Effect of turf growth regulators on morphological traits of carpet grass

Introduction

Turfgrasses are low-growing monocotyledonous plants that form a continuous ground cover maintained at a specific height through mowing. The term "turf," derived from the Sanskrit word Darabha (tuft of grasses), refers to the surface vegetation layer along with the dense root-rhizome zone of the soil. Turf is valued not only for its functional role in erosion control, dust suppression, groundwater recharge, and temperature moderation but also for its recreational and aesthetic benefits. It provides a safe and cost-effective surface for sports and leisure activities, while also enhancing landscape beauty, psychological well-being, and urban livability (Beard & Green, 1994; Singh et al., 2016) [3,8] . Additionally, the turf industry generates employment in seed production, sod farming, landscaping, and maintenance. Warm and cool-season grasses are commonly used depending on climatic adaptability. Warm-season species such as Cynodon dactylon and Zoysia japonica thrive in tropical climates, whereas cool-season species like Poa pratensis and Lolium perenne are preferred in temperate zones (Stier et al., 2006) [11] . Among warm-season species, Carpet grass (Axonopus spp.) has gained popularity for its adaptability to shade, tolerance to low inputs, and ability to spread by stolons. It is widely used along roadsides, in parks, and in lowmaintenance lawns. Despite these advantages, research on its growth regulation and management remains limited. One of the major challenges in turfgrass management is excessive shoot growth under favorable conditions, which increases mowing frequency, labor costs, nutrient depletion, and equipment wear. Thus, sustainable strategies to reduce vertical growth while maintaining turf quality are urgently required. In this context, Plant Growth Regulators (PGRs) have proven to be effective management tools. These compounds influence hormonal activity, cell elongation, and division, thereby regulating plant architecture. Ethephon, for instance, promotes ethylene release and horizontal growth while reducing shoot elongation (Arteca, 1997) [2] . Similarly, paclobutrazol and trinexapac-ethyl inhibit gibberellin biosynthesis, resulting in shorter internodes, denser canopy, and improved turf color (Rademacher, 1986) [7] . Conversely, Gibberellic Acid (GA₃) enhances stem elongation, seed germination, and

Planting material and establishment

Stolons of warm-season Carpet grass (Axonopus spp.) were used. Healthy, disease-free stolons (10-12 cm long) were planted in HDPE grow bags (6 × 24 inches) filled with prepared soil amended with well-rotted Sand, Soil and FYM. Stolons were placed at 5 cm spacing in March 2025, followed by irrigation and light pressing to ensure contact with soil. Fertilizers were applied at 150:100:100 kg N:P:K ha⁻¹ yr⁻¹. Nitrogen was split in three doses (April, June, August), while phosphorus and potassium were applied basally.

Experimental design and treatments

The trial was laid out in a Completely Randomized Design (CRD) with 13 treatments replicated thrice, totaling 39 experimental units. Treatments included different doses of paclobutrazol, Gibberellic Acid (GA₃), ethephon, and trinexapac-ethyl, along with a control (water spray).

Treatments evaluated in the study included:

Treatment details

Treatment

Treatment details T0

Control (Water spray) T1 Paclobutrazol @ 0.24 kg ha -1 T2 Paclobutrazol @ 0.48 kg ha -1 T3 Paclobutrazol @ 0.96 kg ha -1 T4 Gibberellic acid @ 0.04 kg ha -1 T5 Gibberellic acid @ 0.08 kg ha -1 T6 Gibberellic acid @ 0.16kg ha -1 T7 Ethephon @ 4.0 kg ha -1 T8 Ethephon @ 8.0 kg ha -1 T9 Ethephon @ 16.0 kg ha -1 T10

Trinexapac-ethyl @ 0.08 kg ha -1 T11 Trinexapac-ethyl @ 0.16 kg ha -1 T12 Trinexapac-ethyl @ 0.32kg ha -1

Application of growth regulators

Chemical solutions were prepared by calibrating a hand sprayer. Approximately 20 ml of solution was required per m². Active ingredient quantities were calculated based on recommended doses per hectare and adjusted to bag surface area. Treatments were applied uniformly, and observations were recorded periodically.

Cultural practices

Standard practices for turfgrass were followed. Irrigation was provided every second day until establishment and as required thereafter. Manual weeding was done regularly. No pesticides or fungicides were used.

Observations recorded

Quantitative observations were recorded on various morphological traits of carpet grass to assess the influence of different plant growth regulators. These included canopy height (cm), stolon internode length (cm), stolon diameter (mm), leaf length (cm) and leaf width (mm). Together, these parameters provided a comprehensive understanding of turfgrass growth behavior and structural modifications under different treatments.

Statistical analysis

Data on growth and quality parameters were analyzed using ANOVA under CRD (Panse and Sukhatme, 1985) [6] . Standard error of mean (S.Em.±), Critical Difference (CD at 5%), and Coefficient of Variation (CV) were computed. Significance was tested using the F-test.

