METHOD FOR CULTIVATING TUNG TREE SEEDLING BY HYPOCOTYLE GRAFTING

Abstract

A method for cultivating a Tung tree seedling through hypocotyle grafting includes selection of a sand storage time of a rootstock (Vernicia montana Lour.) seed, seedbed construction, scion collection, scion cutting, rootstock cutting, bandaging, transplantation and management, and the like. A grafted plant obtained by a traditional grafting method (bud grafting) for Tung tree is easy to break at a grafting interface; and when the stem grafting is conducted, because a scion is thick, a rootstock for grafting must be cultivated one year in advance. These grafting methods have production problems such as long cycle and high cost, which can be solved by the present disclosure. The present disclosure has a short rootstock cultivation time, simple grafting operations, a high grafting efficiency, and a high survival rate, greatly shortens a cycle of asexual propagation-based seedling cultivation for Tung tree.

Claims

1. A method for cultivating a Tung tree seedling through a hypocotyle grafting, comprising the following steps: (1) a rootstock cultivation: from early April to late June of a year, subjecting a Vernicia montana Lour. seed to a sand storage for 25 d to 50 d before a grafting until an epicotyl is exposed above a sand surface and a true leaf grows to obtain a rootstock; (2) a scion collection: from May to July of the year, collecting a semi-lignified shoot with robust growth, full buds, and no diseases and pests of the year as a scion; (3) a scion cutting: cutting a lower part of the scion with an axillary bud to form a cut scion with a wedge-shaped bevel; (4) a rootstock cutting: for the grafting, cutting off an upper plumular axis of the rootstock at a position with a closest thickness to the scion, and cutting a grafting interface downward longitudinally on a section of a hypocotyl in a direction perpendicular to a transverse section to form a cut rootstock; (5) the grafting: inserting the cut scion into the grafting interface of the cut rootstock, making the cut rootstock and the cut scion tightly joined together with at least one pair of cambium layers aligned, and bandaging for a fixation to form a grafted seedling; (6) a transplantation: before the grafting, arranging a shading net above a seedbed as a whole; transplanting the grafted seedling to the seedbed with the grafting interface higher than a soil plane, and after the transplantation is completed, watering for a first time; and when an axillary bud length of the grafted seedling reaches greater than or equal to 10 cm, removing the shading net to improve a photosynthetic efficiency; and (7) a management: after the grafted seedling is transplanted, watering to keep a soil at a specified humidity; and after the grafted seedling is cultivated for 50 d, spraying urea on leaves of the grafted seedling.

2. The method according to claim 1, wherein a specific process of the rootstock cultivation in step (1) is as follows: selecting a sunny slope with a high altitude and an excellent water drainage as a sand storage site; spreading the Vernicia montana Lour. seeds on a clean river sand layer with a thickness of 18 cm to 22 cm, spreading a river sand layer with a thickness of 8 cm to 12 cm on the Vernicia montana Lour. seeds, and watering to keep a river sand at a humidity of 8% to 10%, wherein the Vernicia montana Lour. seeds is prevented from overlapping with each other to cultivate robust seedling rootstocks; and selecting a robust seedling with a hypocotyl diameter of greater than or equal to 0.8 cm for the grafting.

3. The method according to claim 1, wherein a specific process of the rootstock cultivation in step (1) is as follows: subjecting the Vernicia montana Lour. seeds to the sand storage under natural conditions for 25 d to 50 d to obtain the rootstocks for the grafting, wherein from early April to late May, because a temperature is low and a long time is required for the Vernicia montana Lour. seed to germinate, the sand storage is conducted for 45 d to 50 d; and from early June to late June, because a temperature is high and the Vernicia montana Lour. seed& germinates rapidly, the sand storage is conducted for 25 d to 30 d.

4. The method according to claim 1, wherein in step (2), after the scion is collected, leaves of the scion are removed, and a petiole with a length of 0.1 cm to 1.0 cm is left for the grafting.

5. The method according to claim 1, wherein a specific process of the scion cutting in step (3) is as follows: cutting the scion into a 3 cm to 5 cm-long segment with a single axillary bud, and cutting a lower part of the 3 cm to 5 cm-long segment to form a wedge-shaped bevel with a vertical length of 1 cm to 2 cm.

