Preliminary Study on Propagation Methods and Technical Key Points of Taxus wallichiana var. mairei
Taxus wallichiana var. mairei, also known as beautiful yew, shan gongzi, and hailuo pine, is a rare evergreen tree under first-class national protection. It has a graceful form, with a purplish-red, straight trunk, and when the seeds mature they turn red, with a vividly colorful aril. It has strong regional adaptability and can be planted anywhere south of Shaanxi. This tree species prefers a humid and cool climate environment, and is suitable for growing in moist, loose, well-drained acidic to slightly acidic soil. It is a semi-shade-tolerant species; seedlings tolerate shade and grow slowly, with growth increasing after 3 years. Because it also tolerates poor soil and has strong resistance to pests and diseases, it is the preferred species for reforestation on mountain land in East China after pine species have been harmed by pine wilt disease. At the same time, this tree species has enormous economic value; its branches, leaves, bark, and roots can be used to extract the expensive anticancer drug paclitaxel. Since our institute began implementing the provincial agricultural three-item project "Industrialized Development of Yew Seedlings" in 2000, we have accumulated a relatively mature set of propagation techniques, now introduced as follows:
1 Seed propagation
1.1 Seed collection: Harvest the red fruits in late October, rub off the red aril and flesh, wash clean, disinfect the seeds by soaking in a 0.05% potassium permanganate solution for 0.5 h, then wash clean and air-dry, and store mixed with moist sand.
1.2 Breaking the seed coat: The seeds have a relatively long after-ripening period and dormant characteristics. Under natural conditions, they must go through two winters and one summer before they can germinate, that is, placed outdoors in winter to freeze, then exposed to high temperatures and rain in summer, and sown in autumn of the following year. If sown in spring, they can remain outdoors in the soil to freeze after winter begins, then be moved into a warm house in late March to early April for germination acceleration before sowing, and seedlings can emerge more than 20 days after sowing. If the seeds can be repeatedly rubbed with coarse sand using the sole of a shoe on rough concrete ground, wearing through the inconspicuous tough seed coat and thinning the hard seed shell (do not rub the kernel to pieces), the seeds will readily absorb water and air, and germinate faster after sowing.
1.3 Variable temperature treatment: Yew seeds have the habit of double dormancy of the radicle and hypocotyl. The radicle needs to pass through a high-temperature stage above 25°C for about 1 month to break dormancy, and the hypocotyl needs about 1 month at -3 to -20°C to release dormancy. In order to advance and accelerate seed germination, simply mix the yew seeds with broken seed coats with moist sand, and freeze them in an environment below -3°C for 25 to 40 d to release hypocotyl dormancy. After sowing in late winter or early spring, after about 2 months, when temperatures above 25°C are encountered, radicle dormancy can be broken, and the seeds can sprout and emerge from the soil.
1.4 Sowing and seedling raising: Drill sowing, with row spacing of 20 cm and depth of 2 cm. About 30 d after sowing, the seeds begin to push through the soil and emerge. At this time, it is the spring rain season. Because of abundant rain and high air humidity, the seedlings are susceptible to infection by pathogens, causing root rot and damping-off disease. Therefore, when the seedlings are pushing through the soil, control should be carried out once every week with an 800-fold thiophanate solution; after the seedlings emerge, spray once every week with half-strength Bordeaux mixture or 800-fold thiophanate solution. After emergence, shading is required. The seedlings are afraid of sunscald, so the shade shed should have a light transmittance of 30% to 40%, and weeds must be frequently removed. Water once every 15 to 20 d with dilute urea water or clear manure water to promote seedling growth. After 1 year, they can be transplanted in the open field.
2 Cutting propagation
2.1 Collecting cuttings: From May to June at the turn of spring and summer all the way to late November, cut current-year young branches from mother trees aged 4 years or more as cuttings.
2.2 Cutting treatment: Cut branches 15 cm or longer as cuttings, remove the lower leaves, and girdle the base of the branch to create a wound of 0.5 to 1 cm. After tumor-like tissue forms around the wound, cut the branch off below the girdled part, and soak the basal end in 100×10E-6 indoleacetic acid or phenylacetic acid for 3 h, or soak in 200×10E-6 ABT No. 2 rooting powder solution for 8 to 10 h.
2.3 Cutting method: Insert the treated cuttings into a prepared seedbed or a substrate of vermiculite plus weathered sand (1:1) with sawdust, at a cutting depth of 3 to 5 cm and a plant-row spacing of 8 to 10 cm. After insertion, water thoroughly, and use a plastic film arch cover to retain moisture. At first, spray water 2 times a day, and after 2 weeks, once a day. Shading is the same as for seed propagation. Roots form 45 to 50 d after insertion. With careful management, the seedling survival rate can reach more than 90%.
3 Bud seedling transplanting
About 30 d after sowing, the seeds begin to push through the soil and emerge. When the bud seedlings grow to 2 to 3 cm tall and 3 to 4 true leaves appear (generally in mid-April), transplanting can be carried out. During transplanting, first use a bamboo chopstick to make a small hole in the nutrient pot, move the bud seedling in, and then press the soil firm. The best time for transplanting is on cloudy days; on sunny days, it should be done in the morning and evening, and water thoroughly promptly after transplanting. Transplant 2 plants per nutrient pot. Nutrient soil preparation: Prepare the nutrient soil with 40% loess, 40% river sand, and 20% humus soil, crush and sieve before use. Disinfect the nutrient soil with 0.5% potassium permanganate solution; ferrous sulfate and 65% zineb powder can also be used for soil disinfection. Compared with the traditional method of sowing and seedling raising, bud seedling transplanting has a higher emergence rate, saves seeds and land resources, produces seedlings of good quality and high yield, and can significantly extend the growth period of the seedlings. The average growth of the seedlings in the same year can reach 15 cm. As long as management techniques are in place, the survival rate for afforestation and greening can reach more than 96%.
4 Seedling management and field release for afforestation
4.1 Seedling overwintering management: Seedlings are afraid of frost, so in winter an arch shed must be used to keep them warm and protect them. It is even better to add a straw curtain over the plastic film.
4.2 Seedling transplanting and hardening: After 1 year of cultivation, both sown seedlings and cutting seedlings should be transplanted and hardened. Transplant the seedlings to an open-field seedbed at a plant-row spacing of 25 to 30 cm, build a 1.5 m high shade shed with six parts shade and four parts light, water frequently, and apply dilute urea water or light manure water at the appropriate time to cultivate strong seedlings.
4.3 Various insect pests: These include cutworms, white grubs, leaf-eating pests, and others. Use 50% dichlorvos emulsifiable concentrate 6 ml plus 2.5% deltamethrin emulsifiable concentrate 2 ml, 48% chlorpyrifos emulsifiable concentrate, and 90% trichlorfon soluble powder 30 g, mixed with water 15 kg, and spray on the bud seedlings. Sterilization and insect control are carried out simultaneously, with relatively good control effects.
4.4 Field release for afforestation: After 1 year of hardening, yew seedlings can be released for afforestation when the seedling height is 40 to 60 cm. Planting in late winter and early spring is good, with a planting plant-row spacing of 1.6 m × 2 m.