Effects of Different Concentrations of Exogenous Auxins (IAA, IBA, and NAA) on Growth and Rooting Ability of Philodendron hederaceum var. oxycardium (Schott) Croat Stem Cuttings
Article information
Abstract
Background and objective
This study aimed to investigate the effects of different types and concentrations of exogenous auxins on growth and rooting ability of Philodendron hederaceum var. oxycardium stem cuttings.
Methods
Auxins used included indole acetic acid (IAA) at concentrations of 80, 160, and 320 mg·L−1, and 3-indolebutyric acid (IBA) and 1-naphthylacetic acid (NAA) at concentrations of 250, 500, and 1000 mg·L−1, respectively.
Results
The application of auxins significantly improved the mean survival rate to 97.4%, compared to 91.4% in the control. The mean rooting rate also increased with auxin treatments, to 94.5% compared to 85.4% in the control. Additionally, shoot length, width, and both fresh and dry weights peaked at an IAA concentration of 320 mg·L−1, while leaf length and width were optimal at an IAA concentration of 160 mg·L−1. In contrast, the best results for root length and biomass, both fresh and dry weights, were observed with an IBA concentration of 250 mg·L−1. The Commission Internationale de l’Eclairage Lab (CIELAB) color space analysis showed that the control had higher L* (lightness) and b* (yellowness) values, indicating a lower ornamental value.
Conclusion
The findings confirm that auxins effectively enhance the stem-cutting propagation of P. hederaceum var. oxycardium, regardless of type and concentration. For optimal shoot growth, an IAA concentration of 320 mg·L−1 is recommended, while an IBA concentration of 250 mg·L−1 is most effective for root growth.
Introduction
As people today spend more time indoors, typically 80–90% of their time, the design of their indoor environment directly affects their health (Deng and Deng, 2018). For this reason, the use of ornamental indoor foliage plants to improve indoor spaces has increased, leading to steady growth in the market size in South Korea (Park et al., 2010). Previous studies have reported that placing ornamental foliage plants indoors not only reduces psychological stress and improves workers’ health (Fjeld et al., 1998; Toyoda et al., 2020), but also promotes the physical and mental health of patients undergoing rehabilitation (Raanaas et al., 2010). Moreover, indoor foliage plants have been shown to be effective in reducing carbon dioxide (CO2) and fine dust (PM2.5) in the air, which helps improve the indoor environment (Yang et al., 2022). Among these plants, studies on the genus Philodendron, which is widely used as an indoor plant, have focused on indoor vertical gardens (Gautam et al., 2021; Phonpho and Saetiew, 2017), particulate matter reduction (Jeong et al., 2020), and hydroponic nutrient solutions (Dhanraj, 2020).
The genus Philodendron has over 700 species distributed throughout the Americas. It is the second most species-rich genus in the family Araceae, after the genus Anthurium (Croat, 1997; Gauthier et al., 2008). Most species in the genus Philodendron are characterized by their growth as epiphytes or climbers (Mayo et al., 1997). Of these, Philodendron hederaceum var. oxycardium is available on the South Korean market as an ornamental foliage plant. This species is relatively unknown academically, except for a study on the effects of shading levels and fertilizer sources on its growth and quality (Conover and Poole, 1974), and reports on various diseases affecting it (Knauss et al., 1970, 1972; Wang et al., 2016). There are currently no physiological studies with this species. It is, therefore, necessary to determine an efficacious cutting propagation method and to study approaches to improving the rooting and survival rates of stem cuttings, as well as their growth using exogenous auxin, in order to promote the distribution of P. hederaceum var. oxycardium.
Auxin, a phytohormone commonly referred to as a rooting promoter, plays multiple roles in regulating plant growth and development (Leyser, 2018). This includes localized responses such as endocytosis, cell polarity, cell cycle control, cell elongation, and differential growth, as well as macroscopic phenomena like embryogenesis, tissue patterning, and the de novo formation of organs (Sauer et al., 2013). Since the 1930s, the most common methods used to apply auxin in vegetative propagation within the horticultural industry have been the basal quick-dip, powder application, and dilute soak methods (Blythe et al., 2007). Of these, the quick-dip method is an easy way to apply auxin that is highly effective and is still widely used by farmers today. It is recognized as a useful method for stable mass propagation using cuttings with traits identical to the mother plant.
