Effects of Exogenous Auxin (IBA or NAA) and Combined Auxin-BA Dipping Treatments on Propagation Performance, Development, and Physiological Responses of Philodendron hederaceum Schott Stem Cuttings
Article information
Abstract
Background and objective
Philodendron hederaceum Schott is a widely cultivated ornamental foliage plant that is commonly propagated by stem cuttings; however, uneven rooting and establishment, along with variability in early growth, can reduce production uniformity. This study aimed to evaluate the effects of exogenous auxin (indole-3-butyric acid; IBA or 1- naphthaleneacetic acid; NAA) dipping, applied either alone or in combination with a low concentration of 6-benzyladenine (BA), on propagation performance and subsequent morphophysiological quality of P. hederaceum stem cuttings.
Methods
Single-node stem cuttings (approximately 5 cm) with one leaf were dipped (basal 0.5 cm for 1 min) in ten solutions, including a control (25% ethanol), BA (0.1 g·L−1), IBA or NAA (0.5 or 1.0 g·L−1), and auxin-BA combinations, and then grown for four months. Survival and rooting rates, growth parameters, biomass components, remote sensing-based vegetation indices (e.g., anthocyanin reflectance index 2 and normalized difference vegetation index), and chlorophyll fluorescence parameters (Fv/Fm and PIABS) were assessed. Data were analyzed using Duncan’s multiple range test, and principal component analysis (PCA) was performed to interpret multivariate response patterns.
Results
Survival and rooting rates did not differ significantly among treatments, but several growth parameters (e.g., shoot length and width, internode length, and root length) responded to dipping treatments. Leaf-size parameters showed treatment-dependent changes, while leaf number was not significantly affected. Shoot fresh weight showed limited treatment effects, whereas root fresh and dry weights varied among treatments, indicating that the auxin-BA combination (IBA 0.5 g·L−1 with BA 0.1 g·L−1) was associated with relatively greater post-establishment vigor, particularly in root biomass accumulation. Optical and leaf pigment-related metrics (e.g., SPAD units, CIELAB L* and a*, and selected vegetation indices) differed across treatments, but Fv/Fm and PIABS were not significantly affected. PCA indicated that PC1 (31.2%) represented a morphology/biomass axis and PC2 (18.2%) reflected vegetation-index variation, with cumulative variance reaching 59.6% by PC3.
Conclusion
Overall, auxin-only and auxin-BA combined dipping treatments mainly affected post-establishment growth and quality-related traits rather than rooting rate. Within the tested range, IBA at 0.5 g·L−1, particularly in combination with BA at 0.1 g·L−1, was associated with more favorable growth and root biomass responses, whereas NAA at 1.0 g·L−1 tended to show less favorable responses. PCA further supported the interpretation that growth/biomass traits and optical traits represented partly distinct response dimensions.
Introduction
Recent increases in demand for indoor landscaping and home gardening have elevated the value of foliage plants, not only for enhancing the aesthetic quality of indoor spaces but also for improving environmental comfort and promoting psychological well-being (Bringslimark et al., 2009; Bui et al., 2024). As in other horticultural industries, the stable operation of the ornamental horticulture sector largely depends on the establishment of propagation systems capable of supplying uniform, high-quality young plants reliably and consistently (Jung et al., 2023; Lee et al., 2024a).
Philodendron hederaceum Schott is a tropical, climbing herbaceous species belonging to the family Araceae and is native to Central America and the Caribbean region (Nah et al., 2024). This species is widely recognized as an important foliage plant cultivated in the Republic of Korea and international markets due to its high shade tolerance, ease of maintenance, and strong ornamental value (Suárez-Cáceres and Pérez-Urrestarazu, 2021; Weerasinghe et al., 2023). It is primarily propagated vegetatively through stem cuttings (ISUEO, 2025), highlighting the need for research focused on the efficient production of healthy and uniform young plants.
In practical propagation settings, issues such as non-uniform rooting, delayed establishment, and variability in early growth rates among cuttings frequently occur, leading to fluctuations in productivity and market quality (Druege, 2020; Lebedev, 2019). The success of stem cutting propagation largely depends on adventitious root formation and subsequent root system development (Agulló-Antón et al., 2014; Druege et al., 2019), which are directly associated with shoot growth and biomass accumulation following establishment (Torres and Lopez, 2011). Notably, during the early stages of propagation, limited root development restricts water and nutrient uptake, rendering cuttings highly susceptible to stress. This often results in physiological disturbances such as unstable stomatal function, reduced chlorophyll content, and decreased photosynthetic capacity (Da Costa et al., 2013; Lee et al., 2025b). Therefore, evaluation of cutting propagation should extend beyond simple rooting percentages to include an integrated assessment encompassing root-related traits—such as root length and root biomass accumulation—as well as shoot growth and physiological status.
