Introduction
Prostrate knotweed (Polygonum aviculare L.) is becoming a challenging weed in the Australian broadacre (large-scale farming) cropping system. The key traits that make this weed difficult to manage are its extended emergence windows, prolific seed production over a longer period, and high persistence (Kloot Reference Kloot and Boyce1982). Further, the prostrate growth habit of this weed may complicate the harvest operations by entangling machinery during harvest and reducing harvesting efficiency (Burnett et al. Reference Burnett, Young, McLaren, Norng, Norton, Lemerle, Cousens, van Klinken, Osten, Panetta and Scanlan2008). In pastures, P. aviculare infestation may lower forage quality by suppressing more desirable species and offering little nutritional value for livestock (Bowcher Reference Bowcher2002).
Globally, this weed has evolved resistance to Groups 5 (atrazine) and 34 (amitrole) herbicides, highlighting its adaptability to different selection pressures (Heap Reference Heap2025). Polygonum aviculare can germinate in a wide range of temperatures (5 to 25 C); therefore, it can maintain a persistent seedbank, ensuring continuous reinfestation (Battla et al. Reference Batlla, Grundy, Dent, Clay and Finch-Savage2009). Moreover, it exhibits seed dormancy as an adaptive survival mechanism that allows it to thrive in diverse and challenging environments (Saunders and Field Reference Saunders and Field1983).
Dormancy may allow P. aviculare seeds to remain viable in the soil for extended periods, delaying germination until favorable conditions arise, such as adequate moisture and temperature. It was hypothesized that this trait might help weeds escape control measures and synchronize germination with crop growth, increasing their competitiveness (Mahajan and Chauhan Reference Mahajan and Chauhan2020). Dormancy in weeds is influenced by factors like seed coat impermeability, which prevents water and oxygen penetration, and hormonal regulation, particularly high levels of abscisic acid (Nautiyal et al. Reference Nautiyal, Sivasubramaniam, Dadlani, Dadlani and Yadava2023). A high level of dormancy in P. aviculare seeds may increase seed persistence in the soil and make weed control tasks difficult (Batlla et al. Reference Batlla, Ghersa and Benech-Arnold2020). Therefore, understanding the dormancy-breaking mechanism in P. aviculare is crucial for developing effective weed management strategies.
Dormancy in P. aviculare can be broken using various methods. For example, cold stratification mimics winter conditions to help some winter weeds germinate (improved by 65% in common lambsquarters [Chenopodium album L.] by breaking their dormancy [Hock et al. Reference Hock, Knezevic, Petersen, Eastin and Martin2006]). Treating seeds with sodium hypochlorite (NaOCl) for different durations may weaken the seed coat, facilitating water and oxygen penetration (Mahajan et al. Reference Mahajan, Mutti, Jha, Walsh and Chauhan2018). Smoke water, often used in native plant propagation, can stimulate germination by mimicking natural fire cues (Baker et al. Reference Baker, Steadman, Plummer, Merritt and Dixon2005). Warm-water treatment and exposure to fluctuating temperatures also disrupt dormancy by softening seed coats or altering hormonal balances (Yan and Chen Reference Yan and Chen2020). Additionally, gibberellic acid (GA3) application is known to overcome dormancy by promoting germination-related processes (Mahajan et al. Reference Mahajan, Mutti, Jha, Walsh and Chauhan2018).
Despite the availability of dormancy-breaking techniques under controlled conditions, a significant research gap exists in their field applicability for P. aviculare. There is limited knowledge of how these methods interact with or simulate the variable soil, climatic, and farming conditions typical of eastern Australia. In particular, growers currently lack practical indicators or tools to assess dormancy status in the field, making it difficult to predict emergence timing and implement timely weed control measures. Understanding the environmental cues that regulate P. aviculare seed dormancy and germination, especially under field conditions in eastern Australia, is crucial to develop reliable, sustainable weed management strategies for this persistent and dormant seedbank species.
Seed populations collected from different habitats in most weeds may vary in their seed germination behavior due to environmental adaptation, soil moisture variation, and climate change. Therefore, studying the germination ecology of P. aviculare populations is essential for developing better management strategies. The literature suggests that germination and emergence in many weeds are influenced by temperature, light, salinity, water potential, seed burial depth, and residue cover (Baskin and Baskin Reference Baskin and Baskin1990; Mahajan et al. Reference Mahajan, Prasad and Chauhan2021). Temperature may play a key role in the seasonal emergence patterns of weeds. Fluctuations in temperature can either promote or suppress the germination of weeds, depending on species-specific thresholds (Chauhan and Johnson Reference Chauhan and Johnson2010).
It was reported that the persistent seedbank of P. aviculare showed a seasonal change in dormancy status due to thermal and light variations (Battla et al. Reference Batlla, Grundy, Dent, Clay and Finch-Savage2009). Light exposure is another important factor that triggers germination, as many weed species require it to break dormancy (Bewley et al. Reference Bewley, Bradford, Hilhorst and Nonogaki2013). Conservation agriculture practices such as minimal tillage and residue retention can alter light availability, affecting weed emergence (Chauhan et al. Reference Chauhan, Singh and Mahajan2012).
