Introduction

The World Health Organization (WHO) has emphasized the importance of the traditional indigenous medicines, since majority of rural people in the developing countries still use these medicines as the first defense in health care (Goleniowski et al., 2006). There are about 4,200 plant species growing wild in Korea, and about 1,000 of them are cultivated and used as medicinal plants which have medical effects on human bodies to some extents (Rural Development Administration, 2011).

The P. frutescens has been used as an important traditional herbal medicine for treating various diseases including depression, anxiety, tumor, cough, antioxidant, allergy, intoxication, and some intestinal disorders (Ha et al., 2012; Makino et al., 2003; Yang et al., 2012) in East Asian countries such as Korea, China, and Japan. Sophora is a genus of the Fabaceae family, and contains about 52 species, nineteen varieties and seven forms (Krishna et al., 2012). They are widespread in warm and dry habitats, including Asia, North and South Americas, and New Zealand (Jana et al., 2013; Lai et al., 2003). The root of A. gigas Nakai (Umbelliferae), popularly known as Korean “Dang Gui”, has been used to treat female afflictions and anemia in traditional oriental herbal medicine since ancient times in Korea (Konoshima et al., 1968; Son et al., 2010).

However, if weather condition is not suited for cultivation of medicinal plants, it will bring about difficultly in cultivation and problems of having low contents of medicinal properties. Another issue is not sufficient supply of these herbal materials to meet the steadily increasing demand. Therefore, it is necessary to have a mass production system be established to solve such problems as lack of stable supplies, dis- proportional contents of medicinal properties, and safety issues caused by uncertain sources.

Plug seedling production technology was introduced to Korea in the early 1990s and has been widely used in recent years especially for vegetable crops because it saves labor for raising seedlings, facilitates mass production of uniform seedlings, and allows division of production labor (Jeong, 1998, 2000). The advantages of using quality transplants include: (1) higher quality and yield; (2) greater uniformity; (3) reduction of the growers’ propagation cost of producing their own transplants, and thus (4) reduction of the overall cost for the plant production (Jeong, 1998, 2000). Many commercial transplant producers tend to choose more cells per tray (smaller cell sizes) to increase the number of plants produced, and to reduce transplant production space (Vavrina, 1995). This also reduces propagation cost per plant, since production costs are directly related to container size and type (Dufault and Waters, Jr., 1985).

With such advantages as year-round production, seed saving, fast growth, and feasibility of producing uniform seedlings, utilizing the plug seedling production system is expected to meet the need for stable supply of propagated seedlings to the growers and hence, demand for mass production of medicinal plants in the country. Domestic plug seedling system has been used mainly in wide ranges of seed-propagated vegetables and growers to facilitate seedling supply to growers. Improved standard of living of citizens and increased level of interest toward health caused increasing demand for medicinal plants. Thus, more research is needed to establish a plug seedling production system for medicinal plants for the stable supply of medicinal plants. The objective of this study was to investigate the effect of cell size on the growth and development of plug seedlings to provide a guideline for production of plug seedlings to be supplied to growers of most commonly grown traditional medicinal plant species.

Materials and Methods

Three indigenous medicinal plant species were used. Seeds of Perilla frutescens var. acuta Kudo were collected from Gyeongsangnam-do Agricultural Resources Management Institute, Miryang, Korea in April 2011. And seeds of Sophora tonkinensis and Angelica gigas Nakai were collected from a medicinal crop farm, Sancheong, Korea in Nov. 2011. Seeds of P. frutescens var. acuta Kudo, S. tonkinensis, and A. gigas Nakai were sown in either 128, 200 or 288-cell plug trays, containing a commercial medium (Tosilee Medium, Shinan Grow Co., Jinju, Korea), on Apr. 21, Apr. 13, and Sep. 8, 2012, respectively.

The experiment was carried out in a glasshouse at Gyeongsang National University. The volume of each cell in 128, 200, and 288 plug cell trays were 23.3, 11.4, and 7.6cm², respectively. Seedlings were fed with a nutrient solution [containing in mg·L⁻¹ 436.6 Ca(NO₃)·4H₂O, 232.3 KNO₃, 272.0 KH₂PO₄, 209.1 MgSO₄·7H₂O, 80.0 NH₄NO₃, 15.0 Fe-EDTA, 17.4 K₂SO₄, 1.4 H₃BO₃, 0.2 CuSO₄·5H₂O, 2.1 MnSO₄·4H₂O, 0.12 NaMoO₄·2H₂O, 0.8 ZnSO₄·7H₂O] with pH 5.96 and EC 1.2-1.6mS·cm⁻¹ once a day. Plants were grown with RH and temperature of the glasshouse air of 70% and 18-25°C, respectively.

The growth of seedlings of P. frutescens var. acuta Kudo, S. tonkinensis, and A. gigas Nakai were measured at 45, 53, and 75 days after sowing, respectively when the seedlings filled the plug trays. Growth parameters measured were plant height, length of the longest root, stem diameter, leaf length, leaf width, leaf area, internode length, no. of leaves, fresh weight, dry weight, total chlorophyll and anthocyanin contents, and root ball formation. Internode length was measured at the closest node to the top with the full-grown leaf. Dry weight was measured after drying the plant for 72h in a dry oven (JSOF-150, JSR Micro, Gongju, Korea) at 70°C. Total chlorophyll content was estimated by grinding 10mg of fresh leaf sample in 1 mL of 80% acetone, and filtered using Whatman #1 filter paper and brought up to 10mL using the same solution. The absorbance of the extracted solution was recorded at 663 and 645 nm, and contents of total chlorophyll were calculated according to the method described by Dere et al. (1998). Anthocyanin content was measured using the method described by Fuleki and Francis (1968). Root ball formation was rated on a 1 to 5 scale, where 1 being the worst and 5 being the best.