Physiological stability is a key determinant of rooting success and subsequent growth during cutting propagation, underscoring the use of non-destructive diagnostic indicators for its quantitative evaluation (Lee et al., 2025b; Mesén et al., 1997, 2001; Oh and Lee, 2022). Remote sensing vegetation indices can capture changes in leaf optical properties, enabling the assessment of leaf pigment status and canopy vigor (Park et al., 2024; Xue and Su, 2017), and can serve as useful supplementary indicators for evaluating overall vigor and shoot health following exogenous plant growth regulator treatments (Ferus et al., 2017; Hou et al., 2020; Lee et al., 2025b). In addition, chlorophyll fluorescence analysis sensitively reflects the photochemical efficiency of photosystem II (PSII), photoprotective responses, and cumulative stress levels (Jang et al., 2023; Maxwell and Johnson, 2000), thereby facilitating a more integrated interpretation of treatment effects.
Auxins are plant hormones involved in adventitious root formation and root primordium differentiation during cutting propagation (Blakesley et al., 1991; Blythe, 2012). Accordingly, exogenous auxin treatments are widely used to promote rooting in cuttings. In practice, indole-3-butyric acid (IBA) and 1-naphthaleneacetic acid (NAA) are widely used (Kaushik and Shukla, 2020; Susaj et al., 2012). IBA is generally more stable than indole-3-acetic acid (IAA) and has demonstrated consistent rooting-promoting effects across a wide range of species, making it a commonly used standard treatment (De Andrade et al., 2023; Kohler et al., 2022). In contrast, although NAA can promote rooting under certain conditions, it may also induce adverse effects such as excessive callus formation or necrosis at the cut surface depending on treatment concentration and the physiological state of the cuttings, thereby necessitating optimization of treatment conditions (Henrique et al., 2006; Zimmerman, 1982). Moreover, auxin effectiveness varies significantly depending on species, cultivar, and compound type, highlighting the need to identify suitable auxin types and treatment strategies for P. hederaceum stem cuttings.
Meanwhile, 6-benzyladenine (BA), a synthetic cytokinin, is involved in regulating cell division and shoot growth (Grossman et al., 2012) and has been reported to promote axillary bud activation and branching (Chabikwa et al., 2019). Cytokinin treatments may also enhance shoot physiological stability during cutting propagation by delaying leaf yellowing and senescence (Currey et al., 2013; Gan and Amasino, 1995), thereby contributing to the maintenance and development of shoot function during early stages (Wróblewska, 2013). However, auxins and cytokinins are two major plant hormones that interact during organogenesis and differentiation (Schaller et al., 2015), and cytokinins may inhibit adventitious root formation or attenuate auxin-induced rooting depending on species, cultivar, treatment concentration, timing, and cutting condition, potentially delaying root initiation (Mao et al., 2019; Pernisová et al., 2009; Wróblewska, 2012). Therefore, systematic investigation is required to evaluate the effects of combined auxin-BA dipping treatments, particularly with respect to cutting establishment and shoot-root resource allocation.
Although P. hederaceum is commonly propagated via stem cuttings, studies comprehensively comparing the relative effectiveness of exogenous auxin (IBA or NAA) alone and combined auxin-BA dipping treatments—while considering cutting performance, shoot and root development, and physiological responses—remain limited. From a practical production perspective, treatment simplicity, reproducibility, and maintenance of physiological stability during the propagation period are critical considerations. In this respect, it is necessary to identify optimal combinations and concentrations of plant growth regulators that can simultaneously enhance cutting performance and promote both shoot and root development.
Therefore, this study aimed to apply exogenous auxin treatments (IBA or NAA) and combined auxin-BA dipping treatments to stem cuttings of P. hederaceum and to comprehensively evaluate cutting performance, shoot and root development, and physiological responses.
Research Methods
Plant Materials and Growing Conditions
This experiment was conducted from April to August 2025 in an experimental greenhouse at the Department of Environmental Horticulture, Sahmyook University, located in Nowon-gu, Seoul, Republic of Korea. The greenhouse was open-sided and equipped with a 25% shading system. Stem cuttings of P. hederaceum were used for the experiment. Mother plants were selected from individuals exceeding 1 m in shoot length that had been cultivated in the green-house for at least two years. All mother plants were derived from the same clone. Cuttings were prepared to a length of approximately 5 cm, with the basal end cut at a 45° angle prior to treatment. Each cutting retained one node and one leaf.
Rectangular pots (48.5 cm × 33.0 cm × 8.0 cm) were used for planting. The growing medium consisted of a 1:1:1 (v/v/v) mixture of a non-fertilized horticultural substrate (Hanareumsangto, Shinsung Mineral, Republic of Korea), vermiculite (Verminuri, GFC, Republic of Korea), and perlite (New Pearl Shine No. 1, GFC, Republic of Korea). Irrigation was applied twice weekly using overhead irrigation. To promote cutting growth, overhead irrigation was replaced once per month with 2 L of nutrient solution containing premix fertilizer (Masterblend 4-18-38, Masterblend International, USA) at 750 mg·L−1, magnesium sulfate (MgSO4) at 375 mg·L−1, and calcium nitrate [Ca(NO3)2] at 750 mg·L−1. Environmental conditions for the experimental plants were maintained at 24.8 ± 3.7 °C and 64.8 ± 14.9% relative humidity.