Salinity and water potential may also impact seed viability in P. aviculare. It was found that high salt levels and low moisture reduce seedling establishment in Persicaria perfoliate (Polygonum perfoliatum L.), a species closely related to P. aviculare (Farooq et al. Reference Farooq, Huseyin, Sonnur, Cumali, Samy, Marian, Marek, Milan and Ahmed2021). As the salinity-affected area in Australia is on the rise (Rengasamy Reference Rengasamy2010), understanding the germination behavior of P. aviculare under salt stress may provide important insight into its invasiveness. Burial depth can also influence seedling emergence in P. aviculare, as it was reported that, in general, deeply buried small weed seeds receive less oxygen and light, while shallowly buried seeds have higher emergence rates (Chauhan and Johnson Reference Chauhan and Johnson2010). Therefore, like other weeds, residue cover in conservation tillage systems may also affect the germination of P. aviculare by modifying soil temperature, moisture retention, and light penetration (Grundy et al. Reference Grundy, Mead and Burston2003).
Germination of P. aviculare is likely influenced by key environmental cues such as temperature, light, moisture, and burial depth. However, the specific thresholds and interactions of these factors under eastern Australian conditions remain poorly understood. For instance, extreme temperatures or low water availability may suppress germination, while light exposure and shallow burial may trigger it. Understanding how these environmental factors regulate dormancy release and seedling emergence in P. aviculare is essential for predicting field emergence patterns and designing region-specific, sustainable weed management strategies.
This study aimed to evaluate various dormancy-breaking methods in P. aviculare for enhanced germination and investigate how environmental factors such as temperature, light, salinity, water potential, burial depth, and residue cover may affect P. aviculare germination and emergence in Australian cropping systems. The specific objectives of this study were to (1) identify cues for breaking seed dormancy in P. aviculare, (2) determine the optimal temperature range for enhanced germination, (3) assess the impact of light regimes on germination, (4) investigate the effects of salt and water stress on seed germination, (5) examine how residue cover affects emergence by modifying microclimatic conditions, and (6) evaluate the influence of burial depth on seedling emergence.
Materials and Methods
Seed Description
Experiments were conducted in 2024 to 2025 at the Weed Science Laboratory of the Queensland Alliance for Agriculture and Food Innovation (QAAFI), University of Queensland, Gatton, Australia, using fresh seeds of P. aviculare. Foundational studies for breaking seed dormancy were conducted using three populations of P. aviculare (Gatton, Nangwee, and Warwick), collected from the Queensland region. Seed germination ecology studies were conducted using two populations of P. aviculare (Gatton and Nangwee). Fresh seeds collected in November 2024 were used for these studies. The GPS coordinates of Gatton, Nangwee, and Warwick populations are −27.538630/152.334398, −27.509321/151.279341, and −29.206871/152.102118, respectively.
The Gatton population was originally collected from Kingaroy (wheat [Triticum aestivum L.]–fallow) in 2023 and multiplied for seed production in the winter season of 2024 at Gatton; fresh seeds from this population were used for the study. The Nangwee population was collected from the fence lines of wheat in November 2024. The Warwick population was collected from wheat fallows in November 2024. Seeds were collected from mature plants by shaking them and were separated from the chaff. Care was taken not to damage the seed coat. The collected seed samples were dried in an oven at 40 C for 3 d to avoid microbial contamination and physiological deterioration before being stored in plastic containers at room temperature (25 ± 2 C).
Foundational Studies for Breaking Seed Dormancy
The freshly harvested seeds of P. aviculare exhibited high dormancy when tested using the standard germination protocol (described later using tap-water media); therefore, a series of experiments were conducted to overcome this dormancy.
General Protocol for Foundational Studies
In each foundational experiment, 25 seeds were placed in each 9-cm-diameter petri dish, with three replicate dishes per treatment. Dishes were lined with two layers of filter paper (MN615, 85 mm; Macherey-Nagel, Düren, Germany), moistened with 5 ml of tap water or treatment solution, sealed in plastic bags to prevent moisture loss, and incubated under controlled conditions. Each foundational experiment was conducted using a completely randomized design. When three populations were included, data were analyzed in a factorial arrangement. Germination percentages were calculated for each petri dish based on total germination counts at the termination of each experiment. The germination percentage for each petri dish was calculated based on the total number of germinated seeds at the end of the experiment. Viability of nongerminated seeds was assessed by applying force with forceps; firm seeds were considered viable, whereas soft seeds lacking structural integrity were deemed nonviable.
Foundational Study 1: Evaluating Different Dormancy-breaking Methods
This study evaluated 15 treatments (Table 1), including a control, in a completely randomized design (CRD) with three replications. The experiment was conducted with the Gatton population, and the germination test was conducted in an incubator set at alternating day/night temperatures of 25/15 C. For water immersion, seeds were soaked in chilled water and refrigerated at 4 C for 5 h before incubation. In the scarification treatment, seeds were rubbed twice with 60-grit sandpaper. For the warm-water treatment, seeds were placed in a beaker containing water maintained at 45 C and subsequently kept in an oven at 45 C for 5 h. For the smoke-water treatment, seeds were soaked for 5 h in smoke water (Regen smoke water, Grayson Australia, Morwell, Australia) solution (1:10) prepared by mixing 5 ml of smoke water with 50 ml of tap water. Leaching treatments included placing seeds in petri dishes containing either an extract of potting mix with water or a 1% (w/v) potassium nitrate (KNO3) solution was prepared by dissolving 1 g of KNO3 in 100 mL of distilled water.
