① in vitro seedling culture. Sterilized embryos, shoot tips and other explants were inoculated on germination and growth medium. After about 2 weeks, the shoot tips germinated, and after 20 days, the buds increased rapidly. After 30 days, it differentiated into tufted buds, and after 45 days, it grew to about 2 cm, becoming a test-tube seedling with 4-5 leaves.

② Rapid propagation. After cutting the test-tube seedlings, they can grow to 4-6 cm in height in about 30 days and become rootless seedlings with 4-8 leaves. Once every 30 days, the proliferation coefficient is more than 5 times, and the growth is neat.

③ Induced rooting culture. Rootless seedlings over 2 cm were inoculated on rooting medium to induce rooting, and roots grew after 20 days of culture. Activated carbon was added to keep the roots of test-tube seedlings white for a long time, which was easy to survive after transplantation. At the initial stage of root induction, the growth of the stem was obviously inhibited, and after the root appeared, the stem elongated rapidly.

④ Domestication and transplantation. Rooted plantlets were cultured in the culture room for 20 days, then moved to the greenhouse, cultured in natural light for 5- 10 days, opened the cork for 3 days, and then transplanted. Generally, the three-step transplantation method is adopted. Firstly, the test-tube seedlings are planted in the sand of a small river, and the greenhouse temperature is about 20℃; Second, after two weeks of greenhouse planting, the number of new roots will increase to more than four, and new leaves will grow at the same time. Domesticated seedlings will be cultivated in pots, and loam is suitable for pots. 1 week, the outdoor air will be gradually released to prepare for the entrance. The third is to transplant the domesticated seedlings in the upper pot to the soil. Generally, the test-tube seedlings planted in the field from May to July can grow to more than 1 m in the same year, and can grow to more than 40 cm in the same year planted from August to September, and grow healthily and consistently. (2) Advantages of virus-free vaccine

① Non-toxic seedlings can be obtained. Viruses, fungi and bacteria in most plants are removed by shoot tip culture or heat treatment, and the seedlings have developed roots, healthy growth and strong stress resistance.

(2) The reproduction speed is fast and the reproduction coefficient is large. In vitro rapid propagation can save propagation materials, and a large number of high-quality seedlings needed by the market can be produced in a short time only by taking out a small piece of tissue or organ from the raw materials, and tens of thousands or even millions of plants can be propagated every year.

③ The bred offspring are neat and consistent, and can maintain the excellent characters of the original variety. Tissue culture propagation is a kind of miniature asexual propagation, which is based on somatic cells rather than sex cells of the same individual, so its offspring are genetically identical and can maintain the excellent characteristics of the original variety. A large number of seedlings with uniform specifications and high quality can be obtained, and the commercialization of seedlings is good.