What standards must high-quality jujube tree nursery stock meet?

⑴ Extra-grade stock: seedling height 1.2 to 1.4 m, diameter near the ground 1.5 to 2 cm, retaining permanent secondary branches more than 40 cm above the ground, thick roots with a diameter of 3 mm reaching a length of 30 cm, and the ratio of the total length of fine roots with a diameter below 2 mm to the weight of the seedling reaching 1.0 or more; ⑵ Grade I stock: seedling height 0.8 to 1.2 m, diameter near the ground 0.8 to 1.5 cm, retaining secondary branches more than 50 cm above the ground, thick roots with a diameter of 3 mm reaching a length of 20 cm or more, and the ratio of the total length of fine roots with a diameter below 2 mm to the weight of the seedling reaching 0.8 or more; ⑶ Grade II stock: seedling height below 80 cm, diameter near the ground 0.6 to 0.8 cm, thick roots with a diameter of 2 mm reaching a length of 30 cm or more.