Table 1. Effect of different dormancy-breaking treatments on the germination of Polygonum aviculare (Gatton population).
a Means followed by different letters are significantly different at P ≤ 0.05.
The NaOCl immersion treatment used 100 ml of commercial sodium hypochlorite (42 g L−1, 4% chlorine w/v, 9 g L−1 NaOH) for 0.5 or 5 h, after which the seeds were rinsed thoroughly with tap water for 10 min. In the NaOCl + GA3 treatment, NaOCl-treated seeds were incubated with a 100 mg kg−1 gibberellic acid (GA3) solution as a medium (5 ml) in petri dishes. For the dark treatment, seeds in petri dishes were wrapped in aluminum foil to maintain darkness for 3 wk during incubation, followed by a light/dark treatment. Cold stratification was performed by placing seeds in petri dishes containing filter paper moistened with 5 ml of water and incubating them in the dark at 4 C for 4 and 8 wk, with germination counted 3 wk after placing them in a light/dark environment. The experiment was started on November 20, 2024, and terminated after 11 wk.
Foundational Study 2: Optimizing NaOCl Immersion Duration and Temperature for Germination
This experiment was conducted using three P. aviculare populations (Gatton, Nangwee, and Warwick), with six NaOCl immersion durations (0, 2, 4, 6, 8, and 10 h), and two alternate day/night temperature regimes (20/10 C and 25/15 C for incubation in separate incubators).
Seeds were immersed in 100 ml of full-strength NaOCl for the designated immersion durations (0, 2, 4, 6, 8, or 10 h), then thoroughly rinsed in tap water for 10 min. After draining, seeds were placed in petri dishes at two temperature regimes for germination testing following the general protocol. The experiment was conducted in a completely randomized factorial design (CRD) with three replications. The experiment started on December 12, 2024, and terminated after 4 wk, as no further improvement in germination was observed beyond the third week.
Foundational Study 3: Optimizing NaOCl Immersion Duration for Three Populations
This study repeated Foundational Study 2 with a single temperature regime (optimized alternate day/night temperature regime 20/10 C). The germination response of P. aviculare seeds to the selected two temperature regimes (20/10 C and 25/15 C) was similar in Foundational Study 2. Therefore, we selected an optimized temperature of 20/10 C in the third foundational study, which simulates the temperatures experienced by winter crops. Thus, treatments in this study comprised three populations (Gatton, Nangwee, and Warwick) of P. aviculare and six immersion times (0, 2, 4, 6, 8 and 10 h) of NaOCl. Seeds were incubated at a temperature regime of 20/10 C with three replications following the same protocol as used in Foundational Study 2. The experiment started on January 16, 2025, and terminated after 4 wk, as no further improvement in germination was observed beyond the third week.
Follow-up Study on Seed Germination Ecology
In the foundational studies, we found the dormancy-breaking method by immersing P. aviculare seeds in NaOCl for 8 h. Therefore, before initiating each experiment for germination ecology, seeds were treated with NaOCl for 8 h, followed by a 10-min wash, and then used. Each germination experiment ran for 21 d and was conducted between February 2025 and April 2025. Each experiment was repeated after the termination of the first experiment. Germination was assessed by evenly distributing 25 seeds (NaOCl treated for 8 h) from two populations (Gatton and Nangwee) in 9-cm-diameter petri dishes lined with a double layer of filter paper (MN615, 85 mm, manufactured by Macherey-Nagel) moistened with 5 ml of tap water or treatment solution. petri dishes were sealed in plastic bags to prevent moisture loss and incubated under controlled conditions.
Six experiments evaluating the effects of (1) temperature regimes, (2) light regimes, (3) osmotic stress, (4) salt stress, (5) burial depth, and (6) residue amounts were conducted in an incubator set at 20/10 C (day/night) temperature, with a 12-h photoperiod synchronized with the thermoperiod. Fluorescent lamps with a light intensity of 85 µmol m⁻2 s⁻¹ were used as the light source. Germination in complete darkness was assessed by wrapping petri dishes in three layers of aluminum foil, which were opened only once for germination counts after 21 d.
Seeds were considered germinated when the radicle extended at least 2 mm. Germination percentages were calculated for each petri dish based on total germination counts after 21 d. Viability of nongerminated seeds was assessed by applying force with forceps; firm seeds were considered viable, whereas soft seeds lacking structural integrity were deemed nonviable. Each experiment was conducted in a completely randomized design with a factorial arrangement using three replicates per treatment.
Effect of Temperature
To determine the optimal temperature conditions for germination of P. aviculare, seeds of two populations (Gatton and Nangwee) were incubated under alternating day/night temperature regimes (15/5, 20/10, 25/15, 30/20, and 35/25 C). These temperature regimes simulated spring, winter, autumn, and summer fluctuations in eastern Australia’s cropping region.
Effect of Light
To determine the optimal light conditions for germination of P. aviculare, seeds of both populations (Gatton and Nangwee) were incubated at optimal temperature conditions of 20/10 C under light/dark regimes and complete darkness conditions, following the general protocol described earlier. The optimal temperature conditions for P. aviculare were determined based on the temperature experiment.