The experiment was carried out in 3 replicates per treatment in a completely randomized design. Data collected were analyzed for statistical significance with the SAS (Statistical Analysis System, V. 9.1, Cary, NC, USA) program. The experimental results were subjected to an analysis of variance (ANOVA) and Duncan’s multiple range tests at 5%.

Results and Discussion

Percent seed germination of P. frutescens var. acuta Kudo taken after 7 days in 128, 200, and 288-cell trays was 78, 85, and 84%, respectively. Twenty days after sowing, leaf began to change its color from green to purple. Growth of the shoot and the root in the 128-cell trays observed just prior to transplanting was better than that in other treatments (Fig. 1). Quality characteristics of plug seedlings of P. frutescens var. acuta Kudo as affected by plug cell size are shown in Table 1. The growth of seedlings of P. frutescens var. acuta Kudo was measured at 45 day after sowing. Overall shoot and root growth, except total chlorophyll and anthocyanin contents, were the greatest in the 128-cell tray. Similar results were reported by Cantliffe (1993) that as container size increases the leaf area, and shoot and root biomass increase. However, length of the longest root, leaf length, width and area, internode length, root fresh weight, and root ball formation in the 200 and 288-cell trays were not significantly different each other. Therefore, it would be more economical to use the 288-cell trays than 200-cell trays. However, to prevent leaf rolling problems in the 288-cell trays caused by high planting density, it would be desirable to transplant seedlings earlier than 45 days after sowing in 288-cell trays.

Fig. 1.

Effect of plug cell size on shoot and root growth of three indigenous medicinal plant species: A, P. frutescens var. acuta Kudo; B, S. tonkinensis; and C, A. gigas Nakai.

Root growth of S. tonkinensis was obviously greater in the 128-cell trays than other cell sizes (Fig. 1). Shoot and root growth in the 128-cell trays observed just prior to transplanting was greater than that in other treatments. Green color of the mature leaves was deeper than the newly-formed young leaves. Quality characteristics of plug seedlings of S. tonkinensis measured at 53 day after sowing as affected by plug cell size are shown in Table 2. Overall shoot and root growth, except length of the longest root, stem diameter, leaf width and area, shoot fresh weight, and root ball formation, was not significantly affected by the plug cell size. Length of the longest root and root ball formation were the greatest in the 128-cell trays, indicating potential benefits of larger volume cell trays for production of medicinal plant species for the root is used for medicinal purpose. The greatest biomass of the seedlings gained in a plug tray was obtained in the 288-cell trays in Sophora tonkinensis. Shoot growth was greatly impacted by container size and root restriction. Effect of container size and root restriction on leaf growth was documented for bell pepper (NeSmith et al., 1992; Weston, 1988), marigold (Latimer, 1991), euonymus (Dubik et al., 1992), soybean (Krizek et al., 1985), cabbage (Csizinszky and Schuster, 1993), tomato (Weston and Zandstra, 1986), watermelon (Liu and Latimer, 1995), and salvia (van Iersel, 1997). Generally, larger container volumes have greater water and nutrients availability, along with more space for root development (McConnughay and Bazzar, 1991). Hall (1989) also noted that the rate of vine growth of watermelon was greater in plants grown in larger cells than in smaller ones once transplanted to the field. Shoot height and biomass reduction in small containers have been reported for tomato (Peterson et al., 1991), marigold (Latimer, 1991), muskmelon (Maynard et al., 1996), and watermelon (Hall, 1989; Liu and Latimer, 1995).

Root growth of A. gigas Nakai measured at 75 days after sowing was the greatest in the 128-cell trays. Shoot and root growth in the 128-cell trays observed just prior to transplanting was better than that in other treatments (Fig. 1). Quality characteristics of plug seedlings of A. gigas Nakai measured at 75 day after sowing as affected by plug cell size are shown in Table 3. Overall shoot and root growth, except total chlorophyll content, was the greatest in the 128-cell trays. However, length of the longest root, stem diameter, no. of leaves, and shoot and root fresh weights in the 200 and 288-cell trays were not significantly different each other. Total biomass of the shoot and root was the greatest in 200- cell trays (9,340g), followed by 288-cell trays (8,985.6g), and 128-cell trays (7,475.2g). Therefore, it would be more economical to use the 200-cell trays than 128-cell trays. Plants grown in small cells are less expensive to produce than those in large cells because less greenhouse space is required for each plant (Weston and Zandstra, 1986).

In conclusion, based on the total biomass, it is concluded that 288-cell trays are recommended for production of plug seedlings of medicinal plant species P. frutescens var. acuta Kudo and S. tonkinensis. In A. gigas Nakai, it would be more economical to use the 200-cell trays than 128-cell trays due to total biomass.