rooting induction of a mature pterocarpus indicus willd

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Rooting Induction of a Mature Pterocarpus indicus Willd. Using Stem Cuttings Derived from Stump Epicormic Shoots

Albert A. Piñon*, Tomas D. Reyes Jr., Wilfredo M. Carandang, and Vida Q. Carandang

Institute of Renewable Natural Resources, College of Forestry and Natural Resources University of the Philippines Los Baños, College, Laguna 4031 Philippines

Shoots arising from the stump of a mature tree of Pterocarpus indicus Willd. were used to evaluate the within-tree variation in rooting induction. Collected rejuvenated stem cuttings were separated into three different positions (base, middle, and top) and treated with various indole butyric acid (IBA) concentrations (0, 500, and 1000 ppm). Cuttings were planted in an improvised rooting chamber for rooting induction. Results of the analysis of variance achieved non-significant effects (P > 0.05) due to IBA treatment in all rooting parameters evaluated after 33 d. In contrast, a highly significant increase in the number of roots (0.93, P = < 0.001) was detected in terms of cutting position, particularly at the middle part. Similarly, apart from callus formation (P > 0.05), significant increase in percent rooting (46.83%, P = 0.0012) and number of secondary roots (0.93, P = 0.0011) were obtained from the same position. Meanwhile, non-significant effects were also recorded in terms of IBA and cutting position interaction, except from callus formation (P = 0.036). Means separated by DMRT revealed that the interaction effect between middle position and IBA500 ppm (0.13) and those between top position and IBA1000 ppm (0.58) were significantly different. This study has proven the presence of within-stem variation; hence, rooting responses vary in cuttings collected from epicormic shoots arising from the stump of physiologically mature P. indicus.

Keywords: cutting position, epicormic shoot, Pterocarpus indicus, rooting, stump

*Corresponding Author: [email protected]

INTRODUCTIONPterocarpus indicus Willd. (narra) of the family Fabaceae is a native species in Southeast Asia, particularly in Cambodia, Malaysia, Papua New Guinea, Southern Burma, and the Philippines. Included as among the priority species in many reforestation efforts owing to its premium wood quality. P. indicus has become the primary source of raw material for the manufacturing of fine furniture, cabinetry, wood carving, and musical instruments in the country (Joker 2000; Orwa et al. 2009; ERDB 2010). Such importance of this tree species has resulted in various

studies that ranged from its biology to wood utilization (Joker 2000; Orwa et al. 2009; ERDB 2010; Mendoza et al. 2019). Research on its reproductive biology, particularly the mating system, had discovered that this tree is a prolific seeder and produces flowers annually with 1–4 seeds per fruit (Joker 2000; Flores et al. 2021). Apart from the availability of seeds in large quantity, P. indicus can grow even in highly degraded areas, hence being among the species used in many reforestations in the country (Pulhin et al. 2006).

However, parallel to the increasing demand for seedlings is the rise of mortality coupled with poor growth and survival after field planting. Despite the presence of

Philippine Journal of Science150 (5): 1089-1098, October 2021ISSN 0031 - 7683Date Received: 02 Mar 2021

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a national policy that ensures the use of high-quality planting materials for better growth and survival, the production of low-quality seedlings from seeds of unknown sources and quality remains a common practice in the country (Mercado and Duque-Piñon 2008; Gregorio et al. 2017). Such a problem intensifies, especially when seedling production relies purely on seedlings of seed origin (Linkies et al. 2010; Rao et al. 2017). That is because capturing the superior traits of the mother trees is a challenge when planting materials are produced from seed (Zobel and Talbert 2003; Wendling et al. 2014). Likewise, while vegetative propagation using juvenile cuttings from seedlings collected from identified seed sources may capture a certain degree of the donor’s tree traits, it can only be transferred completely when cuttings are collected directly from phenotypically superior mother trees (Zobel and Talbert 2003; NIFOS 2016). In this technique, the genetic blueprint of a tree with desirable traits can be multiplied unlimitedly (Saya et al. 2008; NIFOS 2016).

