Breeding of a new early-maturing walnut cultivar Shuxiangzao

Shuxiangzao is a newly developed walnut (Juglans regia) cultivar selected from superior seeding trees in the hilly regions of Santai County of Sichuan’s hilly region. It exhibits early maturation, high yield, strong adaptability, and good fresh-eating quality. Since 2004, a program was implemented to select superior genotypes from local walnut (Juglans regia) resources in Santai County, Sichuan Province. During surveys in Liuquan Village, Shian Town, a superior seedling tree was identified, exhibiting early maturation, high yield, strong adaptability, and good fresh- eating quality. Through multi-year comparative observations, its clonedprogeny demonstrated consistent performance with the mother tree, including low kernel astringency, notable resistance to walnut black spot disease (caused by Marssonina juglandis), and stable early maturation. The cultivar was officially recognized and registered by the Forest Variety Approval Committee of Sichuan Province in 2025. Shuxiangzao is vigorous with an open, semi-circular crown. Its odd-pinnate compound leaves are 40-65 cm long and consist of 7-9 leaflets. Pistillate flowers are borne in clusters of 1-3. The fruits are predominantly double-nutted, and the pericarp surface shows conspicuous white dots. The nut is elliptical in shape. The peeled fresh nut weighs 24.2 g, the dry nut 15.4 g, and the kernel 8.8 g. The shell thickness is 1.2 mm, yielding a kernel extraction rate of 57.1%. The shell surface is relatively smooth with deep grooves and sparse reticulation patterns. The arithmetic mean of the three principal diameters (length, width, and height) is 36.55 mm. The suture line is flush with the shell surface, demonstrating tight adherence between the two shell halves. The kernel has a fat content of 62.1% and a protein content of 15.4%. It is plump with a uniform brownish-yellow color and has a fragrant, lingering sweetness without perceptible astringency. In Mianyang, Sichuan, the pistillate flowers of this cultivar bloom in mid-March, and the fruit mature in late July, approximately 20 days earlier than the control cultivar (Chuanzao No.1). Black spot disease caused by anthracnose is relatively mild. The shell rate and damage rate are low, and the nuts are relatively resistant to storage. The cultivar shows high graft compatibility with Juglans sigillata rootstocks. It is suitable for cultivation in low mountainous and hilly areas with deep soil in the Sichuan Basin, as well as in other climatically similar regions. Grafted onto 5-year-old rootstocks, it begins to flower and fruit in the second year. By the fifth year, the yield reached 380 g · m- 2 of canopy projection area, equivalent to 118.5 kg per mu or 1 777.5 kg·hm-2 ). By the thirteenth year, the yield increased to 930 g·m-2 (227.4 kg per mu or 3411 kg·hm-2 ). The pollination varieties can be selected from local walnuts or other cultivars with similar flowering periods. The recommended ratio of the main cultivar to the pollinizer trees is 10∶ 1. The trees can be of the open-pyramidal type or the three-layer open-pyramidal type. The initial pruning height should be 80-120 cm. Orchards should maintain favorable soil moisture and fertility conditions, with weeds controlled through regular weeding or black plastic mulching. Irrigation should be applied sufficiently during spring and summer droughts and combined routinely with fertilization.