Detailed Explanation of the Key Grafting Techniques for Michelia 'Mozhi'

Michelia 'Mozhi' belongs to the Magnoliaceae family, subfamily Magnolioideae. It blooms all year round, with the flowering period from March to June and the fruiting period from August to September. It is extremely drought-resistant and rarely affected by pests and diseases. Next, the editor will talk about the 2012 central government finance forestry science and technology extension project "New Rare Landscape Flower Variety - Application and Demonstration of Michelia 'Mozhi' in Urban Forest Construction."

1 Test Materials and Methods

1.1 Overview of the Test Site

Hunan Forest Botanical Garden, altitude 50 to 106 m, hilly terrain, average annual temperature 16.9 °C, maximum temperature 40.6 °C, minimum temperature -9.5 °C, average annual precipitation 1,400.6 mm, average annual relative humidity 80%, average annual sunshine hours 1,726 h. The soil is acidic red soil developed on Quaternary red clay parent material, with a pH range of 4.0 to 5.5.

1.2 Test Methods

1.2.1 Grafting Test with Different Tree Species as Rootstock

Using Magnolia liliiflora, Magnolia denudata, Magnolia biondii, Michelia platypetala, Michelia chapensis, and Manglietia guinanensis as rootstock, vigorous seedlings were selected as rootstock to graft Michelia 'Mozhi', and the grafting survival rate was investigated.

1.2.2 Test with Different Grafting Methods

In spring, the cut grafting method was used; in summer, the tender shoot bark-tearing grafting method was used; in autumn, the bud grafting method was used. The grafting survival rate and scion growth were investigated.

1.2.3 Test with Different Grafting Times

Cut grafting was carried out in stages in late February, mid-March, and late March, and the grafting survival rate, scion growth, and overall growth of the grafted plants were investigated.

1.2.4 Test with Different Rootstock Diameter Grades

In late February, vigorous Michelia 'Mozhi' branches were selected, and Magnolia liliiflora with different ground diameter thicknesses were used as rootstock for grafting. The grafting survival rate and growth were investigated;

The rootstock diameter grades were divided into: < 0.5 cm, 0.6 to 1.0 cm, 1.1 to 1.5 cm, 1.6 to 2.0 cm, 2.1 to 3.0 cm.

1.2.5 Test with Different Numbers of Bud Removal After Grafting

After the seedlings are grafted, since the main buds, lateral buds, and latent buds on the rootstock can continuously sprout and grow, removing buds once is not enough.

This study set different numbers of bud removal: 0, 4, 6, 10 times, and investigated the survival rate of grafted seedlings and scion growth.

1.2.6 Test with Different Times of Unbinding After Grafting

When the scion is grafted onto the rootstock, plastic strips (bands) are used to bind and fix it to the rootstock, but after a certain period of time this will affect the growth of the scion and rootstock. Therefore, this study set different unbinding times: no unbinding, 40 d after grafting, and 60 d after grafting, and investigated the survival rate of grafted seedlings and scion growth.

1.3 Data Statistics and Analysis

Excel 2007 software was used for data preprocessing, and SPSS 17.0 statistical software was used for data analysis.

2 Results and Analysis

2.1 Effect of Different Tree Species as Rootstock on Grafting Survival Rate

In the experiment, 6 tree species from 3 genera of Magnoliaceae were used as rootstock, and the cut grafting method was used. The grafting survival rate was investigated, and the results are shown in Table 1;

Table 1 Effect of Different Rootstock Species on Grafting Survival Rate and Growth

From Table 1, it can be seen that there are significant differences in grafting survival rate between different tree species as rootstock and Michelia 'Mozhi' scions. The grafting survival rates of Michelia platypetala and Michelia chapensis rootstocks of the genus Michelia were relatively low, only 42.5% and 40.0% respectively, and Manglietia guinanensis of the genus Manglietia was the lowest, only 16.7%.

2.2 Effect of Different Grafting Methods on Grafting Survival Rate and Growth

Table 2 Effect of Different Grafting Methods on Grafting Survival Rate and Growth

From Table 2, it can be seen that among the 3 grafting methods, the cut grafting method had the highest grafting survival rate and scion height growth, while the tender shoot bark-tearing grafting method had the lowest survival rate. The cut grafting method is simple to operate, highly efficient, and does not require waiting for the rootstock bark to slip before grafting, so the grafting period can be advanced, extending the grafting time.

