Introduction
The porcelain berry belongs to the family Vitaceae and the genus Ampelopsis. Porcelain berries grow naturally in South Korea and Japan. It is a wild resource that has been traditionally used as herbal folk medicine to treat liver diseases. Many researchers have reported that porcelain berry extracts can be used to treat liver diseases and inflammation. Ethanol extracts (95%) of Ampelopsisbrevipedunculata showed high performance in terms of anti-oxidative capacity and reduced food-borne pathogenic bacteria (Choi and Rhim 2010; Rhim and Choi 2010; Yabe et al. 1998). Since the raw fruit of porcelain berry is inedible, early researchers focused mainly on its extracts than on the cultivation method. Porcelain berry, which is a native resource of the Korean peninsula, has seldom been investigated.
The cutting propagation method is applied to various horticultural crops, especially woody plants. Usually, hardwood cuttings are used for woody plant propagation, but sometimes softwood cuttings are used for rapid propagation of certain species. Generally, a mist or fog system and shading are essential to avoid dehydration and increase of temperatures during cutting propagation.
There is a difference in the success ratio of rooting and surv iv al d epending o n the state of t he b ranch at t he t ime of propagation; therefore, the selection of healthy cuttings is important. Many studies show that the stem diameter of a cutting is closely related to the rooting ratio. In the case of peach trees, rooting ratio was reported to decrease as the stem diameter of the cuttings increased (Lim et al. 1996). On the contrary, according to a study conducted by Jung et al. (2008), rooting of blueberry semi-hardwood cuttings increased with stem diameter.
Plant growth regulators are also important, and their effects have been studied on the rooting of apple tree rootstocks (Kang et al. 2001) and hardwood peach tree cuttings (Lim et al. 1996). In Actinidia, hardwood cuttings treated with auxin PGRs, such as indole-3-butyric acid (IBA), rooted easily (Kwack et al. 2010). Furthermore, many studies have been conducted on the use of various types of auxin-like PGRs, i.e., horticultural crops as well as various other plants such as Phragmites australis (Hong and Kim 2013), Acer mono (Kim et al. 2013), Prunus yedoensis (Kim and Kim 2012), and Acanthopanax senticosus (Kim et al. 2000). In case of Acer mono (Kim et al. 2013), 100 mg·L-1 of IBA treatment showed the high rooting ratio, and Prunus yedoensis (Kim and Kim 2012) cuttings treaeted with IBA 1,000 mg·L-1 showed 90.8% rooting ratio, and in Acanthopanax senticosus (Kim et al. 2000) cuttings shown the highest number of roots in Rooton treatment grown on mixed with v ermiculite a nd p erlite ( 1:1, v /v ).
The selection of substrate is important for the survival ratio of cuttings. The propagation medium must have adequate moisture to prevent excessive dehydration of the cuttings, as well as prevent decay due to high levels of humidity. In the case of roses, a mixed medium consisting of granular rockwool and peat moss (1:1, v/v) propagated by on the propagation bed with fog (200 sec./5 min.) showed high the rooting ratio and growth (Jeong et al. 2007). It has also been reported that chrysanthemum cuttings rooted well in a perlite and perlite + peat moss (3:1, v/v) mixed medium (Oh et al. 1996). However, it was reported that Vaccinium vitis-idaea L. cuttings showed better rooting in the control group in kanumatsuchi medium, which is kind of volcanic eruption, without PGRs (Choi et al. 2016).
Many researchers have shown that the optimum conditions for cutting propagation vary among plants; consequently, it is necessary to determine the optimal cutting conditions for each plant. Therefore, the objectives of this study were to determine the effects of stem diameter, rooting medium, and IBA concentration on the rooting of hardwood cuttings of Ampelopsisbrevipedunculata (Maxim.) Trautv .
