Breeding of the improved walnut cultivar Daliangshan Ziyi No. 2 (Juglans sigillata)

Juglans sigillata‘Daliangshanziyi 2’is a superior clone identified during a walnut germplasm survey in Liangshan Prefecture, Sichuan Province. In 2006, a comprehensive germplasm survey of Juglans sigillata was conducted across Liangshan Prefecture through road- transect surveys combined with townships/village-level recommendations and grower nominations. After three-stage selection (preliminary, secondary, and final screening), the indigenous cultivar Daliangshan Ziyi No. 2 was identified for its superior disease resistance, high- yield traits, and exceptional nut quality. Following multi-year field observations, trait documentation, and data compilation, this genotype was designated as an elite cultivar by the Sichuan Forest Cultivar Approval Committee in 2012. It was formally certified (Approval No.: Chuan S-SC- JS-007-2024) by the same committee in 2025. Tree vigor is strong with a distinct main trunk. Branching capacity is vigorous, with branching angles exceeding 30 degrees. One-year-old shoots are grey-brown, smooth, and glabrous, exhibiting short internodes. Terminal buds are large and conical. Axillary buds are appressed, spherical, and densely covered with white pubescence. Primary and accessory buds are distinctly separated. Leaves are odd-pinnately compound. Terminal leaflets are often vestigial. Leaflets number is 7-13 (typically 9), broadly lanceolate in shape. Leaf base is elliptical; leaf apex is acuminate. Abaxial surfaces are glabrous. Petioles are nearly sessile. Nuts are subglobose with slightly raised and tight sutures. Shells exhibit moderate pitting, intact structure, and brown coloration. Average nut weight is 11.93 g, with longitudinal, transverse, and lateral diameters of 31.98 mm, 29.83 mm, and 33.44 mm, respectively. Kernels are extracted whole or half. Kernel recovery rate reaches 51.05%. Kernels contain 64.36% crude fat and 17.70% crude protein on average, with plump pale-purple testa and a sweet flavor. In Dechang County, leaf emergence begins in mid-March, with full expansion by late March. Male flowering occurs in late March, female flowering in early April, and fruit maturity in late August. Leaf fall initiates in early November. The cultivar demonstrates high fruit set (1-3 nuts per inflorescence), ＞50% fruiting shoots, and consistent annual bearing. Trees exhibit vigorous growth and strong adaptability. The cultivation areas are recommended in southwestern Sichuan at 800-2400 m elevation. Grafted trees bear fruit in 2-3 years after planting, reaching full production in 5-6 years, and demonstrating early fruiting and high-yield potential. Orchards should be established on sheltered, sunny gentle slopes with gradients under 15°. Implement land preparation with planting hole dimensions of 1 m×1 m×1 m (L×W×D). Within a planting hole, apply 30-50 kg well-decomposed farmyard manure and 1-2 kg formulated walnut fertilizer. Thoroughly mix amendments with topsoil, and then backfill into the bottom of planting holes.