Effect of Salt and Osmotic Stress
Germination responses to salt stress were evaluated using sodium chloride (NaCl) solutions of 0, 25, 50, 100, 150, 200, and 250 mM (using the solution as media in a petri dish). This range corresponds to salinity levels in salt-affected cropping regions of Australia (Rengasamy Reference Rengasamy2002, Reference Rengasamy2010). Osmotic stress was assessed using polyethylene glycol 8000 (PEG-8000) solutions with osmotic potentials of 0, −0.1, −0.2, −0.4, −0.8, and −1.0 MPa, prepared following Michel and Radcliffe (Reference Michel and Radcliffe1995).
Effect of Wheat Residue Amount on Seedling Emergence
Fifty seeds of both populations were sown in 14-cm-diameter plastic pots filled with clay loam soil (organic carbon 0.76%, pH 6.3, and electrical conductivity 0.095 ds m⁻¹). Finely chopped wheat straw (2 to 3 cm) from the cultivar ‘Sunmaster’ was evenly distributed at rates equivalent to 0, 1, 2, 4, 6, and 8 Mg ha⁻¹. The pots were placed in plastic trays and kept in a growth chamber maintained at 20/10 C (day/night temperature), with a 12-h photoperiod. Pots were watered once a week to maintain soil moisture, and emergence in each pot was recorded after 3 wk.
Effect of Seed Burial Depth on Seedling Emergence
Fifty seeds of each population were buried at depths of 0, 1, 2, 4, and 8 cm in 14-cm-diameter plastic pots filled with clay loam soil. Seedling emergence was defined by the appearance of two cotyledons, and observations were recorded 3 wk after planting.
Statistical Analyses
A completely randomized design with three replications was used for all experiments. Each experiment was repeated after the termination of the first run, except for foundational studies. No significant time by treatment interaction was detected in each seed germination ecology experiment via ANOVA, so data from both runs were pooled for analysis. ANOVA was conducted (using OPStat - Online Statistical Analysis Tools, Chaudhary Charan Singh Haryana Agricultural University, Hisar, India) to detect significant treatment effects (P < 0.05). Where significant differences occurred, means were separated using Fisher’s protected LSD test (P < 0.05). Before ANOVA, data were tested for normality using the Shapiro-Wilk test in OPStat. Levene’s test is not available in OPStat, so homogeneity of variances was assessed by comparing error mean squares and examining residual patterns in the ANOVA output.
Nonlinear regression analysis was applied to quantify the relationship between germination and salt concentration potential. Data were described using a three-parameter sigmoid model using SigmaPlot v. 15.0 (Grafiti LLC, Palo Alto, CA, USA):
$$y = {y_{{\rm{max}}}}/\left[ {1 + {\rm{exp}}\left( {x - {x_{50}}} \right)/{y_{{\rm{rate}}}}} \right)]$$
where y represents total germination (%) at osmotic potential concentration x, y max denotes maximum germination (%), x 50 represents the osmotic potential required for 50% inhibition of maximum germination, and y rate defines the slope of inhibition.
The relationship between salt concentration and germination (%) was established in a logistic model, and described as:
$$y = {y_{{\rm{max}}}}/1 + {\left( {x/{x_0}} \right)^{{y}}}^{{\rm{rate}}}$$
where y represents total germination (%) at salt concentration x, y max denotes maximum germination (%), x 50 represents the salt required for 50% inhibition of maximum germination, and y rate defines the slope of inhibition. The fit of the selected models was determined using R 2 values.
Results and Discussion
Foundational Study 1: Evaluating Different Dormancy-breaking Methods
Germination was greater than 80% when seeds were either immersed in NaOCl for 5 h or subjected to cold stratification for 4 or 8 wk before incubation (Table 1). In the control treatment (without NaOCl immersion), germination was only 12%; however, it increased to 28% when seeds were immersed in NaOCl for 30 min. Leaching, warm water, and smoke treatments did not improve P. aviculare germination compared with the control. However, when weed seeds were transferred to light/dark conditions after being kept in darkness for 3 wk, germination reached 53%.
From this experiment, seed immersion with NaOCl emerged as a highly effective dormancy-breaking method, particularly when seeds were immersed for extended durations (5 h compared with 0.5 h). These findings suggest that NaOCl plays a significant role in overcoming dormancy. Shorter immersion durations, such as 0.5 h, provided only a modest improvement. These results indicate that NaOCl likely weakens or degrades the seed coat, removes inhibitory compounds, or enhances water uptake, thereby facilitating germination (Chaves et al. Reference Chaves, Silva and Ribeiro2017; Hsiao Reference Hsiao1979). However, the current study only tested two NaOCl immersion times, highlighting the need for further research to optimize immersion durations for enhanced germination of P. aviculare. Therefore, to address this issue, a second experiment was conducted.
The success of cold stratification for enhanced germination in the current study suggests that P. aviculare may have a physiological dormancy component that responds to prolonged exposure to low temperatures, similar to Asiatic tearthumb (Polygonum perfoliatum L.), as reported by earlier researchers (Farooq et al. Reference Farooq, Huseyin, Sonnur, Cumali, Samy, Marian, Marek, Milan and Ahmed2021). By mimicking natural winter conditions, cold stratification appears to be an effective method for breaking P. aviculare, allowing this weed to germinate in late winter and spring seasons.