Exogenous Auxin Alone and Combined Auxin-BA Dipping Treatments
Dipping solutions were prepared using 6-benzyladenine (BA), indole-3-butyric acid (IBA), and 1-naphthaleneacetic acid (NAA) (Sigma-Aldrich, USA), resulting in a total of ten treatments (Table 1). These included a control (25% ethanol); five single-regulator treatments consisting of BA at 0.1 g·L−1 (BA0.1), IBA at 0.5 and 1.0 g·L−1 (IBA0.5 and IBA1.0), and NAA at 0.5 and 1.0 g·L−1 (NAA0.5 and NAA1.0); and four combined treatments comprising IBA or NAA (0.5 and 1.0 g·L−1) in combination with BA at 0.1 g·L−1 (IBA0.5BA0.1, IBA1.0BA0.1, NAA0.5BA0.1, and NAA1.0BA0.1).
Treatment symbols and concentrations of exogenous indole-3-butyric acid (IBA), 1-naphthaleneacetic acid (NAA), and 6-benzyladenine (BA)
For the BA-alone treatment (BA0.1) and all BA-containing combined treatments, BA was dissolved in 95% ethanol using a water bath at approximately 50 °C with continuous stirring until complete dissolution (i.e., no visible precipitate remained). All treatment solutions were prepared by first dissolving the plant growth regulators in 95% ethanol and then diluting with distilled water to achieve a final ethanol concentration of 25%. The control treatment consisted of 25% ethanol only. The dipping method followed Lee et al. (2024a, 2025b). The basal end of each cutting was immersed to a depth of approximately 0.5 cm in the respective solution for 1 min.
Measurement of Quantitative and Qualitative Parameters
To evaluate the effects of auxin-alone and combined auxin-BA dipping treatments on the propagation performance, growth, and physiological responses of P. hederaceum stem cuttings, the following parameters were assessed: survival rate, rooting rate, shoot length, shoot width, internode length, stem diameter, root length, node number, leaf length, leaf width, leaf area, leaf thickness, petiole length, leaf number, fresh and dry weights of shoots and roots, total relative moisture content (RMC), chlorophyll content (SPAD units), Commission Internationale de l’Éclairage Lab (CIELAB) color space values (L*, a*, and b*), anthocyanin reflectance index 2 (ARI2), carotenoid reflectance index 2 (CRI2), normalized difference vegetation index (NDVI), modified chlorophyll absorption ratio index (MCARI), photochemical reflectance index (PRI), structure- insensitive pigment index (SIPI), Fv/Fm (maximum quantum yield), and PIABS (performance index on an absorption basis).
Plant size measurements were conducted following the methods described by Lee et al. (2024a, 2025b). Shoot length was measured from the junction between the shoot and root to the terminal bud when the stem was fully extended. Shoot width was determined at the widest lateral point of the plant with the stem fully extended. Root length was defined as the length of the longest root per individual. Dry weight was measured after drying samples in a hot-air drying oven (HK-DO135F, Hankuk S&I, Republic of Korea) at 85 °C for 12 h. RMC was determined according to Lee and Nam (2024) by comparing total fresh weight and total dry weight of each individual, as expressed in Equation (1).
(FW: fresh weight; and DW: dry weight)
For quality-related traits, leaf color was measured using a spectrophotometer (CM-2600d; Konica Minolta, Japan), and L*, a*, and b* values were obtained in the CIELAB color space. CIELAB values were measured in D65/10° mode with specular component included (SCI) following the method of Lee (2023). Chlorophyll content was determined using a portable chlorophyll meter (SPAD-502Plus; Konica Minolta, Japan).
Remote sensing vegetation indices were obtained using a portable spectroradiometer (PolyPen RP 410, Photon Systems Instruments, Czech Republic). ARI2 (Equation 2), CRI2 (Equation 3), NDVI (Equation 4), MCARI (Equation 5), PRI (Equation 6), and SIPI (Equation 7) were calculated based on PSI (2026) and Xue and Su (2017), and the equations are as follows.
(where ρ denotes the unitless reflectance in the specified spectral band)
Chlorophyll fluorescence parameters were measured using a portable fluorometer (FluorPen FP 110/D, Photon Systems Instruments, Czech Republic). Prior to measurement, leaves were dark-adapted for 15 min using a detachable leaf clip, following the manufacturer’s instructions (PSI, 2025). Fv/Fm and PIABS were selected to analyze PSII physiological performance (Lee et al., 2025a; PSI, 2025; Stirbet and Govindjee, 2011) and are presented in Equations (8) and (9), respectively. Measurements were obtained following Shin et al. (2024). After setting the excitation wavelength to 455 nm, the leaves were irradiated with a light intensity of 1,500 μmol·m−2·s−1 (equivalent to 50% of the super pulse) to induce Fm, the maximum fluorescence level in the JIP test. All measurements of CIELAB values, SPAD units, vegetation indices, and chlorophyll fluorescence were performed while avoiding the leaf midrib.
