141381

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