In this study, dormancy-breaking methods such as leaching, warm-water treatment, and smoke exposure failed to stimulate germination. Polygonum aviculare seeds did not respond to leaching, suggesting that water-soluble chemical inhibitors alone do not control their dormancy. Warm-water treatment that softens seed coats to improve water absorption did not improve P. aviculare seed germination. This suggests that seeds may have physiological dormancy, or the warm-water treatment was not hot enough or not applied for a long enough duration, that it may have had a significant effect on the seed. The fact that smoke treatment did not work is noteworthy, as smoke compounds typically help fire-adapted species sprout. The lack of response suggests that dormancy in this weed operates through different regulatory mechanisms compared with fire-adapted plants.
Light plays a crucial role in enhancing the germination of seeds. When P. aviculare seeds were kept in complete darkness for 3 wk before exposure to alternating light/dark cycles, germination improved significantly compared with the control. This response suggests that light acts as an environmental cue for germination enhancement. Most small-seeded weed species need light to initiate germination, resulting in seeds sprouting only near the soil surface, where they find the best conditions for seedling growth (Riemens et al. Reference Riemens, Scheepens and Van der Weide2004). This study’s germination stimulation response to light supports that P. aviculare dormancy is mainly physiological and is affected by environmental factors.
Foundational Study 2: Optimizing NaOCl Immersion Duration and Temperature for Germination
The interaction effect between NaOCl immersion time and populations was significant for germination (Table 2). For the Gatton population, germination increased to 54% and 89% when seeds were immersed in NaOCl for 2 and 8 h, respectively, compared with the control treatment (21%). For the Nangwee population, germination was 42% in the control treatment, and it increased to 80% when seeds were immersed in NaOCl for 8 h. The Warwick population exhibited the lowest germination in the control treatment (5%) and increased to 59% when seeds were immersed in NaOCl for 8 h. NaOCl immersion durations of 8 and 10 h produced comparable germination rates in each population; however, the 8-h treatment was chosen for subsequent experiments to limit prolonged chemical exposure without compromising germination efficacy.
Table 2. Interaction effect of NaOCl immersion times and populations on the germination of Polygonum aviculare (averaged over temperature regimes; 20/10 C and 25/15 C).
a Means followed by different letters are significantly different at P ≤ 0.05.
The nonsignificant effect of temperature (20/10 and 25/15 C) on the germination of P. aviculare populations suggests that the seed response to NaOCl treatment is independent of temperature fluctuations within the tested range. This could be due to intrinsic seed dormancy mechanisms, in which impermeability or endogenous inhibitors play a greater role than temperature variations. The selected temperature regimes may not have been extreme enough to induce differences, and the strong influence of NaOCl immersion likely overshadowed any minor temperature effects.
Polygonum aviculare seeds may be adapted to germinate across various temperatures, making them less sensitive to moderate fluctuations (Baskin and Baskin Reference Baskin and Baskin1990; Khan and Ungar Reference Khan and Ungar1998). These observations suggest that chemical scarification with NaOCl is a reliable dormancy-breaking method, regardless of temperature, and can be effectively used in the laboratory for dormancy breaking in P. aviculare for further studies on seed germination ecology.
This study demonstrated that the germination behavior of P. aviculare varied with populations. Furthermore, this study highlighted that NaOCl immersion of seeds significantly improved germination in each population, although the extent of improvement varied. These results suggest population-specific dormancy differences, which could be attributed to genetic variation, environmental conditions at seed maturation, low proportion of viable seeds, or variation in seed coat permeability (Debeaujon et al. Reference Debeaujon, Lepiniec, Pourcel, Routaboul, Bradford and Nonogaki2007).
In this study, NaOCl demonstrated effectiveness for breaking dormancy in the three tested populations but produced varying results, indicating it is necessary to adopt population-specific approaches to breaking dormancy. NaOCl treatment may release dormancy in P. aviculare through two possible mechanisms: increasing oxygen availability and weakening the seed coat structure. In johnsongrass [Sorghum halepense (L.) Pers.], NaOCl did not remove the hull but enhanced oxygen diffusion, leading to improved germination (Mohammadi et al. Reference Mohammadi, Noroozi and Nosratti2013). Similarly, in wild mustard (Sinapis arvensis L.), acid scarification broke dormancy by modifying the seed coat structure (Edwards Reference Edwards1969). These findings suggest that NaOCl may either oxidize growth inhibitors or alter the testa in P. aviculare, thereby promoting gas exchange and triggering germination.
Foundational Study 3: Optimizing NaOCl Immersion Duration for Three Populations
Similar to the previous experiment, we found a significant interaction between NaOCl immersion duration and populations for germination in this study (Table 3). In the control treatment, Warwick had lower germination (24%) than the Gatton (56%) and Nangwee (45%) populations. These germination values increased to 91%, 75%, and 76% for Gatton, Nangwee, and Warwick populations, respectively, when seeds were immersed in NaOCl solution for 8 h and incubated at alternating day/night temperatures of 20/10 C. The variability in mean germination among populations (especially in the control treatment) in Foundational Studies 2 and 3 could be due to temperature variation, as Foundational Study 2 measured germination under two temperature regimes. Additionally, the possibility that seed viability improved over time cannot be ruled out.
Table 3. Interaction effect of NaOCl immersion times and populations on the germination of Polygonum aviculare (seeds were incubated at alternate day/night temperatures of 20/10 C).
a Means followed by different letters are significantly different at P ≤ 0.05.