(where Fo and Fm are the minimal and maximal chlorophyll fluorescence yields from dark-adapted leaf tissue, respectively; variable fluorescence (Fv) is defined as Fm-Fo, and Fv/Fm (= ΦPo) represents the maximum quantum yield of PSII primary photochemistry. PIABS is the performance index on an absorption basis. ABS refers to the absorbed- photon flux of PSII, RC/ABS denotes the number of active QA-reducing PSII reaction centers per PSII antenna chlorophyll (i.e., the reciprocal of ABS/RC), and Ψo is the probability that a trapped exciton moves an electron beyond the primary quinone acceptor QA into the electron transport chain)
Statistical Analysis
This experiment was conducted using a completely randomized design (CRD), with five replicates consisting of seven individuals per treatment group. All statistical analyses were performed using SAS 9.4 (SAS Institute, USA). Treatment effects were evaluated using one-way analysis of variance (ANOVA). For post-hoc analysis, mean comparisons were conducted using Duncan’s multiple range test (DMRT) at a significance level of α = 0.05. Differences were considered statistically significant at p < .05.
Principal component analysis (PCA) was performed to summarize multivariate patterns in morphological traits, biomass components, and vegetation indices. Key parameters and indices selected for the analysis included shoot length, shoot width, internode length, root length, leaf length, leaf width, leaf area, and leaf thickness, shoot and root dry weights, as well as SPAD units, ARI2, CRI2, NDVI, MCARI, and SIPI. Prior to PCA, all variables (i.e., key parameters and indices) were standardized using Z-scores. The PCA was conducted via eigenvalue decomposition of the correlation matrix, and no rotation was applied to the principal component loadings. A loading plot illustrating the loadings of variables on the PC1-PC2 axes and a correlation circle depicting relationships between variables and PC1 and PC2 were generated. Information for PC3 was presented separately in tabular form for clarity.
Results
Analysis of Cutting Propagation, Development, and Biomass Accumulation
Representative photographs showing the growth appearance of P. hederaceum stem cuttings four months after the dipping treatments are presented in Fig. 1. The survival rate ranged from 91.4% to 100.0%, with no statistically significant differences observed among treatments (Table 2). Similarly, rooting rate did not differ significantly among treatments. Shoot length was relatively longer in the IBA0.5 and IBA0.5BA0.1 treatments, measuring 15.21 and 14.65 cm, respectively, whereas it was comparatively lower under the NAA1.0 treatment (8.51 cm). A similar trend was observed for shoot width, which was wider in the IBA0.5 and IBA0.5BA0.1 treatments (15.24 and 14.67 cm, respectively) and narrower under NAA1.0 (9.42 cm). Internode length followed the same pattern, being longer in the IBA0.5 and IBA0.5BA0.1 treatments (2.63 and 2.70 cm, respectively) and shorter in the NAA1.0 treatment (1.56 cm). In contrast, stem diameter did not show significant differences among treatments. Root length was greater in the IBA0.5 and IBA0.5BA0.1 treatments, measuring 13.36 and 13.87 cm, respectively, whereas it was shorter in the NAA0.5, NAA1.0, and NAA1.0BA0.1 treatments (7.48, 7.62, and 7.82 cm, respectively). Similar to stem diameter, node number did not differ significantly among treatments.
Representative growth appearance of Philodendron hederaceum stem cuttings four months after dipping treatments: (A) control; (B) 6-benzyladenine (BA) 0.1 g·L−1; (C) indole-3-butyric acid (IBA) 0.5 g·L−1; (D) IBA 1.0 g·L−1; (E) 1-naphthaleneacetic acid (NAA) 0.5 g·L−1; (F) NAA 1.0 g·L−1; (G) IBA 0.5 g·L−1 with BA 0.1 g·L−1; (H) IBA 1.0 g· L−1 with BA 0.1 g·L−1; (I) NAA 0.5 g·L−1 with BA 0.1 g·L−1; and (J) NAA 1.0 g·L−1 with BA 0.1 g·L−1. Scale bar = 5 cm.
Survival and rooting rates, plant sizes, and node number of Philodendron hederaceum stem cuttings four months after exogenous auxin (IBA or NAA) and combined auxin-BA dipping treatments
Among leaf size-related parameters, leaf length was greatest in the IBA0.5BA0.1 treatment (6.83 cm), whereas shorter leaves were observed under IBA1.0, NAA1.0, and NAA1.0BA0.1 treatments (5.34, 5.17, and 5.61 cm, respectively; Table 3). Leaf width exhibited a similar pattern, with the widest leaves observed in the IBA0.5BA0.1 treatment (3.55 cm), while narrower leaves were found in the control, NAA0.5, and NAA1.0 treatments (2.88, 2.90, and 2.59 cm, respectively). Consequently, leaf area was also greatest in the IBA0.5BA0.1 treatment (25.44 cm2). Meanwhile, leaf thickness ranged from 0.316 to 0.323 mm in the control, BA0.1, IBA1.0, NAA1.0, and IBA0.5BA0.1 treatments, indicating relatively thicker leaves, whereas the NAA1.0BA0.1 treatment exhibited thinner leaves (0.298 mm). Petiole length and leaf number did not differ significantly among treatments.