Materials and Methods
Plant materials
Ampelopsisbrevipedunculata ( Maxim.) Trautv . cutting materials were collected from Jeju Island in Korea on April 20, 2017 by National Institute of Biological Resources (NIBR) and were transferred to Gyeongsang National University for experimental purposes. The cutting materials were stored for 6 days in a refrigerator maintained at 90% RH and 4℃. For the experiments 1 and 3, commercial propagation medium (Tosilee Medium, Shinan Gro, Jinju, Korea) was filled in a 72-cell plug tray (Horticultural model, 72 squared cells/tray, Famwin Co., Jeongeup, Korea), after which the materials were stuck. In all experiments, the cuttings were stuck at a depth of 2 cm and were maintained at a 45° angle. After planting in the medium, planted cuttings were placed on a bench in a controlled environment with an intermittent fog system; approximately 95% of natural sunlight was shaded, and RH and temperature were maintained at 95±5% and 23±5℃, respectively. Sixteen days after sticking, the trays were moved out from the fog bench. After confirming that the root system was approximately 1 mm or longer, the planted samples were transferred to a bench in the glasshouse of Gyeongsang National University. After the transfer, a greenhouse multipurpose nutrient solution [in mg·L−1 Ca(NO3)2·4H2O 737.0, KNO3 343.4, KH2PO4 163.2, K2SO4 43.5, MgSO4·H2O 246.0, NH4NO3 80.0, Fe-EDTA 15.0, H3BO3 1.40, NaMoO4·2H2O 0.12, MnSO4·4H2O 2.10, and ZnSO4·7H2O 0.44 (electrical conductivity 0.8 mS·cm−1)] w as p rov ided daily for a two weeks period.
Experiment 1. Effect of cutting diameter on the rooting of hardwood cuttings of A. brevipedunculata
The diameter of A. brevipedunculata cuttings was measured using a vernier caliper (CD-20CPX, Mitutoyo Korea Co., Gunpo, Korea) 5 mm below the bud. A. brevipedunculata cuttings were divided as follows based on diameter measured 5 mm above the bud: less than or equal to 4.5 mm, greater than 4.5 mm but less than 6.5 mm, and equal to or greater than 6.5 mm.
Experiment 2. Effect of rooting medium on the rooting of hardwood cuttings of A. brevipedunculata
In the 2nd and 3rd experiments, only cuttings with a diameter greater than 4.5 mm were used. Four different types of rooting medium were tested (rockwool cube, perlite, 3 :1 v /v mixture o f peat m oss and perlite, a nd vermiculite). Plug trays (Horticultural model, 72 squared cells/tray, Famwim Co., Jeongeup, Korea) were filled with the various media, and sufficient water was added.
Experiment 3. Effect of IBA concentration on the rooting of hardwood cuttings of A. brevipedunculata
Four IBA concentrations were used (0, 100, 200, or 400 mg·L-1). Only cuttings with a diameter greater than 4.5 mm were used. Cuttings were dipped for 30 seconds at a time and were then planted in each medium.
Growth measurements of cuttings
To investigate the rooting and growth patterns in each experiment, growth parameters were measured on the 28th day after sticking. Ten cuttings from among the newly emerged shoots after sticking were selected based on the measured shoot length and diameter.
Statistical analysis
A randomized complete block design with 3 replicates of 24 plants each was used in this experiment. Data were analyzed and compared using SAS 9.1 (SAS institute, Inc., Cary, NC, USA). Differences among the treatment means were estimated by Tukey’s test at P ≤ 0.05.
Results
Experiment 1. Effect of cutting diameter on the rooting of hardwood cuttings of A. brevipedunculata
The growth of the shoots of rooted cuttings differed significantly among the cuttings with different stem diameters. As the diameter of the cuttings increased, the length of the new shoots increased significantly, and the longest shoot length (67.8 mm) was measured on cuttings with a diameter equal to or greater than 6.5 mm (Fig. 1). The shoot lengths of the treatments with diameters greater than 4.5 mm but less than 6.5 mm and less than or equal to 4.5 mm were 45.7 and 27.5 mm, respectively. Additionally, as the diameter of the cuttings increased, the diameter of the shoots increased significantly. The maximum diameter of shoots from cuttings with a diameter equal to or greater than 6.5 mm was 2.59 mm, compared with 2.31 mm (diameter greater than 4.5 mm but less than 6.5 mm) and 1.98 mm (less than or equal to 4.5 mm).
