CULTIVAR AND GERMPLASM RELEASES

HORTSCIENCE 54(12):2257–2259. 2019. https://doi.org/10.21273/HORTSCI14276-19 Bark is light gray and split into narrow rough ridges. Twigs are green and smooth. The leaves are odd pinnate compound leaves that ‘Zhong Ning Sheng’: A New Distant are 20–60 cm with a petiole of 4.0–9.5 cm. There are 9–15 leaflets that are yellow–green, Hybrid Cultivar of Walnut lanceolate or oblong lanceolate, symmetric or falcate, and 6.5–13.5 cm · 2.5–5.0 cm. The Xiaobo Song, Shengke Xi, Junpei Zhang, Qingguo Ma, Ye Zhou, margins are serrate, the apex is narrowly and Dong Pei acuminate, and the terminal leaflets are State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree well-developed. Terminal buds are conic Breeding and Cultivation of State Forestry Administration, Research Institute and flattened. Few flowers and fruits are of Forestry Chinese Academy of Forestry, Beijing 100091, China present. Staminate catkins are 5.0–9.0 cm. Fruits are subglobose or long ovoid, smooth, Huzhi Xu and Jianwu Zhang and densely covered with capitate glandular Forestry Bureau of Luoning County, Henan Province Luoyang 471700, China hairs and peltate scales. Nuts are ovoid and light brown. The fruit tip is slightly pointed Additional index words. Juglans sp., breeding, distant hybrid, rootstock and the fruit base is flat. Fruit has an aver- age longitudinal diameter of 2.2 cm, average transverse diameter of 1.6 cm, and average Walnut (Juglans regia) is one of the and LNJR-01 (Juglans regia) performed at a lateral diameter of 1.6 cm; it is shallowly oldest cultivated fruits and an economically seedling field in Luoning County, Henan, longitudinally grooved, and the surface be- important tree, now widely cultivated in China. The objective of the breeding program tween grooves is coarse and warty. temperate regions for both its nuts and timber was to breed rootstocks with high vigor and In the Luoning County area of Henan (Chen et al., 2014). In China, this species has resistance. JH-8202 is vigorous and has a Province (11108#E–11149#Eto3405#– been cultivated for at least 2000 years (Xi and high yield. LNJR-01 is a native superior 3438#N), budbreak of ‘ZNS’ begins in late Zhang, 1996), and in the late 1980s, the first individual with high resistance to various March, which is almost at the same time as batch of precocious walnut cultivars was pests and diseases. In 1982, the University of that of Juglans hindsii and 5–7 d later than released. These cultivars can begin to bloom California–Davis gifted Northern California Juglans reiga; leaf expansion occurs in early within 1 year of planting, entering the full walnut (Juglans hindsii) scions to the Research April. The female flowers open in late April, fruiting period 5 years later, thereby offering Institute of Forestry of the Chinese Academy 5–7 d later than those of J. regia. Crown leaf another advantage in the form of thin-shelled of Forestry. In 1990, through artificial pollina- fall starts in late November. nuts and high yield favored by the majority of tion, nearly 500 hybrid F1 seeds were obtained. ‘ZNS’ showed good grafting affinity with growers and consumers (Germain et al., 1995; Then, from 1991 to 1993, after preliminary walnut, with apparently no significant differ- Pei and Lu, 2011; Vahdati and Mohseniazar, phenotypic identification and screening, 16 ence from that of walnut seeding rootstock; 2015). However, across China, most walnut strong seedlings were selected from 56 hybrid both were >96% (Table 2). Compared with trees were planted in shallow hilly areas, seedlings (candidate pool). From 1994 to 1999, walnut rootstock, ‘ZNS’ as a rootstock sig- where the soil layer is thin and dry. The one seedling was selected based on its growth nificantly improved the growth potential of precocious walnut has high susceptibility to performance and pest and drought stress re- the whole tree (Fig. 1 E), enhanced its re- bacterial blight (Germain et al., 1995). Fur- sistance. From 2005 to 2017, after their propa- sistance to pests and diseases, and delayed thermore, the extremely early fruiting onset of gation, the resulting plants were cultivated and premature senescence of precocious walnuts substantial nuts broke the balance between monitored for their field performance in the linked to early fruiting of large crops of nuts tree vegetative growth and reproduction, lead- Henan, Hebei, Shandong, Hubei, Chongqing, (Song et al., 2016). Therefore, we concluded ing to premature aging and greater suscepti- and Fujian provinces (Table 1). All propagated that ‘ZNS’ may be used as an excellent bility to pests and diseases, thereby restricting plants showed a stable and consistent phenotype walnut rootstock. In terms of the growth rate, the benefits of precocious walnuts cultivars with high grafting affinity to walnut, strong both tree top height and diameter at breast (Song et al., 2016). Most species of Juglans growth potential, high drought resistance, and height (DBH) indicators of ‘ZNS’ exceeded are interfertile. Through interspecific hybrid- high resistance to pest and disease. Conse- those of their parents by >11%. ization, a series of commercial hybrid root- quently, in 2015, the new cultivar ‘ZNS’ was Beyond those traits, ‘ZNS’ also has ex- stocks possessing tolerance to soil-borne designated by the State Forestry Administration cellent material properties (Table 3), espe- diseases has been extensively used for walnut of the People’s Republic of China (Beijing, cially in terms of air dry density, absolute dry production in California (Potter et al., 2018; China) as certificate no. 20150059. In 2018, this density, bending strength, and end-face hard- Vahdati et al., 2002; Zhu et al., 2019). Root- new cultivar was officially authorized for its ness. Its wood quality index is significantly stock breeding studies have been relatively release and use as ‘ZNS’ by the Forestry Variety better than that of the male parent (J. hindsii), backward in China. To resolve this problem, Certification Committee of the State Forestry suggesting it could also be used as a precious we started a distant crossbreeding program, and Grassland Administration (under accession high-quality timber species. ‘ZNS’ features using Juglans regia, Juglans hindssii, Juglans no. S-SV-JH-014–2018). strong asexual reproduction ability, with a nigra,andJuglans major as breeding parents, rooting prevalence of >95% attainable by with the goal of breeding excellent walnut Description and Performance the cutting propagation technique of walnuts rootstocks for walnut industry growing in (Pei et al., 2005). Finally, ‘ZNS’ also has China. ‘ZNS’ has strong vigor, compact tree many of the same characteristics as tall architecture, and strong sprouting ability. trees, such as beautiful architecture and Origin

