Assessment of boron and paclobutrazol foliar sprays on yield attributes of Beetroot (Beta vulgaris L.) under polyhouse conditions

Introduction

Beetroot (Beta vulgaris L.), belonging to the Chenopodiaceae family, is a highly nutritious root vegetable believed to have originated in the Mediterranean region with a chromosome number of 2n = 18. It is valued for its rich composition of minerals, vitamins, and bioactive compounds and is widely used in traditional medicine for its antioxidant, antimicrobial, antiinflammatory, diuretic, and other therapeutic properties (Yadav et al., 2016) [18] . Beetroot contributes to cardiovascular health by lowering blood pressure and cholesterol, helps regulate blood glucose levels in diabetics, alleviates anaemia, and reduces fatigue. In India, beetroot is mainly cultivated in Haryana, Uttar Pradesh, Himachal Pradesh, Maharashtra, and Tamil Nadu (Kale et al., 2018) [10] . Boron is an essential micronutrient involved in cell wall integrity, membrane stability, carbohydrate and nitrogen metabolism, sugar transport, and enzyme activity (Shireen et al., 2018) [14] . Its deficiency in sugar beet results in a physiological disorder known as "brown heart," causing internal tissue browning and loss of root quality (Vera-Maldonado et al., 2024) [17] . Paclobutrazol is a triazole-based, water-soluble plant growth regulator that inhibits gibberellic acid synthesis and is widely used in agriculture (Davis and Curry, 1991) [6] . It induces morphological changes such as reduced stomatal size, increased leaf thickness, and enhanced root density, thereby improving stress tolerance and disease resistance (Chaney et al., 2005) [4] .

Materials and Methods

The experiment was conducted at the Center of Excellence on Protected Cultivation and Precision Farming Unit, under polyhouse conditions, at the College of Agriculture (CoA), Raipur, Indira Gandhi Krishi Vishwavidyalaya (IGKV), Raipur (C.G.), during the rabi season of 2024. The experimental plot size was 2.8 × 3 m 2 with plant spacing 45 cm × 10 cm. Sixteen treatments of the Beetroot crop were used in this experiment, which was set up in a factorial randomized block design (FRBD) with three replications. The experiment involved two factors-boron and paclobutrazol to assess their effects on plant response. The different levels of boron (4 levels) were B 0 -0 ppm, B 1 -100 ppm, B 2 -150 ppm, B 3 -200 ppm and Paclobutrazol (4 levels) P 0 -0 ppm, P 1 -100 ppm, P 2 -200 ppm, P 3 -300 ppm respectively.

Statistical Analysis

Pre-harvest observations were the statistically analysed following studies of Gomez & Gomez (1984) [8] by using the F-test the significance of treatment effects was determined. Differences among treatments were tested at a 5% probability level using standard error and critical difference values. Analysis of variance (ANOVA) was conducted using OPSTAT and MS Excel software.

Results and Discussion

At different levels of boron, boron 200 ppm significantly increased root length (9.72 cm) over the control (8.73 cm), likely due to its role in enhancing cell division and meristematic activity through cytokinin regulation ( [2,11,12] . Among different levels of PBZ, the highest root length (9.41 cm) was recorded at 300 ppm, attributed to improved photosynthetic efficiency and assimilate translocation (Tekalign and Hammes, 2004) [15] . The boron × PBZ interaction was significant, with the maximum root length (10.33 cm) under the combined application of boron 200 ppm and PBZ 0 ppm, indicating a synergistic effect on root elongation.

The highest root girth (5.73 cm) was recorded with 200 ppm boron, while the lowest (5.13 cm) occurred at 0 ppm boron at different levels of boron. Among different paclobutrazol levels, PBZ at 300 ppm produced the maximum root girth (5.64 cm), whereas the control showed the minimum. Increased root girth under higher boron levels may be due to improved sugar assimilation and translocation, enhancing root development, as also reported by Nemeata et al. (2017) [13] . Similarly, PBZ likely improved root girth by increasing chlorophyll content and photosynthetic rate, leading to greater assimilate accumulation (Tekalign and Hammes, 2004) [15] . The highest interaction effect (6.34 cm) was observed with 200 ppm boron, while the lowest (4.35 cm) occurred in the control.

The highest root weight (153.33 g) was obtained with 200 ppm boron, while the lowest (137.88 g) occurred at 0 ppm boron, likely due to boron's role in enhancing photosynthate translocation to roots. Similar effects were reported by Makhlouf et al. (2020) [11] , Mekdad and Shaaban (2020) [12] , Abbas et al. (2014), and Dewdar et al. (2015) [7] . Among paclobutrazol treatments, PBZ at 300 ppm produced the maximum root weight (152.68 g), whereas the control recorded the minimum (141.72 g). The highest interaction effect (163.23 g) was observed with 200 ppm boron + PBZ 0 ppm, while the control showed the lowest (130.40 g), confirming the combined positive influence of boron and paclobutrazol on beetroot root weight.

The highest yield per plot (7.67 kg) was recorded with 200 ppm boron, while the lowest (6.89 kg) occurred at 0 ppm, likely due to boron's role in enhancing foliage growth, root size, and photosynthate translocation (Nemeata, 2017; Makhlouf et al., 2020; Mekdad and Shaaban, 2020) [13,11,12] . Among paclobutrazol treatments, PBZ at 300 ppm produced the maximum yield (7.63 kg), whereas the control showed the minimum (7.09 kg), supporting the findings of Xu et al. (2023). The highest interaction yield (8.19 kg plot⁻¹) was obtained with 200 ppm boron + PBZ 0 ppm, while the control recorded the lowest (6.52 kg plot⁻¹).

Root yield (q ha -1 ) 1. Foliar application of boron and paclobutrazol (PBZ) significantly enhanced beetroot yield under polyhouse conditions. Among different levels of boron, the highest yield recorded with boron at 200 ppm can be attributed to its role in promoting cell division, carbohydrate translocation, and root development, which agrees with the findings of Abbas et al. (2014) [1] , Dewdar et al. (2015), and Nemeata (2017) [13] in sugar beet. Similarly, at different levels of paclobutrazol, PBZ at 300 ppm improved yield by enhancing assimilate partitioning towards storage roots through hormonal regulation (Tekalign and Hammes, 2005; Gomathinayagam et al., 2007) [16] . The significant boron × PBZ interaction indicates a synergistic effect, resulting in superior root bulking and overall productivity under protected cultivation. Table 1: Main effects and interaction effects of concentration of boron, PBZ and their combinations on Root length(cm), Root girth(cm), Root weight(g)per plant Root yield (Kg plot -1 ), Root yield (q ha -1 ).

Conclusion

Boron at 200 ppm recorded the highest root length, girth, root weight per plant, and yield per plot and hectare, while the lowest values were observed under 0 ppm boron at different levels of boron. Among paclobutrazol levels, PBZ at 300 ppm produced the maximum values for all yield attributes, whereas the control recorded the minimum. The interaction effect showed that the combination involving boron 200 ppm + PBZ 0 ppm resulted in superior root length, girth, and root weight, and consistently achieved the highest yield under polyhouse conditions.

Acknowledgement

AcknowledgementI express my sincere gratitude to my advisor, Dr. Annu Verma and all the members of my advisory committee for their continuous guidance, encouragement, and valuable suggestions throughout this study. I also extend my thanks to the faculty members, technical staff, and the team at the Center of Excellence on Protected Cultivation and Precision Farming Unit for providing the necessary facilities and support during the research work. I am grateful to my family and friends for their motivation and cooperation, which contributed significantly to the successful completion of this research.

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