A previous study reported that in a cutting propagating experiment with Pseudolysimachion ovatum, indole-3-butyric acid (IBA) was more effective than 1-naphthaleneacetic acid (NAA), with the best effect on cutting propagation and growth at a concentration of 500–1000 mg·L−1 (Kwon and Cho, 2023). Hwang et al. (2021) found that cuttings of the strawberry cultivar "Maehyang" had the highest number of leaves at an IBA concentration of 100 mg·L−1, and the highest number of primary roots at an indole acetic acid (IAA) concentration of 100–150 mg·L−1. Meanwhile, rooted grape cuttings were reported to have the highest root fresh and dry weights at an IBA concentration of 4000 mg·L−1 (Galavi et al., 2013). As such, the concentration of auxin required for cuttings varies depending on the species, and different experimental approaches are needed to determine the appropriate auxin concentration for each species.
In this study, P. hederaceum var. oxycardium, commonly used as an ornamental indoor foliage plant in the horticultural industry, was selected as the experimental subject. The rooting ability of stem cuttings and the potential for enhancing growth were assessed based on the type and concentration of exogenous auxin.
Research Methods
Plant material and auxin type and concentration used
This study aimed to determine the effects of the type and concentration of exogenous auxin applied to the base of stem cuttings when propagating Philodendron hederaceum var. oxycardium. An experiment was conducted over three months, from June to September 2023, in the experimental greenhouse of the Department of Environmental Horticulture at Sahmyook University. The experimental greenhouse is located in Nowon-gu, Seoul. The greenhouse is 25% shaded and has all sides open.
In this study, three auxins, including indole acetic acid (IAA), 3-indolebutyric acid (IBA), and 1-naphthylacetic acid (NAA), were selected (Sigma-Aldrich, USA) and applied to cuttings after dissolving them in 50% ethanol. 50% ethanol without auxin was used as a control. IAA at concentrations of 80, 160, and 320 mg·L−1, and IBA and NAA at concentrations of 250, 500, and 1000 mg·L−1 were used, resulting in the design of a total of ten treatments (Table 1). Stem cuttings were prepared from P. hederaceum var. oxycardium, which had been cultivated for a minimum of two years and reached a length of over 1 m. The cuttings, each with one leaf, were taken from nodes measuring approximately 3 cm with one axillary bud. The base of the stem cuttings was immersed to a depth of 5 mm for one minute in all types and concentrations of auxin.
Auxin types and concentrations used in this study
Cutting cultivation environment and research parameters
The pots used for P. hederaceum var. oxycardium stem cuttings were rectangular, measuring 48.5 cm in width, 33.0 cm in length, and 8.0 cm in height. The culture media consisted of a mixture of fertilized horticultural substrate (Hanareumsangto, Shinsung Mineral, South Korea), 5 mmsized vermiculite (Verminuri, GFC, South Korea), and perlite (New Pearl Shine No. 1, GFC, South Korea) in a ratio of 1:1:1 (v/v/v). Spray irrigation was performed twice a week. 2 L of liquid fertilizer (Hyponex High Grade S, HYPONeX, Japan) with an N-P-K ratio of 7-10-6 was applied once a month at a concentration of 1000 ppm. The average temperature during the experimental period was 29.8 ± 4.7 °C, and the relative humidity was 68.4 ± 14.8%.
The following parameters were measured to investigate the growth and rooting ability of P. hederaceum var. oxycardium cuttings affected by the type and concentration of exogenous auxin: survival and rooting rates, shoot length, shoot width, stem diameter, root length, and leaf length and width; chlorophyll fluorescence parameter Fv/Fm representing maximum quantum yield of photosystem II; fresh and dry weights and relative moisture content of shoots and roots; relative chlorophyll content (SAPD units); and Commission Internationale de l’Eclairage Lab (CIELAB) color space coordinates L*, a*, and b*. Survival and rooting rates were calculated as a percentage of the total cuttings, including those that did not survive. Fv/Fm was measured with a portable fluorometer (FluorPen FP 110/D, Photon Systems Instruments, Czech Republic) after randomly selecting newly developed leaves from cuttings and dark adapting them for 15 minutes with detachable dark-adapted leaf-clips according to the manufacturer’s guideline (PSI, 2024). Relative moisture content was estimated by comparing the fresh and dry weights of each rooted cutting. Dry weight was obtained by drying the samples at 85°C for 24 hours using a drying oven (HK-DO135F, HANKUK S&I, South Korea).
