The zygote begins to divide on the 15th day after the female walnut flower is pollinated. After multiple divisions to form a torpedo-shaped embryo, it quickly differentiates into hypocotyls, radicles, cotyledons and embryos. The development of endosperm precedes zygote division, but as the embryo develops, all endosperm cells are absorbed, so mature walnut seeds have no endosperm. It takes about 130 days for walnuts to mature from fertilization to nut maturity. According to the observations of Luo Xiujun et al. (1988), the development process of walnut fruit is divided into the following four stages based on fruit volume, weight growth and fat formation:

(1) Fruit rapid and long term

Early May to early June, about 30 to 35 days, is the period of rapid fruit growth. During this period, the volume and weight of the fruit increase rapidly, with the volume reaching more than 90% and the weight reaching about 70% when mature. The average daily growth in longitudinal and transverse diameters from May 7 to 17 can reach 1.3 mm, and the average daily growth in weight from May 12 to 22 is 2.2 grams. As the size of the fruit increases rapidly, the embryo sac continues to expand and the core shell gradually forms, but the fruit is white and tender.

(2) Hard core stage

From early June to early July, about 35 days, the core shell gradually hardens from the top to the base, and the elasticity of the septum and pleats in the core becomes The hardness gradually increases, the shell surface becomes engraved, the hardness increases, and the kernel gradually turns white, crisp and tender. The size of the fruit is basically finalized, and nutrients accumulate rapidly. Within 20 days from June 11 to July 1, the kernel yield increased from 13.7 to 24.0, and the fat content increased from 6.91 to 29.24.

(3) Rapid oil conversion period

From early July to late August, about 50 to 55 days. After the fruit size is finalized, the weight still increases and the kernels continue to be full and plump. , the kernel yield increased from 24.1 to 46.8, the kernel moisture content decreased from 6.20 to 2.95, the fat content increased from 29.24 to 63.09, and the kernel flavor changed from sweet to fragrant.

(4) Fruit maturity period

From late August to early September, the weight of the fruit increases slightly, the color of the involucre (green skin) changes from green to yellow, and the surface is bright and hairless. Some of the involucres are cracked and the nuts are easily peeled off, indicating that they are fully mature.

Early or late harvesting has a great impact on the quality of walnut nuts. Early harvesting seriously reduces nut yield and kernel quality.

Walnut flower and fruit drop is relatively serious. Generally it can reach 50-60, and in severe cases it can reach 80-90. Flower drop occurs mostly at the end of the flowering stage. Fruit drop begins when the young fruit grows to about 1 cm 10 to 15 days after flowering, reaches a peak when the fruit diameter is about 2 cm, and basically stops at the hard core stage. The lateral fruiting branches usually lose more fruit than the terminal fruiting branches.