In experiment 1, 8.33% of rooting ratio shown in the less than or equal to 4.5 mm cuttings, and 6.94% of rooting ratio shown in the greater than 4.5 mm but less than 6.5 mm cuttings at 1 month after sticking (Fig. 3). The highest number of rooted cuttings was 6, in the less than or equal to 4.5 mm class, while 5 cuttings rooted in the diameter class that was greater than 4.5 mm but less than 6.5 mm. No rooting was observed on cuttings with a diameter equal to or greater than 6.5 mm. The number of roots on cuttings with a diameter less than or equal to 4.5 mm was 3.5 mm, which was significantly lower than that (18.8 mm) observed for cuttings with a diameter greater than 4.5 mm but less than 6.5 mm. However, no significant differences were observed with respect to the length of the longest root (Fig. 2). Fig. 4-Fig. 5
Experiment 2. Effect of rooting medium on the rooting of hardwood cuttings of A. brevipedunculata
There was no significant difference in the shoot length of rooted cuttings among the different treatments. The shoot length, i.e., 42.6 mm, was measured in the mixed peat moss and perlite treatment, followed by the perlite and vermiculite treatments, i.e., 42.5 mm and 40.5 mm, respectively. The lowest shoot length was observed in the rockwool cube treatment.
In Experiment 2, 2.78% of rooting ratio shown in the rockwool medium treatment, 2.78% of rooting ratio shown in the vermiculite treatment, and 1.39% of rooting ratio shown in the mixed peat moss and perlite treatment at 1 month after sticking (Fig. 6). No rooting was observed in the perlite treatment, whereas 2 cuttings produced roots in both the rockwool cube and the mixture with peat moss and perlite (3:1, v/v), and 1 cutting produced roots in the vermiculite treatment. The number of roots was 1.5 and 4 in the rockwool cube and perlite + peat moss (3:1, v/v) mixed medium, respectively, and 2 in the vermiculite treatment. The root length was 5.46 mm in the rockwool cube, 9.96 mm in the perlite + peat moss (3:1, v/v) mixed medium, and 8.52 mm in the vermiculite treatment.
Experiment 3. Effect of IBA concentration on the rooting of hardwood cuttings of A. brevipedunculata
No significant difference was observed in the shoot growth of the cuttings in response to IBA concentration (Fig. 7). The shoot lengths were 112.4 mm in the control, 92.8 mm at a concentration of 200 mg·L-1, 76.7 mm at 100 mg·L-1, and 38.5 mm at 400 mg·L-1. The lowest new shoot diameter was observed in response to 400 mg·L-1, i.e., 2.26 mm, whereas the largest shoot diameter was measured in the control (2.50 mm); however, there was no significant difference between the treatments.
Discussion
Experiment 1. Effect of cutting diameter on the rooting of hardwood cuttings of A. brevipedunculata
Shoot growth in thicker cuttings were better than that in thinner cuttings (Fig. 1). In Chrysanthemum ‘Baekma’ (Yoo and Roh 2012) and ‘Shinma’ (Yoo et al. 2007), better shoot growth corresponded to a higher diameter of cuttings. Many other studies on Chrysanthemum reported similar results. Thus, it is considered that the growth of shoots by cuttings is different depending on plant species or specific environmental conditions.
In A. brevipedunculata, a high diameter of the cuttings resulted in a low rooting ratio, especially for cuttings with a diameter equal to or greater than 6.5 mm, which did not root ( Fig. 2 ). This result i s similar to t hose of prev ious studies (Jeong et al. 2007; Lim et al. 1996). Previous studies reported that the larger the diameter of the cuttings, the greater the carbohydrate content in the stem, which is used to induce rooting (Veierskow 1988; Yoo and Roh 2012). However, in the case of Lycium chinese Mill., cuttings with a greater diameter exhibited better rooting than thinner cuttings (Lee et al. 1996). According to previous studies, rooting and root growth based on the cutting diameter will vary between species.
