Impaginato 61 Adv. Hort. Sci., 2020 34(1): 61­69 DOI: 10.13128/ahsc­8402 Production of seed­propagated com­ pact potted Corylopsis plant in one year J.H. Kim 1, J.K. Suh 1, S.T. Yoon 2, M.S. Roh 3 (*) 1 Department of Environmental Horticulture, Dankook University, Cheonan, Chungnam, 31116, Korea. 2 Department of Crop Science and Biotechnology, Dankook University, Cheonan, Chungnam, 31116, Korea. 3 The Institute of Natural Resources Development, Mokpo National University, Cheonggye‐myeon, Muan‐gun, Jeonnam, 58554, Korea. Key words: Corylopsis coreana, Corylopsis sinensis var. calvescens, new orna­ mental plant, pinching, plant growth regulator, slow release fertiliz­ er. Abstract: The feasibility to produce compact Corylopsis sinensis var. calvescens and C. coreana plant in a 10 cm pot in one year from transplanting seedlings with maximized number of short shoots and inflorescences was investigated. Corylopsis sinensis var. calvescens was selected as a suitable species to produce compact plant with inflorescences. Slow release fertilizer (SRF) at a rate of 0, 0.125, 0.25, and 0.5 g per pot was applied to the surface of the growing medi­ um (Expt. 1). Shoots were pinched 2 (Feb. 28), 4, 6, and 8 weeks (May 16) (Expt. 2) after transplanting, and ancymidol, paclobutrazol, chlormequat, and daminozide plant growth retardants were treated (Expt. 3). Application of a SRF at 0.5 g per pot and pinching four times at 2­week intervals before May 16 effectively increased the flowering percentages and the number of stems with inflorescences, to accelerate flowering, and also produced a compact plants. Paclobutrazol at 10­20 mg/L applied as soil drench was effective in inhibiting stem elongation in the first year; however, higher concentrations should be avoided to prevent excessive reduction in the growth of shoots and production of malformed inflorescences. 1. Introduction The genus Corylopsis Siebold & Zucc., commonly known as Winter Hazel that flowers early in the spring in China and Korea, is a shrub or small tree. Most of the Corylopsis species grows tall reaching a height of 2­4 meters (Bean and Anisko, 2014). Flowers are bisexual and seeds are produced. Among 29 species, 19 species are endemic in China (Zhang et al., 2003). Chinensis sinensis Hems. var. calvescens Rehder & E.H. Wilson is growing in the mountains in Guangxi, Sichuan, and Jiangxi, among other provinces in China (Zhang et al., 2003) and C. coreana Uyeki (Son et al., 2016) in a rather restricted area in Korea. All species are deciduous shrubs producing light yellow pendant racemes (inflorescence) measuring (*) Corresponding author: marksroh@gmail.com Citation: KIM J.H., SUH J.K., YOON S.T., ROH M.S., 2020 ­ Production of seed‐propagated compact potted Corylopsis plant in one year. ­ Adv. Hort. Sci., 34(1): 61­69. Copyright: © 2020 Kim J.H., Suh J.K., Yoon S.T., Roh M.S. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. Received for publication 19 June 2019 Accepted for publication 25 October 2019 AHS Advances in Horticultural Science http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2020 34(1): 61­69 62 about 5 cm in length, followed by appearance of leaves (Fig. 1). Corylopsis, one of many germplasms native and indigenous to China that includes an endangered Acer pentaphyllum Diels (Roh et al., 2008 b), are not well known to horticulturist, growers, and landscape industry, but has a great potential to develop as a new ornamental plant. Although Corylopsis may be available from rooted cuttings or tissue­cultured propagules for a mass propagation (Moon et al., 2002; Koh and Lim, 2006), the success of the rooting of cuttings depends on the season when cuttings were collected and may not provide a large number of plants (Kwon et al., 2011) and acclimatization of tissue culture propagules is not easy (Moon et al., 2002; Koh and Lim, 2006). Therefore, seeds are a viable alternative source for mass propagation and