How to Efficiently Propagate Lychee Seedlings? Latest Technical Method Tutorial

Grafting Propagation of Seedling Rootstock

1. Nursery Site Selection

Choose a standard rectangular field plot with abundant sunlight, open terrain, ample water sources, convenient drainage and irrigation, and complete supporting water conservancy ditches and field roads, suitable for the operational needs of nursery site construction.

2. Nursery Site Fertilization

The cohesiveness of the seedbed soil should be suitable for rootstock growth and for holding soil together when lifting seedlings. For relatively fertile soil with weak cohesiveness, it is not suitable for operations such as lifting seedlings with a seedling lifter while retaining a soil ball. Therefore, different soil types need to be blended into the seedbed. If the seedbed is paddy field, water control, plowing, sun-drying of soil clods, and deep plowing for maturation are required, which helps raise soil temperature and soil oxygen content, while killing soil pathogens and insect eggs and loosening the soil. On the basis of proper field water control and sun-drying, red clay should be transported from elsewhere and blended in to enhance cohesiveness, which is beneficial for later lifting of seedlings with soil balls. This is a key measure to avoid bare-root seedlings and ensure survival after planting. If the seedbed soil is poor and weak, it should be fertilized. It is recommended to additionally apply, according to the fertility level, 500-600 kg of decomposed sheep manure, 50-100 kg of superphosphate, 50-100 kg of compound fertilizer, and 50 kg of lime per mu, and mix thoroughly and evenly with the soil.

3. Seedbed Ridging

Two months after the soil fertilization and maturation work in the nursery, begin ridging the seedbed, specifically as follows:

① Ridge surface preparation. Ridging requirements: ridge surface width 2 m, length depending on the field terrain and ridge arrangement, ditch width 30 cm, depth 30 cm, drainage ditch depth 50 cm. After the sowing ridges are opened, break up the soil and level it, then wait for sowing.

② Set up fencing. To prevent pigs, cattle and other livestock from intruding into the nursery and trampling and damaging it, fencing is needed around the nursery base. The specific method is: bind cement bricks tightly around the nursery with iron wire, or make a fence with bamboo poles.

③ Build a shade shed. Standard: greenhouse span 6 m, length 15-20 m, shoulder height 1-1.5 m, ridge height 1.8-2 m, bottom cross-section diameter 6 m. Procedure: set one upright post every 2 m along the width (span) direction, with post thickness 6-8 cm, form an arch at the top, bury 50 cm deep underground, pad with bricks or tie crossbars, tamp solid, fix bamboo poles at the top of the posts to form an arch, add crossbars at both ends, bury them underground and tamp solid; arch frame spacing 1 m, connected as a whole with longitudinal tie rods; cover the arch frames with shade netting, and after tightening, bury the ends of the net in the surrounding soil; between arch frames, press the shade netting tight with net-pressing wire or No. 8 aluminum wire, bamboo poles, etc.

4. Rootstock Cultivation

According to experience, old lychee varieties have good compatibility with varieties such as Shuidong, Xiaohei Sanyuehong, and Feizixiao. Select local old lychee varieties as grafting rootstocks. The specific work is:

① Seed collection and germination promotion. After the fruit matures in April-May, collect old-variety lychee seeds in a centralized manner. To raise 100,000 seedlings, about 130,000 seeds are needed. Lychee seeds cannot be stored for a long time, so they should be collected in batches for germination and sowing. Germination method: choose a flat piece of land, pile 3-5 cm of wet sand on it, place the washed seeds flat on the sand surface without overlapping the seeds, then cover the seeds with 5 cm of rice straw, water frequently to keep the straw moist, and after 4-5 days when the radicle of the seeds emerges, they can be taken out and sown.

② Sowing and seedling raising. Sowing specifications: plant spacing and row spacing of 18 cm × 12 cm is appropriate. Sowing method: sow single seeds. When sowing, first open sowing furrows according to row spacing, furrow depth about 3 cm, place the seeds flat in the furrows according to the originally set plant spacing, water, then cover with soil. The soil cover thickness should preferably be 2 cm. Too shallow and the seeds easily dry out and die; too deep and the seedlings have difficulty emerging.

5. Rootstock Grafting

① Scion selection. The grafting varieties are mainly Shuidong, Xiaohei Sanyuehong, and Feizixiao, with other varieties appropriately blended in. In the early stage before collecting shoots, branch and shoot pruning management should be done well. Requirements for collecting scions: select 3-5 year old, vigorously growing fruiting mother trees as the source of scion wood, and choose 1-2 year old branches from the middle and upper outer canopy that are full, have plump buds, and fully mature leaves. Storage requirements: if conditions permit, graft immediately after cutting; if placement for a short period is truly necessary, wrap the scion branches with fresh lychee leaves, then wrap a layer of wet towel, seal with a plastic bag, and place in a cool place.

② Grafting time. According to experience, lychee grafting should preferably be chosen in March-April each year, with supplementary grafting carried out in September-October of the same year.

③ Grafting method. Nursery seedling grafting adopts the branch grafting and cut grafting method. Grafting method: first, cut the rootstock. Cut off the top of the rootstock at 30 cm above the ground, choose a straight side facing upward and make 1 horizontal cut to form a 45° slope, then below the slope on the straight part, cut vertically downward along the cambium or slightly into the xylem for 1 cut, with an incision length of 3-4 cm. Next, cut the scion. Hold the scion branch straight downward, cut the lower end of the branch into a 45° slope, reverse the branch so that the straight side faces upward, and cut 1 smooth long cut surface slightly longer than the rootstock incision by cutting downward to the cambium or slightly into the xylem, leaving 2-4 buds. Finally, join and seal. Insert the cut scion with the long cut surface facing inward into the rootstock incision so that the cambium between rootstock and scion aligns with each other, then bind and seal with plastic film strips.