Experiment 2. Effect of rooting medium on the rooting of hardwood cuttings of A. brevipedunculata
In experiment 2, there was no significant difference in the shoot length, but diameter of newly shoot growth on vermiculate medium was higher than other treatments (Fig. 4). The best rooting of cuttings of the grapevine rootstock ‘Teleki 5BB’ w as o bserv ed i n perlite, w hereas the w orst root growth occurred in a mixed medium consisting of coarse s oil and fermented compost at a r atio o f 1:1, v /v (Lim et al. 1999). In the case of roses, it was reported that growth was generally good in a mixed medium consisting of granular rockwool and peat moss at a ratio of 1:1, v/v (Jeong et al. 2007). In addition, kanumatsuchi medium resulted in the best rooting of Vaccinium vitis-idaea L. cuttings (Choi et al. 2016). It is generally known that the use of a peat moss-based medium is suitable for blueberries, as the pH is less than 5.0. However, according to Schute and Hancock’s report, different media are required for each cultivar (Schute and Hancock 1983). But in this study, root development was no significant difference by propagation medium (Fig. 5). Therefore, the selection of a medium suitable for rooting and root growth of A. brevipedunculata can only be concluded after further detailed studies.
Experiment 3. Effect of IBA concentration on the rooting of hardwood cuttings of A. brevipedunculata
In experiment 3, no effects of rooting acceleration were observed in A. brevipedunculata using the instant immersion method. In white Forsythia cuttings, it has been reported that immersion treatment for 1 minute in an auxin solution d id n ot h av e any significant effect a t a concentration below 1,000 mg·L-1 (Yoo and Kim 1997). In addition, 1,500 mg·L-1 of IAA showed good results with respect to the rooting ratio and seedling quality of Stephanandra incisa Zabel (Yoo et al. 2016). Based on these previous studies, it seems to be effective to immerse the cuttings in a high concentration of auxin solution for more than 30 minutes. However, the rooting of Crassula cuttings showed good results after immersion for only 5 seconds at a low concentration of IBA, i.e., 50 mg·L-1. Thus, the response to auxin appears to vary among species. In this experiment, rooting was not effective, even at 400 mg·L-1 IBA for 30 seconds, indicating that immersion treatment for longer than 30 minutes or using an auxin concentration higher than 400 mg·L-1 may be more effective. Therefore, further study on appropriate auxin treatment for cutting propagation of A. brevipedunculata plants is required.
Conclusion
The results indicate that a greater cutting diameter was advantageous to shoot growth but did not promote rooting. The highest number of treated cuttings that rooted had a diameter less than or equal to 4.5 mm. The lowest shoot growth occurred in the rockwool cube. The cuttings that were p lanted i n perlite appeared t o hav e the lowest r oot growth. In the case of Actinidia, it was reported that a mixture of sand and vermiculite at a 1:1 (v/v) ratio would be more efficient than perlite only, considering the amount of rooting, the acclimatization ratio and the working efficiency (Kwack et al. 2010). Thus, further investigation is needed on the various types and ratios of mixed media. In blueberries, immersion treatment using an IBA concentration higher than 50 mg·L-1 had negative effects on the shoot growth of the cuttings, and the 100 mg·L-1 treatment significantly reduced the development of the root ball (Lee and Lee, 2008). The results of this study are similar to those of a previous study, i.e., compared with softwood cuttings, the effect of IBA treatment on hardwood cuttings is unclear (Eck and Childers 1989). However, in previous studies such as those conducted on apple trees (Kang et al. 2001) and white Forsythia (Yoo and Kim 1997), it was reported that auxin treatment at a concentration higher than 1,000 mg·L-1 was very effective. Therefore, further research is required to determine the optimal concentrations and immersion times of plant growth regulators to promote root emergence.