for forcing seedlings to flower. Suitable species should first be identified and then excessive stem elongation must be controlled using plant growth retardants (Currey and Lopez, 2016), and pinching combined with plant growth retardant treatment (Jeong, 2000). Stem elongation can be inhibited by practices such as pinching shoots in many floral and ornamen­ tal plants, resulting in short plant height (Lee et al., 2006; Latimer and Whipker, 2013). Growth and flow­ ering is also affected by treatment with plant growth regulators. Among the many growth retardants, ancymidol (ɑ­Cyclopropyl­ɑ­(4­methoxyphenyl)­5­ pyrimidinemethanol), daminozide (Butanedioic acid mono(2,2­dimethylhydrazide), chlormequat (2­ Chloro­N,N,N­trimethylethanaminium chloride), and paclobutrazol [(2RS, 3RS)­1­(4­Chlorophenyl)­4,4­ dimethyl­2­(1H­1,2,4­triazol­1­yl) penta­3­ol] have been used in many floral and ornamental plants to inhibit stem elongation (Currey and Lopez, 2016). Generally, ancymidol and paclobutrazol is effective when applied as a soil drench, and daminozide and chlormequat when applied as a foliar spray. Germination of Corylopsis seeds as affected by warm and cold stratification and the X­ray imaging to separate full seeds from empty seeds is well docu­ mented (Kim et al., 2015, 2017, 2018). To produce compact and flowering Corylopsis plants in small pots in one year after transplanting seedlings, selection of proper species and the most suitable cultural prac­ tices should be identified. However, there is no report on the growth and flowering of Corylopsis starting from small propagules regardless of propaga­ tion methods: seed propagation, rooting of cuttings, and in vitro propagation. Shortening the total pro­ duction time from 2­3 years to one year while ensur­ ing the qualities of plants at flowering from seedlings in Lilium longiflorum Thunb. bulbils in L. ×elegans Thunb. and tissue­cultured propagules in interspecif­ ic hybrids between L. longiflorum and L. ×elegans was reviewed (Roh, 1992, 1996). Production of Corylopsis in a small pot with inflo­ rescence will attract and enable consumers to pur­ chase at the nursery or the garden center in the early spring, and then plant them in the garden to enjoy the beauty of flowers for many years. The objectives of this research were (1) to select the species to grow starting from seeds in small pots, and to study the effect of (2) slow release fertilizer (SRF) treatments, (3) the pinching frequencies, and (4) plant growth retardant treatments to produce compact seed­prop­ agated Corylopsis plants in 10 cm pots in one year from transplanting seedlings. 2. Materials and Methods Preliminary field evaluation to select a suitable species for final evaluation Seeds of 45 accessions (data not presented) including C. glabrescens (NA50804, Longwood 1997­ 0068B, Longwood Chimes), C. spicata (NA37208, NA40102, Arnold 7950A), C. pauciflora (NA37205, L o n g w o o d 1 9 4 4 ­ 0 2 1 3 * H ) , a n d C . v i e t c h i a n a (NA37208, NA65619) were sown between Oct. 2 and Nov. 2 and planted into 10 cm pot filled with ProMix BM (Premier Horticulture Inc., Quakertown, PA, USA) between Mar. 1 and Apr. 2, and grown in the field. The final evaluation based on the number of plants that flowered and the growth habits, C. coreana and C. sinensis var. calvescens (NA 57391) (Roh et al., Fig. 1 ­ Appearance of C. sinensis var. calvescens at anthesis pro­ duced in a 10 cm pot from seeds. Clusters of flower buds (inflorescences) are well developed on long shoots. Kim et al. ‐ Compact Corylopsis plant production 63 2008 a) were selected (Table 1) for evaluation in the next three experiments. Effect of slow release fertilizer treatment on growth and flowering (Expt. 1) A b o u t 2 0 0 s e e d s e a c h o f C . s i n e n s i s v a r . calvescens and C. coreana were sown on Oct. 20, 2009 in a 15 cm pot and received temperature treat­ ments [20oC (Oct. 21 ­ Dec. 1) and 5oC (Dec. 2, 2009 ­ Feb. 16, 2010)]. One seedling was transplanted per 10 cm pot filled with ProMix BM on Mar. 4, 2010. On Mar. 18, 2010 when seedlings formed 4 nodes, the main shoot was pinched leaving two pair of leaves. Slow release fertilizer (SRF; Osmocote, 14 N ­ 6.2 P ­ 11.6K; Scotts Co., Marysville, OH, USA) was applied to the surface of the growing medium at transplant­ ing seedlings at a rate of 0, 0.125, 0.25, and 0.5 g per 10 cm pot (Table 2). During the culture, plants were fertilized with 1.33 g/L of 15N ­ 7P ­ 12.8K water solu­ ble fertilizer once a month. Greenhouse day temperature was maintained at 21­22oC on Oct. 1, 15­17oC on Nov. 1, 13­14oC on Nov. 16, 10­12oC on Dec. 1, 7­8oC on Dec. 16, 2010 and at 4­5oC on Jan. 1, 21­24oC on Apr. 16, 2011, and was raised by 2.5oC every 2 weeks until Sept. 1, 2011. Night temperature was maintained 2oC lower than the day temperature. The number of weeks to flower counted from the date of transplanting seedlings to pots, and the number and length of nodes with inflo­ rescences from the three longest shoots, and the number of nodes with 2 inflorescences was recorded from 15 plants per treatment. Flowering date was recorded when two florets each from two inflores­ cences reached anthesis, and data were subjected to t h e r e g r e s s i o n a n a l y s i s f o r e a c h s p e c i e s u s i n g Statistical Analysis System program (SAS, 2002). Effect of pinching frequencies on growth and flower‐ ing (Expt. 2) After sowing about 200 seeds as described in Expt. 1, seedlings were transplanted. On Mar. 18, 2010, 0.25 g of slow release fertilizer was applied to the surface of growing medium and the effect of pinching frequencies on C. sinensis var. calvescens was evaluated. Shoots were either not­pinched or pinched 2 (Feb. 28), 4 (Apr. 18), 6 (May 2), and 8 weeks (May 16) after transplanting as outlined (Table 3). To the surface of the growing medium at trans­ planting seedlings 0.8 g of slow release fertilizer per pot was applied, and plants were fertilized with 1.33 g/L of 15N ­ 7P ­ 12.8K water soluble fertilizer once a month. The number of weeks to flower, and the total number of shoots with flowers and flower buds, and the length and number of flowers from the first and second longest shoots was recorded from 15 plants per treatment. The number of days to flower was counted from the date of transplanting. Data were subjected to the analysis of variance (ANOVA) and means were compared with Tukey’s honestly signifi­ cant difference (HSD) test. Effect of growth retardants treatment on growth and flowering (Expt. 3) Corylopsis sinensis var. calvescens seeds were sown and transplanted, and pinched as described in Expt. 1, and pinched again on May 26, 2010. Plants w e r e g r o w n i n g r e e n h o u s e m a i n t a i n e d a t 1 8 ­ 21oC/16­19oC (day/night) and then in greenhouse maintained at 22­25oC/20­23oC until July 6. To the surface of the growing medium at transplanting seedlings 0.8 g of slow release fertilizer per pot was applied, and plants were fertilized with 1.33 g/L of 15N ­ 7P ­ 12.8K water soluble fertilizer once a month. Growth retardants were applied on Jul. 7, when new shoots were about 5­8 cm long. Each pot was treated with 25 mL of ancymidol [0.026% active ingre­ dient (a.i.)] and paclobutrazol (0.4% a.i.) at 0, 10, 20, 40, and 80 mg/L was applied as a soil drench. Daminozide (85% a.i.) and chlormequat (11.8% a.i.) at 0, 2,500, Table 1 ­ Evaluation of flowering and growth habit in the field C. coreana and C. sinensis var. calvescens z Range and mean of flowering. y Plants that produced inflorescence and the total number of plants evaluated (parenthesis). x Number of plants ( parenthesis) showing upright and prostrate growth characteristics. Species Seed harvest 2008 2009 Germi­ nation Trans­ planting Flowering z No. of plants y Growth characteristics x C. coreana 2007 Mar. 6 Mar. 12 Mar. 19­25 (Mar. 21) 9 (21) Upright (12), prostrate/upright (1) C. sinensis var. calvescens 2007 Mar. 1 Apr. 2 Mar. 27­Apr. 7 (Apr. 2) 14 (16) Upright (13), prostrate/upright (1) 2008 Feb. 26 Apr. 8 Mar. 22­Apr. 3 (Mar. 28) 16 (16) Upright (16) Adv. Hort. Sci., 2020 34(1): 61­69 64 5,000, 7,500, and 10,000 mg/L was applied as a foliar spray, and 200 mL of solution was applied to 15 plants. On Nov. 20, 2010, plants were grown in a greenhouse maintained at 4­5oC for cold treatment until Mar. 1, 2011. Dates of flowering, when two florets from an inflorescence reached anthesis were recorded and the lengths of two longest shoots (shoot length A) per plant and shoots longer than 3 cm were counted on Jan. 16. Plants were moved outdoors on Mar. 27, and the new growth of two longest shoots (shoot length B) was also recorded on May 10, 2011. Data collected from 15 plants per treatment were ana­ lyzed by two­way ANOVA with plant growth retar­ dants and concentration as variables. 3. Results Selection of a suitable species for final evaluation Following evaluation of 45 accessions including C. glabrescens,C. spicata, C. pauciflora, and C. vietchi‐ ana (data not presented), C. sinensis var. calvescens and C. coreana showing upright growth characteris­ tics of shoots and flowering response were selected­ for the final evaluation. All accessions grew taller than 1.3 m and spread over 65 cm wide in case of C. spicata, but with a few inflorescence (data not pre­ sented). The selection criteria were based on the number of plants that had flowered exhibiting upright growth characteristics. In less than one year counting from the time of transplanting, 14 from 16 C. sinensis var. calvescens plants flowered showing up­right growth (Table 1). Corylopsis coreana was also selected for its large foliage for its good fall foliage color, even though only nine out of 21 plants had flowered. Effect of slow release fertilizer treatment on growth and flowering (Expt. 1) The number of weeks to flower in 52 to 53 weeks in C. sinensis var. calvescens and C. coreana was not affected by the rate of SRF treatments (Table 2). The number of total shoots and of shoots with inflores­ cences increased linearly with SRF treatment from 2.5 to 4.1 in C. coreana and from 2.1 to 4.1 in C. sinensis var. calvescens. The lengths of the three longest shoots also increased in both species, from 11.9 to 25.6 cm for the longest shoot, from 4.8 to 15.8 cm for the third shoots in C. coreana, and from 12.8 cm to 29.3 cm for the longest shoot in C. sinen‐ sis var. calvescens. The number of nodes with inflorescences in all the three shoots of C. coreana received 0.5 g SRF treat­ ment was 0.3 or less than 0.3 and there was only one node with more than 2 inflorescences. However, the number of nodes with inflorescence produced and the number of nodes with 2 inflorescences was high­ er in C. sinensis var. calvescens than in C. coreana. The number was increased to 4.8 nodes in the first Table 2 ­ The effect of slow release fertilizer treatment on the growth and flowering of Corylopsis coreana and C. sinensis var. calvescens z z There was a significant difference between two species; data for each species were subjected to the linear regression analysis. y The number of weeks to flower was counted from the date of transplanting seedlings. x Nodes with inflorescence that were formed on new growth by pinching. w Non­significant (NS), significant at P≤0.05 (*) and P≤0.01 (**). Species Slow release fertilizer (g/10 pot) No. of weeks to flower y No. of total shoots Length (cm) of three longest shoots (SH) No. of nodes with inflorescences x SH 1 SH2 SH 3 SH1 SH2 SH 3 C. coreana 0 52 2.5 11.9 6.7 4.8 0.1 0.1 0.0 0.125 52 3.3 14.4 9.8 7.4 0.3 0.1 0.0 0.25 53 4.6 20.3 13.6 10.1 0.1 0.0 0.0 0.5 52 4.1 25.6 22.0 15.8 0.1 0.3 0.3 Regression analysis ­ linear effect w NS * ** ** ** NS NS NS C. sinensis var. calvescens 0 53 2.1 12.8 6.7 4.5 0.1 0.0 0.0 0.125 53 2.9 14.3 9.9 7.5 0.8 0.7 