Applied Agriculture Sciences

1. Introduction

Wheat (Triticum aestivum L.) has, for centuries, remained one of the most indispensable cereal crops, not merely as a dietary staple but as a pillar of global food security and economic stability. Its adaptability across diverse agroecological zones has allowed it to sustain large populations, particularly in developing regions where food demand continues to rise steadily. According to recent global estimates, wheat is cultivated on over 220 million hectares worldwide, with an average productivity of approximately 3.5 tons per hectare (USDA, 2021). Despite this seemingly robust global footprint, productivity levels in several countries—including Iraq—remain comparatively modest, often constrained by environmental stressors, suboptimal agronomic practices, and, perhaps most persistently, weed competition (FAO et al., 2022).

Weeds, in many ways, represent a quiet but relentless adversary in agricultural systems. They compete aggressively with crops for essential resources—light, nutrients, water, and space—often with remarkable efficiency. It is estimated that more than 8,000 weed species exist globally, many of which are capable of causing substantial yield losses (Kumbhar & Dharmistha, 2016). In wheat cultivation, these losses can reach up to 34%, depending on weed density, species composition, and timing of infestation (Khawar et al., 2015). What makes this challenge particularly complex is not simply the presence of weeds, but their dynamic adaptability. Over time, many weed species have evolved mechanisms to withstand conventional control strategies, especially chemical herbicides.

The widespread reliance on synthetic herbicides, while initially effective, has gradually led to unintended consequences. Herbicide resistance, for instance, has emerged as a significant concern, reducing the long-term efficacy of many commonly used compounds. At the same time, environmental and health considerations have prompted increasing scrutiny of chemical inputs in agriculture. Residual toxicity, soil degradation, and potential impacts on non-target organisms have all contributed to a growing sense that alternative, more sustainable weed management strategies are not just desirable—but necessary.

It is within this broader context that interest in plant-derived compounds and endogenous regulatory molecules has begun to gain momentum. Among these, allelopathy stands out as a particularly intriguing phenomenon. At its core, allelopathy refers to the biochemical interactions between plants, whereby certain species release secondary metabolites that can influence the growth and development of neighboring plants (Rice, 2012). These compounds—often released through root exudates, leaf leachates, or decomposing residues—can inhibit seed germination, suppress growth, or otherwise alter physiological processes in competing species. In agricultural systems, this natural form of chemical interaction has been increasingly explored as a potential tool for weed management (Farooq et al., 2011).

One plant that has attracted attention in this regard is Eruca sativa (rocket). Known for its rich phytochemical profile, E. sativa contains various bioactive compounds, including glucosinolates and phenolics, which may exhibit allelopathic properties. When applied in the form of aqueous extracts, these compounds have the potential to interfere with weed growth, offering a biologically derived alternative to synthetic herbicides. However, while preliminary findings are promising, the consistency and field-level effectiveness of such extracts remain somewhat variable, often influenced by factors such as concentration, application timing, and environmental conditions.

Parallel to these developments, plant hormones—or phytohormones—have also been investigated for their potential role in crop management. Among them, abscisic acid (ABA) occupies a somewhat paradoxical position. Traditionally characterized as a stress hormone, ABA is known to regulate a wide range of physiological processes, including stomatal closure, seed dormancy, and responses to abiotic stress (Zhang et al., 2006). Under drought conditions, for instance, ABA accumulates rapidly, triggering adaptive responses that help plants conserve water and maintain cellular integrity (Anjum et al., 2011).

Yet, beyond its role in stress physiology, ABA also exhibits growth-regulatory effects that may have indirect implications for weed management. By modulating plant metabolism and developmental pathways, exogenous application of ABA could potentially influence competitive interactions between crops and weeds. Some studies have suggested that ABA may suppress certain growth processes, particularly in sensitive species, thereby altering the balance of competition in favor of the crop (Park et al., 2009; Vishwakarma et al., 2017). However, this effect is not straightforward. The response to ABA can vary significantly depending on species, concentration, and environmental context, making its practical application both promising and, admittedly, somewhat uncertain.

Given these complexities, there is a growing need to explore integrated approaches that combine biological and physiological strategies for weed control. The simultaneous use of allelopathic plant extracts and plant growth regulators, such as ABA, presents an interesting avenue in this regard. Such an approach could, in theory, leverage both direct inhibitory effects on weeds (via allelochemicals) and indirect modulation of plant growth dynamics (via hormonal regulation). However, empirical evidence supporting this combined strategy, particularly under field conditions, remains limited.