6. The method according to claim 1, wherein a specific process of the rootstock cutting in step (4) is as follows: for the grafting, selecting the rootstock with robust growth and a hypocotyl diameter of greater than or equal to 0.8 cm, cutting off the upper plumular axis of the rootstock at a position 5 cm to 8 cm from a root of the rootstock, and cutting a 1.2 cm to 2 cm-long grafting interface downward longitudinally on the section of the hypocotyl in the direction perpendicular to the transverse section, and a vertical joining length between the rootstock and the scion is 1.5 cm.

7. The method according to claim 1, wherein step (5) specifically comprises: inserting the cut scion into the grafting interface of the cut rootstock, making the cut rootstock and the cut scion tightly joined together with the at least one pair of cambium layers aligned, and bandaging with a grafting film for the fixation to form the grafted seedling, wherein when the grafting film is used for the fixation, a first side of the grafting film is fixed, a second side of the grafting film winds around a cut to wrap the cut tightly, and after the fixation is completed, a knot is tied; and immersing a base of a radicle of the grafted seedling in water for a moisturization.

8. The method according to claim 1, wherein the transplantation in step (6) specifically comprises: preparing t seedbed with a height of 10 cm to 20 cm and a width of 0.9 m to 1.2 m for the transplantation; at a transplantation density defined by: a plant spacing: 15 cm to 20 cm, a row spacing: 20 cm to 30 cm, and a reserved row edge width: 4 cm to 6 cm, transplanting the grafted seedling with the grafting interface higher than a ground to prevent rot of the scion; after the transplantation is completed, watering for the first time, and arranging the shading net above the seedbed as the whole for shading; and when the axillary bud length of the grafted seedling reaches greater than or equal to 10 cm, removing the shading net to improve the photosynthetic efficiency.

9. The method according to claim 1, wherein in step (6), a seedling medium used in the seedbed is obtained by blending 5% to 10% of a peat soil into a yellow soil; and a shading degree for the seedbed is configured to ensure a light transmittance of 3% to 10% and a humidity of greater than or equal to 60%.

10. The method according to claim 1, wherein the management in step (7) specifically comprises: after the transplantation, keeping the soil at the specified humidity of greater than or equal to 60%; after the grafted seedling is cultivated for 50 d, spraying the urea with a mass concentration of 0.1% to 0.4% to replenish nutrients, gradually enhancing light, and removing buds and weeds in time; and after the grafted seedling is cultivated for 3 months, cutting a grafting film, such that the grafting film automatically falls off with a growth of a callus at the grafting interface to prevent a strangulation mark from occurring at a grafting site because the grafting film hinders a normal healing of the grafting interface.

11. The method according to claim 4, wherein the petiole with the length of 0.5 cm is left for the grafting.

12. The method according to claim 5, wherein the single axillary bud of the scion is 1 cm from a top and 3 cm from a bottom, and the wedge-shaped bevel has the vertical length of 1.5 cm.

13. The method according to claim 8, wherein the seedbed with the height of 15 cm and the width of 1.2 m is prepared for the transplantation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Description of Drawings

[0041] FIG. 1 is a picture of cultivation and germination of the Tung tree rootstocks in the present disclosure;

[0042] FIG. 2 is a picture illustrating that the hypocotyl of the Tung tree rootstock in the present disclosure has a similar thickness to a scion;

[0043] FIG. 3 is a picture of the cut Tung tree scion in the present disclosure;

[0044] FIG. 4 is a picture of the Tung tree rootstock and the Tung tree scion that are joined together in the present disclosure;

[0045] FIG. 5 is a picture of grafted Tung tree seedlings in the present disclosure;

[0046] FIG. 6 is a picture of grafted Tung tree seedlings placed in a water-filled basin to be transplanted in the present disclosure;

[0047] FIG. 7 is a picture of grafted Tung tree seedlings with axillary buds beginning to germinate after growing for 5 d in the present disclosure;

[0048] FIG. 8 is an overall picture of grafted Tung tree seedlings growing for 1 month in the present disclosure;