0.0 0.25 52 3.4 21.3 13.0 10.4 3.1 2.8 1.8 0.5 52 4.1 29.3 21.8 19.8 4.8 4.4 2.7 Regression analysis ­ linear effect w NS ** ** ** ** * * * Kim et al. ‐ Compact Corylopsis plant production 65 control. T h e l e n g t h o f t h e fi r s t a n d t h e s e c o n d n o n ­ pinched shoot was 49.3 and 33 cm, respectively, with a difference of 16.3 cm (Table 3). However, when pinched 4 times, the lengths were 38.0 and 31.8 cm with a difference of 6.2 cm. The number of inflores­ cences in non­pinched and pinched shoots, which was 9.2 and 7.1 in the first shoot and 4.0 and 6.9 in the second shoot, respectively, did not vary signifi­ cantly. However, the difference in the number of inflorescences (0.2) between the first and the second shoot was significantly lower in the pinched shoot compared with the non­pinched shoot (5.2). In gen­ eral, when pinched, the difference in the inflores­ cences between the first and the second shoot was less than 1.9, which was significantly less than that of the control. Effect of growth retardant treatments on growth and flowering (Expt. 3) W h e n p l a n t s w e r e t r e a t e d w i t h a n c y m i d o l , chlormequat, and daminozide, flowering took 22 to 28 days regardless of treatment concentrations, which was not significantly different from that of control (Table 2). However, soil drench treatments with paclobutrazol (20 mg/L or higher concentra­ tions) took longer than 36 days. Flowering percent­ age was higher than 60% when plants were treated with ancymidol, chlormequat, and daminozide, regardless of treatment concentrations.Treatment with 20 mg/L of paclobutrazol severely inhibited the extension of peduncle bearing inflorescence trigger­ ing the death of inflorescence immediately after shoot and to 4.4 nodes in the second shoot following treatment with 0.5 g of SRF and the number of nodes with more than 2 inflorescences was also increased. C. sinensis var. calvescens treated with 0.125, 0.25, and 0.5 g SRF has the potential to produce a small potted plant (Fig. 2). Effect of pinching frequencies on growth and flower‐ ing (Expt. 2) Regardless of frequencies and timing of pinching, the flowering of C.sinensis var. calvescens occurred in 53 weeks (Table 3). Flowering ranged between 73 and 93%, and the highest flowering rate was record­ ed when pinched for 4 times at 2, 4, 6, and 8 weeks, yielding a significantly higher number of shoots with inflorescences (5.3) and consequently the highest number of inflorescences (22.1) compared with the Fig. 2 ­ Appearance of the Corylopsis sinensis var. calvescens plants in a 10 cm pot treated with 0.125, 0.25, and 0.5 g of slow release fertilizer per pot prior to leaf emergence and anthesis. Table 3 ­ The effect of pinching frequencies on growth and flowering of Corylopsis sinensis var. calvescens z Not pinched (x) or pinched (o) 2 (Feb. 28), 4 (Apr. 18), 6 (May 2), and 8 weeks (May 16) after transplanting. y The number of weeks to flower was counted from the date of transplanting seedlings. x Nodes with inflorescence induced by pinching. w Non­significant (NS) or significance at P≤0.05, F­test. Pinching z No. of weeks to flower y Flowering % Total shoots no. with inflores­ cences Flowers (Total No.) Shoot length (cm) No. of nodes withinflorescences x 2 Weeks 4 Weeks 6 Weeks 8 Weeks First shoot Second shoot Difference First Second shoot Difference x x x x 53 87 2.9 17.2 49.3 33.0 16.3 9.2 4.0 5.2 o x x x 53 87 2.1 12.8 49.0 38.8 10.2 6.9 6.8 0.1 o o x x 54 73 2.4 13.1 47.1 35.5 11.6 6.4 4.8 1.6 o o o x 53 87 3.5 18.5 41.6 35.2 6.4 6.8 5.7 1.1 o o o o 53 93 5.3 22.1 38.0 31.8 6.2 7.1 6.9 0.2 o x o o 53 87 4.3 17.3 32.4 29.2 3.2 5.7 5.2 0.5 o o x o 54 80 3.1 10.4 37.3 26.0 11.3 4.7 3.9 0.8 o x o x 53 73 3.3 14.8 39.5 29.8 9.7 6.5 6.3 0.2 o x x o 53 87 3.3 16.3 39.0 22.2 16.8 7.6 5.7 1.9 Level of significance w HSD at P<0.05 NS ­ 0.94 3.58 8.25 5.61 5.82 4.27 3.84 1.59 66 Adv. Hort. Sci., 2020 34(1): 61­69 e m e r g e n c e f o l l o w i n g l e a f e m e r g e n c e ( F i g . 