Origin

‘Chongtian’ originated as a seedling selection with unknown pedigree. In 2007, the open-pollinated seeds of Z. schneideriana from Dongshanqiao forestry farm were planted at a plant nursery of Jiangsu Academy of Forestry (118°45′57.30″E, 31°51′27.94″N). In 2012, one exceptional individual with small-angle branching was observed among the progeny. The unique plant was propagated asexually through grafting in 2012 and 2013. The clones were evaluated for a period of 3 successive years (2013–15). All propagated plants showed stable and consistent morphological traits. In 2016, ‘Chongtian’ was selected as a promising cultivar and authorized by the State Forestry Administration of China (accession no. 20160103).

Description

In Jiangsu province, budbreak of the ‘Chongtian’ tree occurs in mid-March. It is then slow-growing in April and May. As the air temperature increases in June, ‘Chongtian’ becomes fast-growing for a period of 3 months (from June to August). During September to November, it enters a slow-growth stage. The leaf fall of ‘Chongtian’ starts in late November and early December, which is ∼20 d later than most Z. schneideriana accessions. At the end of abscission, ‘Chongtian’ is dormant from December to March.

The leaf of ‘Chongtian’ is oval in shape. Foliage color varies with the season, turning from dark green in summer to yellow-purple in fall (Fig. 1A). A distinguishing morphological trait of ‘Chongtian’ is its small branching angle. The branches spread with a narrow branch angle (∼30°, Fig. 1B), producing a short canopy diameter. A 10-year-old plant has a canopy diameter of 4.23 m, a tree height of 12.79 m, and a diameter at breast height of 10.90 cm. Compared with the commonly planted Z. schneideriana Feilong cultivar (Fig. 1C), the canopy diameter of ‘Chongtian’ is conspicuously smaller (Fig. 1D).

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Characteristics of autumn foliage at 10 Nov 2020, (A) and branches at 20 Dec 2020 (B) of ‘Chongtian’ and comparison of the canopy between ‘Feilong’ (C) and ‘Chongtian’ (D) at 15 Sep 2020 in Yangzhou, China.

Citation: HortScience 58, 4; 10.21273/HORTSCI17015-22

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Performance

In 2016–20, the performance of ‘Chongtian’ and ‘Feilong’ was evaluated in a field trial located at Yangzhou, China. The 2-year-old Z. schneideriana seedlings with stems ∼2 cm in diameter were used as rootstock. Both accessions were grafted through spring branch grafting in March 2016. At the end of growing season in October, the morphological traits included tree height, diameter at breast height (DBH), and canopy diameter was recoded from 10 plants of each accession. The measurement differences of plant performance in each year were statistically significant according to Duncan’s multiple range test, determined using IBM SPSS Statistics 25.

The primary difference between ‘Chongtian’ and ‘Feilong’ is the canopy diameter. The canopy diameter of ‘Chongtian’ plants was always significantly smaller than those of ‘Feilong’ trees during the evaluation period. When ‘Chongtian’ plants were 2 years old, the mean canopy diameter was 1.12 m (Table 1). In contrast, the corresponding value in the ‘Feilong’ tree was 1.59 m (Table 1). For 3- and 4-year-old ‘Chongtian’ trees, the average canopy diameters were 1.60 and 2.02 m, respectively (Table 1). In contrast, the canopy diameter of 3- and 4-year-old ‘Feilong’ trees were 2.77 and 3.76 m, respectively (Table 1), When the tree reached 5 years of age, the canopy diameter of ‘Chongtian’ was 1.82-fold smaller than that of ‘Feilong’ (Table 1).

Table 1.

Growth performance of ‘Chongtian’ and ‘Feilong’.

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Overall, we found that ‘Chongtian’ had similar height growth rate to ‘Feilong’. When plants were 1, 2, 3, 4, and 5 years old, the average tree heights of ‘Chongtian’ were 1.71, 2.83, 4.42, 5.12, and 5.53 m (Table 1), whereas the corresponding values in ‘Feilong’ were 1.60, 2.64, 4.35, 4.90, and 5.42 m (Table 1). In terms of DBH, the two genotypes also performed similarly at the same plant age. The DBH of ‘Chongtian’ ranged from 1.34 (1 year) to 9.30 cm (5 years) (Table 1), and the corresponding values increased from 1.33 to 9.47 cm in ‘Feilong’ plants (Table 1).

Reproduction

‘Chongtian’ can be propagated by grafting or cutting. One-year-old dormant branches harvested from the mother plant are used as scions. After collection, the scions are cut into 4 to 5 cm lengths (leaving two or three buds on each branch), the cut is sealed with paraffin wax, and the branches are kept in darkness at ∼4 °C. One- or 2-year-old Z. schneideriana seedlings with a stem diameter of 0.8 to 2.0 cm are used as rootstock. Grafting is performed in mid-March. The survival rate of grafting generally may reach 90%. Cutting is carried out in late June and early July. Semihardwood is collected and trimmed to 8- to 10-cm lengths. Leaves adjacent to the basial portion were discarded, leaving two or three at the top. The basal part of the cuttings is then immersed in a solution containing 400 mg·L⁻¹ ABT1 for 6 h. Next, the cuttings are inserted vertically into the rooting media in the greenhouse to approximately one-half their total length. The rooting media consists of 2 peat: 1 vermiculite: 1 perlite (by volume). An intermittent misting system is used to maintain high air humidity. Generally, the rooting rate is ∼50%.

Cultivation Techniques

‘Chongtian’ exhibits strong adaptability, high pest and disease resistance, and excellent tolerance to drought and cold stresses. It is suitable for afforestation and beautifying the environment. A 2 m × 2 m cultivate spacing provides plants with adequate light and ventilation. Young trees need to be pruned to create one dominant trunk. Once there are multiple codominant branches, select the strongest and remove any competitors.

Availability

Inquiries regarding the research or use of ‘Chongtian’ plants can be addressed to Dr. Yunzhou Lyu at the Jiangsu Academy of Forestry, Nanjing, China.