Effect of paclobutrazol on vegetative, floral and root parameters of a winter season annual: Gazania

Introduction

Seasonal flowers have aesthetic appeal in a variety of locations, making them essential ornamental plants for landscape design (Fediw, 2015) [6] . However, because of their highwater requirements, these plants-including bedding plants like Gazania-are extremely vulnerable to water shortage stress. Plant morphology and physiology are adversely affected by drought stress, which results in decreased growth and marketability. Although plants have built-in antioxidant defense systems, severe water deprivation can overwhelm these systems, degrade photosynthetic pigments and stop structural growth. A synthetic organic molecule called paclobutrazol (PBZ) has become a useful tool for reducing water stress since it is a strong plant growth suppressor (Fletcher et al., 2000) [7] . According to Kondhare et al. (2014) [10] , PBZ mainly inhibits gibberellic acid (GA), which limits cell elongation and produces stouter stems, better stem diameter, and increased lateral branching. Beyond its architectural advantages, PBZ stabilizes the plant's internal environment, shields cell membranes from degradation caused by reactive oxygen species (ROS), and improves osmotic control to promote systemic resistance to abiotic stress, especially drought (Gopi et al., 2007) [8] . This enables plants to sustain blooming production and aesthetic qualities even in the face of extreme environmental restrictions by maintaining physiological hydration, boosting antioxidant defenses, and preserving photosynthetic capacity (Dwivedi et al., 2018) [4] . This study intends to optimize specific dosages for commercially significant seasonal flowers like Gazania under varied irrigation regimes, given the strong evidence of PBZ's effectiveness in a variety of crops. This study especially examines the impact of paclobutrazol treatment on vegetative and root parameters in order to mitigate water deficit stress in Gazania.

Materials and Methods

The experiment was carried out inside protected structure at experimental farm, division of floriculture and landscaping, Sher-e-Kashmir University of Agricultural Sciences and Technology of Jammu, Chatha (J&K) during December, 2023-March, 2024. Meteorological data for the year in which study was conducted is given in Figure 1

Results

The results for plant height, plant spread, number of flowers (NoFP), root length, and dry weight of root, across different field capacities and paclobutrazol concentrations are presented in the table 1 and the comparison between different treatment combinations is shown in Plate 1. Throughout the experiment, an inverse association between shoot growth and Paclobutrazol (PBZ) concentration was noted. The largest plants (Height: 19.75 cm, Spread: 22.45 cm) were produced at Full Field Capacity with 0 ppm PBZ. This occurred because the high moisture content without PBZ allowed for unconstrained development. Both height and spread sharply decline when PBZ rises from 0 to 10 ppm. Regardless of the irrigation schedule, height decreases to about 8 cm at 10 ppm PBZ. The lowest irrigation level (25% FC) results in the least plant spread (11.50 cm to 12.25 cm), demonstrating how PBZ and water stress cooperate to limit lateral expansion. It was observed that PBZ sometimes acts as a floral stimulant rather than decreasing flower count. Increasing PBZ actually increased floral production at Field Capacity. At 0 ppm, the count was 12 flowers; at 5 ppm, it peaked at 15 blooms. The count remains comparatively high after 5 ppm, although it starts to plateau or gradually decline. Only four flowers were produced as a result of severe water stress (25% FC) and high PBZ (10 ppm), indicating that the plant's metabolic energy was too low to sustain reproduction. We also observed that PBZ greatly encourages root development while suppressing the top of the plant. Higher PBZ concentrations resulted in longer and heavier roots at all irrigation levels. At the greatest stress level (25% FC + 10 ppm PBZ), the longest root (49.20 cm) and highest dry weight (1.83 g) were noted.

Discussion

The study's findings are consistent with previous research on paclobutrazol's (PBZ) effects on plant growth and drought stress reduction. PBZ's well-established function as a plant growth suppressor is consistent with the observed decrease in plant height and spread with increasing PBZ concentrations. Its capacity to prevent gibberellic acid (GA) biosynthesis, which limits cell elongation and internodal development, is the main cause of this impact (Desta & Amare, 2021; Fletcher et al., 2000) [2,7] . For decorative bedding plants like Gazania, this results in more compact plants, which improves their visual appeal and marketability.

The harmful effects of dryness on growth and flowering in Gazania are confirmed by the overall decrease in plant height, plant spread, and number of flowers under reduced field capacity (water deficit stress). Water scarcity is a major environmental limitation that restricts plant growth and productivity globally, resulting in detrimental physiological and morphological reactions (Farooq et al., 2009) [5] . The use of paclobutrazol, however, seems to lessen some of these detrimental effects, indicating its potential as a drought-mitigating medication. One noteworthy discovery is the rise in root length and dry weight with increasing PBZ concentrations, especially in water-stressed situations. This implies that PBZ encourages the growth of roots, which is an essential adaptation strategy for plants to deal with drought. A larger root system improves the plant's capacity to absorb nutrients and water from the soil, increasing its capacity to endure and flourish in situations when water availability is restricted (Berova & Zlatev, 2003) [1] . Other ornamental species have also shown increased root growth following PBZ treatment, which helps to enhance water relations under stress (Hatamifar & Babadaei Samani, 2017) [9] . There may be an ideal PBZ dosage for maximizing flowering under particular water stress levels, according to the intricate relationship between field capacity and paclobutrazol concentration for the number of flowers. Higher PBZ concentrations may assist sustain blooming under mild stress by reallocating resources or enhancing stress tolerance, even though they typically decrease vegetative growth. This supports the theory that PBZ enables ornamental plants to maintain their vital aesthetic qualities, flowering production, and structural development even in the face of extreme environmental restrictions (Dwivedi et al., 2018) [4] . Sustained flowering may be facilitated by PBZ's capacity to increase water use efficiency and shield photosynthetic pigments from stress (Dwivedi et al., 2017) [3] . The necessity of adjusting PBZ doses according to the particular irrigation regime is shown by the strong interaction effects found across all parameters. Understanding these relationships is essential for sustainable floriculture, particularly in areas where water constraint is a problem. According to the data, PBZ can be a useful instrument for controlling the growth of Gazania and strengthening its resistance to drought, which would increase its marketability. PBZ's promise in horticulture operations is further supported by prior research demonstrating the effectiveness of PBZ treatment techniques, especially soil drench, in influencing plant development and stress tolerance (Nasr, 1995) [11] .

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