[0049] FIG. 9 is a picture of grafted Tung tree seedlings that grow for 1 month and are pulled out from the soil in the present disclosure;

[0050] FIG. 10 is a picture of a grafted Tung tree seedling on which a wound is healed after growing for 1 month in the present disclosure;

[0051] FIG. 11 is a picture of grafted Tung tree seedlings growing for 3 months in the present disclosure;

[0052] FIG. 12 is a picture of grafted Tung tree seedlings that grow for 3 month and are pulled out from the soil in the present disclosure;

[0053] FIG. 13 is a picture of a single grafted Tung tree seedling growing for 3 months in the present disclosure (a height of the seedling is 50 cm or more); and

[0054] FIG. 14 is a picture of grafting interfaces on grafted Tung tree seedlings growing for 3 months in the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Description of Embodiments

[0055] The present disclosure is described in further detail below with reference to the example, which is not intended to limit the present disclosure.

Example 1

[0056] In order to improve a grafting survival rate, impact factors existing in a grafting process were explored, and the optimal factors obtained accordingly were adopted in all subsequent experiments. In the experiments, 30 plants were grafted per treatment, and 3 replicates were set per treatment. The following operations were conducted sequentially: [0057] 1. Collection of seeds for rootstock cultivation: Ripe fruits of an improved Vernicia montana Lour. mother tree were collected in mid-November, placed in a woven bag, and stacked at a shady and humid place for 2 months to 3 months until peels were softened and rotted; and then the seeds were separated, air-dried at a shady and dry place for 5 d to 7 d, then placed in a woven bag, and stored at a moist and shady place for later use. [0058] 2. Rootstock cultivation: 25 d to 50 d before grafting, the stored Vernicia montana Lour. seeds were subjected to the following sand storage until an epicotyl was exposed above a sand surface and a true leaf grew: a sunny slope with a high altitude and excellent water drainage was selected as a sand storage site, the seeds were spread on a clean river sand layer with a thickness of 20 cm, then a river sand layer with a thickness of 10 cm was spread on the seeds, and the sand storage was conducted under natural conditions for 25 d to 50 d during which watering was conducted once every 2 d to 3 d to keep the river sand at a humidity of 8%, where the seeds were prevented from overlapping with each other to cultivate robust seedling rootstocks; and then robust seedlings with a hypocotyl diameter of 0.8 cm or more were preferably selected for grafting.

TABLE-US-00002 TABLE 1 Impacts of different rootstock varieties on a grafting survival rate Rootstock Number of Number of Survival variety grafted buds survived plants rate (%) Growth status Tung tree 90 80 88.9 Fast growth and excellent wound healing Vernicia 90 78 86.7 Fast growth and montana Lour. excellent wound healing

[0059] In the present disclosure, a lot of experiments had been conducted at a pre-test stage, and the optimal conditions for hypocotyle grafting of the Tung tree seedling were determined. Tung tree and Vernicia montana Lour. seedlings cultivated through sand storage were adopted as rootstocks for grafting. During the grafting, an axillary bud of a scion was 1 cm from a top and 3 cm from a bottom, a petiole was 0.5 cm long, and a vertical length of a section of a scion was 1.5 cm; and a grafted seedling was bandaged with a grafting film for fixation, then transplanted to a 15 cm-high seedbed, and cultivated. Final test results were shown in Table 1, and showed that grafting survival rates of the two rootstocks were almost equal to each other. However, because root rot had a huge harm on Tung tree in production practice and Vernicia montana Lour. exhibited better resistance to root rot than Tung tree, Vernicia montana Lour. was selected as a rootstock in the subsequent tests and actual production. [0060] 3. Scion collection: In mid-June, a semi-woody shoot with robust growth, full buds, and no diseases and pests of the year was collected as a scion. [0061] 4. Scion cutting: The scion was cut into a 4 cm-long segment with a single axillary bud, where 0.5 cm to 1.5 cm above the axillary bud, 2 cm to 3 cm below the axillary bud, and 0.1 cm to 1 cm of a petiole were left.