Different P. aviculare populations responded differently to NaOCl immersion duration, showing that seed dormancy is complex and needs precise management strategies. Therefore, this study emphasizes the importance of tailored dormancy-breaking treatments based on the unique traits of each population.
Overall, these foundational studies suggest that the NaOCl treatment method works effectively to break P. aviculare in a laboratory setting. Therefore, this knowledge was used in overcoming seed dormancy of fresh populations of this weed under laboratory conditions for conducting subsequent experiments on seed germination ecology.
Seed Germination Ecology
Effect of Temperature
A significant interaction between temperature regimes and populations was observed for the germination of P. aviculare (Table 4). The Gatton population exhibited similar germination (83% to 85%) at temperatures ranging from 15/5 C to 30/20 C and recorded the lowest germination (51%) at 35/25 C. The Nangwee population showed the highest germination (70%) at 25/15 C, which decreased to 58% and 56% at 15/5 and 35/15 C, respectively. At each temperature regime, the Nangwee population had lower germination than the Gatton population, except at 35/15 C, where both populations exhibited similar germination.
Table 4. Effect of alternating day/night temperatures (15/5 to 35/25 C) on the germination (%) of two populations of Polygonum aviculare a .
a Seeds were incubated for 21 d under light/dark (12-h photoperiod).
b Means followed by different letters are significantly different at P ≤ 0.05.
This study demonstrated that P. aviculare can germinate across a wide temperature range. Previous research has shown that most P. aviculare seeds could germinate in spring at temperatures as low as 5 C, with lower germination occurring in summer and autumn at 20–25 C (Baskin and Baskin, Reference Baskin and Baskin1990). Similarly, in closely related species, research has shown that P. perfoliatum could germinate between 5 C and 40 C, with the highest germination observed at an alternating day/night temperature of 20/15 C (Farooq et al. Reference Farooq, Huseyin, Sonnur, Cumali, Samy, Marian, Marek, Milan and Ahmed2021). Germination of both populations in this study remained more than 50% even at 35/15 C, highlighting that year-round control for P. aviculare is needed in eastern Australia. Population differences of P. aviculare in response to temperature in this study suggest that targeted management depending upon local climatic conditions could be an effective approach to managing this weed.
For instance, the Gatton population germinated well from 15/5 C to 30/20 C, indicating its ability to establish across winter and summer seasons. The Nangwee population had peak germination at 25/15 C, showing a preference for moderate temperature conditions. Reduced germination of both populations at 35/15 C suggests that extremely high temperatures may limit establishment, affecting weed management in hotter regions or seasons.
Variations in germination patterns in both populations suggest local adaptation or genetic differences may influence dormancy and establishment in P. aviculare. Therefore, in moderate-temperature regions, such as southern Queensland and northern New South Wales, early-season control can prevent its establishment. In warmer regions, such as northern Queensland, extremely high temperatures during summer may naturally reduce its germination. However, residual seeds may still be an issue under climate change conditions. These results highlight that region-specific management of this weed is needed, and climate change conditions may increase its invasiveness. Therefore, this study suggests that integrated weed management strategies involving manipulating sowing time and strategic tillage may help manage this weed.
Understanding temperature-driven germination patterns for this weed under field conditions could further help in improving weed control decisions in Australian cropping systems. The population-level variability in response to temperature in this study supports the concept of local adaptation (Guillemin et al. Reference Guillemin, Gardarin, Reibel, Munier-Jolain and Colbach2013). Similar temperature-mediated responses have been reported in other weeds, such as pigweed (Amaranthus spp.) and C. album (Baskin and Baskin Reference Baskin and Baskin2014), reinforcing the need to understand ecotypic diversity for P. aviculare in relation to changing climatic conditions.
Effect of Light
Averaged over both populations, seeds exposed to a 12-h light/dark cycle showed higher germination (92%) compared with seeds incubated in complete darkness (49%) (Figure 1). These results highlight the positive photoblastic nature of P. aviculare seeds. Light regulates germination by stimulating phytochrome-mediated pathways, particularly the conversion of phytochrome from its inactive (Pr) to its active (Pfr) form, which promotes germination-related gene expression (Baskin and Baskin Reference Baskin and Baskin2014; Bewley et al. Reference Bewley, Bradford, Hilhorst and Nonogaki2013). The reduced germination of P. aviculare in complete darkness suggests that light is either necessary to break residual dormancy or acts as a strong promoting signal to initiate metabolic processes required for radicle emergence.
Figure 1. Effect of light regimes on the germination (%) of Polygonum aviculare (averaged over populations). Seeds were incubated for 21 d under light/dark (12-h photoperiod) and complete dark (24-h photoperiod) at 20/10 C.
The results from this study suggest that the germination of P. aviculare may occur near the soil surface where light is available under field conditions. These results aligned with earlier research on small-seeded weeds such as redroot pigweed (Amaranthus retroflexus L.) and C. album, in which light stimulated seed germination (Baskin and Baskin Reference Baskin and Baskin1977; Chauhan and Johnson Reference Chauhan and Johnson2009, Reference Chauhan and Johnson2010). The strong positive response of P. aviculare to light in this study also suggests that surface-disturbing tillage practices may enhance the germination and emergence of this weed, informing decisions for weed management around tillage.
