Introduction
Spathiphyllum wallisii Hort. is an evergreen herbaceous plant belonging to the Araceae family. The species is distributed in Central America and Southeast Asia. It is used as an indoor ornamental plant in Korea, and its glossy evergreen leaves are highly ornamental. Its flowers resemble those of the calla (Zantedeschia aethiopica L.), also a member of the Araceae family. Both leaves and flowers have an ornamental value for a pot plant. The inflorescence of the Araceae family are called spadix, surrounded by bract called spathe. The ornamental value of the S. wallisii Hort. depends on the presence or absence of flowers (Chen et al., 2005). Recently, it has been reported that S. wallisii Hort. is effective in purifying indoor air by absorbing pollutants such as benzene and formaldehyde (Kakoei and Salehi, 2013).
Plant growth regulators are substances synthesized within plants. They promote physiological and morphological functions of plants. Cytokinins promote cell division and the development of apical and lateral buds (Kieber and Schaller, 2018). Gibberellins play a critical role in seed germination, stem elongation, and cell elongation (Rademacher, 1993;Hooley, 1994;Kende and Zeevaart, 1997). They are known to promote flower bud differentiation and flowering in some seed plants (Ruth et al., 1992). Furthermore, gibberellin treatment has been reported to promote flower bud differentiation and flowering in long-day plants requiring a period of low temperature for flowering such as Hyoscymus niger L., but not in short-day plants such as Glycine max L. (Anton, 1957).
When using plants for pot plant, plants that are excessively higher compared to the pot pose a risk of lodging and have low ornamental value. Therefore, smaller plants with numerous branches are preferred for pot plants. Studies have attempted to enhance the ornamental value of pot plants by using plant growth regulators to control plant height, promote branching, and induce flowering. BA treatment to promote branching in Euphorbia pulcherrima Willd. and Ardisia pusilla (Lee, 2005;Semeniuk and Griesbach, 1985), BA treatment to induce flowering in Cymbidium encifolium (Lee et al., 1998), and paclobutrazol treatment to suppress plant height in Kalanchoe blossfeldiana Poelln. (Kim et al., 2021) have been conducted.
Therefore, this study was conducted to develop a plant growth regulator treatment method to enhance the ornamental value of S. wallisii Hort. as a pot plant.
Materials and Methods
Plant materials
The experiment was conducted in the greenhouse of Chungcheongbuk-do Agricultural Research and Extension Services (N36°72′64″, E127°46′60″) located in Cheongju city, Chungcheongbuk-do province. Spathiphyllum wallisii Hort. used in the experiment were purchased in April 2018. Plant with 20~25 cm in height and with approximately 30 leaves were transplanted into pot with an upper diameter of 15 cm filled with horticultural growing media (Shinsung Mineral Co. Ltd., Korea). S. wallisii Hort. were cultivated in a double layered greenhouse for 90 days from April to July 2018.
Plant growth regulator treatment
Two types of plant growth regulators, BA (MBcell, Korea) and GA3 (MBcell, Korea), were treated as single or mixed agents. The concentrations of plant growth regulators were 300, 500, and 1,000 mg‧L-1. After transplanting, foliar applications of 20~30 ml of plant growth regulator per plant were treated twice at 1 week interval. The experiment was designed for completely randomized block with 3 replications and each treatment consisted of 15 plants.
Growth characteristic research
Plant height, leaf length, leaf width, number of leaves, number of tillers, SPAD value, flower number, and abnormal flower number were measured. Plant height was measured from the media surface to the highest point of the plant. Leaf length was measured as the length of the leaf lamina excluding the petiole. Leaf width was measured as the widest width of the leaf lamina. Number of leaves was measured based on the number of fully spread out leaves per plant. Number of tillers was measured by determining the part of the growing point where new leaves developed. SPAD value was measured using a portable SPAD meter (JP/SPAD-502, Konica Minolta, Japan). Flower number was measured as flower stalks emerged per plant. Abnormal flower number was measured per plant of flowers in which the spathe was not normally colored in white.
Statistical analysis
Statistical analysis was performed using CoStat (CoHort software, version 6.45, USA) program, Duncan’s multiple range test at a 5% significance level, and analysis of variance.
Results and Discussions
Growth characteristic
When plant growth regulator BA treated, plant height of S. wallisii Hort. tended to increase by BA treatment (Table 1). At control, the plant height was 31.8 cm. The plant height increased to 35.0~35.9 cm at BA treatment. Leaf length and leaf width were 20.1~21.3 cm and 8.0~8.9 cm with no statistical difference between control and BA treatments. The number of leaves ranged from 40.3 to 47.1, with no statistical difference among treatments. The number of tillers ranged from 11.0 to 12.8, and SPAD value also ranged from 55.5 to 54.6, without significance among treatments.
