Rootstock top grafting method capable of improving freezing resistance of citrus plants

Abstract

The invention belongs to the technical field of crop grafting, and provides a rootstock top grafting method capable of improving freezing resistance of citrus plants. The rootstock top grafting method comprises the steps that cultivated trifoliate orange seedlings are selected and cultured for 2-5 years to obtain a small-leaf fructus aurantii tree, the small-leaf fructus aurantii tree serves as a rootstock, a smooth place at the height of 1-2.5 m above the ground of the rootstock is selected, the outer skin of a stem is cut off, a scion is placed at the position, and the scion is cut off; the cut surfaces of the scion and the stock are tightly attached, a grafting film is wound upwards from the lower portion of the stock connector to the upper connector of the scion, and the scion and the stock are tightly wrapped. By adopting the rootstock top grafting, the freezing resistance of citrus plants can be greatly improved, the method can be widely popularized in middle and subtropical zones, the freezing injury problem is solved, the citrus plants can be planted in citrus producing areas in northern areas, courtyards, communities, villas, villages and towns and places blocking northwest wind in cities, the history that the citrus plants cannot be planted in the areas is broken, and the method is suitable for popularization and application. And the problems of freezing injury and freezing death of the middle-subtropical citrus plants in the northern edge zone of the subtropical zone are solved.

Description

Technical Field

[0001] The invention relates to the technical field of crop grafting, and in particular to a rootstock high-position grafting method capable of improving the frost resistance of citrus plants. Background Art

[0002] Frost damage to citrus is a global problem. In recent years, due to abnormal climate change, citrus plants in my country's mid-subtropical citrus growing areas such as Guangxi, Sichuan, Zhejiang and other places have suffered severe winter frost damage. The damage is even more serious than the frost damage to the Xingjin mandarin oranges in the citrus producing areas in the northern subtropical zone of Henan Province. The causes of the frost damage are multifaceted. One is abnormal climate change, and the other is the problem of rootstock grafting method. Grafting of mid-subtropical citrus plants is generally low-position grafting of the rootstock (the root of the rootstock is about 5 cm above the ground). Summary of the invention

[0003] The object of the present invention is to provide a rootstock high-position grafting method which can improve the frost resistance of citrus plants, so as to overcome the defects of the prior art.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a rootstock high-position grafting method capable of improving the frost resistance of citrus plants, characterized in that the method comprises the following steps:

[0006] (1) selecting well-cultivated trifoliate orange seedlings and cultivating them for 2 to 5 years to obtain small-leaved trifoliate orange trees as rootstocks;

[0007] (2) From the time of Jingzhe in spring to before the National Day in autumn, select 1 to 2 mature spring or autumn shoots with full buds and a diameter of ≥ 1 cm from citrus trees at a height of 1 to 2.5 meters;

[0008] (3) Using a grafting tool, select a full bud on the branch selected in step (2), cut horizontally from 1 to 2 cm above the bud to 1 to 2 cm below the petiole, and then cut at a 45-degree angle from 1 to 1.5 cm below the petiole to remove the bud as a scion;

[0009] (4) Select a smooth place at a height of 1 to 2.5 meters from the ground, cut off the outer bark, place the scion in step (3) at this position, and align the cambium of the stock and the scion on the upper side to ensure that the cut surface of the scion and the stock are closely attached, and use a grafting film to wrap upward from the bottom of the stock interface to the upper interface of the scion, wrap the scion and the stock tightly, if it is spring, adopt exposed bud grafting, expose the grafting bud point, if it is autumn, adopt wrapped bud grafting, wrap the bud tightly, and the grafting is completed.

[0010] Preferably, the method for cultivating the rootstock in step (1) comprises the following steps:

[0011] a. Collect mature small-leaf Citrus aurantium fruits in October and November of the first year, peel the seeds from the fruits, select seeds with full grains, plant them, and use a small arch shed to keep warm and moist to promote seed germination;

[0012] b. Between May 20th and June 10th of the second year, transplant the young trifoliate orange seedlings. After 2 to 5 years of cultivation, the trunk will be straight without side branches, and you will get the small-leaved trifoliate orange tree, which will be used as the rootstock.

[0013] Preferably, the transplanting spacing in step (b) is 25 to 35 cm, and the transplanting row spacing is 35 to 45 cm.

[0014] Preferably, in step (1), the height of the rootstock is 1 to 2.5 meters, and the diameter of the rootstock is 0.8 to 2 cm.