Effect of Salt and Osmotic Stress
A significant interaction between NaCl concentrations and populations was observed for the germination of P. aviculare (Figure 2 ). The fitted logistic regression models for both populations, respectively, confirmed a strong relationship between salinity levels and germination. A clear declining trend in germination was observed with increasing NaCl concentrations for both populations. However, marked differences between the populations were observed with increased salt concentrations. The Gatton population maintained relatively high germination across all salinity levels and declined to 50% at 250 mM. In contrast, the Nangwee population was more sensitive, and germination decreased to below 20% across the same salinity gradient. This suggests that the Gatton population had greater tolerance to salt stress than the Nangwee population.
Figure 2. Effect of sodium chloride (NaCl) on the germination of two populations of Polygonum aviculare. Seeds were incubated for 21 d at alternating day/night temperatures of 20/10 C. The lines represent a logistic model fit to the data. Vertical bars represent the ±SEs of the mean (n = 6).
This population-specific tolerance of P. aviculare to salt is of significant agronomic relevance, particularly in eastern Australia, where soil salinity is an emerging challenge (Rengasamy Reference Rengasamy2006, Reference Rengasamy, Fath and Jorgensen2020). The high ability of the Gatton population to germinate and establish under salt stress indicates its potential to compete with crops in salt-affected environments. It has been reported that salt-tolerant weed species such as salt bush (Atriplex spp. Rydb and C. album could thrive in saline soils, complicating weed management in stressed agroecosystems (Baskin and Baskin Reference Baskin and Baskin1977; Khan and Gul Reference Khan, Gul, Khan and Weber2006). The persistence of P. aviculare under such conditions demands site-specific weed control strategies that take into account both weed adaptation and local soil salinity status. If not managed properly under such an environment, this species may not only survive but may also increase its invasiveness and threaten crop productivity, particularly in saline-prone regions of Australia.
A significant interaction between osmotic potential concentrations and populations was observed for the germination of P. aviculare (Figure 3 ). The sigmoid regression models fit the data well, with R² values of 0.97 (Gatton) and 0.98 (Nangwee), indicating reliable prediction of germination responses under varying moisture stress levels. Germination declined progressively in both populations with decreasing osmotic potentials (from 0 to −1.6 MPa). However, the extent of inhibition varied significantly between populations. The Gatton population exhibited greater tolerance to osmotic stress, maintaining >80% germination at −0.4 MPa and ∼60% at −0.8 MPa, whereas the Nangwee population showed a sharper decline, falling below 50% at −0.8 MPa.
Figure 3. Effect of osmotic potential on the germination of two populations of Polygonum aviculare. Seeds were incubated for 21 d at alternating day/night temperatures of 20/10 C. The lines represent a sigmoid model fit to the data. Vertical bars represent the ±SEs of the mean (n = 6).
These results suggest that the Gatton population is more capable of germinating under drought-like or osmotically stressful conditions. This phenomenon could be due to superior physiological mechanisms such as higher osmotic adjustment capability, efficient water uptake, or desiccation tolerance (Bewley et al. Reference Bewley, Bradford, Hilhorst and Nonogaki2013). This finding has practical implications for Australian agriculture, particularly in eastern regions, where salinity and water deficit often co-occur (Rengasamy Reference Rengasamy2006). The ability of P. aviculare to germinate under such conditions implies that this weed may successfully establish in saline- and drought-prone cropping systems, where crop emergence and early vigor are often suppressed. This may lead to increased weed–crop competition, especially in the early growth stages, when moisture stress limits crop establishment.
Comparable studies have shown similar patterns in other salt- and drought-tolerant weed species, such as C. album, common purslane (Portulaca oleracea L.), and Atriplex spp., for which higher germination under osmotic stress correlated with field invasiveness in stressed environments (Gulzar and Khan Reference Gulzar and Khan2001). Therefore, the greater osmotic tolerance in populations such as the Gatton population may enhance their competitive advantage in salinity- and drought-affected soils, posing a serious challenge for weed management in eastern Australian farming systems.
Effect of Wheat Residue Amount on Seedling Emergence
Seedling emergence varied significantly between populations and residue levels (Table 5). However, seedling emergence was lower in the pot assay than in petri dish assays. This might be due to mechanical resistance, variable moisture, and reduced light availability in the soil environment compared with petri dish tests (Baskin and Baskin Reference Baskin and Baskin2014; Bewley et al. Reference Bewley, Bradford, Hilhorst and Nonogaki2013).
Table 5. Seedling emergence of two populations of Polygonum aviculare in response to residue amount (Mg ha−1) when grown in an incubator at alternating day/night temperatures of 20/10 C under a 12-h photoperiod a .
a Seeds were incubated for 21 d under light/dark (12-h photoperiod).
b Means followed by different letters are significantly different at P ≤ 0.05.