TABLE-US-00003 TABLE 2 Impacts of scions obtained under different treatments on a grafting survival rate Above-bud Below-bud Petiole Number of Number of part length part length length grafted survived Survival (cm) (cm) (cm) plants plants rate (%) 1 0.5 3.0 0.5 90 53 58.9 2 1.0 3.0 0.5 90 66 73.3 3 1.5 3.0 0.5 90 55 61.1 4 1.0 2.0 0.5 90 62 68.9 5 1.0 2.5 0.5 90 59 65.6 6 1.0 3.0 0.5 90 71 78.9 7 1.0 3.0 0.1 90 45 50.0 8 1.0 3.0 0.5 90 62 68.9 9 1.0 3.0 1.0 90 44 48.9

[0062] When impacts of the three factors of above-bud part length, below-bud part length, and petiole length on a grafting survival rate were investigated, a Vernicia montana Lour. seedling was adopted as a rootstock and a vertical length of a section of a scion was set to 1.5 cm for grafting; and after the grafting was completed, a wound was bandaged with a grafting film for fixation, and a grafting interface was buried in soil on a 15 cm-high seedbed for cultivation. It can be seen from Table 2 that grafts obtained under different treatments lead to different grafting survival rates; and in order to effectively improve a grafting survival rate, it should be determined that an axillary bud of a scion is 1 cm from a top and 3 cm from a bottom and a petiole length is 0.5 cm, which can make a grafting survival rate reach 78.9%. [0063] 5. Rootstock cutting: For grafting, a rootstock with robust growth and a hypocotyl diameter of 0.8 cm or more was selected, an upper plumular axis of the rootstock was cut off at a position that was 5 cm to 8 cm from a root of the rootstock and had the closest thickness to a scion, and a grafting interface with a vertical length of 1.2 cm to 2 cm was cut downward longitudinally on a section of a hypocotyl in a direction perpendicular to a transverse section, which could make the rootstock and the scion tightly joined together.

TABLE-US-00004 TABLE 3 Impacts of scion sections of different vertical lengths on a grafting survival rate Vertical length of a section of a Number of Number of Grafting survival Growth scion (cm) grafted plants survived plants rate (%) status 1.0 90 53 58.9 Short section, easy deviation, and uneasy fixation 1.5 90 68 75.6 Appropriate section length and fast callus growth 2.0 90 55 61.1 A section length is large, and a callus can hardly wrap the entire wound

[0064] A vertical length of a scion section has a significant impact on a grafting survival rate. In an experiment, a Vernicia montana Lour. seedling was adopted as a rootstock, an axillary bud of a scion was 1 cm from a top and 3 cm from a bottom, and a petiole length was 0.5 cm; and after grafting was completed, a grafting interface was bandaged with a grafting film for fixation, and then buried in soil on a 15 cm-high seedbed for cultivation. Finally, it can be seen from Table 3 that, in actual production, a scion with a wedge-shaped bevel having a vertical length of 1.5 cm should be selected for grafting with a rootstock. [0065] 6. Grafting: For grafting, a Vernicia montana Lour. seedling was adopted as a rootstock, and a scion was cut according to the following criteria: an axillary bud of the scion was 1 cm from a top and 3 cm from a bottom, a petiole length was 0.5 cm, and a vertical length of a section of the scion was 1.5 cm. A cut scion was inserted into a grafting interface of the rootstock, the rootstock and the scion were allowed to be tightly joined together with at least one pair of sides (cambium layers) aligned, and a joined part was bandaged with a grafting film for fixation, where when the joined part was fixed with the grafting film, one side of the grafting film was fixed, the other side of the grafting film wound around a cut to wrap the cut tightly, and after the fixation was completed, a knot was tied; and a base of a radicle was immersed in water with a height of about 1 cm in a basin for moisturization.

