Detailed Explanation of Seed Seedling-Raising Techniques for Taxus yunnanensis
Taxus yunnanensis Cheng et L. K. Fu is a rare evergreen tree under first-class national protection, suited to the high mountain zones of northwestern Yunnan at 2000-3500 m. Because its branches, leaves, bark and roots can all yield the expensive anti-cancer drug taxol, the Taxus market has boomed in recent years and prices have soared all the way up. World annual demand for taxol exceeds 4800 kg, while actual annual production is only about 250 kg. Although China has built taxol processing plants one after another in Beijing, Shanghai, Liaoning, Yunnan and Sichuan, wild resources are limited and are strictly protected by the state, so raw material supply is extremely tight.
In 2004 the management station formed a research group to carry out experimental research on artificial propagation of Taxus yunnanensis, exploring greenhouse seedling-raising of the species. Through 3a of trials, a whole set of techniques was worked out, from seed treatment and germination forcing to seedling cultivation, laying a solid foundation for meeting future market demand for Taxus afforestation. At present the management station has raised a total of 35,000 bag seedlings of Taxus, with an average height of 14.6 cm and an average ground diameter of 4.72 mm, and the seedlings are growing normally.
1 Seed treatment
1.1 Breaking the seed coat
Taxus yunnanensis seeds have a long after-ripening period and a dormant character; under natural conditions they need two winters and one summer before they can germinate, that is, frozen outdoors in winter, exposed to high temperature and rain in summer, and sown in autumn the following year; if sown in spring, they can remain frozen in outdoor soil after winter begins, then be moved into a warm house from late March to early April for germination forcing before sowing, and seedlings emerge 20 d after sowing. Before sowing, abrade the tough seed coat and hard seed shell (do not rub the kernel to pieces) so that water and air can pass through more easily and germination after sowing is faster.
1.2 Alternating temperature treatment
Taxus yunnanensis seeds have the habit of double dormancy of 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. To speed up germination earlier, simply mix Taxus yunnanensis seeds whose seed coat has been broken with a small amount of moist sand and freeze them at below -3°C for 25-40 d to release hypocotyl dormancy; after sowing in late winter or early spring, about 2 months of temperature above 25°C is needed to break radicle dormancy, and only then will the seeds sprout and emerge.
1.3 Germination forcing
Mix Taxus seeds that have been through seed-coat breaking and alternating temperature treatment with moist sand at a 1:2 ratio and store them to force germination. When seed is needed, take the seeds out, soak them in 0.5% potassium permanganate solution for 1-2 h, then remove them and rinse clean with clear water.
2 Land preparation, bed making and soil disinfection
2.1 Land preparation
Choose well-aerated sandy loam as the seedling bed. Use full land preparation, deeper than 20-25 cm, break clods, clear grass roots and stones, and level the land.
2.2 Bed making
On the prepared land, make a low bed, with the bed surface 3-5 cm lower than the path (ridge), bed surface width 1-
1.2 m; place the topsoil in the center of the seedling bed, use the subsoil to make the ridge, then spread the topsoil flat.
2.3 Soil treatment
Disinfect the soil while making the bed; apply carbendazim at 6-8 g per sq m evenly over the bed surface as the bed is made, and turn it into the soil.
3 Sowing
Use drilling. Open sowing furrows 15-20 cm wide and 3-5 cm deep on the bed surface, with row spacing 10-15 cm. Mix the germination-forced seeds with humus soil or plant ash so they do not stick together, then scatter the seeds evenly into the sowing furrows. After sowing, cover with burnt soil or humus soil to a thickness of 1 cm, then cover with a layer of pine needles and water thoroughly.
4 Seedling management
The seedling-raising season coincides with high temperatures and dry weather, so water management is a main task in seedling-stage management. Germination-forced seeds must not be allowed to dehydrate, otherwise the seeds will lose germination capacity from water loss. Generally water thoroughly once every 2 d; in especially hot, dry weather water thoroughly once a day.
4.1 Light management
After the seedlings emerge but before they push through the pine needles, remove the pine needles in 2-3 batches. Seedlings are susceptible to sunscald, so shade promptly after removing the pine needles, with the shade frame's light transmittance at 15%-20% to prevent the seedlings from being scorched and burned. When removing the pine needles, take care not to damage the seedlings, and finally pick out dead branches, fallen leaves and broken grass.
4.2 Spraying for disease prevention
To prevent damping-off, which seedlings are prone to, before the small seedlings emerge, drench once with 0.125%-0.167% dexon wettable powder solution. After the mulch is removed, spray with 0.5:1 Bordeaux mixture at 0.5%-0.67% solution or 0.08%-0.1% kangku Ling solution, once every 7-10 d, alternating the two.
4.3 Weeding
As temperatures rise, weeds grow rapidly. Therefore weed promptly, removing them as early and as small as possible, to avoid weeds affecting the growth of the small seedlings.
5 Preparation of the nutrient substrate
Choose 12 cm x 15 cm nutrient bags; take humus soil, loam, plant ash and potassium dihydrogen phosphate at 50%, 30%, 19% and 1% and mix thoroughly to make the nutrient substrate. After mixing, spray with 1% ferrous sulfate, stir evenly, and cover tightly with plastic film for 24 h.