Result and Discussion

The canopy height of carpet grass was significantly influenced by the application of plant growth regulators (Table 1). The tallest canopy was recorded in T₆ (GA₃ @ 0.16 kg ha⁻¹) with 6.90 cm, which was significantly superior to all other treatments. This was closely followed by T₅ (GA₃ @ 0.08 kg ha⁻¹) and T₄ (GA₃ @ 0.04 kg ha⁻¹), which produced canopy heights of 6.47 cm and 6.23 cm, respectively. By contrast, the lowest canopy height (2.93 cm) was observed in T₃ (Paclobutrazol @ 0.96 kg ha⁻¹), followed by T₂ (3.37 cm) and T₁ (3.60 cm). Comparable outcomes were observed in earlier studies by Volterrani et al. (2015) [13] and Lambert et al. (2011) [14] . The reduction in canopy height under paclobutrazol and trinexapac -ethyl treatments may be attributed to their inhibitory effect on gibberellin biosynthesis, which restricts cell elongation and results in compact turf growth.

Conversely, GA₃ treatments promoted stem elongation, thereby increasing canopy height, as gibberellins are known to enhance cell elongation and division. Ethephon treatments produced intermediate canopy heights (3.83 -4.53 cm), likely due to the ethylene-mediated modification of growth processes.

Stolon internodal length was significantly affected by PGR application (Table 1). The longest internodes were recorded in T₆ (GA₃ @ 0.16 kg ha⁻¹) with 2.57 cm, which was significantly greater than the control (1.80 cm) and superior to all other treatments. This was followed by T₅ (GA₃ @ 0.08 kg ha⁻¹) and T₄ (GA₃ @ 0.04 kg ha⁻¹), with internode lengths of 2.42 cm and 2.33 cm, respectively. In contrast, the shortest internodes (1.25 cm) were observed in T₃ (Paclobutrazol @ 0.96 kg ha⁻¹), which was significantly lower than the control. These results indicate that GA₃ enhanced internodal elongation by stimulating cell expansion, while paclobutrazol restricted internodal growth by suppressing gibberellin biosynthesis. These observations are consistent with the results of Hudgins et al. (2017) [4] and Sidhu et al. (2014) [10] . Stolon diameter (mm) Significant differences were observed in stolon diameter of carpet grass under different growth regulator treatments (Table 1). The thickest stolons were obtained in T₃ (Paclobutrazol @ 0.96 kg ha⁻¹) with 0.63 mm, which was significantly higher than the control (0.48 mm) and statistically comparable with T₁ (0.61 mm), T₂ (0.60 mm), and T₉ (0.62 mm). In contrast, the minimum stolon diameter (0.39 mm) was recorded in T₆ (GA₃ @ 0.16 kg ha⁻¹). The increase in stolon thickness under paclobutrazol and ethephon can be attributed to assimilate partitioning towards lateral thickening rather than elongation, while GA₃ stimulated elongation growth at the expense of stolon diameter. Similar findings were reported by Shahzad et al.

(2023) [9] , Hudgins et al. (2017) [4] , and Sidhu et al. (2014) [10] .

Leaf length of carpet grass was significantly influenced by growth regulator treatments (Table 1). The longest leaves were recorded in T₆ (GA₃ @ 0.16 kg ha⁻¹) with 5.05 cm, which was significantly greater than the control (3.12 cm). This was followed by T₅ (4.92 cm) and T₄ (4.77 cm). In contrast, the shortest leaves were observed in T₂ (Paclobutrazol @ 0.48 kg ha⁻¹) with 1.54 cm, and T₃ (1.47 cm), both of which were significantly lower than the control. These findings indicate that GA₃ promoted leaf elongation by enhancing cell division and expansion, whereas paclobutrazol restricted leaf growth through inhibition of gibberellin biosynthesis. Similar results have been reported by Lambert et al. (2011) [14] and Shahzad et al. (2023) [9] .

Leaf width (mm) Application of growth regulators significantly influenced leaf width (Table 1). The maximum width was observed in T₃ (Paclobutrazol @ 0.96 kg ha⁻¹) with 1.92 mm, which was significantly greater than the control (1.45 mm). This was followed by T₂ (1.87 mm) and T₁ (1.84 mm). The narrowest leaves (1.30 mm) occurred in T₄ (GA₃ @ 0.04 kg ha⁻¹). These results suggest that paclobutrazol promoted leaf thickening, likely due to its growth-retarding effect that enhances assimilate accumulation in leaf tissues. In contrast, GA₃ stimulated elongation growth, producing narrower leaves. Similar trends have been reported by Shahzad et al.

(2023) [9] and Hudgins et al. (2017) [4] .

Conclusion

The study revealed that Plant Growth Regulators (PGRs) significantly influenced the growth and turf quality of carpet grass. GA₃ (0.08-0.16 kg ha⁻¹) promoted canopy height, internode elongation, and leaf length, aiding in faster lawn establishment but leading to higher maintenance due to excessive growth. In contrast, paclobutrazol (0.24-0.96 kg ha⁻¹) and trinexapac-ethyl (0.08-0.32 kg ha⁻¹) effectively reduced vertical growth, increased stolon thickness and leaf width, and produced compact, dense lawns with reduced mowing needs. Ethephon (4.0-16.0 kg ha⁻¹) provided moderate suppression of canopy height with improved stolon girth. From a turf management perspective, GA₃ supports faster lawn establishment, whereas paclobutrazol and trinexapac-ethyl provide lasting benefits by promoting compact, high-quality lawns with minimal maintenance needs

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