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Xiao-Juan Wei, Jinlin Ma, Kai-Xiang Li, Xiao-Jing Liang and Haiying Liang

The flowers of Camellia chrysantha, commonly named as golden camellia, are treasured for their unique yellow color and are popularly used for tea. Compared with common camellia flowers that are either red, purple, pink, or white, golden camellia flowers are rare and are in high market demand. Our study was aimed to induce flowering in juvenile C. chrysantha grafted plants with urea and paclobutrazol (PBZ), a growth retardant. Generally, it takes 6–8 years for C. chrysantha seedlings and 5–6 years for grafted plants to set flower buds. With a 4 × 4 factorial design, four dosages of urea (1, 3, 5, or 8 g/plant) and four concentrations of PBZ (50, 150, 350, and 750 ppm) were tested on 4-year-old C. chrysantha grafted plants. Significant interaction between urea and PBZ was observed, and nine of the 16 combinations produced significantly more flower buds than the control, although not all flower buds could open because of abscission. High concentrations of PBZ and high dosages of urea were generally associated with severe defoliation and slow growth of basal stem diameter. When taking bud abscission into account, combinations of 150 ppm PBZ with 1 g urea and 350 ppm PBZ with 3 g urea resulted in significant flowering in juvenile C. chrysantha grafted plants without negative effects on vegetative growth and flower bud size and severe defoliation. This is the first report on flowering induction in a golden camellia species using juvenile plants. Our results suggest that application of optimized PBZ and urea doses can be a potential means for manipulation of early flowering in golden camellia species.

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Xiao-Juan Wei, Xiao-Jing Liang, Jin-Lin Ma, Kai-Xiang Li and Haiying Liang

Camellia flowers are highly prized for their beauty worldwide and are strongly symbolic in many cultures. A new interspecific hybrid cultivar, Camellia ‘Maozi’, generated by crossing Camellia pubipetala with C. japonica ‘Dahong Mudan’, exhibits strong hybrid vigor and has small flowers with a rare light tone of purple. In southwest China with a subtropical monsoon climate, young Camellia ‘Maozi’ trees flush shoots three times in spring, summer, and autumn, with an average annual growth of 12.9 cm. Adult trees flush once a year. Floral bud formation occurs in late April and early May. Camellia ‘Maozi’ flowers are sterile with no fruits and seeds produced. While an individual flower wilts 4–8 days after opening, the blossom can last 1–3 months. Frost damage can be found in young leaves when temperature drops to 4–7 °C. Under direct sunlight with temperatures of 37–39 °C lasting for more than 2 days, young leaves can turn yellow on their edges. Its primary diseases include sooty mold, shoot tip blight, and peony leaf tip blight. Its primary insect pests are tea green leafhopper (Jacobiasca formosana) and tea aphid (Toxoptera aurantii). Rooting of stem cuttings occurs directly from stems, mostly without callus development. Two hours of treatment with 500 mg·L−1 indole-3-butyric acid and rooting in a mix of latosolic red soil and vermiculite (2:1 v/v) resulted in high rooting rate and quality of aboveground growth. Grafting can be carried out from May to September, while survival rate and new shoot length are highest in July. The most compatible rootstock is C. oleifera, followed by C. polyodonta. The results of this study are of value for understanding the reproductive biology of Camellia ‘Maozi’ and further disseminating it as a new cultivar for camellia collection.

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Xiao-Juan Wei, Jinlin Ma, Kun Wang, Xiao-Jing Liang, Jin-Xuan Lan, Yue-Juan Li, Kai-Xiang Li and Haiying Liang

Camellia chrysantha flowers are in great market demand as a result of their high ornamental and medicinal values. To induce early flowering in 4-year-old juvenile C. chrysantha seedlings, three levels of paclobutrazol (PBZ) concentration (100, 200, and 300 ppm) were applied to the roots. PBZ is a triazole-type cytochrome P450 inhibitor that was found successful in inducing flowering in juvenile C. chrysantha grafted plants in a prior report. The current study shows that all three PBZ concentrations were equally effective in induction of floral buds, resulting in an average of 20 floral buds per treated plant. In comparison, none of the untreated plants flowered. Although the induced flowers were smaller than the ones from mature trees, PBZ treatment did not affect C. chrysantha flowers’ medical values, because there was no significant change in the content of pharmacologically active compounds (polysaccharide, polyphenols, flavonoids, and saponins). None of the PBZ treatments had a negative effect on the current year’s growth in height and basal diameter, photosynthesis, and levels of water-soluble sugars and nutrients [phosphorus (P), nitrogen (N), potassium (K), and carbon (C)]. It is concluded that PBZ is an effective flowering inducer for juvenile C. chrysantha plants. It was also found that PBZ-treated plants experienced defoliation, and there existed a strong correlation between severity of defoliation and PBZ concentration. This might be attributed by the stress induced by PBZ, as demonstrated by the increased activities of some of the stress-related enzymes [ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD)], and the level of malondialdehyde (MAD). Considering that severe defoliation can cause stunted or malformed plants and reduce aesthetic value, 100 ppm is the optimal PBZ concentration for flowering induction in C. chrysantha seedlings.