Benefits and Key Technical Points of Green Branch Grafting in Grapes

Green branch grafting for seedling propagation is a method commonly adopted by nursery growers. During the growing season, green branches of varieties are used as scions and rootstocks for green branch grafting, and the resulting seedlings are called green branch grafted seedlings.What are the benefits of green branch grafting in grapes? What are the related key technical points?

1. Benefits of green branch grafting in grapes

With hard branch grafted seedlings, the graft wound generally heals slowly and unevenly, the survival rate of grafted seedlings is relatively low, and in production there often occurs the problem of uneven plant growth and development in vineyards of hard branch grafted seedlings. Compared with hard branch grafting, green branch grafting has the advantages of fast wound healing, good healing, high survival rate, and high grafting efficiency, and in recent years it has become the main method for cultivating grape grafted seedlings and for variety replacement and upgrading.

2. Key technical points of green branch grafting in grapes

1 Rootstock types

Cold-resistant rootstocks include Beta and Shanhe No. 1, 2, 3, and 4; root-knot nematode-resistant and phylloxera-resistant rootstock includes SO4. At present, Beta is widely used in the north, and SO4 is widely used in the south.

2 Rootstock cultivation

To allow the rootstock to be grafted in the same year it is cuttings-propagated, nutrient bag seedling propagation is needed. Use commercially sold plastic bags with a height of 10 cm and a mouth diameter of 10 cm, cut a small hole with a diameter of 1 cm in the bottom of the bag or cut open 2 corners of the bag bottom to facilitate drainage. At the same time, prepare nutrient soil by mixing soil, sieved fine sand, and decomposed barnyard manure in the ratio V sand:V soil:V manure = 2:1:1. Put the soil into the bags and place them in a sun-facing cold frame for seedling propagation. In Liaocheng, Shandong, cuttings are taken in mid-March. Cut the stored cuttings into bud segments; thick branches can be cut into single-bud cuttings, and thinner branches can be cut into double-bud cuttings, cutting flat 1 cm above the bud eye, and cutting obliquely leaving 8 cm below the bud (for double-bud cuttings, cut obliquely near the lower part of the second bud, cutting into a horseshoe shape). After treating the cut bud segments with a root-promoting agent, insert them straight into the center of the already arranged nutrient bags, with the top bud of the cutting level with the soil surface in the bag. After cutting, irrigate once thoroughly, and at the same time set up arched supports on the sun-facing cold frame and cover with plastic film. Keep the temperature inside the frame at 20-30°C during the day and above 10°C at night. The management work after cutting is relatively simple, mainly maintaining appropriate moisture in the bags, and strictly avoid waterlogging in the bags. When nutrition is insufficient, after 2-3 leaves have grown, spray 1-3 times with 0.3% urea and potassium dihydrogen phosphate solution. When the seedlings grow to 20 cm, they can be planted in the open field, about mid-to-late May. After planting, strengthen fertilizer and water management, and grafting can be done in mid-June.

3 Scion collection

Scions are collected from plants with pure variety characteristics, robust growth, and no pests or diseases, and this can be combined with summer pruning tasks such as thinning branches, pinching, and removing lateral shoots. It is best to collect them near the nursery, grafting as soon as they are cut, for a high survival rate. When collection from other places is needed, the cut green branches should promptly have their leaves removed, be wrapped well with a new wet towel and plastic film or placed in a wide-mouth thermos bottle with a little ice at the bottom, and the scions can remain fresh for 2-3 days during transport.

4 Grafting method

First select semi-lignified green branch scions; for the bud eye, it is best to use a summer bud that has just sprouted but not yet unfurled leaves, as the survival rate after grafting is high and growth is fast. If the summer bud has already grown 3-4 leaves, remove the lateral shoot and use the winter bud. Winter buds sprout slowly, but after sprouting they grow quickly and robustly. When the rootstock and scion branches are consistent in thickness and maturity, the survival rate is high. Before grafting, first cut the green branches of the scions apart at each grafting bud node with a sharp budding knife or razor blade, and place them in a basin covered with a wet towel for storage. When grafting, leave 3-4 leaves on the rootstock, remove the bud eyes, cut off the part above, and split vertically in the middle of the cut surface to a length of 2.5-3 cm. Select a scion similar in thickness and maturity to the rootstock, and about 0.5 cm below the bud, cut downward from both sides into a 2.5-3 cm slanted surface, forming a wedge shape, and the cut edge must be smooth. Immediately insert the prepared scion into the cut in the rootstock, align the cambium on one side of the two, and let the scion slant surface show 0.5 mm of white, which is beneficial for healing. Then use a thin plastic strip 0.5-0.6 cm wide, wrap upward from below the rootstock joint, exposing only the grafting bud, wrapping all the way to the upper cut of the scion, and after sealing tightly, wrap back down and tie a loose knot.

5 Field management of grafted seedlings

After green branch grafting, irrigate promptly, and do well the work of removing rootstock sprouts and disease control. Promote the normal growth of shoots sprouting from scion buds, and remove other excess branches promptly. When the scion branches grow to about 50 cm, set up wire along the direction of the grape seedling rows above them, and then tie the branches onto it. From July to September, spray Bordeaux mixture about every 10 days to control downy mildew. Spray imidacloprid + beta-cypermethrin about every 20 days to control leafhopper damage.