Effect of plant growth regulators on the shoot growth of black pepper (Piper nigrum L.) stem cuttings under shade net conditions.

Introduction

Black pepper (Piper nigrum L.), a perennial climbing vine belonging to the family Piperaceae, is one of the most important spice crops cultivated in tropical regions of the world. India is recognized as the center of origin of black pepper, and the crop plays a crucial role in the national economy through domestic consumption and export earnings. Owing to its pungency, flavor, and medicinal properties attributed mainly to the alkaloid piperine, black pepper is widely used in food, pharmaceutical, and nutraceutical industries (Ahmad et al., 2012 [2] and Ravindran, 2010) [18] . The increasing global demand for black pepper necessitates the production of large quantities of quality planting material for sustainable cultivation. Vegetative propagation through stem cuttings is the most preferred method for black pepper multiplication, as seed propagation leads to genetic variability and poor field performance (Parthasarathy et al., 2008; Kandiannan et al., 2015) [10,14] . However, successful establishment of stem cuttings is often hindered by delayed sprouting, weak shoot growth, poor leaf development, and low survivability, particularly under nursery conditions. Early and vigorous shoot growth is essential for producing healthy seedlings capable of better rootshoot balance and successful field establishment. Plant growth regulators (PGRs) play a pivotal role in regulating physiological processes such as cell division, elongation, and differentiation, thereby influencing sprouting and shoot growth in vegetatively propagated crops. Auxins such as indole-3-acetic acid (IAA), naphthalene acetic acid (NAA), and indole-3-butyric acid (IBA) have been widely reported to enhance rooting and also promote shoot elongation, leaf initiation, nodal development, and overall vegetative vigor in black pepper and other spice crops (Hartmann et al., 2011; Akshay et al., 2019) [9] . Among auxins, IBA is considered more stable and effective under nursery conditions, followed by NAA and IAA, depending on concentration and method of application (Davies, 2010& Alexandre et al., 2017) [5,6] . Shade net cultivation provides a favorable microclimate by reducing light intensity, moderating temperature, and maintaining higher relative humidity, which closely resembles the natural understorey habitat of black pepper. Such protected conditions minimize moisture stress, reduce transplant shock, and enhance physiological activity in stem cuttings (Prasath et al., 2014; Prajapati et al., 2018) [17,15] . The combined application of suitable plant growth regulators under shade net conditions has been shown to significantly improve shoot growth parameters such as number of shoots, shoot length, number of leaves, internodal length, and seedling vigor (Mustakim et al., 2022; Prajwal et al., 2024) [13,16] . Therefore, the present investigation was undertaken to evaluate the effect of different plant growth regulators and their concentrations on the shoot growth of black pepper (Piper nigrum L.) stem cuttings under shade net conditions, with the aim of standardizing an efficient propagation protocol for quality seedling production.

Methodology

The effect of different plant growth regulators on shoot growth of black pepper (Piper nigrum L.) stem cuttings was assessed under shade net conditions using a Completely Randomized Design (CRD). Healthy, uniform stem cuttings of variety Panniyur-1 were treated with different concentrations of IAA, NAA, and IBA as per the treatment schedule, along with an untreated control. The treated cuttings were planted in polybags filled with a standardized potting mixture and maintained under a 50% shade-net structure with uniform irrigation and management practices. Observations related to shoot growth were recorded at 30, 60, and 90 days after planting (DAS). The number of shoots per cutting was determined by counting all newly emerged shoots on each cutting at each observation stage. Shoot length was measured in centimeters using a measuring scale from the base of the shoot to the apical tip. The number of fully expanded leaves per shoot was recorded manually, while leaf length was measured from the base of the leaf blade to the tip. The number of nodes per shoot was counted visually along the main shoot, and internodal length was calculated by measuring the distance between two successive nodes and averaging the values for each treatment. All observations were recorded from randomly selected plants in each replication to ensure uniformity and accuracy. The girth of new shoots was measured at approximately 2 cm above the base of the shoot using a vernier caliper and expressed in centimeters. Mean values for each parameter were computed treatment-wise and stage-wise. The data collected were subjected to statistical analysis following standard procedures applicable to CRD, and treatment means were compared using the critical difference (CD) test at the 5% level of significance.