3 ) . Therefore, days to flower were estimated on the date of leaf emergence. Flowering percentage was significantly reduced to less than 30% when plants were treated at 20 and 40 mg/L paclobutrazol. When shoot lengths following 80 mg/L ancymidol were recorded on Jan. 16 (26 weeks after growth retardant treatment), the length of the first and the second longest shoots was significantly reduced from 26.3 cm to 15.6 cm and from 16.4 cm to 12.2 cm, respectively (Table 4). The length of the two longest shoots treated with daminozide and chlormequat showed similar trends as observed in plants treated with ancymidol. The length of the two longest shoots was significantly reduced to 12.9 cm and 9.8 cm following treatment with 10 mg/L paclobutrazol (Fig. 3), responding to the quadratic effect of concentrations. The length of shoot B showing new growth on May 10 was signifi­ cantly inhibited to less than 5.0 cm when treated with paclobutrazol. The number of shoots longer than 3 cm varied from 4.8 to 5.7, from 3.8 to 4.8, 4.3 to 5.5, and 5.0 to 3.9 upon treatment with ancymi­ dol, chlormequat, daminozide, and paclobutrazol, respectively. The numbers were not affected by con­ centrations of these three retardants (data not pre­ sented). 4. Discussion and Conclusions Successful acclimatization rate of in vitro propa­ gated C. coreana was low (Moon et al., 2002) and limited time of the season to propagate by rooting of cuttings (Kwon et al., 2011) are the limiting factors for mass propagation to secure sufficient and uni­ form propagules for experiments, and further, reports are not available on flowering of in vitro propagules and rooted cuttings. This clearly indicates that seeds can be used as a propagule to produce sufficient number of seedlings to produceflowering plants in a year from transplanting seedlingsby vari­ ous cultural practices reported in this study. The mor­ p h o l o g i c a l c h a r a c t e r i s ti c s o f C . s i n e n s i s v a r . calvescens are suitable to produce in 10 cm pots compared with C. coreana, if stem elongation can be controlled and many shoots with well­developed inflorescences can be formed (Fig. 1). Growth and flowering as influenced by slow release fertilizer (SRF) There is a clear difference between C. coreana and C. sinensis var. calvescens responding to SRF a p p l i c a ti o n p e r 1 0 c m p o t . R e s p o n d i n g t o t h e increased rates of slow release fertilizer, especially at 0.5 g SRF application, and C. sinensis var. sinensis is recommended to produce as a 10 cm potted plant in one year as the number of inflorescences and of n o d e s w i t h m o r e t h a n t w o i n fl o r e s c e n c e s a r e increased. Production of C. coreana may not be rec­ ommended due to fewer numbers of nodes with inflorescences and only 0.1 node produced more than 2 inflorescences. Growth and flowering as influenced by pinching and growth retardant treatments Stem length is one of the limitations to produce compact C. sinensis var. calvescens in small pots, which can be reduced either by pinching or growth retardant treatments. Manual or mechanical pinch­ i n g i s a s s o c i a t e d w i t h i n c r e a s e d l a b o r c o s t s . Treatment with growth retardant may not induce branching when compared with pinching. Pinching shoots four times in 2, 4, 6, and 8 weeks prior to May 2 is an effective cultural practice to pro­ duce compact plants for small pots without affecting days to flowering and flowering percentage. The increase in the number of shoots with inflorescences, the total number of inflorescences, and the number of nodes with inflorescences may result from an increased number of shoots that are formed prior to the development of inflorescence, which may occur Fig. 3 ­ Corylopsis sinensis var. calvescens in a 10 cm pot treated with 25 mL of 40 mg/L paclobutrazol (A). Blasted