Leaf sizes, leaf area, leaf thickness, petiole length, and leaf number of P. hederaceum stem cuttings four months after exogenous auxin (IBA or NAA) and combined auxin-BA dipping treatments
With respect to biomass accumulation, shoot fresh weight did not show significant differences among treatments (Table 4). In contrast, root fresh weight was highest in the IBA0.5BA0.1 treatment (0.71 g) and lower in the NAA1.0 treatment (0.37 g). Shoot and root dry weights were also highest in the IBA0.5BA0.1 treatment (0.360 and 0.102 g, respectively), whereas root dry weight was low in the NAA1.0 treatment (0.045 g). RMC did not differ significantly among treatments.
Fresh weight, dry weight, and total relative moisture content (RMC) of P. hederaceum stem cuttings four months after exogenous auxin (IBA or NAA) and combined auxin-BA dipping treatments
Qualitative Parameters, Leaf Pigments, and Physiological Responses
Among the CIELAB color space values, L* (lightness) was relatively higher in the NAA0.5BA0.1 treatment (38.51), whereas a* (green-red opponent axis) was less negative under IBA1.0BA0.1 (−2.61) (Fig. 2). In contrast, a* values were more negative in the NAA0.5BA0.1 treatment (−5.68). Meanwhile, b* (blue-yellow opponent axis) did not differ significantly among treatments. Chlorophyll content, expressed in SPAD units, reached its highest value under the IBA0.5 treatment (29.48 SPAD units) and was comparatively lower under IBA1.0BA0.1 (26.18 SPAD units) (Fig. 3). Furthermore, the remote sensing vegetation indices anthocyanin reflectance index 2 (ARI2) and carotenoid reflectance index 2 (CRI2) were highest under IBA0.5BA0.1, with values of 1.89 and 10.19, respectively. In contrast, ARI2 values were relatively lower under NAA1.0, NAA0.5BA0.1, and NAA1.0BA0.1, ranging from 1.26 to 1.32, while CRI2 was lowest under NAA1.0 (8.22).
Commission Internationale de l’Éclairage Lab (CIELAB) color space values (L *, a *, and b *) of P. hederaceum stem cuttings four months after exogenous auxin (IBA or NAA) and combined auxin-BA dipping treatments. Values are presented as means ± standard error (SE). Statistical significance is denoted by p < .05 (*), p < .001 (***), and non-significant (NS). Bar colors indicate the measured parameters (gray: L *; dark gray: a *; and black: b *). Different lowercase letters indicate significant differences among treatments within each parameter according to Duncan’s multiple range test (DMRT) at α = 0.05; means sharing a lowercase letter are not significantly different. If no lowercase letters are shown for a parameter, no significant differences among treatments were detected.
Chlorophyll content (SPAD units), anthocyanin reflectance index 2 (ARI2), and carotenoid reflectance index 2 (CRI2) of P. hederaceum stem cuttings four months after exogenous auxin (IBA or NAA) and combined auxin-BA dipping treatments. Values are presented as means ± SE. Statistical significance is denoted by p < .05 (*) and p < .01 (**). Different lowercase letters indicate significant differences among treatments within each parameter according to DMRT at α = 0.05; means sharing a lowercase letter are not significantly different.
Normalized difference vegetation index (NDVI), an indicator of overall plant vigor, showed relatively higher values in the control, IBA0.5 and IBA0.5BA0.1 treatments (0.728–0.733), whereas lower values were observed in IBA1.0BA0.1, NAA0.5, and NAA1.0 (0.696–0.699) (Fig. 4). Modified chlorophyll absorption ratio index (MCARI), which is associated with chlorophyll content, was relatively high in the IBA1.0BA0.1 treatment (0.437). In contrast, the photochemical reflectance index (PRI), an indicator of photochemical efficiency, did not show significant differences among treatments. Structure-insensitive pigment index (SIPI), used to estimate the ratio of total carotenoids to chlorophyll, was relatively higher in the control, IBA0.5, IBA0.5BA0.1, and IBA1.0 treatments (0.792–0.797), whereas a lower value was observed under NAA1.0 (0.772). Finally, Fv/Fm (maximum quantum yield) and PIABS (performance index on an absorption basis) did not differ significantly among treatments.