2.3 Effect of Different Grafting Times on Grafting Survival Rate

When cut grafting in spring, choosing the appropriate time point is very important for the grafting survival rate. The investigation results are shown in Table 3.

Table 3 Effect of Different Grafting Times on Grafting Survival Rate

From Table 3, it can be seen that the suitable grafting time for Michelia 'Mozhi' is from February to mid-March. Grafting during this period gives a relatively high grafting survival rate and better growth of the grafted seedlings. However, starting from late March, the grafting survival rate of Michelia 'Mozhi' drops sharply, and the scion growth also decreases.

2.4 Effect of Rootstock Diameter Grade on Scion Growth

Table 4 Effect of Rootstock Diameter Grade on Scion Growth

From Table 4, it can be seen that when the rootstock ground diameter is less than 0.5 cm, the grafting survival rate is the lowest, and when the rootstock ground diameter is greater than 2 cm, the grafting survival rate is the highest, that is, the grafting survival rate increases with the increase of rootstock thickness;

SPSS software was used to conduct analysis of variance on the scion height growth after grafting survival with different rootstock thicknesses. The results showed that when the rootstock ground diameter is greater than 0.6 cm, the effect of rootstock thickness on the current-year scion height growth is not significant.

2.5 Effect of Bud Removal Frequency on Seedling Growth After Grafting

Table 5 Effect of Bud Removal Frequency on Growth of Grafted Seedlings

From Table 5, it can be seen that different bud removal frequencies have a significant effect on the survival rate of grafted seedlings. With the increase in bud removal frequency, the survival rate of Michelia 'Mozhi' grafted seedlings increases, and the scion growth is also better.

2.6 Effect of Binding Strips on Seedling Growth After Grafting

Table 6 Effect of Binding Strips on Growth of Grafted Seedlings

From Table 6, it can be seen that removing the binding strips 40 d after grafting is most beneficial to the survival and growth of grafted seedlings, with a grafted seedling survival rate of 95.23%.

3 Conclusion and Discussion

When selecting rootstock for Michelia 'Mozhi', using Magnolia liliiflora of the genus Magnolia as rootstock gives the highest grafting survival rate. The grafting survival rates of Michelia platypetala and Michelia chapensis of the same family are not high, so in production practice they can be selected as grafting rootstock for Michelia 'Mozhi';

Different grafting methods have a significant effect on the grafting survival rate of Michelia 'Mozhi', with the cut grafting method having the best effect;

Different grafting times have an extremely significant effect on the grafting survival rate of Michelia 'Mozhi'. The best grafting time is from late February to mid-March. Later than this period, the grafting survival rate decreases significantly;

The management after grafting survival of Michelia 'Mozhi' is also an important factor affecting the growth of grafted seedlings. The survival rate of grafted seedlings increases with the increase in bud removal frequency.

Grafting Propagation Techniques for Michelia

   Grafting propagation of Michelia has the advantages of fast growth, early flowering, high survival rate, simple operation, and no time restrictions.

I. Rootstock Selection
Magnolia liliiflora, Magnolia denudata, Magnolia hwangshanensis, Magnolia amoena, Magnolia zenii, etc. can all be used as rootstock for grafting Michelia. Among them, Magnolia liliiflora has well-developed fibrous roots and is most suitable for pot cultivation; the others have thick lateral roots and are suitable for ground planting.

II. Selection of Scions

Since old trees flower early, old Michelia trees can be used as mother trees as much as possible. Select branches from the outer middle-upper part of the crown with greenish bark, plump axillary buds, and no pests or diseases. 1-year-old to 2-year-old branches. If there is sufficient scion source, the shoot section should be used as the scion. The scion length is about 6 cm, leaving only 1 to 2 leaves at the top.

III. Original Timing

Outdoors, grafting can be done from the end of February to the end of September, and the specific time can depend on the rootstock seedlings. Generally, for rootstock seedlings propagated by sowing, grafting can be done as long as they are taller than the scion. For root suckers transplanted with roots, since they already have a certain thickness, they can be grafted after survival.