In addition to treatment effects, varietal differences in wheat must also be considered. Genetic variability among cultivars can significantly influence growth traits, resource use efficiency, and competitive ability. Some cultivars may inherently possess greater tolerance to stress or enhanced capacity to outcompete weeds, owing to differences in physiological and morphological characteristics (Mwadzingeni et al., 2016; Shehzad et al., 2022). Understanding how these genetic factors interact with external treatments is essential for developing optimized management strategies.

Therefore, this study was undertaken with the aim of evaluating the effects of foliar application of Eruca sativa aqueous extract and abscisic acid on weed control and growth performance of two wheat cultivars. It seeks, more specifically, to examine whether these treatments can effectively reduce weed pressure and enhance key growth and yield parameters, including plant height, leaf area, tiller number, grain number per spike, and thousand-grain weight. By situating the experiment within a field-based context and incorporating varietal comparisons, the study attempts to provide a more comprehensive understanding of how biological and hormonal interventions may be integrated into sustainable wheat production systems.

While it may be premature to consider such approaches as definitive replacements for conventional herbicides, they nonetheless represent a step toward more ecologically balanced agricultural practices. And perhaps, in a landscape increasingly shaped by the need for sustainability, even incremental advances in this direction carry meaningful significance.

2. Materials and Methods

2.1 Study Site and Experimental Conditions

The field experiment was conducted during the winter growing season of 2024–2025 at the Field Crops Research Station, College of Agriculture, Tikrit University, located in Salah Al-Din Governorate, Iraq. The site is characterized by a semi-arid climate, with moderate winter temperatures and limited rainfall, conditions that are generally suitable for wheat cultivation but often conducive to weed proliferation.

Although environmental parameters such as daily temperature, relative humidity, and soil physicochemical characteristics were not continuously monitored throughout the experiment, standard agronomic practices for the region were followed. The soil was prepared using conventional tillage methods prior to sowing, and irrigation was applied through a surface flooding system at intervals determined by crop requirements and prevailing weather conditions. These management practices were maintained uniformly across all experimental plots to minimize confounding variability.

2.2 Experimental Design and Treatments

The experiment was arranged in a Randomized Complete Block Design (RCBD) with three replicates (blocks), ensuring control over field heterogeneity. Each experimental unit measured 3 m² (1.5 m × 2.0 m) and consisted of four rows of wheat, with a row spacing of 20 cm. A total of 18 experimental units were established.

Two experimental factors were evaluated:

Factor A: Wheat Varieties

• Iba’a 99
• Babylon

These cultivars were selected based on their regional importance and known variability in growth and yield performance.

Factor B: Foliar Spray Treatments

Three treatment levels were applied:

• Control (T₀): No foliar application
• Eruca sativa aqueous extract (T₁): Direct foliar spray targeting weed species
• Abscisic acid (ABA) (T₂): Foliar application at a concentration of 100 ppm

The selection of ABA concentration was informed by its known regulatory role in plant stress physiology and growth modulation (Zhang et al., 2006; Vishwakarma et al., 2017). The use of Eruca sativa extract was based on its reported allelopathic potential due to bioactive secondary metabolites (Rice, 2012; Farooq et al., 2011).

2.3 Crop Establishment and Agronomic Practices

Wheat seeds were sown manually on November 25, 2024, using a seeding rate of 160 kg ha⁻¹ for both cultivars. Prior to sowing, the field was leveled and marked according to the experimental layout.

To simulate natural weed–crop competition, seeds of common weed species were intentionally sown between wheat rows at a uniform density. Although the exact weed density (plants m⁻²) was not quantified, efforts were made to ensure homogeneous distribution across plots.

Fertilization was applied as follows:

• Nitrogen (N): 90 kg ha⁻¹, split into two equal applications (at sowing and 30 days after sowing)
• Phosphorus (P₂O₅): 240 kg ha⁻¹ applied as triple superphosphate before planting

All plots received identical fertilizer inputs to maintain consistency across treatments.

2.4 Collection and Preparation of Eruca sativa Extract

Fresh vegetative parts (leaves and stems) of Eruca sativa were collected from fields within the College of Agriculture, Tikrit University. The plant material was first air-dried under sunlight for several days and subsequently oven-dried at 70°C for 72 hours to remove residual moisture.