Remote sensing vegetation indices and chlorophyll fluorescence parameters of P. hederaceum stem cuttings four months after exogenous auxin (IBA or NAA) and combined auxin-BA dipping treatments: (A) normalized difference vegetation index (NDVI); (B) modified chlorophyll absorption ratio index (MCARI); (C) photochemical reflectance index (PRI); (D) structure-insensitive pigment index (SIPI); (E) maximum quantum yield (Fv/Fm), and (F) performance index on an absorption basis (PIABS). Values are presented as means ± SE. Statistical significance is denoted by p < .05 (*), p < .01 (**), p < .001 (***), and non-significant (NS). Different lowercase letters indicate significant differences among treatments within each parameter according to DMRT at α = 0.05; means sharing a lowercase letter are not significantly different. If no lowercase letters are shown for an index, no significant differences among treatments were detected.
Principal Component Analysis (PCA)
Principal component analysis revealed that PC1 and PC2 accounted for 31.2% and 18.2% of the total variance, respectively, with a cumulative contribution of 49.4% (Fig. 5). Inclusion of PC3 explained an additional 10.2% of the variance, increasing the cumulative explanatory power to 59.6% (Table 5). In the correlation circle, PC1 was strongly associated with morphological and biomass-related parameters. In particular, leaf area, length, and width showed high positive loadings on PC1, and shoot dry weight, as well as shoot length and width, were also aligned in the same positive direction. In contrast, PC2 was primarily characterized by vegetation indices. SIPI, NDVI, CRI2, and ARI2 were strongly aligned in the negative direction of PC2, whereas MCARI was positioned in the opposite direction. Leaf thickness and SPAD units exhibited relatively low contributions in the PC1-PC2 plane. PC3 further explained variation through the separation of certain leaf pigment-and optical signal-related variables, including SPAD units, ARI2, and MCARI. Notably, SPAD units, which showed a relatively low contribution in the PC1-PC2 plane, exhibited a loading of -0.451 on PC3, indicating an association with its negative axis.
Principal component analysis (PCA) biplot of various parameters and indices of P. hederaceum stem cuttings after exogenous auxin and auxin-BA dipping treatments. PC1 and PC2 accounted for 31.2% and 18.2% of the variance, respectively, explaining 49.4% in total (PC1-PC2). RL: root length; RDW: root dry weight; LL: leaf length; LA: leaf area; SDW: shoot dry weight; LW: leaf width; IL: internode length; SL: shoot length; WD: shoot width; and LT: leaf thickness.
Variable loadings on principal component analysis (PCA) components (PC1–PC3)
Discussion
Stem cutting propagation is a widely utilized vegetative method for the mass production of plants across horticultural and forestry industries. However, rooting uniformity can vary depending on the type of plant growth regulators applied, environmental conditions, and the physiological status of the cuttings (Druege et al., 2019; Kim et al., 2025; Liu et al., 2025). In addition, post-establishment growth rates may also differ. Such variability can directly affect not only the uniformity of plant production but also marketability (Beruto et al., 2024), underscoring the need for experimental approaches incorporating a range of plant growth regulators.
This study investigated the effects of auxin (IBA or NAA) applied alone and in combination with BA. The results indicated that these dipping treatments did not induce significant differences in the survival and rooting rates of P. hederaceum cuttings. Similarly, Lee et al. (2024a) reported that, in P. hederaceum var. oxycardium, a botanical variety of P. hederaceum, dipping treatments with IBA and NAA did not result in significant differences in rooting rate among treatments, which is consistent with the present findings. These results suggest that endogenous hormone levels in both P. hederaceum and P. hederaceum var. oxycardium may already be sufficiently high. In addition, although auxinic rooting promoters are well established as key regulators of adventitious root formation (Da Costa et al., 2013; Tien et al., 2020), their effects extend beyond rooting rate alone (Lee et al., 2024a, 2025b; Patel et al., 2017). They may broadly affect post-rooting processes, ranging from shoot-root development and resource allocation patterns to various physiological traits (Abbas et al., 2015; Agulló-Antón et al., 2014; Štefančič et al., 2005), indicating the need for multidimensional evaluation using diverse parameters and indicators.
Overall, the IBA treatment at a specific concentration (IBA0.5) and the combined IBA-BA treatment (IBA0.5BA0.1) tended to promote shoot expansion and root elongation. In contrast, NAA treatments—particularly at the higher concentration (NAA1.0)—tended to reduce these parameters. These differences suggest that the process of adventitious root development at the nodes of P. hederaceum, as well as moisture content and resource allocation during the early rooting stage, may vary depending on the type and concentration of auxin applied (Agulló-Antón et al., 2014; Pamfil, 2011). Previous studies have reported that IBA treatment can enhance both shoot and root development (Abbas et al., 2015; Sevik and Guney, 2013; Štefančič et al., 2005), which is consistent with the tendency observed in this study for increased shoot expansion and root length. IBA is known to be converted into IAA through a peroxisome-based β-oxidation pathway inside plants, thereby providing signals necessary for rooting (Strader et al., 2010), and may therefore be relatively effective in inducing rooting in cuttings. In contrast, NAA exhibits a broad response range depending on its concentration, and this pronounced variability aligns with a previous report (Lee et al., 2025b). Notably, concentrations exceeding the optimal range appear to exert negative effects on morphological traits and biomass accumulation (Ghimire et al., 2022), consistent with earlier findings that NAA can suppress cutting growth and development (Lee et al., 2025b; Sevik and Guney, 2013; Yan et al., 2014). While higher concentrations of NAA may stimulate initial rooting induction, they may subsequently inhibit root elongation and shoot growth during subsequent developmental stages. Furthermore, high concentrations of exogenous auxin can induce ethylene production (Chae et al., 2000), and ethylene-mediated increases in abscisic acid (ABA) may trigger physiological responses such as inhibition of shoot elongation (Hansen and Grossmann, 2000). Therefore, the growth suppression and reduced biomass accumulation observed under the NAA1.0 treatment likely reflect complex hormonal interactions associated with high auxin concentrations (Muday et al., 2012), warranting further detailed investigation.