Colors were obtained by converting the L*, a*, and b* values, measured using the Converting Colors tool designed by Zettl (2024), into color chips for visual evaluation. Relative chlorophyll content was measured using a portable chlorophyll meter (SPAD-502, Konica Minolta, Japan). CIELAB measurements were made by referring to the leaf color measurement methodology suggested by Lee (2023); the spectrophotometer (CM-2600d, Konica Minolta, Japan) was set to CIELAB D65/10° to obtain CIELAB L*, a*, and b* values including the specular component (SCI).
Statistical analysis
The results of the experiment were analyzed using one-way ANOVA with the aid of the SAS 9.4 software package (SAS Institute, USA). The comparison of means was subjected to a statistical analysis using Duncan’s multiple range test at the p < .05 level. The experiment was conducted using a completely randomized design, with seven cuttings per repetition, for a total of five repetitions, and 35 stem cuttings were placed for each treatment.
Results and Discussion
The visual evaluation image of Philodendron hederaceum var. oxycardium stem cuttings affected by different auxin types and concentrations in this study are shown in Fig. 1. The survival rate of P. hederaceum var. oxycardium affected by different auxin types and concentrations was 100% for the IAA160 (160 mg·L−1 IAA), IBA500 (500 mg· L−1 IBA), and IBA1000 (1000 mg·L−1 IBA) treatments, while it was the lowest at 91.4% for the control and NAA1000 (1000 mg·L−1 NAA) treatments (Fig. 2). Meanwhile, the rooting rates were 97.1% for the IAA160 and IAA320 (320 mg·L−1 IAA), and NAA500 (500 mg·L−1 NAA) treatments, but 91.4% for the control and NAA1000 treatments, indicating a tendency for lower rooting rates. However, there was no significant difference among the treatments.
Photo of growth in Philodendron hederaceum var. oxycardium stem cuttings three months after treatment with various concentrations and types of auxins. Control is using purified water with ethanol; IAA80, IAA160, and IAA320 involve treatments with indole acetic acid (IAA) at concentrations of 80, 160, and 320 mg·L−1, respectively; IBA250, IBA500, and IBA1000 are treated with 3-indolebutyric acid (IBA) at concentrations of 250, 500, and 1000 mg·L−1, respectively; NAA250, NAA500, and NAA1000 use 1-naphthylacetic acid (NAA) at concentrations of 250, 500, and 1000 mg·L−1, respectively.
Survival and rooting rates of P. hederaceum var. oxycardium stem cuttings three months after treatment with different types and concentrations of auxins. Control is using purified water with ethanol; IAA80, IAA160, and IAA320 involve treatments with IAA at concentrations of 80, 160, and 320 mg·L−1, respectively; IBA250, IBA500, and IBA1000 are treated with IBA at concentrations of 250, 500, and 1000 mg·L−1, respectively; NAA250, NAA500, and NAA1000 use NAA at concentrations of 250, 500, and 1000 mg·L−1, respectively. Vertical bars represent mean ± standard error. Different lowercase letters indicate significant differences at p < .05 based on Duncan’s multiple range test (n = 5). The same lowercase letters indicate no significant differences.
Oh and Lee (2022) reported that the rooting rate of Sedum takesimense cuttings treated with auxin was 95% or higher at an IBA concentration of 250–500 mg·L−1 and an NAA concentration of 500 mg·L−1. Meanwhile, Kwon and Cho (2023) observed that Pseudolysimachion ovatum stem cuttings exhibited a survival rate of 90% or higher, regardless of the auxin concentration. It was reported that Ginkgo biloba cuttings had the highest survival rate at a concentration of 10.0 μM IBA (Pandey et al., 2011). In another study, Viburnum lantanoides exhibited a rooting rate of 51.1% in the control group, but a rooting rate of 70.0–73.3% at a concentration of 1000–8000 ppm IBA. In contrast, Eubotrys racemosa showed a higher rooting rate in the control group compared to the above IBA concentration range (Lubell and Gardner, 2017). As such, it was determined that the effects of auxin on survival and rooting rates vary depending on the plant species. Additionally, since the duration of dipping may also have an effect (Bak et al., 2023), different experimental approaches are needed.