The dried material was then ground into a fine powder using an electric grinder. For extract preparation, 2 g of powdered material was mixed with 100 mL of distilled water, resulting in a 2% (w/v) aqueous extract. The mixture was homogenized using a laboratory blender for 15 minutes, followed by filtration through three layers of gauze cloth and subsequently through Whatman No. 1 filter paper to obtain a clear solution.

The extract was stored in tightly sealed glass containers at 5°C until use, to preserve its biochemical integrity. This preparation method was adapted based on established protocols for extracting allelopathic compounds from plant tissues (Farooq et al., 2011).

2.5 Preparation and Application of Treatments

Abscisic Acid (ABA) Solution

ABA was prepared at a concentration of 100 ppm by dissolving the appropriate amount of commercially available ABA in distilled water. The solution was freshly prepared prior to application to ensure stability.

Application Procedure

Both the Eruca sativa extract and ABA solution were applied using a hand-held pressure sprayer. The treatments were applied as foliar sprays directly onto weed populations, rather than on wheat plants, in order to target weed suppression more specifically.

Although the exact spray volume per plot was not strictly quantified, application was performed until uniform wetting of weed foliage was visually achieved. Spraying was conducted during calm weather conditions to minimize drift and ensure treatment accuracy.

The timing of application occurred during the early vegetative stage of wheat, when weed competition is typically most intense. This timing aligns with previous findings emphasizing the importance of early-stage weed control in optimizing crop performance (Gharde et al., 2018).

2.6 Measured Parameters

At appropriate growth stages, the following agronomic traits were measured:

• Plant height (cm): Measured from soil surface to the tip of the spike at maturity
• Flag leaf area (cm²): Estimated using standard leaf area measurement techniques
• Number of tillers per plant: Counted manually for representative plants
• Number of grains per spike: Determined by sampling mature spikes
• 1000-grain weight (g): Measured using a precision balance

Measurements were taken from randomly selected plants within each plot to ensure representative sampling.

2.7 Statistical Analysis

Data were analyzed using the SAS statistical software package. A two-way ANOVA was conducted to evaluate the effects of wheat variety, treatment, and their interaction on measured parameters.

Mean comparisons were performed using Duncan’s Multiple Range Test (DMRT) at a significance level of P ≤ 0.05, allowing for differentiation between treatment means.

Although assumptions of normality and homogeneity of variance were not explicitly tested, the use of RCBD and replication was intended to reduce experimental error and improve statistical reliability.

2.8 Considerations for Reproducibility

While every effort was made to standardize procedures across treatments, it is worth acknowledging that certain variables—such as environmental conditions and weed density—were not fully quantified. Future studies may benefit from more precise environmental monitoring and standardized weed population assessments to enhance reproducibility and comparability across different agroecological contexts.

3. Results and Discussion

3.1 Integrated Overview: Genotype–Treatment Interactions Under Weed Pressure

A careful examination of the dataset reveals not a simple linear response, but rather a layered interaction between genotype and treatment effects. Across all measured parameters, Iba’a 99 consistently outperformed Babylon, with overall means of 61.23 cm vs 54.02 cm for plant height, 31.83 vs 29.19 cm² for leaf area, 6.70 vs 5.00 tillers plant⁻¹, 37.46 vs 31.86 grains spike⁻¹, and 33.18 vs 28.21 g for 1000-grain weight (Table 1–5). This persistent superiority strongly suggests a genotype-driven advantage in resource acquisition and allocation, consistent with earlier findings on wheat genetic variability under stress conditions (Al-Jubouri & Al-Asadi, 2021; Mwadzingeni et al., 2016).

Yet, what becomes more intriguing—and perhaps more novel—is how external treatments modulate this inherent genetic advantage. Both abscisic acid (ABA) and Eruca sativa extract appear to reshape plant–weed competition, not simply by suppressing weeds, but by subtly altering crop physiological responses. This aligns with the broader understanding that plant growth regulators and allelopathic compounds can influence competitive dynamics beyond direct toxicity (Hussain et al., 2022; Rice, 2012).

3.2 Plant Height: Growth Suppression Versus Competitive Advantage

Plant height exhibited clear and statistically significant variation across treatments and cultivars (Table 1). The control treatment produced the highest mean height (64.83 cm, group “a”), significantly exceeding E. sativa (56.05 cm, “b”) and ABA (52.00 cm, “c”). At the varietal level, Iba’a 99 maintained a significantly greater mean height (61.23 cm, “a”) compared to Babylon (54.02 cm, “b”).