Result 3.1 No. of shoot per cuttings

The data pertaining to no. of shoot per cuttings as influenced of plant growth regulator on rooting, growth and survivability of Black Pepper (Piper nigrum) stem cutting under shade net condition has been recorded and presented in Table 1. Among the treatments at 30 DAS, performance of treatments varied, with T8 (IBA 1000 ppm) recording the highest no. of shoot per cuttings (1.59), while this was at par with the treatment T5 (NAA 1000 ppm) and T2 (IAA 1000 ppm) showed (1.55) and (1.53) respectively. The least performance (1.41) was noted in the treatment T0 (Control) and at 60 DAS, performance of treatments varied, with T8 (IBA 1000 ppm) recording the highest no. of shoot per cuttings (2.14), while this was at par with the treatment T5 (NAA 1000 ppm) and T2 (IAA 1000 ppm) showed (2.13) and (2.08) respectively. The least performance (1.87) was noted in the treatment T0 (Control). Among the treatments at 90 DAS, performance of treatments varied, with T8 (IBA 1000 ppm) recording the highest no. of shoot per cuttings (2.68), while this was at par with the treatment T5 (NAA 1000 ppm) and T2 (IAA 1000 ppm) showed (2.59) and (2.57) respectively. The least performance (2.28) was noted in the treatment T0 (Control). The enhanced shoot proliferation in these treatments may be attributed to the ability of auxins to stimulate cell division and elongation in the nodal region, thereby encouraging multiple shoot initiation. Among the different regulators, IBA proved to be the most effective, followed closely by NAA and IAA, suggesting its superior role in promoting both rooting and shoot development simultaneously. The better root system induced by IBA likely facilitated improved nutrient and water uptake, which in turn supported vigorous shoot growth. These findings align with those of earlier researchers who reported that the application of auxin-based growth regulators enhances shoot multiplication and overall vegetative growth in black pepper and other spice crops propagated through stem cuttings. Similar results were also observed by Santoso et al., (2016).

The data pertaining to length of new shoot (cm) as influenced of plant growth regulator on rooting, growth and survivability of Black Pepper (Piper nigrum) stem cutting under shade net condition has been recorded and presented in Table 2 In treatment T8 (IBA 1000 ppm), the length of new shoot (cm) at (4.64 cm), emerging as the significantly superior value across treatments at 30 DAS. A nearly equivalent length of new shoot (cm) was at par with the treatment T5 (NAA 1000 ppm) (4.52 cm) and the treatment T2 (IAA 1000 ppm) (4.44 cm). At the other end, T0 (Control) exhibited the poorest length of new shoot (cm) (3.56 cm) and treatment T8 (IBA 1000 ppm), the length of new shoot (cm) at (11.52 cm), emerging as the significantly superior value across treatments at 60 DAS. A nearly equivalent length of new shoot (cm) was at par with the treatment T5 (NAA 1000 ppm) (11.19 cm) and the treatment T2 (IAA 1000 ppm) (10.93 cm). At the other end, T0 (Control) exhibited the poorest length of new shoot (cm) (8.67 cm).

In treatment T8 (IBA 1000 ppm), the length of new shoot (cm) at (21.18 cm), emerging as the significantly superior value across treatments at 90 DAS. A nearly equivalent length of new shoot (cm) was at par with the treatment T5 (NAA 1000 ppm) (20.04 cm). At the other end, T0 (Control) exhibited the poorest length of new shoot (cm) (15.76 cm).

The data indicated that the application of plant growth regulators had a significant effect on the length of new shoots in black pepper cuttings under shade-net conditions.

Treatments involving auxins such as IBA, NAA, and IAA promoted greater shoot elongation at all stages of observation compared to the untreated control. The superior performance of IBA-treated cuttings suggests that this regulator effectively stimulates cell elongation and apical dominance, leading to increased shoot growth. The enhanced shoot length observed under auxin treatments can be attributed to improved root activity, which facilitates better absorption of water and nutrients, thereby supporting vigorous vegetative growth. The gradual increase in shoot length from 30 to 90 days after planting reflects the sustained physiological response of the cuttings to auxin treatment. These results are consistent with the findings of earlier researchers who reported that IBA and NAA treatments enhance shoot elongation by promoting meristematic activity and hormonal balance in vegetatively propagated spice crops such as black pepper. These outcomes are consistent with findings of Akshay et al., (2018) [4] and Nikita Prajapati et al., (2018) [15] . [17] .