Numerous studies in the use of synthetic auxins, particularly IBA, and cutting positions in vegetative propagation of various forest tree species have been reported (e.g. Amri et al. 2010; Azad and Matin 2015; Frick and Strader 2018). In the Philippines, some tried the use of synthetic auxins in root induction of juvenile cuttings taken from P. indicus seedlings or saplings (e.g. Capa 2015; ERDB 2017), but none or few attempted the true-to-type cloning that uses coppice or epicormic shoots arising from a mature tree.

The benefits of true-to-type cloning in few forest tree species in the county were firstly realized with the use of exotic trees for commercial plantation such as Gmelina arborea, Acacia mangium, A. aulocarpa, and A. auriculiformis (Nuevo 2001). Unfortunately, despite the long existence of tree cloning technology, its practice and application remain juvenile with most germplasms used derived from either seedlings or young trees, particularly in the Philippines (Pollisco 2006; ERDB 2012; ERDB 2017). At that age, economically important traits (e.g. diameter and height) are not yet fully expressed; hence, taking advantage of the trees’ genetic potential is hard to realized (Zobel and Talbert 2003; Nascimento et al. 2018).

Clonal propagation using cuttings collected from an adult phenotypically superior tree has been beneficial to the wood industry (Nuevo 2001; ERDB 2012). Unfortunately, many trees are considered hard-to-root, particularly with the use of the usual vegetative propagation due to physiological aging type of phase change – a phenomenon under the environment and genetic regulation (Pijut et al. 2011; Wendling et al. 2014; Groover 2017). As such many researchers look for alternatives and discovered that epicormic shoots offer a better option as studies show high rooting success in various trees owing to cuttings’

reinvigorated quality (Wendling et al. 2014; Stuepp et al. 2014; Nascimento et al. 2018). This is because shoots arising from the stump are younger ontogenetically compared to shoots coming from the crown (Wendling et al. 2014).

Determining the genetic effect is one of the primary objectives in tree improvement (Zobel and Talbert 2003; Leakey 2004; Nasholm et al. 2014). One can manipulate the existing environment once a certain degree of certainty is established that such improvement on the subject tree is under strong genetic control, which includes the rooting of stem cuttings (Zobel and Talbert 2003; Nasholm et al. 2014). While this can be done via tree breeding using comparison field trials, recent advances in genomics and molecular analysis through identification of a certain gene (DNA marker) that is responsible for the expression of a particular trait have been made easier and more reliable nowadays (Zobel and Talbert 2003; Piñon et al. 2019; Lebedev et al. 2020). This technique can be applied in cuttings prior to rooting induction, but inherent sophistication limits its use, particularly if one is looking for a low-cost alternative.

While calculating the genetic effect is one vital aspect in tree improvement, others eliminated such effect for the attainment of best and unbiased results. Examples include the nutrients and fertilizer application studies on trees and plants that used clone materials, instead of those that originated from seeds to ensure that growth improvements are mainly affected by applied treatments rather than varying tree genotypes (e.g. Ferreira et al. 2015; de Melo et al. 2017). In fact, other studies have used a single donor plant to determine the within-tree variation, like in terms of susceptibility to insect and intra-organism rate of mutation (Low and Hanley 2012; Wang et al. 2019). Such studies have proved the importance of the use of a single genotype to come up with more reliable and credible results.

With the same objective in mind, this study was carried out primarily to determine the within-tree variation in rooting of cuttings from various positions of rejuvenated epicormic shoots collected from the stump of a mature P. indicus using IBA and a low-cost rooting chamber.