inflore­ scences (arrow) and emerging of dark green leaves of reduced size indicate excessive doses of paclobutrazol (B). Photographed on Mar. 27, 2011. Kim et al. ‐ Compact Corylopsis plant production 67 after May 2. Since the time of floral bud initiation has not been examined anatomically, it requires further studies. Increase in the number of lateral shoots and flowers were increased as the pinching frequencies in Sedum rotundifolium D.B. was increased (Jeong, 2000). The length of shoots exceeding 30 cm follow­ ing pinching is considered excessive for producing Corylopsis in a 10 cm pot. Flowering of C. sinensis var. calvescens plants t r e a t e d w i t h a n c y m i d o l , c h l o r m e q u a t , a n d daminozide that produced higher than 60% plants with inflorescences regardless of treatment concen­ trations did not differ significantly from that of con­ trol. The longest shoot length (A) on Jan. 16 respond­ ing linear effect to ancymidol, chlormequat and daminozide was the shortest, especially when treat­ ed with 80 ppm ancymidol. Ancymidol is,therefore, recommended for C. sinensis var. calvescens in 10 cm pot. Since the length of new shoot (B) on May 16 was not affected, the effect of these three plant growth Table 4 ­ Growth and flowering of Corylopsis sinensis var. calvescens as influenced by growth retardant treatments Plant growth regulator No. of days to flower (Mar. 1) (flowering percent) Shoot lenght A (cm) (Jan. 16, 2011 z) Shoot length B (cm) of new growth (May 10, 2011) FIR y SEC FIR SEC Ancymidol (soil drench) (mg/L) 0 22 (60) 26.3 16.4 21.0 20.0 10 23 (80) 28.4 17.5 20.2 19.4 20 24 (70) 27.9 21.7 20.2 20.0 40 25 (70) 23.9 19.1 21.9 17.9 80 25 (60) 15.6 12.2 16.5 16.3 Regression analysis NS L* L* NS NS Paclobutrazol (soil drench) (mg/L) 0 22 (60) 24.7 20.0 24.0 20.0 10 28 w (50) 12.9 9.8 5.0 3.5 20 38 w (30) 11.2 8.1 1.7 1.2 40 36 w (10) 10.3 7.9 1.3 0.8 80 36 w (30) 11.0 8.5 1.1 0.6 Regression analysis x ­ Q** Q** Q** Q** Chlormequat (foliar spray) (mg/L) 0 22 (70) 28.9 20.3 23.1 20.9 2.5 22 (80) 35.1 24.9 22.9 20.1 5 25 (70) 26.5 20.0 18.3 18.1 7.5 27 (60) 23.7 14.5 17.9 17.0 10 25 (70) 24.3 18.5 20.2 19.9 Regression analysis NS L* NS NS NS Daminozide (foliar spray) (mg/L) 0 23 (60) 29.2 23.0 21.0 19.9 2.5 27 (80) 33.3 23.5 23.5 18.5 5 25 (70) 28.5 22.0 22.5 18.9 7.5 25 (60) 29.3 22.7 22.7 19.1 10 27 (70) 25.5 19.5 21.2 18.5 Regression analysis NS L* NS NS NS Level of significance v Growth retardant (PGR) NS *** *** *** *** Concentratio NS ** * * * PGR × Concentration NS ** ** ** ** z Data collected from over­wintered plants. y Length of the first (FIR) and second (SEC) longest shoots. x Analysis was not carried out due to the estimated days of flowering and low flowering percentage, and regression analysis was per­ formed for each growth retardant. Linear (L) and quadratic (Q) effect. w Days to flower following paclobutrazol treatment were recorded upon leaf emergence following the death of inflorescence. Generally, about 15 days elapsed between flowering and the appearance of leaf emergence. v Non­significant (NS) or significance at P<0.05 (*), 0.01 (**) or 0.001 (***), F­test. Adv. Hort. Sci., 2020 34(1): 61­69 68 retardants may not last long when compared with paclobutrazol. A single application of ancymidol is not effective and may require two treatments to pro­ duce quality Mussaenda ‘Queen Sirikit’ as a short­ stemmed potted plant without reducing the number of flowers per plant and delaying the flowering (Cramer and Bridgen, 1998). Application of ancymidol requires further testing since growth retarding effects of ancymidol do not persist as reported in L. lancifolium Thunb. (Roh, 1979) and shoot length is increased under a long day photoperiod during June o r J u l y a s o b s e r v e d i n L . l o n g i fl o r u m ( R o h a n d Wilkins, 1977). Soil drench treatment with paclobutrazol 20 mg/L or higher concentrations which took longer than 36 days to flower (Table 4) compared with 22 days with the control. When treated with 20 mg/L of paclobu­ trazol, the extension of peduncle­bearing inflores­ cence was severely inhibited resulting in the death of inflorescence immediately following leaf emergence, thus lowering the flowering rate from 60% to 10% ( F i g . 