Make a low bed in the greenhouse, with the bed surface 10 cm lower than the path, and level it with a wooden board. To prevent weed growth, the bed surface can be sprayed with Nongminle. After filling the nutrient bags with substrate, place them neatly on the bed surface and fill the gaps tightly with fine soil.
6 Bag seedling cultivation management
6.1 Transplanting seedlings into bags
When Taxus yunnanensis seedlings grow to 7-8 cm, with the main root about 10 cm long and well-developed lateral roots, they can be moved from the seedling bed into nutrient bags for cultivation.
Transplant on cloudy days or in the evening of sunny days; to reduce damage to the seedling root system, when taking seedlings use a hoe to dig them out with soil in one direction, pick out the seedlings, and place the roots in No. 50 x 10-66 ABT rooting powder solution for 0.5-1 h before bagging. The nutrient bags should also be watered thoroughly once 2-3 d in advance, so that when the small seedlings are bagged the soil is loose, making the work easier and helping the seedling roots spread and raising the transplant survival rate. When bagging, sharpen a wooden stick, bore a hole in the center of the bag, put the small seedling in, spread the roots, and firm the soil.
6.2 Water management
After transplanting the small seedlings, water thoroughly promptly. Over the following 25 d pay special attention to soil moisture; choose morning or afternoon for watering, and in continuous sunny weather water once in the morning and once in the afternoon to ensure normal seedling growth.
6.3 Shading the seedling bed
Taxus yunnanensis seedlings like shady environments, so after transplanting the small seedlings shade promptly, with the shade frame's light transmittance at 25%-30%. Within 10-20 d after transplanting, observe the survival of the seedlings; whenever dead seedlings are found, replant promptly. After 2-3 rounds of replanting, the number of bags with seedlings can reach more than 95%.
6.3 Fertilization
Topdressing can be combined with watering, mainly watering once every 15-20 d with dilute urea water or clear manure water to boost the seedlings; after watering, rinse the seedlings promptly with clear water so the fertilizer does not burn them. Topdressing should be done little and often. After early October, gradually control water and fertilizer to promote further lignification of the seedlings; after November, stop fertilizing.
6.4 Temperature and humidity control
In greenhouse seedling-raising of Taxus yunnanensis, control the temperature inside the greenhouse well; when the temperature exceeds 35°C, open the doors and ventilation holes at once to create air convection inside and lower the greenhouse temperature. Control the humidity in the greenhouse at about 85%-90%.
7 Pest and disease control
The main pests and diseases of Taxus yunnanensis seedlings are damping-off, snails and so on; carry out the policy of "prevention first", observe often, spray on schedule for control, and actively do prevention work well. According to observation, Taxus yunnanensis moved into nutrient bags, because the density becomes smaller and resistance increases, showed no pest or disease damage.
According to observation, from June, when Taxus yunnanensis was moved into nutrient bags, to September, within 3 months the seedling height increased by 1.23 cm and the ground diameter increased by 0.82 mm, showing that Taxus yunnanensis seedlings grow slowly; therefore afforestation the same year gives poor results, and it is better to raise 2-year-old seedlings and lift them from the nursery in July of the following year.
8 Summary
(1) Taxus yunnanensis is a rare tree species under first-class national protection, and there have been no reports of large-scale seed seedling-raising and afforestation, mainly because seed seedling-raising is very difficult and has not been well solved. Through 3a of experimental research, the research group made a major breakthrough in seed seedling-raising techniques for Taxus yunnanensis, basically solving the whole set of technical steps from seed treatment and germination forcing to seedling cultivation, taking an important step for Yunnan Province in developing and utilizing a nationally rare protected tree species, which is of great significance.
(2) The key to seed seedling-raising of Taxus yunnanensis is mastering the seed treatment steps well. Because its seeds have the habit of double dormancy of radicle and hypocotyl, dormancy must be broken early through steps such as breaking the seed shell, alternating temperature treatment and moist sand germination forcing, in order to achieve uniform and strong seedlings.
(3) Seed seedling-raising of Taxus yunnanensis is better done early. Generally sowing can be done before the Beginning of Spring, and seedlings are transplanted into bags for cultivation from late May to early June to increase seedling growth. Alternating temperature treatment greatly shortens the emergence time, and emergence is very uniform. Seedlings must be partly lignified, with the main root about 10 cm long and well-developed lateral roots, before they can be bagged for cultivation. Otherwise the seedlings grow slowly and some show the "squatting in the bag" phenomenon. In the later stage of bag seedling cultivation, water and fertilizer should be moderately controlled to promote further lignification of the seedlings, which helps raise the afforestation survival rate.
(4) Because wild resources of Taxus yunnanensis are very limited and it is a nationally rare protected tree species, its rich taxol content makes market supply fall short of demand, and prices have soared all the way up. Therefore, carrying out large-scale artificial afforestation of Taxus yunnanensis to meet market demand will play a positive role in increasing farmers' income and helping them escape poverty.