Hydrangea (Hydrangea macrophylla) is popular for landscaping and as a flowering potted plant. Sales in the United States increased from 2009 to 2019, and the wholesale value reached $154 million in 2019 (US Department of Agriculture, National Agricultural Statistics Service 2021). Hydrangeas grown outdoors initiate and partially develop the cymose inflorescence within the resting terminal bud during the autumn. After defoliation and winter chilling, the cymes usually expand into full bloom by late June (Shanks et al. 1986). New early-flowering hydrangea cultivars/lines are desirable because tropical and subtropical growers are anxious to reduce the hydrangea susceptibility to wilting in summer. In subtropical areas, growers can force some hydrangeas to flower for Chinese New Year markets guided by the literature (Bailey 1989; Yeh and Chiang 2001) by transporting plants in late summer to highland fields at 14 to 18 °C for flower formation, then defoliating and storage in the dark at 4 to 8 °C for flower budbreak, and finally moving to 16 to 24 °C greenhouses to force the plants to anthesis. However, this off-seasonal production has practical difficulties because of global warming and increased energy costs.
Hydrangea chinensis is an evergreen shrub native to subtropical regions of south and southeast Asia. This plant species is commonly seen in forests at low altitudes of Taiwan, flowers naturally in early spring, and could be used as a parent to breed and select early-flowering hydrangea progenies. Interspecific hybridization barriers to Hydrangea include endosperm degeneration and require ovule or cotyledonary culture (Alexander 2017; Kudo and Niimi 1999; Kudo et al. 2008). In the present work, several interspecific early-flowering hydrangea progenies from crossing Hydrangea chinensis and H. macrophylla cultivars were obtained without ovule/embryo rescue.
Origin
Cuttings of Hydrangea chinensis were collected from the northern part of Taichung in Taiwan (long. 23°188 N, lat. 120°732 E), and those of H. macrophylla ‘Leuchtfeuer’ and ‘Freudenstein’ were obtained from a local grower. Cutting propagation was performed in a 60% shaded greenhouse condition with an average noontime photosynthetic photon flux density (PPFD) of 150 to 200 μmol⋅m−2⋅s−1 and mean daily temperatures of 24 to 28 °C. Mist was provided every 30 minutes for 1 minute. Then, rooted cuttings were planted in 15-cm pots containing 4 peatmoss:1 perlite:1 vermiculite (6D; BVB Substrates, De Lier, The Netherlands) and transferred to a greenhouse. Plants were fertilized weekly with water-soluble 20N–8.7P–16.6K fertilizer (20–20–20 General Purpose; JR Peters, Allentown, PA) at 1 g⋅L−1 and irrigated as needed. Plants were kept separately in small net houses to avoid any insect pollination in a greenhouse. Each fertile flower was emasculated before pollination. Reciprocal cross-pollinations between H. chinensis and H. macrophylla ‘Leuchtfeuer’ and ‘Freudenstein’ were performed. Each combination consisted of at least 20 flowers.
Freshly harvested seeds were sown in a transparent plastic box containing fine particles of peatmoss and placed in a growth chamber with day/night temperatures of 25/20 °C and an average PPFD of 200 μmol⋅m−2⋅s−1. A total of 45, 25, 91, and 83 vigorous hybrid seedlings were raised from H. macrophylla ‘Leuchtfeuer’ × H. chinensis, H. chinensis × H. macrophylla ‘Leuchtfeuer’, H. macrophylla ‘Freudenstein’ × H. chinensis, and H. chinensis × H. macrophylla ‘Freudenstein’, respectively. These young hybrid seedlings were transplanted to 15-cm pots containing 4 peatmoss:1 perlite:1 vermiculite. Fertilization and irrigation were the same as described previously. The parents and hybrid seedlings were raised in natural greenhouse conditions with temperatures between 20 and 28 °C, with natural daylengths of 11.5 to 13 h and an average noontime PPFD of 500 μmol⋅m−2⋅s−1. Growth habits, leaf shapes, time to flowering, inflorescence type, and sepal color of the parents and hybrid seedlings were recorded when plants flowered.
Hydrangea hybrid HB01C-01, derived from H. macrophylla ‘Freudenstein’ × H. chinensis, and CHR06-09, derived from H. chinensis × H. macrophylla ‘Leuchtfeuer’, were selected for their vigorous growth and inflorescence appearance. Plants of H. chinensis and H. macrophylla cultivars and the two hybrid lines were propagated by cuttings and grown in the same greenhouse at 16 to 32 °C with natural daylengths of 12 to 14 h and an average noontime PPFD of 536 μmol⋅m−2⋅s−1. Morphological characteristics were recorded at the flowering stage.
Description and Performance
Plants of H. chinensis have lanceolate leaves, H. macrophylla ‘Leuchtfeuer’ and ‘Freudenstein’ have circular leaves, and hybrids produce elliptical leaves (Table 1, Fig. 1). Hydrangea macrophylla ‘Leuchtfeuer’ and ‘Freudenstein’ are deciduous, with mophead inflorescences, whereas H. chinensis and the hybrid seedlings are evergreen, with lacecap inflorescences (Table 1, Fig. 2), confirming that the lacecap flower form is dominant over the mophead type. Kudo et al. (2008) reported that all F1 hybrid plants from crossing H. macrophylla and H. scandens ssp. chinensis produced lacecap inflorescences. Wu and Alexander (2020) also reported a marker that could be used to screen lacecap and mophead progenies, and they showed the dominant inheritance of the lacecap inflorescence trait. Hydrangea chinensis and the hybrid seedlings flowered starting from February and March, respectively, which is earlier than that of H. macrophylla ‘Leuchtfeuer’ and ‘Freudenstein’ in May in greenhouse conditions (Table 1). Hydrangea chinensis have white sepals, and the two H. macrophylla cultivars have deep pink ones, whereas most of the hybrid plants have white or light pink sepals, and few hybrids have pink sepals (Table 1, Fig. 2).