6. Seedling Lifting and Nursery Release

① Seedling standards. First, the rootstock and scion are well compatible, the graft union develops evenly above and below, and there are no adverse phenomena such as swelling at the base or strangling of the trunk and leaf yellowing caused by removing the binding too late. Second, the grafting site is at 30-35 cm and must not be too high; the trunk is thick and straight, seedling height 50-60 cm, with 3-4 branches, growing robustly, with neat leaves and deep green leaf color. Third, the branches and trunk are thick and strong, and the root system is well developed.

② Seedling lifting and nursery release. Seedling lifting method: first make a cylindrical seedling lifter. When lifting seedlings, take the main trunk of the seedling as the center, insert the seedling lifter into the soil from both sides of the seedling, strike the seedling lifter with a large iron hammer until the seedling lifter is fully inserted into the soil, then grip the iron handle of the seedling lifter tightly, pull up the seedling lifter together with soil and seedling, trim off overly long main roots, open the seedling lifter, and it becomes a lychee seedling with a cylindrical soil ball; then wrap the entire soil ball of the lifted seedling with plastic film, tie the film tightly with fiber tape, and it can be released from the nursery for supply.

③ Transportation and supply. When the first new shoot of the grafted seedling ages and matures, it can be released from the nursery for planting. During loading and transport, it should be placed neatly and can be loaded in two layers. Seedlings released on the same day must be transplanted and planted within no more than three days. The year-round nursery release time is June-October.

7. Nursery Site Management and Protection

For the construction and management of the nursery site, personnel should be assigned to watch over and guard the base. In addition to being responsible for guarding the base property and seedlings, management and protection personnel also shoulder daily nursery management and farming operations.

8. Seedbed Management

① Post-sowing management. That is, management work from after sowing to before grafting. First is water management. After sowing, water frequently on sunny days to keep the soil moist, which helps seed emergence. Second is fertilizer management. When the first true leaf of the seedling turns green, begin applying dilute manure water, and afterward lightly apply ternary compound fertilizer and potassium sulfate. During low-temperature periods in winter, cover the ridge surface with plastic film to raise the seedbed temperature. Finally is pest and disease management. Do a good job in controlling underground pests, and promptly remove dead seedlings when found.

② Grafted seedling management. That is, management work from after grafting to before nursery release. First, ensure the survival of grafted seedlings. Those still not surviving within 20 days after grafting should be supplemented and grafted in time. Second is removing the binding. After checking survival, promptly cut through the film at the bud eye area to let the bud grow out, and after grafting survival, promptly cut off the rootstock top to accelerate sprouting and growth of the grafted bud. Third is removing rootstock sprouts. After grafting survival, rootstock sprouts often emerge and should be promptly removed to ensure growth of buds and shoots on the scion. Finally is tree shaping and strengthening fertilizer and water management. When seedling height is 40-50 cm, shaping and pruning should be carried out to cultivate strong main branches, selecting and retaining 3-4 strong branches distributed evenly as main branches. At the same time, fertilizer and water management should be strengthened, ensuring “one shoot, two fertilizations”, mainly by mixing with water and pouring, not by flooding irrigation. Urea, potassium sulfate, compound fertilizer and other chemical fertilizers may be appropriately added, with the amount depending on soil fertility and seedling condition.

③ Management of nursery-release seedlings. That is, management work from after nursery release to planting. First is seedling nursery-release management. One month before nursery release, the top should be pinched to promote branch maturation and strength and to increase lateral branches. At nursery release, seedlings should be lifted ridge by ridge. Those too small to be released should be gathered to one side for strengthened management. Second is seedling sales. Seedling prices should be set reasonably. If the nursery construction is a government action, it should follow the principle of supply at a fair price or with small profit.

Air-Layering Propagation

Lychee air-layered seedlings are also called air-layered cuttings. This seedling-raising method is technically simple, easy to operate, has a short seedling-raising time, and bears fruit early after planting. It is suitable when the mother tree source can meet the demand. However, this method has a low propagation coefficient. When there are few superior mother trees, it cannot meet the demand for seedlings. After planting, if management is slightly poor, the survival rate is low, and the recovery period is long.

1. Propagation Season

Generally choose April-June as the best time. At this time, propagation can produce 2-3 rounds of roots well in the same autumn, and in the same year they can be cut from the tree for temporary planting or field planting.

2. Branch Selection for Air-Layered Seedlings

First determine the variety to be bred. Second, choose 3-5 year old strong fruiting trees, preferably vigorous, pest-free branches with a diameter of 1.5-2 cm that are upright or obliquely extending out of the canopy and can receive sunlight. In short, branches used for air-layered seedlings should come from robust fruiting mother trees that are high-yielding, stable-yielding, high-quality, and possess the excellent traits of that variety.

3. Branch Girdling, Wound Opening, and Wrapping

On the selected branch, use a ring branch knife to make two ring cuts at the selected position, deep to the xylem, with a distance of about 3 cm between the two cuts. Then remove the bark between the two ring cuts, apply 5000 PPm indolebutyric acid to the cut, wrap with rooting-promoting medium (such as a mixture of lichen and fine mud containing humus), and bind into a spindle shape with plastic film. Generally after 30-40 days, new white tender roots can be seen outside the wrapping material, and after 50-60 days, 2-3 rounds of roots grow, forming a root mass around the outside of the wrapping material. At this time, the air-layered seedling can be cut away from the mother body to become a new plant, for temporary planting or field planting.