IV. Grafting Method

Use the glue grafting method. First clean the side of the rootstock to be grafted, use a sharp blade to make a cut about 7 cm above the soil, with a cut surface 3 cm to 4 cm long. Only reaching the xylem (showing a water-yellow color is best for the cambium layer). Cut the scion end into a slope of about 30 degrees, then on the upper side directly opposite the slope also cut a surface of the same length as the rootstock, only reaching the cambium. Align the cambium of the rootstock and scion, and use a plastic film strip to wrap the entire cut surface from top to bottom, ring by ring. For summer and autumn grafting, a piece of plastic film should be used to wrap the interface together with the scion, and then paper should be used on top as a cover for shade.

V. Management After Grafting

Before and after survival, rootstock buds should be removed frequently. Be careful not to let water accumulate at the base of the rootstock seedlings, otherwise it is easy to cause root rot and even death of the whole plant. One month after grafting, when the interface has healed, remove the shade material and outer covering film, and cut off the upper part from 3 to 5 leaves on the dead wood to promote the sprouting of scion buds. When the scion shoot grows 5 cm to 7 cm, cut off the rootstock above the interface and loosen the binding plastic strip.

Grafting Methods for Michelia figo 'Purpurea'

The appearance of Michelia figo 'Purpurea' is very similar to Michelia figo, but the color and size are still different from Michelia figo. Since Michelia figo 'Purpurea' has a certain fragrance, it is also an aromatic ornamental woody plant. The propagation of Michelia figo 'Purpurea' is generally carried out by grafting, so what issues need to be noted when propagating Michelia figo 'Purpurea' by grafting?

Michelia figo 'Purpurea'

I. Rootstock Selection

Michelia maudiae, Michelia chapensis, Magnolia liliiflora, Michelia macclurei, and other Magnoliaceae plants can all be used as rootstock for grafting Michelia figo 'Purpurea'. Among them, Michelia maudiae has a well-developed taproot and is an ideal rootstock for grafting Michelia figo 'Purpurea'. In production practice, one-year-old Michelia maudiae seedlings are cultivated as rootstock for Michelia figo 'Purpurea'.

II. Selection of Scions

Select vigorous 1-2-year-old branches that have already flowered as scions. One-year-old branches from the outer middle-upper part of the crown with greenish bark, plump axillary buds, and no pests or diseases are best. The scion length is about 2 cm, and one bud is enough.

III. Grafting Season

In southern Jiangxi, grafting can be done from the end of February to the end of March. Generally, for rootstock seedlings propagated by sowing, grafting can be done as long as they are taller than the scion.

IV. Grafting Method

1. Rootstock Treatment

Cut or saw off the rootstock at 5-10 cm above the ground, and smooth the cut into a flat surface to facilitate healing. The specific height should consider factors such as scion thickness and rootstock sprouting. If the scion is thin, the rootstock should also be thin, and the cut should be higher above the ground. To reduce rootstock sprouting, the cut should be low. Then use a grafting knife to gently split vertically downward from the cut surface of the rootstock, with a split opening about 2-3 cm long, and the width of the split opening surface should match the split opening surface of the scion.

2. Scion Treatment

The scion length is the length between two buds, and the scion thickness should match the rootstock. Use a sharp blade to cut off the upper part of the scion at about 1 cm from the bud, then cut downward at about 1 cm from the next bud, which makes one scion stick. Then cut from about 1 cm from the bud with a cut surface 2 cm to 3 cm long, only reaching the xylem. Then cut the opposite side of the scion cut surface into a slope of about 30 degrees, with the slope length about one third of the cut surface length.

3. Grafting Method

Use the cleft grafting method. Insert the treated scion into the split opening of the rootstock, leaving 0.1-0.2 cm exposed to ensure normal growth of the buds on the scion. Align the cambium of the scion and rootstock. If the scion and rootstock are not the same size and the cambium on both sides cannot be aligned at the same time, the cambium on one side must be aligned. The length of the rootstock split opening should match the length of the scion cut. After joining, immediately bind tightly with a plastic film strip to prevent the cambium of the scion and rootstock from shifting.

V. Management After Grafting

Before and after survival, rootstock buds should be removed frequently. Be careful not to let water accumulate at the base of the rootstock seedlings, otherwise it is easy to cause root rot and even death. After the graft survives, remove the shade material and grafting film.