Comparison of leaf morphology of Hydrangea chinensis (left), H. macrophylla ‘Leuchtfeuer’ (middle), and their hybrid progeny (right). Bar = 5 cm.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Comparison of leaf morphology of Hydrangea chinensis (left), H. macrophylla ‘Leuchtfeuer’ (middle), and their hybrid progeny (right). Bar = 5 cm.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Comparison of leaf morphology of Hydrangea chinensis (left), H. macrophylla ‘Leuchtfeuer’ (middle), and their hybrid progeny (right). Bar = 5 cm.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Comparison of inflorescence morphology of Hydrangea chinensis (A), H. macrophylla ‘Leuchtfeuer’ (B), and their hybrid progeny (C). Photographed at Wufeng, Taichung City, Taiwan, on 26 Feb 2019. Bar = 5 cm.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Comparison of inflorescence morphology of Hydrangea chinensis (A), H. macrophylla ‘Leuchtfeuer’ (B), and their hybrid progeny (C). Photographed at Wufeng, Taichung City, Taiwan, on 26 Feb 2019. Bar = 5 cm.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Comparison of inflorescence morphology of Hydrangea chinensis (A), H. macrophylla ‘Leuchtfeuer’ (B), and their hybrid progeny (C). Photographed at Wufeng, Taichung City, Taiwan, on 26 Feb 2019. Bar = 5 cm.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Growth habit, leaf shape, and flowering characteristics among Hydrangea chinensis, H. macrophylla ‘Leuchtfeuer’ and ‘Freudenstein’, and their hybrid progenies, as observed at Wufeng, Taichung City, Taiwan.
Apart from the characteristics shown in Table 1, the selected HB01C-01 exhibited distinct growth and morphology compared with those of the parents (Table 2). HB01C-01 plants have more vigorous growth and wider inflorescences and decorative sterile flowers. Plant height, lateral shoot number, inflorescence type, and whorls of decorative sterile flowers are intermediate between the two parents. Hydrangea chinensis and HB01C-01 have leathery leaves, whereas H. macrophylla ‘Freudenstein’ has papery ones. HB01C-01 and H. macrophylla ‘Freudenstein’ have similar fertile flower colors and medium overlapping broad ovate sepals. Hydrangea hybrid HB01C-01 is suitable for landscape uses (Fig. 3) because of its height, vigorous growth, and white decorative sepals that brighten a shade garden.
Plant appearance of Hydrangea hybrid HB01C-01, derived from H. macrophylla ‘HB01’ × H. chinensis, selected for landscape use. Photographed at Hsinwu, Taoyuan County, Taiwan, on 7 Mar 2017.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Plant appearance of Hydrangea hybrid HB01C-01, derived from H. macrophylla ‘HB01’ × H. chinensis, selected for landscape use. Photographed at Hsinwu, Taoyuan County, Taiwan, on 7 Mar 2017.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Plant appearance of Hydrangea hybrid HB01C-01, derived from H. macrophylla ‘HB01’ × H. chinensis, selected for landscape use. Photographed at Hsinwu, Taoyuan County, Taiwan, on 7 Mar 2017.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Comparison of growth vigor and morphological parameters among the hybrid line HB01C-01 and its parents Hydrangea chinensis and H. macrophylla ‘Freudenstein’. Measurements were performed at Wufeng, Taichung City, Taiwan.
The selected CHR06-09 plants exhibit more vigorous growth and have wider inflorescences than the parents (Table 3). Lateral shoot number, inflorescence type, and whorls of decorative sterile flowers are intermediate between the two parents. Hydrangea chinensis and CHR06-09 have leathery leaves, whereas H. macrophylla ‘Leuchtfeuer’ has papery ones. CHR06-09 and H. macrophylla ‘Leuchtfeuer’ have almost the same sepal diameter and medium overlapping broad ovate sepals. Hydrangea hybrid CHR06-09 is suitable for potted flowering plants because it has compact multiple branches, large decorative sepals, and smaller leaves (Fig. 4).
Plant appearance of Hydrangea hybrid CHR06-09, derived from H. chinensis × H. macrophylla ‘Leuchtfeuer’, selected for flowering potted plants. Photographed at Wufeng, Taichung City, Taiwan, on 26 Feb 2019. Bar = 15 cm.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Plant appearance of Hydrangea hybrid CHR06-09, derived from H. chinensis × H. macrophylla ‘Leuchtfeuer’, selected for flowering potted plants. Photographed at Wufeng, Taichung City, Taiwan, on 26 Feb 2019. Bar = 15 cm.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Plant appearance of Hydrangea hybrid CHR06-09, derived from H. chinensis × H. macrophylla ‘Leuchtfeuer’, selected for flowering potted plants. Photographed at Wufeng, Taichung City, Taiwan, on 26 Feb 2019. Bar = 15 cm.
Citation: HortScience 57, 11; 10.21273/HORTSCI16840-22
Comparison of growth vigor and morphological parameters among the hybrid line CHR06-09 and its parents Hydrangea chinensis and H. macrophylla ‘Leuchtfeuer’. Measurements were performed at Wufeng, Taichung City, Taiwan.
Both interspecific hybrid line HB01C-01 and CHR06-09 were derived from H. chinensis and H. macrophylla without embryo rescue. In subtropical areas, HB01C-01 and CHR06-09 can be propagated by cuttings and flower naturally from early spring.
Availability
A limited quantity of liners may be available for research purposes only by sending a request to the corresponding author.
References
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