[0015] Preferably, in step (2), branches are selected under conditions where the temperature is higher than 25°C and the temperature difference between day and night is greater than 12°C.

[0016] Preferably, water is applied immediately after the grafting is completed, and the suckers on the rootstock are removed. The grafted new shoots are pinched for the first time with 5 to 7 leaves to promote the aging of the shoots. After that, 5 to 7 leaves are left and pinched repeatedly to promote the expansion of the water crown.

[0017] Beneficial effects:

[0018] The invention provides a rootstock high-position grafting method capable of improving the frost resistance of citrus plants. The rootstock high-position grafting method of the invention can greatly improve the frost resistance of citrus plants, can be widely promoted in the mid-subtropical zone, solve the problem of frost damage, and can be planted in citrus producing areas in the northern edge of the region and in courtyards, communities, villas, villages and towns, and places in cities that are shielded from northwest winds, breaking the history that citrus plants cannot be planted in the region, meeting people's living needs, and solving the problem of frost damage and freezing death of mid-subtropical citrus plants in the northern edge of the subtropical zone. DETAILED DESCRIPTION

[0019] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0020] The present invention provides a rootstock high-position grafting method capable of improving the frost resistance of citrus plants, characterized in that the method comprises the following steps:

[0021] (1) selecting well-cultivated trifoliate orange seedlings and cultivating them for 2 to 5 years to obtain small-leaved trifoliate orange trees as rootstocks;

[0022] (2) From the time of Jingzhe in spring to before the National Day in autumn, select 1 to 2 mature spring or autumn shoots with full buds and a diameter of ≥ 1 cm from citrus trees at a height of 1 to 2.5 meters;

[0023] (3) Using a grafting tool, select a full bud on the branch selected in step (2), cut horizontally from 1 to 2 cm above the bud to 1 to 2 cm below the petiole, and then cut at a 45-degree angle from 1 to 1.5 cm below the petiole to remove the bud as a scion;

[0024] (4) Select a smooth place at a height of 1 to 2.5 meters from the ground, cut off the outer bark, place the scion in step (3) at this position, and align the cambium of the stock and the scion on the upper side to ensure that the cut surface of the scion and the stock are closely attached, and use a grafting film to wrap upward from the bottom of the stock interface to the upper interface of the scion, wrap the scion and the stock tightly, if it is spring, adopt exposed bud grafting, expose the grafting bud point, if it is autumn, adopt wrapped bud grafting, wrap the bud tightly, and the grafting is completed.

[0025] In the present invention, the method for cultivating the rootstock in step (1) comprises the following steps:

[0026] a. Collect mature small-leaf Citrus aurantium fruits in October and November of the first year, peel the seeds from the fruits, select seeds with full grains, plant them, and use a small arch shed to keep warm and moist to promote seed germination;

[0027] b. Between May 20th and June 10th of the second year, transplant the young trifoliate orange seedlings. After 2 to 5 years of cultivation, the trunk will be straight without side branches, and you will get the small-leaved trifoliate orange tree, which will be used as the rootstock.

[0028] In the present invention, when planting the seeds of small-leafed Citrus aurantium, the wax must be washed off first, a plot with fertile soil and good moisture content is selected, trenches are dug and watered, the seeds are sown in the trenches, and the surface is covered with 1.5-2 cm of crushed soil.

[0029] In the present invention, after the trifoliate orange seedlings are transplanted, water and fertilizer management and pest and disease control need to be done well.

[0030] In the present invention, the spacing between plants during transplanting in step (b) is preferably 25 to 35 cm, more preferably 26 to 34 cm, and even more preferably 27 to 33 cm.

[0031] In the present invention, the transplanting row spacing is preferably 35 to 45 cm, more preferably 36 to 44 cm, and even more preferably 37 to 43 cm.

[0032] In the present invention, the height of the rootstock in step (1) is preferably 1 to 2.5 meters, more preferably 1.2 to 2.3 meters, and even more preferably 1.5 to 2 meters.

[0033] In the present invention, the diameter of the rootstock is preferably 0.8 to 2 cm, more preferably 1.0 to 1.8 cm, and more preferably 1.2 to 1.6 cm.

[0034] In the present invention, in step (2), branches need to be selected under the condition that the temperature is preferably higher than 25°C and the temperature difference between day and night is greater than 12°C.