The interaction analysis provides deeper insight. Under control conditions, Iba’a 99 reached the maximum height (73.33 cm, “a”), markedly higher than Babylon (56.33 cm, “c”). However, under ABA treatment, both cultivars converged to statistically similar and significantly lower values (52.30 and 51.67 cm; group “e”), indicating a strong

Table 1. Effect of spraying, varieties, and their interaction on plant height (cm). Values followed by similar letters are not significantly different at P ≤ 0.05.

Table 2. Effect of spraying, varieties, and their interaction on flag leaf area (cm²). Values followed by similar letters are not significantly different at P ≤ 0.05.

Table 3. Effect of spraying, varieties, and their interaction on total number of tillers (tillers plant⁻¹). Values followed by similar letters are not significantly different at P ≤ 0.05.

inhibitory effect independent of genotype.

This pattern strongly supports the established physiological role of ABA in suppressing cell elongation and regulating growth under stress conditions (Zhang et al., 2006; Vishwakarma et al., 2017). Yet, the key nuance here lies in interpretation: while height reduction is traditionally viewed negatively, the subsequent yield data suggest otherwise. The decoupling of plant height from productivity hints at a resource reallocation mechanism, where reduced vegetative growth may conserve assimilates for reproductive development—a phenomenon also discussed under stress-adaptive strategies (Fahad et al., 2017).

3.3 Flag Leaf Area: Functional Compensation Through Photosynthetic Investment

Flag leaf area responded differently, showing significant enhancement under treatment conditions (Table 2). ABA recorded the highest mean (35.09 cm², “a”), followed closely by E. sativa (32.31 cm², “a”), both significantly greater than control (24.14 cm², “b”).

The interaction effect further clarifies this trend. Iba’a 99 under ABA achieved the maximum value (37.26 cm², “a”), while the lowest was observed in Babylon under control (23.91 cm², “c”). Interestingly, E. sativa treatments fell into intermediate statistical groups (“b” and “ab”), suggesting partial effectiveness.

This increase in leaf area, despite reduced plant height, suggests a shift toward functional growth optimization. Instead of investing in vertical expansion, plants appear to allocate resources toward expanding photosynthetic surfaces. Such compensatory mechanisms have been previously linked to reduced competition and improved light interception (Gharde et al., 2018; Taiz & Zeiger, 2010).

The lack of significant difference between ABA and E. sativa indicates that allelopathic extracts may, under field conditions, achieve physiological outcomes comparable to synthetic growth regulators—an observation that supports the potential of biologically derived weed management strategies (Farooq et al., 2011).

3.4 Tillering: Enhanced Resource Capture and Competitive Release

Tillering capacity showed one of the most pronounced treatment responses (Table 3). ABA produced the highest mean (7.537 tillers plant⁻¹, “a”), significantly exceeding E. sativa (5.862, “b”) and control (4.158, “c”).

At the interaction level, Iba’a 99 under ABA achieved the highest value overall (8.407 tillers plant⁻¹, “a”), compared to only 4.250 under control. Babylon, while improved under ABA (6.667, “b”), remained significantly lower.

This is particularly interesting because ABA is not typically associated with increased branching. However, in this context, the result likely reflects indirect competitive release rather than direct stimulation. By suppressing weed growth, ABA may reduce competition for nutrients and light, thereby allowing wheat plants to express their tillering potential.

This interpretation aligns with previous studies emphasizing the role of reduced competition in enhancing tiller formation (Fahad et al., 2017; Baqir & Al-Naqeeb, 2019). The genotype-specific response further suggests that Iba’a 99 possesses a higher capacity to capitalize on improved environmental conditions.

3.5 Grain Number per Spike: Reproductive Efficiency Under Reduced Stress

Grain number per spike followed a pattern consistent with vegetative improvements (Table 4). ABA treatment resulted in the highest mean (41.29 grains spike⁻¹, “a”), significantly greater than E. sativa (35.15, “b”) and control (27.55, “c”).

The interaction revealed that Iba’a 99 under ABA achieved the maximum grain number (45.92, “a”), while Babylon under control recorded the lowest (26.26, “e”).

This suggests that early-stage improvements in tillering and leaf area translate directly into enhanced reproductive capacity. The availability of assimilates during spike development appears to be a key limiting factor, and treatments that reduce competition effectively improve this availability.