An examination of the parameters related to plant size showed that the shoot length and width of rooted cuttings of P. hederaceum var. oxycardium under IAA320 treatment were the highest at 20.98 and 18.91 cm, respectively (Table 2), whereas the shoot length and width in the control were significantly lower at 11.32 and 10.77 cm, respectively. Cabahug et al. (2016) reported that Echeveria subsessilis, a type of ornamental succulent, had the greatest shoot length and width at a concentration of 500 ppm IBA, but Echeveria runyonii had the greatest shoot length and width at a concentration of 0–100 ppm IBA. On the other hand, the results of this study showed that the stem diameter of P. hederaceum var. oxycardium was the thickest at 0.40 cm under the NAA1000 treatment, and the root length was the longest at 19.16 cm under the IBA250 (250 mg·L−1 IBA) treatment. Both stem diameter and root length were the lowest in the control at 0.24 and 15.32 cm, respectively. Consequently, all the auxin-treated groups were found to be effective in increasing the size of P. hederaceum var. oxycardium propagated by stem cuttings compared to the control, regardless of the auxin type or concentration. Leaf length was observed to be 9.34 and 9.37 cm under the IAA80 (80 mg·L−1 IAA) and IAA160 treatments, respectively, and leaf width the widest at 5.68 cm under the IAA160 treatment. Among the chlorophyll fluorescence parameters, Fv/Fm, which indicates the maximum quantum yield of photosystem II, was highest at 0.823 under the IAA320 treatment. In contrast, the control had the lowest Fv/Fm value of all treatment groups at 0.796. However, it fell within the range of 0.780–0.840, indicating that the cuttings were not under stress (Björkman and Demmig, 1987; Park et al., 2023; Shin et al., 2023, 2024; Yoo et al., 2012).
Plant growth parameters and maximum quantum yield (Fv/Fm) of Philodendron hederaceum var. oxycardium stem cuttings as influenced by various types and concentrations of auxins
An analysis of fresh weight and relative moisture content showed that the IAA320 treatment had the highest shoot fresh and dry weights at 9.14 and 0.99 g, respectively, while the IBA250 treatment had the highest root fresh and dry weights at 1.54 and 0.33 g, respectively (Table 3). In the control, the fresh and dry weights of the shoots were found to be significantly lower than those of the other treatments (4.56 and 0.63 g, respectively). These findings are consistent with observations regarding plant shoot size and maximum quantum yield of the shoots. Previous studies on cutting propagation of ornamental floricultural crops have suggested that excellent root growth, including root number, length, and both fresh and dry weights, can increase initial survival and promote shoot growth (Kim and Kim, 2015; Lee et al., 2011; Oh and Lee, 2022). However, despite the excellent root growth observed in P. hederaceum var. oxycardium cuttings, shoot growth exhibited relatively different trends. Meanwhile, the relative moisture content of the shoots and roots of P. hederaceum var. oxycardium under the NAA250 (250 mg·L−1 NAA) treatment was the highest at 90.2 and 85.6%, respectively. Conversely, the control had the lowest average shoot and root moisture content of 86.4 and 75.1%, respectively. These trends may result from poorer initial rooting conditions, leading to lower moisture absorption rates and efficiency.
Fresh and dry weights and relative moisture content of P. hederaceum var. oxycardium stem cuttings as influenced by various types and concentrations of auxins
A previous study found a positive correlation between the chlorophyll content and SPAD units of Betula, Triticum, and Solanum tuberosum (Uddling et al., 2007). In this study, the relative chlorophyll content, expressed in SPAD units, reached its highest value of 35.56 under the NAA1000 treatment. This suggests that the high concentration of NAA absorbed from the base increases the density of leaf chlorophyll within the same unit area (Table 4). Czerpak et al. (2002) reported that auxins such as phenylacetic acid (PAA) or NAA generally decrease the chlorophyll and carotenoid content of leaves. Other studies have reported that wheat coleoptiles treated with IAA alone exhibited a relatively lower chlorophyll content compared to the control (Volfová et al., 1978), and NAA treatment resulted in a reduction of chlorophyll content in the Momordica charantia cultivar "Makiling" (Tolentino and Cadiz, 2005). However, in this study, as mentioned above, chlorophyll content was increased by treatment with relatively high concentrations of NAA, which is contrary to the findings of previous studies. This suggests that the effect of auxin on chlorophyll content may vary depending on the species. Moreover, this study showed inconsistent results between Fv/Fm, which indicates maximum quantum yield, and chlorophyll content. Therefore, based on the results of this study, it appears that despite elevated chlorophyll levels, the maximum quantum yield may not necessarily increase in proportion, and the variation of Fv/Fm is more closely associated with the shoot growth level of P. hederaceum var. oxycardium stem cuttings.