Plant height increased in proportion to GA3 concentration (Table 2). The average plant height was 31.8 cm at control, 33.0 cm at GA3 300 mg‧L-1 treatment, 36.8 cm at GA3 500 mg‧L-1 treatment, and 37.7 cm at GA3 1,000 mg‧L-1 treatment respectively. Leaf length was also found to be longer in the GA3 treatment. It was 20.1 cm at control and 21.2~22.3 cm at GA3 treatment. The leaves were observed to be more erect at GA3 treatment than control (Fig. 2). Leaf width was not different among treatments. The number of leaves per plant significantly decreased at GA3 treatment of 500 mg‧L-1 and 1,000 mg‧L-1 compared to control. Number of leaves per plant was 44.9 at control and decreased to 38.3 at GA3 1,000 mg‧L-1 treatment. There was no statistical difference in the number of tillers, which was 10.9~12.2, and SPAD value, which was 53.2~56.4 among treatments. Safeena et al. (2023) reported that when Spathiphyllum was treated with gibberellin, the plant height and leaf length were longer and the leaf width was wider than in untreated plant. In this study, the plant height and leaf length were longer by gibberellin treatment, but there was no difference in leaf width among treatment. The plant height elongation effect by gibberellin treatment has been reported in many plants. The mechanism is that gibberellin induces mRNA synthesis and promotes cell elongation, which ultimately promotes the length of the stem internodes (Beevers, 1966). It is also known that the petioles and pollen tubes of plants elongate through the same mechanism (Hisamatu et al., 2005;Maita and Sotomayor, 2015).
In the combined treatment with BA and GA3, plant height was increased by both plant growth regulators, BA and GA3. GA3 has a higher effect on plant height promotion than BA (Table 3). Leaf length was also promoted by GA3. Leaf width did not differ among treatments. Number of leaves was affected by GA3, similar result obtained from the experiment of single GA3 treatment (Table 2). Number of tillers was unaffected by BA and GA3, but was affected by the combined treatment with both plant growth regulators. SPAD value was not affected by BA or GA3.
Floral induction
Flower development of S. wallisii Hort. was promoted by GA3 treatment, regardless of BA treatment. The average number of flowers per plant was 0.8~1.1 when GA3 was not treated. However, the number of flowers per plant increased to 5.3~9.3 when GA3 was treated (Fig. 1 and Fig. 2). The number of flowers was the highest as 9.3 at BA 300 mg‧L-1+ GA3 1,000 mg‧L-1 treatment. Safeena et al. (2023) reported that BA treatment was effective in flowering of Spathiphyllum. In this study, BA treatment was ineffective in flowering. This difference is thought to be due to experiment, plant growth stage, and the concentration of plant growth regulator. The mechanism how gibberellin promotes flowering in plants is unclear. Anton (1957) reported that gibberellin promotes flowering in plants that require low temperatures for flowering, such as carrot (Daucaus carota L.), and plants that require long day for flowering, such as henbane (Hyoscyamus niger L.), but it is not effective in short-day plants, such as soybean (Glycine max L.). Although the mechanism which gibberellin induces flower bud differentiation is unknown, it is hypothesized that gibberellin does not act alone or directly, but rather indirectly through its involvement in the synthesis of other metabolic substances.
Abnormal flower emerged at GA3 treatment regardless of BA treatment (Fig. 3). White discoloration of the leaf lamina or petiole was observed (Fig. 4). S. wallisii Hort. is a rosette type plant. The stems are stacked on the leaves. The axillary buds between the leaves differentiate into flower buds and bloom. It is considered that gibberellin treatment causes some of the leaf primordia to differentiate into flower buds and initiate flowering. This hypothesis is thought to be supported by the results showing that the number of leaves decreased and the number of flowers increased by gibberellin treatment (Table 2 and Fig. 1). In addition, the effect of inducing flowering by gibberellin treatment has been reported in rosette type plants, such as Limonium sinuatum Mill., Zantedeschia aethiopica L., Paphiopedilum hybrids, Arabidopsis thaliana, and tulips (Tulipa × gesneriana L.) (Chin et al., 2001;Funnell and Go, 1993;Miguel et al., 2006;Ruth et al., 1992;Suh et al., 1992). Similar to this study, it is thought that the effect of gibberellin treatment on flower bud differentiation and flowering induction is significant in rosette type plants, and further research is needed.
With these results, gibberellin treatment was effective in inducing flowering of S. wallisii Hort. The presence of flower is an important factor of ornamental value for pot-plant. Therefore, gibberellin treatment could improve the ornamental value of S. wallisii Hort. by increasing the number of flowers.