3 ) . S h o o t l e n g t h w a s a r r e s t e d u n d e r a n y paclobutrazol treatment which is undesirable. Although 10­20 mg/L paclobutrazol as a soil drench is considered effective to reduce shoot length, the growth of new shoots and inflorescence development is significantly arrested even a year later, which may require double treatments at low concentrations, i. e., 5 mg/L to avoid severe growth retardation and malformation of inflorescence. A sin­ gle foliar spray of 500 mg/L paclobutrazol may be used to test produce compact flowering plants as reported in Rhododendron hybrids, which is a woody ornamental (Wilkinson and Richards, 1991). Generally paclobutrazol was not effective in Mussaenda at 0.125­0.25 mg a.i. per pot as a soil drench compared with ancymidol and daminozide (Cramer and Bridgen, 1998), which is considered effective in producing compact plants with accelerat­ ed flowering although 0.4 g a.i. per pot increased the number of flowers, producing malformed and unac­ c e p t a b l e o f R h o d o d e n d r o n ‘ S i r R o b e r t P e e l ’ (Wilkinson and Richards, 1991). Shoot length of poin­ settia (Euphorbis pucherrima Wild. ex Klotzch) was reduced by daminozide and chlormequat treatments without affecting the flowering (Lewis et al., 2004). C o m b i n e d t r e a t m e n t w i t h c h l o r m e q u a t a n d daminozide can also be considered as reported to be effective to retard stem elongation of zonal (cutting) geraniums [Pelargonium ×hortorum (L.H. Bailey)] (Tayama and Carver, 1990). D u e t o t h e l o n g ­ l a s ti n g i n h i b i t o r y e ff e c t o f paclobutrazol on shoot elongation and reduction in leaf size when applied as a soil drench, a malforma­ tion of inflorescence and formation of inflorescences after leaf emergence result in a lower percentage of plants with inflorescences in both species in this study and in other woody ornamentals such as Dissotis rotundifolia (Sm.) Triana and Tibouchina f o r t h e r g i l l a e × p i l o s a ( H a w k i n s e t a l . , 2 0 1 5 ) . Therefore, paclobutrazol is not recommended to use as a soil drench in Corylopsis. The optimum dosages require further study comparing the effect of soil d r e n c h a n d f o l i a r s p r a y . A s p r a y t r e a t m e n t o f paclobutrazol may be considered as the quality of D i a n t h u s c a r y o p h y l l u s L . , c v . M o n d r i a a n w a s improved (Bañón et al., 2002). This is the first report providing practical and hor­ ticultural strategies to produce flowering Corylopsis plants in small pots with a great potential to utilize under­utilized native plants as ornamental and nurs­ ery plant starting from seeds. Corylopsis sinensis var. calvescens indigenous to China is a suitable species as compared to C. coreana native to Korea to pro­ duce from seeds with application of slow release fer­ tilizer at 0.5 g per pot and pinching for four times at 2­week interval before May 16 to reduce shoot elon­ gation, to increase flowering percentage, and to accelerate flowering with increased number of inflo­ rescences. Treatments with ancymidol as a soil drench and daminozide and chlormequat as a foliar spray at all concentrations evaluated in this study were not effective to produce compact plants as compared to paclobutrazol treatment. Soil drench treatment with paclobutrazol at 10­20 mg/L is considered effective in reducing shoot elongation the first year. However, the inhibitory effects of paclobutrazol last longer than a year, and appear resulting in malformation of inflorescences in the second year. 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