The Nangwee population exhibited higher emergence than the Gatton population across all residue levels except 6 Mg ha−1. Both populations had the highest germination at 4 Mg ha⁻¹ (58% for Nangwee and 36% for Gatton). Interestingly, both populations exhibited low emergence in bare soil (0 Mg ha⁻¹) compared with moderate residue levels (2 to 4 Mg ha⁻¹), suggesting that crop residues, contrary to expectations for a light-requiring species, enhanced rather than inhibited emergence. This may appear unexpected, given that P. aviculare is positively photoblastic and germinates better under light/dark conditions than in complete darkness, as evident in our light/dark experiment. Crop residues, especially at moderate levels of cover, likely failed to completely block light from reaching P. aviculare seeds. Instead, they might have created a filtered light environment that allowed partial transmission of light sufficient to activate the phytochrome system (Benech-Arnold et al. Reference Benech-Arnold, Sánchez, Forcella, Kruk and Ghersa2000), while also moderating soil temperature and conserving moisture, both of which are necessary for germination and emergence (Chauhan et al. Reference Chauhan, Singh and Mahajan2012). Therefore, these results indicate that P. aviculare can germinate and emerge even under partial shading, provided other conditions (moisture, temperature) are favorable.
From a management perspective, these findings are important for eastern Australian cropping systems, where conservation agriculture practices, particularly no-till and residue retention, are widely adopted to improve soil health and water retention (Kirkegaard et al. Reference Kirkegaard, Hunt, McBeath, Lilley, Moore, Verburg, Robertson, Oliver, Ward, Milroy and Whitbread2014). While such systems suppress many light-dependent weed species, P. aviculare may not only tolerate, but may actually benefit from moderate residue environments, giving it a competitive edge during crop establishment. This adaptation increases its risk of becoming a residue-adapted weed in minimum-tillage systems and highlights the need for integrated management, including preemergence herbicides and early-season monitoring.
Effect of Seed Burial Depth on Seedling Emergence
A significant interaction between burial depths and populations was observed for the germination of P. aviculare (Table 6). Emergence significantly declined with increasing depth, and the highest emergence was observed on the soil surface (0 cm). The Nangwee population showed greater overall emergence (27% at 0 cm and 13% at 1 cm) compared with the Gatton population (17% at 0 cm and 6% at 1 cm). However, both populations experienced near-complete suppression at depths ≥4 cm. These results confirm that P. aviculare emergence is highly sensitive to burial, with effective emergence only from shallow depths.
Table 6. Seedling emergence of two populations of Polygonum aviculare in response to burial depth when grown in an incubator at alternating day/night temperatures of 20/10 C under a 12-h photoperiod a .
a Seeds were incubated for 21 d under light/dark (12-h photoperiod).
b Means followed by different letters are significantly different at P ≤ 0.05.
This response is closely related to the species’ positive photoblastic nature, as observed in the light/dark experiment. Burial in soil rapidly reduces light availability to seeds, especially beyond 1 cm, leading to phytochrome deactivation and inhibition of germination (Baskin and Baskin Reference Baskin and Baskin2014; Benech-Arnold et al. Reference Benech-Arnold, Sánchez, Forcella, Kruk and Ghersa2000). Additionally, deeper burial increases mechanical resistance and reduces oxygen diffusion, which may further limit the emergence of small-seeded species such as P. aviculare (Chauhan and Johnson Reference Chauhan and Johnson2009).
Interestingly, P. aviculare also showed enhanced emergence under moderate residue cover (2 to 4 Mg ha⁻¹) in the residue cover experiment, despite the potential for shading. This suggests that partial light transmission through residues, along with improved soil moisture and moderated temperature, can create a favorable microenvironment for the germination for P. aviculare, especially when seeds remain on or near the soil surface.
In the eastern Australian cropping systems, reduced tillage and residue retention are common practices; therefore, these findings are critical. Conservation agriculture practices leave weed seeds on the soil surface, and under moderate residue cover, this may lead to enhanced emergence of P. aviculare. In contrast, strategic deep tillage that buries seeds below 4 cm may suppress emergence effectively. Therefore, burial depth and residue management should be jointly considered when designing integrated management strategies for P. aviculare.
In conclusion, this study demonstrates that P. aviculare seeds exhibit high dormancy, which can be effectively broken by immersing seeds in NaOCl for 8 h. Results implied that P. aviculare possesses multiple adaptive traits that enhance its potential to emerge and compete in Australian cropping systems, particularly under conservation agriculture. Its strong germination response under alternating temperatures, moderate salinity, osmotic stress, and partial residue cover, combined with sensitivity to complete darkness and deeper burial, demonstrates that P. aviculare is highly responsive to surface-level microenvironments. The species’ positive photoblastic nature enables rapid emergence when seeds remain on or near the soil surface, especially under moderate residue that allows partial light transmission and conserves moisture. However, seedling emergence was significantly reduced with increasing burial depth and in complete darkness, indicating the importance of seed positioning and soil disturbance. These traits suggest that P. aviculare may become increasingly problematic in eastern Australian conservation systems, where minimum tillage and residue retention maintain seeds at the surface and create favorable conditions for light- and moisture-responsive weed species. The observed differences in germination between residue cover and similar burial depth suggest that factors beyond light limitation, such as physical impedance and gas exchange, may also be influencing seedling emergence. Population-level variations further highlight the need for site-specific management strategies. Integrated weed management practices that combine strategic deep tillage, residue management, and preemergence herbicides targeting surface-germinating seeds are essential to limit the spread and impact of this species in sustainable Australian cropping systems.
Acknowledgments
The authors thank the Grains Research and Development Corporation (GRDC) for investing in this research. The authors acknowledge the use of ChatGPT (OpenAI) for language editing support.
Funding statement
This research received funding from GRDC under Project UOQ2111-007RTX.
Competing interests
The authors declare none.
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