MATERIALS AND METHODS

Planting MaterialCuttings used in the experiment were collected from the shoots sprouting at the stump of a mature P. indicus tree growing within the University of the Philippines at Los Baños, Laguna (Figures 1a–c). This mother tree

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was planted in 2004 and was cut down last 2017. Stump diameter (about 47 cm) and total height (about 55 cm) were measured using a carpenter’s tape (Stanley, Tape Measure Tylon 5m). Rejuvenated stem cuttings (about 63–104 cm long) arising from the stump were collected using secateurs (Stanley, 8-inch Bypass Pruning Shears). Each stem cutting was separated into three positions such as base, middle, and top. Cutting positions were assigned starting at node 3 from the apex of the shoots as top, followed by middle and base positions sequentially down for each stem cutting. Cuttings were cut into a single node with lengths that ranged from 5–7 cm. The top position had longer cuttings due to longer internodes. After that, one-fourth of the original size of each leaf was cut to reduce water loss due to transpiration leaving 3–4 leaves per nodal cutting. Average final leaf sizes for each leaflet were 13.69 cm (base), 45.96 cm (middle), and 11.25 cm (top). Nodal cuttings were then sterilized by soaking in Dithane M-45 fungicide solution (Dow Agrosciences, USA) with six tablespoonfuls per 16 L of water for 10 min. Cuttings were bundled (24 pieces per treatment) before immersing the basal portion in 0, 500, and 1000 ppm of IBA (Consolidated Chemicals Corporation, USA) for 30 min.

Rooting ChamberAn improvised non-mist propagator was constructed based on a wooden chamber developed and used in vegetative propagation of many high-valued tropical forest tree species (Leakey et al. 1990). Details of such chamber were firstly described in the study conducted by Piñon

and Reyes (2021) in vegetative propagation of Aquilaria cumingiana. It was kept in areas away from direct sunlight and shaded with surrounding potted bamboos and other ornamental leafy plants. The daily temperature was recorded ranging from 26–30°C using a thermometer (Glass Laboratory Thermometer, 0–110 °C). Watering was applied twice daily (7:00–8:00 AM and 5:00–6:00 PM) using a two-liter hand-held mist sprayer. Rooted and unrooted cuttings were harvested 33 d after planting.

A 3 x 3 factorial experiment in a completely randomized design with two treatments was used in the study. Treatment A refers to IBA concentrations such as 0, 500, and 1000 ppm. While treatment B represents the cutting position (base, middle, and top). A total of 216 cuttings were planted wherein, eight cuttings per replicate with three replicates per treatment, and nine possible treatment combinations were used for this experiment.

Data AnalysisAssessment of the experiment was conducted after 33 d using the parameters such as percentage rooting (percentage of cuttings with roots over the total number of cuttings planted), number of roots (average number of roots observed per cutting), number of secondary roots (average number of secondary roots per cutting), and number of cuttings with callus (number of cuttings without roots but with undifferentiated cellular mass formations at the base). Cutting was considered rooted when at least one primary root > 1 mm long was observed (Amri 2010). Gathered data were encoded and organized

Figure 1. The living stump of mature P. indicus with rejuvenated epicormic shoots (a–c). Note the pronounce wider leaf surface area at the middle position (a and c).



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in the Microsoft Excel Office 365 Program. Prior to statistical analysis, data on percent rooting, the number of new shoots, and callusing were converted using the ln(x + 1) transformation, whereas the number of roots and number of secondary roots were converted by square root transformation to attain normality distribution for the analysis of variance. This was followed by post hoc test using Duncan’s multiple range test (DMRT). Statistical computation was performed using the R-Statistics (easyanova packages) software version 3.6.3 of 2020.

RESULTS AND DISCUSSION

Effect of IBA All parameters tested showed no significant effect (P > 0.05) due to the IBA treatments (Figure 2). The overall mean value obtained for the percentages of rooting that ranges from 33.33% (0 ppm) to 40.28% (1000 ppm) suggests two possibilities. On one hand, the cutting’s physiological aging – while auxin concentration and time of treatments on the other – were probably affecting the rooting. Such physiological transition from juvenility to maturity state is called “phase change” (Leakey 2004).