The data pertaining to leaf length (cm) as influenced of plant growth regulator on rooting, growth and survivability of Black Pepper (Piper nigrum) stem cutting under shade net condition has been recorded and presented in Table 4.

The treatments showed clear variation in performance at 30 DAS, with T8 (IBA 1000 ppm) achieving the highest leaf length (cm) (3.55 cm). This was followed by the treatment T5 (NAA 1000 ppm) (3.40 cm) and T2 (IAA 1000 ppm) at (3.32 cm). In contrast, the lowest leaf length (cm) value (2.97 cm) was recorded in T0 (Control).

The treatments showed clear variation in performance at 60 DAS, with T8 (IBA 1000 ppm) achieving the highest leaf length (cm) (7.34 cm). This was at par with the treatment T5 (NAA 1000 ppm) (7.28 cm) and T2 (IAA 1000 ppm) at (7.12 cm). In contrast, the lowest leaf length (cm) value (6.32 cm) was recorded in T0 (Control).

The treatments showed clear variation in performance at 90 DAS, with T8 (IBA 1000 ppm) achieving the highest leaf length (cm) (10.86 cm). This was followed by the treatment T5 (NAA 1000 ppm) (10.50 cm) and T2 (IAA 1000 ppm) at (10.32 cm). In contrast, the lowest leaf length (cm) value (9.22 cm) was recorded in T0 (Control). The results demonstrated that the application of plant growth regulators significantly influenced the leaf length of black pepper cuttings under shade-net conditions. Treatments involving auxins such as IBA, NAA, and IAA produced longer leaves compared to the untreated control across all stages of observation. The increase in leaf length under these treatments may be attributed to the stimulatory role of auxins in promoting cell division and elongation within leaf tissues, resulting in enhanced leaf expansion. Among the different regulators, IBA consistently proved most effective, suggesting its superior role in promoting vigorous vegetative growth through better root establishment and improved nutrient translocation to the developing shoots.

The data pertaining to length of internodes (cm) as influenced of plant growth regulator on rooting, growth and survivability of Black Pepper (Piper nigrum) stem cutting under shade net condition has been recorded and presented in Table 6 It was observed that the treatments differed significantly in length of internodes (cm) at 30 DAS, with treatment T8 (IBA 1000 ppm) attaining the maximum value of (1.47 cm). This was at par with the treatment T5 (NAA 1000 ppm) (1.44 cm) and T2 (IAA 1000 ppm) (1.42 cm). Conversely, T0 (Control) displayed the lowest length of internodes (cm) (1.29 cm).

It was observed that the treatments differed significantly in length of internodes (cm) at 60 DAS, with treatment T8 (IBA 1000 ppm) attaining the maximum value of (2.17 cm). This was at par with the treatment T5 (NAA 1000 ppm) (2.14 cm) and T2 (IAA 1000 ppm) (2.13 cm). Conversely, T0 (Control) displayed the lowest length of internodes (cm) (1.89 cm).

It was observed that the treatments differed significantly in length of internodes (cm) at 90 DAS, with treatment T8 (IBA 1000 ppm) attaining the maximum value of (2.79 cm). This was at par with the treatment T5 (NAA 1000 ppm) (2.71 cm). Conversely, T0 (Control) displayed the lowest length of internodes (cm) (2.34 cm). The results showed that the application of plant growth regulators significantly influenced the internodal length of black pepper cuttings under shade-net conditions. Treatments involving auxins, particularly IBA, NAA, and IAA, resulted in greater internodal elongation compared to the untreated control across all observation periods. The increase in internode length may be attributed to the role of auxins in promoting cell elongation and division within stem tissues, thereby facilitating enhanced vegetative growth. Among the different PGRs, IBA proved most effective, likely due to its strong influence on root establishment and the subsequent improvement in nutrient and water uptake, which supports better shoot elongation. Longer internodes indicate more active meristematic growth and improved hormonal balance, leading to vigorous and healthy plant development. These results are consistent with previous studies reporting that auxin-based treatments, particularly IBA, enhance internodal elongation and overall shoot growth in black pepper and other vegetatively propagated spice crops. Similar results were also observed by Freire et al., (2017) [7] and Adsure (2021) [1] . 7.