Chlorophyll content (SPAD units) and Commission Internationale de l'Eclairage Lab (CIELAB) color space values of P. hederaceum var. oxycardium stem cuttings as influenced by various types and concentrations of auxins
The external qualities of plants, including leaf and flower colors, can serve as indicators for intuitive evaluation (Lee and Nam, 2023). They can also be affected by changes in pigment content, which can be caused by various hormones (Xia et al., 2021). Karatas et al. (2010) reported that the application of auxin resulted in a reduction in the concentration of chlorophyll and carotenoids in Tropaeolum majus. Li et al. (2017) reported that exogenous auxin was also involved in the inhibition of pigment, total phenolic content, and flavonoid accumulation in tomato fruits. Parameters, including CIELAB, Hunter Lab, and RGB, are employed to assess the external quality of plants. Among these, CIELAB has been useful in evaluating leaf color (Park et al., 2023; Shin et al., 2023, 2024), flower color (Jang et al., 2023; Zhang et al., 2020), and root color (Kim et al., 2024a, 2024b). In this study, a comparison of the leaf color measurements between the auxin-treated groups and the control, using CIELAB color space coordinates, showed a tendency for the lightness and yellowness of the leaves to decrease, regardless of auxin type and concentration. In the control, the L* coordinate, which indicates lightness in the color space, and the b* coordinate, which indicates yellow (+) and blue (−), exhibited the highest values at 45.30 and 25.50, respectively. In contrast, in the NAA1000 treatment, those values were significantly the lowest mean values, at 38.29 and 14.85, respectively. Meanwhile, the a* coordinate representing red (+) and green (−) was lower in the control, IAA80, IAA160, and IBA500 treatments at statistically the same level of significance, indicating that it was relatively closer to green, whereas in the NAA1000 treatment, it reached its highest at −8.54. This was likely due to variations in intracellular pigment content caused by exogenous auxin (Sunderland, 1966).
When taken comprehensively, the findings of this study suggest that the application of auxin, regardless of its type or concentration, has a positive effect on the growth promotion of P. hederaceum var. oxycardium propagated using stem cuttings compared to the control. Overall, immersion treatment at an IAA concentration of 320 mg·L−1 was most effective for increasing shoot size and enhancing shoot fresh and dry weights. For leaf size, an IAA concentration of 160 mg·L−1 was optimal. Additionally, IBA at 250 mg·L−1 was most effective for increasing root length as well as fresh and dry weights. According to the Fv/Fm results, the plants showed no signs of stress, regardless of the type or concentration of auxin, including in the control group. Leaf color quality results showed that, on average, the auxin-treated groups outperformed the control, regardless of auxin type or concentration. The highest quality was observed at an NAA concentration of 1000 mg·L−1.
Conclusion
This study aimed to determine the effects of different types and concentrations of auxin applied to the base of Philodendron hederaceum var. oxycardium stem cuttings on their growth and rooting ability. Three types of auxins were applied: indole acetic acid (IAA), 3-indolebutyric acid (IBA), and 1-naphthylacetic acid (NAA). IAA was used at concentrations of 80, 160, and 320 mg·L−1, while both IBA and NAA were used at concentrations of 250, 500, and 1000 mg·L−1. The results showed that the mean survival rate was 97.4% in the auxin treatment groups, compared to 91.4% in the control. Similarly, the mean rooting rate was 94.5% in the auxin treatment groups, compared to 91.4% in the control. Meanwhile, shoot height, width, and both fresh and dry weights were found to be the highest at an IAA concentration of 320 mg·L−1, and mean leaf length and width were the highest at an IAA concentration of 160 mg·L−1. In contrast, the highest root length as well as fresh and dry weights were observed at an IBA concentration of 250 mg·L−1. Based on the Fv/Fm results, the plants showed no signs of stress, regardless of the type and concentration of auxin, not even in the control group. In the CIELAB color space analysis, the control exhibited the highest L* (lightness) and b* (yellowness) values, indicating a lower ornamental value. In conclusion, the application of auxins was found to be effective for the propagation of P. hederaceum var. oxycardium by stem cuttings, regardless of the type and concentration of auxins. An IAA concentration of 320 mg·L−1 was most effective for promoting shoot growth, while an IBA concentration of 250 mg·L−1 was most effective for promoting root growth.