Based on the root dry weight results, the combined application of IBA and BA at a specific concentration (i.e., IBA0.5BA0.1) may exert a synergistic effect on root biomass accumulation compared with the single application of relatively high-concentration NAA, as in the NAA1.0 treatment. De Vries and Dubois (1988) previously reported that under combined IBA and BA treatments, increasing BA concentration reduced both rooting and root fresh weight, whereas low IBA concentrations enhanced shoot length, indicating potentially opposing effects. These findings highlight the importance of optimizing IBA-BA combinations. In the present study, only a single BA concentration (0.1 g· L−1) was evaluated; therefore, future studies should identify optimal auxin-BA concentration ratios.
With respect to leaf-related morphological parameters, dipping treatments had a more pronounced effect on leaf size-related traits (e.g., leaf length, width, area, and thickness) than on leaf number. This suggests that, under the conditions of this study, leaf expansion and tissue development were more responsive to the treatments than an increase in leaf number, which is supported by the findings of Sevik and Guney (2013) using IBA and NAA. Leaf area can influence transpiration and related physiological traits in cuttings, including leaf moisture content and stomatal conductance, and may have long-term effects on moisture-dependent traits such as shoot fresh weight (Aminah et al., 1997; Newton et al., 1992). Moreover, during rooting, leaf photosynthesis can enhance biomass accumulation in the stem and contribute to both root formation and post-establishment growth, as reported in a previous study (Tombesi et al., 2015). Therefore, leaf size-related parameters in P. hederaceum and related species may serve as practical indicator variables for predicting the growth potential of cuttings in future research.
In cutting propagation, rather than simple rooting success, the extent of root system formation and biomass accumulation after establishment are regarded as critical determinants of final cutting quality (Druege et al., 2019; Kadner et al., 2008). Based on biomass results, the treatments exerted relatively limited effects on shoot fresh weight, whereas significant differences were observed in root fresh and dry weights. This suggests that, at the cutting stage, shoots may exhibit short-term variability due to differences in size, moisture content, and leaf area (Ievinsh, 2023). In contrast, roots more directly reflect treatment effects through cumulative root formation and assimilate accumulation (Druege et al., 2004). Furthermore, the absence of significant differences in RMC among treatments in the present study is consistent with this interpretation and indirectly supports the observed trends. Therefore, these findings indicate that the dipping treatments applied in this study induced quality-related differences in rooted cuttings, influencing not only shoot development but also root biomass accumulation and structural stability.
For a specific combined auxin-BA dipping treatment (i.e., IBA0.5BA0.1), some positive effects were observed in leaf expansion and root biomass accumulation. Notably, these effects were expressed primarily as selective improvements in post-establishment traits rather than as increases in rooting rate. This response may be attributed to the complex interactions between auxin and cytokinin in organogenesis, development, and assimilate accumulation (Šmeringai et al., 2023). Therefore, such combined treatments should be applied strategically according to target traits and production objectives. BA is known to activate cytokinin receptor-phosphorelay signaling pathways, thereby stimulating cell division and shoot organogenesis (Hwang et al., 2012; Kieber and Schaller, 2018). However, auxin-BA combinations do not consistently produce synergistic effects on cutting growth (Li et al., 2025), as their interactions may generate contrasting or even opposing responses across rooting and shoot developmental stages, necessitating caution in combined use (Mao et al., 2019).
The CIELAB color space is utilized as a key indicator for evaluating external plant quality across various sectors of the horticulture industry (Kim et al., 2024; Lee et al., 2024b). In addition, remote sensing vegetation indices and chlorophyll fluorescence parameters also serve as useful metrics for evaluating physiological performance (Lee et al., 2025a). Integrating results from various optical and physiological indices revealed significant differences across dipping treatments in SPAD units (as an indirect proxy for chlorophyll content), some CIELAB parameters (e.g., L* and a*), and vegetation indices (e.g., ARI2, CRI2, NDVI, MCARI, and SIPI). Notably, leaf pigment-sensitive indices such as ARI2, CRI2, and SIPI were relatively higher under the IBA0.5BA0.1 treatment compared with the NAA1.0 treatment. This finding supports previous reports indicating that both auxin (Abass et al., 2024; Pourghorban et al., 2019) and BA treatments (Soltanmoradi and Sedaghathoor, 2018) can induce long-term changes in leaf pigment concentration and composition. In contrast, no significant differences were detected in PRI, Fv/Fm, or PIABS, suggesting limited long-term effects of dipping treatments on photochemical efficiency in P. hederaceum stem cuttings. However, as these measurements were conducted four months after cutting, the results should be interpreted with caution.
