Breeding report of a new late-maturing walnut cultivar Dayao No. 1

Dayao No. 1 walnut is a new variety of walnut, characterized by late maturity, high yield, sweet and fragrant flavor, and delicate texture, which was selected and bred from the seedling population of deeply-ribbed walnuts in Yunnan. It is highly popular among the markets and consumers, and is in high demand in the production areas, bringing good economic benefits. The walnut kernel is spherical in shape, with flat shoulders and a slightly convex base. The suture lines are slightly raised and moderately close together. The seed tip is bluntly pointed, and the shell is relatively smooth. The average diameter of the three axes is 3.40 cm, classifying it as a medium-sized fruit variety. The shell thickness is 1.08 mm, with a degenerated inner fold and a membranous septum, making it easy to extract the kernel. The average weight of a single nut is 12.20 g, with a kernel weight of 6.84 g, resulting in a kernel extraction rate of 56.07%. The kernel is plump and light in color. The walnut kernel contains 1.7 g of reducing sugars per 100 g, and has an oil content of 64.7% and a protein content of 17.1%. The tree has a strong growth vigor and a spherical canopy. Each compound leaf consists of 10 to 13 leaflets, with 11 leaflets being the most common. The leaflets are oblong in shape. The mixed buds are round without bud stalks. The branching rate of shoots is 185%, the branch formation rate is 100%, and the fruit-bearing branch rate is 95%. The tree has unisexual flowers with protandry (male flowers open before female flowers). The male inflorescences are 5.0 to 10.0 cm long. On average, each fruit-bearing branch has 3 to 4 female flowers, often more than 3, and the average fruit set is 3 to 4, often more than 3. The fruit is round, with a smooth surface and without no pubescence, and is green in color. In Dayao County, the tree buds and leaves come out in mid-to-late April and leaves shed in mid-November, with a growing period of about 214 days. The tree mainly bears fruit from the terminal buds and the lower 2 to 3 lateral buds of the fruit-bearing branches. The fruits mature in mid-October, about 20 days later than the control variety Dayao Santai walnut. The tree has good growth and fruiting conditions, with no significant alternate bearing. Molecular marker analysis shows that Dayao No. 1 walnut plants differ from Dayao Santai walnut plants at the molecular level. It exhibits good cold resistance, ability to avoid late frosts, and resistance to pests and diseases. Dayao No. 1 walnut can be cultivated in the mid-to-high altitude regions of Yunnan. The breeding of this variety fills the gap in Yunnan for late-maturing walnut cultivars suitable for mid-to-high altitude, and it has a promising future for production and promotion.