‘Zhong Ning Sheng’ (ZNS) is the result of Table 1. Performance of ‘ZNS’ cutting seedlings at different sites. a cross between JH-8202 (Juglans hindsii) Location Age Ht (m) Ground diam (cm) Adaptability Pest Disease Henan 6 7.8 14.4 Good — — Hebei 5 6.1 11.5 Good — — Received for publication 7 June 2019. Accepted for Shandong 5 5.7 11.2 Good — — publication 30 Aug. 2019. Hubei 7 8.2 17.5 Good — — D.P. is the corresponding author. E-mail: pei.dong@ Chongqing 4 6.1 12.1 Good — — caf.ac.cn. Fujian 4 5.3 9.6 Good — —

HORTSCIENCE VOL. 54(12) DECEMBER 2019 2257 Table 2. Comparison of two different walnut crown form, yellow–green leaves, and exu- to the annual rootstocks through bud grafting; rootstocks on survival after grafting. berant foliage with few flowers and fruits. b) grafted plants were horizontally laid in the Graft survival (%)z This new walnut cultivar also shows prom- sand pit of the greenhouse and covered with Yr ‘Zhong Ning Sheng’ ‘Ning You’y ising potential as a border/fence tree or for sand; c) after the germination of buds on the 2013 97.4 96.0 use in landscaping. mother plant, the new tips were removed and 2014 96.6 96.8 used as the cuttings (half-lignification state, 2015 97.6 98.2 Cutting propagation 5–7 compound leaves expanded); and d) the zThe grafting test was conducted three times from cutting bases were dipped in the anhydrous 2013 to 2015, with 30 plants of each grafting Refer to the patents of Pei et al. (2005). ethanol IBA solutions (5 mg/mL) for 2–3 s. combination. The main technical procedures of cutting Then, the cuttings were placed in the root- y Ning You is one of the precocious walnut cultivars propagation are as follows: a) new tips of induced matrix [vermiculite: peat soil = 2:3 bred in Luoning Country. donor plants were used as scions and grafted (v/v)] and incubated in the greenhouse

Fig. 1. Distant hybrid cultivar of walnut ‘Zhong Ning Sheng’. (A) The 22-year-old ‘ZNS’ mature plants. (B)Leaf.(C) Catkins. (D) Female flower. (E) Fruit. (F)Nut.(G) Representative cutting treated with Indole-3-butyric acid formed roots after 20 d. (H) ‘ZNS’ plants from softwood cutting propagation. (I) ‘ZNS’ as a rootstock could significantly improve the growth potential of the whole tree (left), with walnut seeding rootstock as a control (right).

2258 HORTSCIENCE VOL. 54(12) DECEMBER 2019