Such relationships between vegetative growth and

Table 4. Effect of spraying, varieties, and their interaction on number of grains per spike (grains spike⁻¹). Values followed by similar letters are not significantly different at P ≤ 0.05.

Table 5. Effect of spraying, varieties, and their interaction on 1000-grain weight (g). Values followed by similar letters are not significantly different at P ≤ 0.05.

reproductive output are well established in cereal crops (Al-Jubouri & Al-Asadi, 2021). The role of ABA here may again be indirect, acting through competitive suppression rather than direct stimulation of reproductive processes.

3.6 Thousand-Grain Weight: Final Expression of Source–Sink Optimization

The cumulative effects of treatments are perhaps most clearly reflected in 1000-grain weight (Table 5). ABA recorded the highest mean (36.80 g, “a”), followed by E. sativa (31.93, “b”), with control significantly lower (23.35, “c”).

The interaction effect reinforces this trend. Iba’a 99 under ABA achieved the highest value (39.83 g, “a”), while Babylon under control recorded the lowest (21.33, “e”).

This outcome reflects improved source–sink dynamics, where enhanced leaf area (source) and reduced competition allow for more efficient assimilate transfer to grains (sink). Previous studies have emphasized the importance of such balance in determining final grain weight (Fahad et al., 2017).

3.7 Emerging Novelty: ABA as a Competitive Modulator Rather Than Growth Inhibitor

One of the more subtle yet important insights from this study is the reframing of ABA’s role. While traditionally classified as a stress hormone that inhibits growth, the consistent improvements in yield components observed here suggest a more complex function.

Rather than acting solely on the crop, ABA may exert differential effects on weeds, suppressing their growth more strongly and thereby indirectly benefiting wheat. This aligns with its regulatory role in stress signaling pathways (Park et al., 2009), but extends its application into the domain of weed management.

This concept—ABA as a competitive modulator—represents a potential shift in how plant hormones are viewed in agricultural systems.

3.8 Comparative Effectiveness: Biological Versus Hormonal Approaches

The relatively close performance of E. sativa extract and ABA across multiple parameters is particularly noteworthy. While ABA generally achieved higher values, E. sativa consistently performed better than control and often fell within similar statistical groupings.

This suggests that allelopathic extracts may offer a biologically sustainable alternative to synthetic inputs. Given growing concerns over herbicide resistance and environmental impact (Khawar et al., 2015; Kumbhar & Dharmistha, 2016), such approaches warrant further exploration.

3.9 System-Level Interpretation and Implications

Taken together, the results point toward a system where:

• Genotype determines baseline potential
• Treatments modify competitive environment
• Physiological responses optimize resource allocation

The superior performance of Iba’a 99 across all treatments underscores the importance of genetic selection. However, the enhancement observed under ABA and E. sativa indicates that management strategies can significantly amplify this genetic potential.

What emerges, perhaps somewhat unexpectedly, is that weed management need not rely exclusively on direct elimination strategies. Instead, approaches that reshape competitive dynamics—whether through hormonal regulation or allelopathic interactions—may offer equally effective, and potentially more sustainable, alternatives.

While further validation is certainly needed, these findings suggest that integrating physiology, ecology, and genetics may provide a more balanced pathway toward improving wheat productivity under real-world conditions.

4. Conclusion

The findings of this study, when considered collectively, point toward a rather interesting shift in how weed management strategies might be approached in wheat cultivation. Although traditional expectations would favor increased vegetative growth as a marker of productivity, the present results suggest otherwise. Treatments with abscisic acid and Eruca sativa extract did not necessarily promote plant height, yet they consistently improved yield-related traits, including tiller formation, grain number, and grain weight.

This indicates, perhaps, a more efficient internal redistribution of resources—where reduced competition, rather than enhanced growth per se, becomes the dominant driver of productivity. The superior performance of the Iba’a 99 cultivar further emphasizes the importance of genotype selection in maximizing treatment benefits.

While these outcomes are promising, they also raise new questions regarding the mechanisms underlying such responses. Still, the integration of hormonal and allelopathic strategies may represent a viable, and potentially more sustainable, alternative to conventional weed control approaches.

Author Contributions

N.A.H. conceived and designed the study, conducted the field experiment, collected data, and prepared the initial manuscript draft. L.K.A. supervised the research work, contributed to experimental design, performed data analysis, and critically revised the manuscript. O.F.I. assisted in laboratory preparation of treatments, supported data interpretation, and contributed to manuscript editing and final approval.

References