[0035] In the present invention, water is applied immediately after the grafting is completed, and the suckers on the rootstock are removed. The grafted new shoots are pinched for the first time with 5 to 7 leaves to promote the aging of the shoots. After that, 5 to 7 leaves are left and the shoots are pinched repeatedly to promote the expansion of the water crown.

[0036] Example 1

[0037] Cultivation of small-leaved Citrus aurantium rootstock with strong frost resistance:

[0038] In October of the first year, collect mature small-leaf Citrus aurantium fruits, peel off the seeds from the fruits, select seeds with full grains, then wash and remove the wax, select a plot with fertile soil and good moisture, dig trenches and water, sow the seeds in the trenches, cover the surface with 2 cm of crushed soil, plant, and use a small arch shed to keep warm and moist to promote seed germination;

[0039] On June 1st of the second year, transplant the young trifoliate orange seedlings with a plant spacing of 30cm and a row spacing of 40cm. Provide adequate water and fertilizer, and do a good job of disease and insect control. After 4 years of cultivation, the trunk will be straight without side branches, and the small-leaf trifoliate orange tree will be obtained as the rootstock.

[0040] To graft:

[0041] Select the cultivated trifoliate orange seedlings and cultivate them for 4 years to obtain 2-meter small-leaf trifoliate orange trees as rootstocks;

[0042] After the Spring Waking of Insects and before the National Day in the fall, select one mature spring shoot with full buds and a diameter of ≥1cm from a citrus tree at a height of 2 meters;

[0043] Use a homemade grafting tool to select a full bud on the branch selected above, cut horizontally from 1 cm above the bud to 1 cm below the petiole, and then cut at a 45-degree angle from 1 cm below the petiole to remove the bud as a scion;

[0044] Select a smooth place at a height of 2 meters above the ground on the rootstock, cut off the outer bark, place the scion at this position, and align the cambium of the rootstock and the scion on the upper side to ensure that the cut surface of the scion and the rootstock fit closely. Use the grafting film to wrap it upward from the bottom of the rootstock interface to the upper interface of the scion, wrap the scion and the rootstock tightly, use exposed bud grafting, expose the grafting bud point, and the grafting is completed.

[0045] Post-grafting management:

[0046] Water immediately after grafting is completed, remove the suckers on the rootstock, and graft the new shoots that survive, leaving 6 leaves for the first pinching to promote the aging of the branches and shoots. After that, leave 6 leaves and pinch repeatedly to promote the expansion of the water crown. When the branches and shoots are mature, use a homemade tool to cut the grafting film from bottom to top from behind the scion and remove the grafting film. Cut the rootstock above the grafting interface at a 45-degree angle, and use a homemade wound healing agent to apply it tightly to the wound and 1 cm below the wound to facilitate wound healing and reduce diseases.

[0047] Example 2

[0048] Cultivation of small-leaved Citrus aurantium rootstock with strong frost resistance:

[0049] In November of the first year, mature small-leaf Citrus aurantium fruits were collected, the seeds were peeled out from the fruits, and the seeds with full grains were selected. Then, the wax was removed by washing. A plot with fertile soil and good moisture was selected, and the seeds were sown in the trenches. The surface was covered with 2 cm of crushed soil for planting. A small arch shed was used to keep warm and moist to promote seed germination.

[0050] On June 1st of the second year, transplant the young trifoliate orange seedlings with a plant spacing of 30cm and a row spacing of 40cm. Provide adequate water and fertilizer, and do a good job of disease and insect control. After three years of cultivation, the trunk will be straight without side branches, and the small-leaf trifoliate orange tree will be obtained as the rootstock.

[0051] To graft:

[0052] Select the cultivated trifoliate orange seedlings and cultivate them for 3 years to obtain 1.5-meter small-leaf trifoliate orange trees as rootstocks;

[0053] From the time of Jingzhe in spring to before the National Day in autumn, select two mature autumn shoots with full buds and a diameter of ≥1 cm from a citrus tree at a height of 1.5 meters;

[0054] Use a homemade grafting tool to select a full bud on the branch selected above, cut down from 1.5cm above the bud to 1.5cm below the petiole, and then cut at a 45-degree angle from 1.5cm below the petiole, and remove the bud as a scion by oblique cutting;

[0055] Select a smooth place at a height of 1.5 meters above the ground, cut off the outer bark, place the scion at this position, and align the cambium of the stock and the scion on the upper side to ensure that the cut surface of the scion and the stock fit closely. Use the grafting film to wrap it upward from the bottom of the stock interface to the upper interface of the scion, wrap the scion and the stock tightly, use bud grafting, wrap the bud tightly, and the grafting is completed.