With epicormic shoots from the stump of a mature P. indicus treated with 0–1000 ppm IBA, results of the highest rooting percentage (about 40%) in the present study after 33 d were not far from other studies. For instance, the best rooting percentage (about 56%) was recorded from epicormic shoots collected from the

stump of Paulownia fortunei var. mikado applied with IBA (0–2000 ppm) after 60 d (Stuepp et al. 2014). With 0–300 ppm (IBA), epicormic shoots from the stump of Chrysophyllum albidum generated the highest rooting percentage of 58% after 70 d (Boateng 2014). In contrast, rooting percentage of more than 90% were commonly reported on cuttings collected from young seedlings of various dipterocarps as early as 45–100 d after planting (Patricio et al. 2006; Pollisco 2006; Cadiz et al. 2014). These observations suggest that physiological aging type of phase change does affect the rooting, where rooting percentages declined as the cutting’s physiological age progresses (Leakey 2004; Wendling et al. 2014). As such, cuttings collected from mature trees (coppice or epicormic shoots in this case) normally produce roots much longer and fewer than those collected from young seedlings. Additionally, while it appears that the present study had a relatively shorter period of rooting induction compared to other studies mentioned, rooted cuttings were still able to produce enough roots, particularly after allowing them to grow in nutrient-improved growth media (Figure 4).

The non-significant results on rooting performance of P. indicus in the present study seem consistent with other species when subjected to IBA treatment. No significant differences were also found in rooting of Bougainvillea sp. and Campomanesia aurea after soaking the base of cuttings in relatively higher IBA concentration for 5 and 7 s in 0–4000 and 0–8000 ppm, respectively (Babashpour-Asi et al. 2012; Emer et al. 2016). In contrast, significant variations in rooting percentages were recorded in Balanites aegyptiaca despite the use of relatively lower

Figure 2. Effect of IBA in rooting performance of epicormic shoots collected from the stump of mature narra tree. Error bars represent the standard error. Note the non-significant differences in all parameters tested at a 5% confidence level.



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IBA concentration (50–150 ppm) (Mukhtar 2019). In Morus alba, Sokhuma et al. (2018) also achieved a significant difference in rooting percentage with cuttings soaked in 0–3000 ppm IBA in 2 min. These implied that genetic differences may potentially affect the rooting, hence the response to auxin (IBA in this case) and time of treatment on various tree species vary from species to species, and even between provenances and clones within species (Zobel and Talbert 2003; Leakey 2004). As such, while some require a quick treatment period with low concentrations of rooting hormone, others need a longer time with a more concentrated solution (Hu et al. 2020).

Effect of Cutting PositionUnlike with IBA, a significant effect (P < 0.05) was recorded in most of the traits studied in terms of cutting position (Figures 3 and 4). Aside from callus formation (P > 0.05), averaged across treatments revealed that cuttings from middle part had greater percent rooting (45.83%, P = 0.0012) and number of secondary roots (2.11, P = 0.0011). At the same position, a significant increase in the number of roots was also recorded (0.93, P < 0.001). DMRT revealed that among such treatment positions, those cuttings taken from the top were significantly different in terms of rooting percentage and number of roots, while the middle position was significantly different in terms of the number of secondary roots (Figure 3).

It was the middle position in the present study that yielded the best results in all parameters tested except on callus formation, which contrasts with other studies. For instance, best-rooting performance was found in cuttings taken from

base for Dalbergia melanoxylon, Argania spinosa, and Antidesma bunius (Amri et al. 2010; Benbya et al. 2018; Totaan 2019) and from the top for Afzelia rhomboidea (Benabise 2012) and Stevia rebaudiana (Pigatto et al. 2020). Such improvement in rooting success at the basal position was due to an established positive correlation between the increasing diameter of cuttings with increased carbohydrates reserves (Amri et al. 2010), while to a low level of phenolic compounds and higher concentration of naturally occurring auxin in the apex for the top position (Hartmann et al. 2010). Apparently, higher leaf areas in the middle position in the present study helped maintain an increased concentration of carbohydrates in the stem during rooting induction (Caplan et al. 2018). Others, however, believed that variations to rooting due to cutting position are basically physiological and anatomical in nature. Accordingly, cuttings taken from various positions are influenced by leaf water potential, leaf age, stomatal distribution, and stem diameter, among others (Hartmann et al. 2010; Dick et al. 2004). The hastened rooting with increased leaf area has been documented in many tree species (Solis et al. 2017; Caplan et al. 2018; Mbibong et al. 2019). Meanwhile, similar with T. scleroxylon, Dalbergia melanoxylon, and A. spinosa (Dick et al. 2004; Amri et al. 2010; Benbya et al. 2018), the consistent lowest rooting ability for all parameters tested in cuttings from the top position is probably either due to low water retention with increasing susceptibility to water stress in cuttings or apical dominance that negates the rooting (Leakey 1983; Totaan 2019).