NDVI reached its maximum under the IBA0.5BA0.1 treatment, indicating enhanced overall plant vigor, which was consistent with the patterns observed for plant size and biomass. Conversely, under the IBA1.0BA0.1 treatment, relatively low SPAD values were accompanied by increased MCARI, suggesting an inverse relationship and implying that higher IBA-BA concentrations may reduce chlorophyll content. These findings suggest that the dipping treatment applied in this study did not induce distinct improvements or damage to the maximum efficiency of the photochemical apparatus in the long term; rather, it primarily reflected changes in chlorophyll density per unit area and optical properties. Generally, Fv/Fm values in unstressed higher plants range from 0.78 to 0.84 (Asadi-Sanam et al., 2015; Hong et al., 2025; Muniz et al., 2014). In this study, all treatments remained within the 0.787–0.795 range, indicating that no significant physiological stress was induced, regardless of the treatments applied. This response may reflect species-specific tolerance of P. hederaceum to abiotic stress, or the possibility that root system development had already progressed to a certain level, allowing the cuttings to reach a stabilized establishment phase.
PCA identified PC1 as an axis associated with morphological traits and biomass accumulation, supported by strong positive loadings for leaf area, leaf length, and leaf width, shoot dry weight, and shoot length and width. Thus, the primary variance in the dataset appears to be largely driven by the covariance structure related to morphological and biomass-related traits. In contrast, PC2 represents variation in remote sensing vegetation indices, with strong negative loadings for SIPI, NDVI, CRI2, and ARI2, indicating high collinearity among these indices. The opposing loading of MCARI suggests contrasting variations, likely stemming from differences in sensitivity and response patterns among these indices.
Morphological parameters and biomass (PC1) were nearly orthogonal to vegetation indices (PC2), indicating that these two groups of variables vary independently in the PCA space. This pattern is consistent with Lee et al. (2025a), who also reported near-orthogonality between morphological parameters and vegetation indices such as NDVI, MCARI, and SIPI. Meanwhile, leaf thickness and chlorophyll content showed significant differences across treatments but low contributions to the PC1–PC2 plane, suggesting that they are not major contributors to the primary axes (PC1–PC2) of variation. Instead, these parameters may represent independent variation associated with leaf structural properties or localized chlorophyll status. Analysis of PC3 further showed that MCARI had the largest contribution, with ARI2 loading positively, while chlorophyll content and NDVI loaded in the opposite direction. This indicates that SPAD units, which relate to chlorophyll content, are not always synchronized with leaf pigment-based vegetation indices, suggesting that decoupled variations between chlorophyll and optical signals may manifest as additional variance not fully captured by PC1 and PC2.
Overall, the evaluated dipping treatments influenced post-establishment development, biomass accumulation, and leaf optical traits more than survival or rooting rates. PCA results further suggest that treatment responses can be partitioned into distinct axes representing growth/biomass-related traits and optical/pigment-related traits.
Conclusion
Under the tested conditions, exogenous auxin (IBA or NAA) and combined auxin-BA dipping treatments did not significantly affect the survival and rooting rates of P. hederaceum stem cuttings, indicating limited effects on basic propagation success. In contrast, post-establishment morphological and biomass responses varied depending on treatment. The IBA0.5 treatment and, more notably, the IBA0.5BA0.1 treatment were associated with more favorable shoot and leaf expansion, root elongation, and root biomass accumulation, whereas the NAA1.0 treatment showed comparatively less favorable responses. These findings suggest that treatment effects in P. hederaceum were expressed more strongly through post-establishment development and biomass allocation than through increases in rooting rate. Optical and pigment-related traits, including SPAD units, certain CIELAB values (L* and a*), and several vegetation indices, also differed among treatments, whereas Fv/Fm and PIABS did not, indicating limited long-term effects on PSII efficiency under the tested conditions. PCA further supported this interpretation by showing that treatment responses were structured mainly along growth/biomass- related and optical trait-related dimensions. Overall, the results suggest that auxin type and concentration, as well as the specific combination with BA, should be selected according to production objectives and target traits. Among the tested conditions, the combined auxin-BA treatment IBA0.5BA0.1 appears to be a promising option for the propagation of P. hederaceum through stem cuttings, whereas NAA1.0 was associated with less favorable responses. Future studies should evaluate a wider range of BA concentrations, dipping times, and auxin-cytokinin combinations involving other cytokinins (e.g., kinetin or zeatin) to further optimize propagation efficiency.