[0056] Post-grafting management:

[0057] Water immediately after grafting is completed, and remove the suckers on the rootstock. For the new shoots that survive the grafting, leave 6 leaves for the first pinching to promote the aging of the branches. After that, leave 6 leaves and pinch repeatedly to promote the expansion of the water crown. When the branches are mature, use a homemade tool to cut the grafting membrane from bottom to top from behind the scion and remove the grafting membrane. Cut the rootstock above the grafting interface at a 45-degree angle, and use a homemade wound healing agent to apply it tightly to the wound and 1 cm below the wound to facilitate wound healing and reduce diseases.

[0058] Example 3

[0059] Cultivation of small-leaved Citrus aurantium rootstock with strong frost resistance:

[0060] In October of the first year, collect mature small-leaf Citrus aurantium fruits, peel off the seeds from the fruits, select seeds with full grains, wash and remove the wax, select a plot with fertile soil and good moisture, dig trenches and water, sow the seeds in the trenches, cover the surface with 1.5 cm of crushed soil, plant, and use a small arch shed to keep warm and moist to promote seed germination;

[0061] On May 20 of the second year, transplant the young trifoliate orange seedlings with a plant spacing of 25 cm and a row spacing of 35 cm. Provide adequate water and fertilizer, and do a good job of disease and insect control. After two years of cultivation, the trunk will be straight without side branches, and the small-leaf trifoliate orange tree will be obtained as the rootstock.

[0062] To graft:

[0063] Select the cultivated trifoliate orange seedlings and cultivate them for 2 years to obtain 1-meter small-leaf trifoliate orange trees as rootstocks;

[0064] From the time of Jingzhe in spring to before the National Day in autumn, select one mature spring shoot with full buds and a diameter of ≥1cm from a citrus tree at a height of 1m;

[0065] Use a homemade grafting tool to select a full bud on the branch selected above, cut horizontally from 1 cm above the bud to 1 cm below the petiole, and then cut at a 45-degree angle from 1 cm below the petiole to remove the bud as a scion;

[0066] Select a smooth place at a height of 2 meters above the ground on the rootstock, cut off the outer bark, place the scion at this position, and align the cambium of the rootstock and the scion on the upper side to ensure that the cut surface of the scion and the rootstock fit closely. Use the grafting film to wrap it upward from the bottom of the rootstock interface to the upper interface of the scion, wrap the scion and the rootstock tightly, use exposed bud grafting, expose the grafting bud point, and the grafting is completed.

[0067] Post-grafting management:

[0068] Water immediately after grafting is completed, remove the suckers on the rootstock, and graft the new shoots that survive, leaving 5 leaves for the first pinching to promote the aging of the branches and shoots. After that, leave 5 leaves and pinch repeatedly to promote the expansion of the water crown. When the branches and shoots are mature, use a homemade tool to cut the grafting film from bottom to top from behind the scion and remove the grafting film. Cut the rootstock above the grafting interface at a 45-degree angle, and use a homemade wound healing agent to apply it tightly to the wound and 1 cm below the wound to facilitate wound healing and reduce diseases.

[0069] Example 4

[0070] Cultivation of small-leaved Citrus aurantium rootstock with strong frost resistance:

[0071] In November of the first year, mature small-leaf Citrus aurantium fruits were collected, the seeds were peeled out from the fruits, and the seeds with full grains were selected. Then, the wax was removed by washing. A plot with fertile soil and good moisture was selected, and the seeds were sown in the trenches. The surface was covered with 2 cm of crushed soil for planting. A small arch shed was used to keep warm and moist to promote seed germination.

[0072] On June 10th of the second year, transplant the young trifoliate orange seedlings with a plant spacing of 35cm and a row spacing of 45cm. Provide adequate water and fertilizer, and do a good job of disease and insect pest control. After 5 years of cultivation, the trunk will be straight without side branches, and the small-leaf trifoliate orange tree will be obtained as the rootstock.