Figure 3. Effect of cutting position on rooting performance of epicormic shoots from the stump of mature P. indicus. Error bars represent the standard error. Means followed by the same letter(s) are not significantly different at the 5% level according to DMRT.



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IBA and Cutting Position Interaction EffectMost tested parameters except on callus formation (P = 0.036) were non-significant (P > 0.05) in terms of interactive effect between cutting position and IBA treatment (Table 1). Means separation by DMRT showed a significant increase in callus formation in cuttings from middle and top positions treated with IBA at 500 and

1000 ppm, respectively. This suggested that callusing is hastened with increasing leaf areas and higher IBA concentration.

Similar results have also been reported from previous studies on the effect of IBA and cutting position on rooting and callusing in various trees (Benabise

Figure 4. Samples of newly rooted cuttings of P. indicus from various positions such as top (a–b), middle (c–d), and base (e–f) with three randomly selected rooted cuttings visually checked after a year (g–i). Note the pronounced newly induced rooted cuttings taken from the middle part (c–d) compared to other positions.



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2012; Pigatto et al. 2020). Although callusing may be considered as a precursor for rooting (Ikeuchi et al. 2013), it does not always true in other species. For instance, callusing has been found to negatively affect the rooting of Cunninghamia lanceolata since hormone application promotes extensive callusing that seemingly preventing the rooting, especially when used cutting from a mature donor plant (Zhou et al. 2018). This implies that optimization or perhaps low concentrations of exogenous auxins should be applied, especially when using mature cuttings.

CONCLUSION AND RECOMMENDATIONThis study proved the presence of within-tree variation in epicormic shoots arising from the stump of a mature P. indicus. The non-significant effect was obtained in the IBA application, although it slightly improved the rooting percentages of cuttings, while significant effects were detected due to cutting position at the middle position in percent rooting, the number of secondary roots, and the number of roots. Hence, cuttings from such positions are recommended to be used in mass propagation, especially

when using epicormic shoots from a mature P. indicus. Finally, apart from an increase in rooting, the use of IBA and cuttings (middle position) with wider leaf surface area could potentially improve the callusing, which may influence rooting. As such, rooting hormone optimization with a wider IBA concentration range is suggested to be conducted in a future study to determine the ideal auxin treatment, particularly when using mature stem cuttings. It is important, especially since higher IBA concentration could also lead to extensive callusing, which may even reduce the rooting potential.

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Table 1. Interaction effect of different IBA concentrations and cutting positions (CP) on rooting performance of epicormic shoots collected from the stump of mature P. indicus. Root traits tested include percent rooting (PR), number of roots (NR), number of secondary roots (NSR), and cuttings with callus formation (Cal). Error bars represent the standard error. Means followed by the same letter(s) are not significantly different at the 5% level according to DMRT.

CP/IBA PR NR NSR Cal

Base

0 ppm 33.33 0.58 0.46 0.29a

500 ppm 37.50 0.79 0.38 0.33b

1000 ppm 41.67 0.92 1.46 0.29a

Middle

0 ppm 58.33 1.13 2.17 0.42a

500 ppm 25.00 0.50 0.96 0.58a

1000 ppm 54.17 1.17 3.21 0.13b

Top

0 ppm 8.33 0.13 0.17 0.42a

500 ppm 20.83 0.38 0.58 0.46a

1000 ppm 25.00 0.42 0.21 0.58a

Significance ns ns ns *

*Significantly different



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