The results indicated significant variation in the girth of new shoots (cm) at 30 DAS. The maximum value (0.25 cm) was recorded in T8 (IBA 1000 ppm), which was at par with the treatment T5 (NAA 1000 ppm) with (0.25 cm) and T2 (IAA 1000 ppm) with (0.25 cm). The minimum girth of new shoots (cm) (0.23 cm) was recorded In the treatment T0 (Control).

The results indicated significant variation in the girth of new shoots (cm) at 60 DAS. The maximum value (0.37 cm) was recorded in T8 (IBA 1000 ppm), which was at par with the treatment T5 (NAA 1000 ppm) with (0.36 cm) and T2 (IAA 1000 ppm) with (0.36 cm). The minimum girth of new shoots (cm) (0.32 cm) was recorded in the treatment T0 (Control).

The results indicated significant variation in the girth of new shoots (cm) at 90 DAS. The maximum value (0.54 cm) was recorded in T8 (IBA 1000 ppm), which was at par with the treatment T5 (NAA 1000 ppm) with (0.54 cm) and T2 (IAA 1000 ppm) with (0.53 cm). The minimum girth of new shoots (cm) (0.43 cm) was recorded in the treatment T0 (Control). The data clearly indicated that the girth of new shoots in black pepper cuttings was significantly influenced by the application of plant growth regulators under shadenet conditions. Treatments with auxins such as IBA, NAA, and IAA consistently resulted in thicker shoot girth compared to the untreated control across all growth stages. The increase in shoot girth under these treatments may be attributed to the role of auxins in enhancing cambial activity, promoting cell enlargement, and improving the translocation of nutrients and assimilates towards the developing shoot tissues. A well-developed root system induced by auxin treatments likely supported better water and nutrient uptake, which contributed to stronger and more robust shoot growth. Among the tested regulators, IBA was observed to be the most effective, indicating its superior ability to stimulate both root and shoot vigor. These findings are in agreement with earlier reports stating that auxin-based plant growth regulators enhance stem thickening and overall vegetative growth in black pepper and other spice crops propagated through stem cuttings. Also, similar results were reported by Nikita Prajapati et al., (2018) [15] .

Conclusion

The present investigation clearly demonstrated that the application of plant growth regulators had a significant and positive influence on shoot growth of black pepper (Piper nigrum L.) stem cuttings under shade net conditions. Among the different treatments, IBA at 1000 ppm consistently proved superior by recording the highest number of shoots per cutting, maximum shoot length, greater number of leaves, increased leaf size, higher nodal formation, longer internodes, and improved shoot girth at all stages of observation, followed by NAA at 1000 ppm and IAA at 1000 ppm. The enhanced shoot growth under auxin treatments may be attributed to improved root establishment, efficient nutrient and water uptake, and balanced hormonal regulation, which together promoted vigorous vegetative development. The shade net environment further supported uniform growth by providing a favorable microclimate for physiological activity. Overall, the study suggests that treatment of black pepper stem cuttings with IBA at 1000 ppm under shade net conditions is an effective and reliable practice for producing high-quality planting material with superior shoot vigor, which can contribute to better field establishment and sustainable black pepper cultivation.

Acknowledgement

The authors express their sincere gratitude to the Department of Plantation, Spices, Medicinal and Aromatic Crops, College of Horticulture & Research Station, Sankara-Patan, Durg (Chhattisgarh), for providing the necessary facilities, infrastructure, and technical support to conduct the present investigation. The authors are deeply thankful to the respected Dean and faculty members for their constant guidance, constructive suggestions, and encouragement throughout the course of the study. Special thanks are extended to the technical and field staff of the research farm for their assistance in nursery management, data collection, and maintenance of experimental conditions under shade-net structures. The authors also acknowledge the support received from the Agro-Meteorological Observatory for providing weather data during the experimental period. Finally, heartfelt appreciation is conveyed to all individuals who directly or indirectly contributed to the successful completion of this research work.

Conflict of Interest

The authors declare that there is no conflict of interest regarding the of this research.

Future Suggestions

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