[0073] To graft:

[0074] Select the cultivated trifoliate orange seedlings and cultivate them for 5 years to get 2.5-meter small-leaf trifoliate orange trees as rootstocks;

[0075] From the time of Jingzhe in spring to before the National Day in autumn, select two autumn shoots with full buds and a diameter of ≥1 cm from a citrus tree at a height of 2.5 meters;

[0076] Use a homemade grafting tool to select a full bud on the branch selected above, cut down from 2 cm above the bud to 2 cm below the petiole, and then cut at a 45-degree angle from 1.5 cm below the petiole, and remove the bud as a scion by oblique cutting;

[0077] Select a smooth place at a height of 2.5 meters from the ground, cut off the outer bark, place the scion at this position, and align the cambium of the stock and the scion on the upper side to ensure that the cut surface of the scion and the stock fit closely. Use the grafting film to wrap it from the bottom of the stock interface upward to the upper interface of the scion, wrap the scion and the stock tightly, use bud grafting, wrap the bud tightly, and the grafting is completed.

[0078] Post-grafting management:

[0079] Water immediately after grafting is completed, and remove the suckers on the rootstock. Graft the new shoots that survive, leave 7 leaves for the first pinching to promote the aging of the branches, and then leave 7 leaves for repeated pinching to promote the expansion of the water crown. When the branches are mature, use a homemade tool to cut the grafting film from bottom to top from behind the scion and remove the grafting film. Cut the rootstock above the grafting interface at a 45-degree angle, and use a homemade wound healing agent to apply it tightly to the wound and 1 cm below the wound to facilitate wound healing and reduce diseases.

[0080] Results test:

[0081] Experimental group (1)

[0082] More than 2,000 seedlings of Huyou, Xiangyou and Hongxinyou (all purchased seedlings were low-grafted rootstocks) were introduced and planted in the field using conventional methods. They grew well, but in the winter of the same year they suffered from the lowest temperature of -15℃ seen in many years, killing 90% of the seedlings.

[0083] Experimental group (2)

[0084] Seedlings of dwarf late pomelo, three-red pomelo, Majia pomelo and Shatian pomelo were introduced and trial-planted in a one-layer film greenhouse and in the open field. Scions were taken from the introduced varieties and grafted using small-leaved orange peel as rootstock. The spring shoots grew normally. In the winter of the same year, the lowest temperature in the one-layer film greenhouse reached -7.8℃. The ungrafted conventionally planted three-red pomelo suffered fifth degree frost damage, and the dwarf late pomelo suffered third degree frost damage. The same variety of pomelo grafted using small-leaved orange peel as rootstock 30 cm above the ground suffered second degree frost damage, and the same variety of pomelo grafted using small-leaved orange peel as rootstock suffered no frost damage.

[0085] In the same experiment conducted in the open field, the conventionally planted dwarf late pomelo, three-red pomelo, Majia pomelo, and Shatian pomelo trees were all frozen to death at -8.1℃, while those grafted at 30cm using the small-leaved Citrus aurantium as the rootstock suffered third-degree frost damage, and those grafted at 1.2m suffered first-degree frost damage.

[0086] Experimental group (3)

[0087] By introducing the pomelo variety, the pomelo was planted at different positions in the open field and a layer of film greenhouse at different grafting heights (20cm, 30cm, 1.2m, 1.3m and 1.5m) and the temperature data was recorded. It was found that the pomelo grafted at a stock height of 1.5m in the open field was frozen at -13℃ for 5 hours, but it still did not affect the normal fruiting in the next year. By using the small-leaved Citrus aurantium as the rootstock to graft other varieties of citrus plants, high-position grafting of the rootstock can greatly improve the frost resistance.

[0088] In the citrus producing area on the northern edge of the subtropical zone in Henan Province, dwarf late pomelo grafted on high-position rootstocks grown in open fields (32°58′ north latitude) overwinter normally and bear fruit. The frost resistance of rootstocks grafted at high positions is much higher than that of rootstocks grafted at low positions.

[0089] As can be seen from the above embodiments, the present invention provides a method for high-position grafting of rootstocks that can improve the frost resistance of citrus plants, comprising the following steps: selecting a cultivated trifoliate orange seedling and cultivating it for 2 to 5 years to obtain a small-leaved trifoliate orange tree as a rootstock; selecting 1 to 2 mature spring or autumn branches with full buds and a diameter of ≥1 cm from a position where the height of the citrus tree is 1 to 2.5 meters after the Spring Waking of Insects and before the National Day in autumn; using a grafting tool, selecting a full bud point on the branch selected in step (2), cutting downward from 1 to 2 cm above the bud point to a position 1 to 2 cm below the petiole, and then cutting at a 45-degree angle from a position 1 to 1.5 cm below the petiole, and obliquely cutting the bud to take out the scion; selecting a smooth place at a height of 1 to 2.5 meters from the rootstock, cutting off the outer skin, and removing the scion from step (3) The scion is placed at the position, and the cambium of the stock and the scion on the upper side are aligned to ensure that the cut surface of the scion and the stock are closely attached, and the grafting film is wound upward from the bottom of the stock interface to the upper interface of the scion to wrap the scion and the stock tightly. If it is spring, exposed bud grafting is adopted to expose the grafting bud point, and if it is autumn, wrapped bud grafting is adopted to wrap the bud tightly, that is, the grafting is completed. The high-position grafting of the stock of the present invention can greatly improve the frost resistance of citrus plants, can be widely promoted in the mid-subtropical zone, and solve the problem of frost damage. Citrus production areas in the northern edge of the region and courtyards, communities, villas, villages and towns, and places in cities that are blocked by northwest wind can be planted, breaking the history that citrus plants cannot be planted in this area, meeting people's living needs, and solving the problem of frost damage and freezing death of mid-subtropical citrus plants in the northern edge of the subtropical zone.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for high-position grafting of rootstocks capable of improving the frost resistance of citrus plants, characterized in that: The following steps are involved: (1) selecting well-cultivated trifoliate orange seedlings and cultivating them for 2 to 5 years to obtain small-leaved trifoliate orange trees as rootstocks; (2) From the time of Jingzhe in spring to before the National Day in autumn, select 1 to 2 mature spring or autumn shoots with full buds and a diameter of ≥ 1 cm from citrus trees at a height of 1 to 2.5 meters; (3) Using a grafting tool, select a full bud on the branch selected in step (2), cut horizontally from 1 to 2 cm above the bud to 1 to 2 cm below the petiole, and then cut at a 45-degree angle from 1 to 1.5 cm below the petiole to remove the bud as a scion; (4) Select a smooth place at a height of 1 to 2.5 meters from the ground, cut off the outer bark, place the scion in step (3) at this position, and align the cambium of the stock and the scion on the upper side to ensure that the cut surface of the scion and the stock are closely attached, and use a grafting film to wrap upward from the bottom of the stock interface to the upper interface of the scion, wrap the scion and the stock tightly, if it is spring, adopt exposed bud grafting, expose the grafting bud point, if it is autumn, adopt wrapped bud grafting, wrap the bud tightly, and the grafting is completed.

2. A method for high-position grafting of rootstocks capable of improving the frost resistance of citrus plants according to claim 1, characterized in that: The method for cultivating the rootstock in step (1) comprises the following steps: a. Collect mature small-leaf Citrus aurantium fruits in October and November of the first year, peel the seeds from the fruits, select seeds with full grains, plant them, and use a small arch shed to keep warm and moist to promote seed germination; b. Between May 20th and June 10th of the second year, transplant the young trifoliate orange seedlings. After 2 to 5 years of cultivation, the trunk will be straight without side branches, and you will get the small-leaved trifoliate orange tree, which will be used as the rootstock.

3. A method for high-position grafting of rootstocks capable of improving the frost resistance of citrus plants according to claim 2, characterized in that: In the step (b), the plant spacing for transplanting is 25 to 35 cm, and the row spacing for transplanting is 35 to 45 cm.

4. A method for high-position grafting of rootstocks capable of improving the frost resistance of citrus plants according to claim 1, characterized in that: In the step (1), the height of the rootstock is 1 to 2.5 meters, and the diameter of the rootstock is 0.8 to 2 cm.

5. A method for high-position grafting of rootstocks capable of improving the frost resistance of citrus plants according to claim 1, characterized in that: In the step (2), branches need to be selected under the condition that the temperature is higher than 25°C and the temperature difference between day and night is greater than 12°C.

6. A method for high-position grafting of rootstocks capable of improving the frost resistance of citrus plants according to claim 1, characterized in that: After the grafting is completed, water is applied immediately, and the suckers on the rootstock are removed. The new shoots that survive the grafting are pinched for the first time with 5 to 7 leaves left to promote the aging of the shoots. After that, 5 to 7 leaves are left to pinch repeatedly to promote the expansion of the water crown.