TABLE-US-00005 TABLE 4 Impacts of different bandaging materials on a grafting survival rate Grafting Bandaging Number of Number of survival Growth material grafted plants survived plants rate (%) status Grafting film 90 81 90.0 A grafting interface heals quickly and a wound heals well Aluminum foil 90 22 24.4 A grafting interface heals slowly, a rootstock tends to grow a bud- bearing shoot, and a management cost is high

[0066] It can be seen from Table 4 that a bandaging material has a very significant impact on a grafting survival rate of Tung tree, and a survival rate under a grafting film is significantly higher than a survival rate under an aluminum foil. Therefore, the grafting film should be selected as a bandaging material for hypocotyle grafting of the Tung tree seedling. [0067] 7. Transplantation: For grafting, a Vernicia montana Lour. seedling was adopted as a rootstock, and a scion was cut according to the following criteria: an axillary bud of the scion was 1 cm from a top and 3 cm from a bottom, a petiole length was 0.5 cm, and a vertical length of a section of the scion was 1.5 cm; and after the grafting was completed, a joined part was bandaged with a grafting film for fixation Before the grafting, a seedbed with a width of 1.0 m and a height of 5 cm to 20 cm was prepared in a nursery field for transplantation. Generally, at a transplantation density defined by: plant spacing: 15 cm, row spacing: 20 cm, and reserved edge width: 4 cm to 6 cm, a grafted seedling was transplanted to the seedbed with a grafting interface higher than a ground to prevent rot of the scion; after the transplantation was completed, watering was conducted for the first time, and a shading net was arranged above the seedbed as a whole to allow shading for 2 months; and when an axillary bud length of the grafted seedling reached 10 cm or more, the shading net was removed to improve photosynthetic efficiency.

TABLE-US-00006 TABLE 5 Impacts of seedbeds with different heights on a grafting survival rate Seedbed Number of Number of Survival Growth height grafted plants survived plants rate (%) status 5 90 56 62.2 Since a seedbed height is too low, water is easy to accumulate, which seriously affects the growth of a grafted seedling 10 90 58 64.4 Since a seedbed height is relatively low, a growth status of a grafted seedling is average 15 90 72 80.0 This seedbed height is suitable for the growth of a grafted seedling 20 90 62 68.9 Since a seedbed height is high, a grafted seedling grows robustly

[0068] Grafted Tung tree seedlings were transplanted to seedbeds with different heights, and after the grafted Tung tree seedlings grew for a period of time, it was observed that Tung tree seedlings on a seedbed with a height of 15 cm had the optimal growth status (as shown in Table 5). Therefore, in actual production, a seedbed with a height of 15 cm can be prepared.

TABLE-US-00007 TABLE 6 Impacts of different transplantation heights on a grafting survival rate Transplantation Number of Number of Survival height grafted plants survived plants rate (%) Growth status A grafting 90 88 97.8 Robust growth interface is and fast healing higher than a of the grafting ground interface A grafting 90 71 78.9 Relatively-fast interface is growth parallel to a ground A grafting 30 64 71.1 Slow growth, interface is and the grafting below a ground interface is prone to rot in water

[0069] It can be seen from the data in Table 6 that a transplantation height has a significant impact on a grafting survival rate; and when grafting is conducted under the following conditions: an axillary bud of a scion is 1 cm from a top and 3 cm from a bottom, a petiole length is 0.5 cm, and a vertical length of a section of the scion is 1.5 cm, the transplantation should be conducted with a grafting interface of a grafted seedling higher than a ground. [0070] 8. Management: After the transplantation, the soil was kept at a humidity of 60% or more; after a grafted seedling was cultivated for 50 d, urea with a mass concentration of 0.3% was sprayed on leaves of the grafted seedling to replenish nutrients, light was gradually enhanced, and buds and weeds were removed in time; and after the grafted seedling was cultivated for 3 months, the grafting film was gently cut vertically by a knife, such that the grafting film would automatically fall off with the healing of a wound to prevent a strangulation mark from occurring at a grafting site because the grafting film hinders the normal healing of the interface.

[0071] After a large number of pre-tests were conducted, the present disclosure had basically determined the optimal conditions required for hypocotyle grafting of the Tung tree seedling. In order to verify and optimize these conditions, based on a single-factor experiment design, when a specified factor was explored, other factors were treated according to the optimal conditions. The growth of grafted seedlings was observed after the grafted seedlings were cultivated for 20 d, and a survival rate was counted. It can be seen from the data in the table that, when some conditions are explored, even under the optimal grafting conditions, a grafting survival rate is still low (but under the same conditions, a large number of parallel tests can determine that these optimal conditions do have a huge impact on a grafting effect). The analysis and summary of this situation shows that there are many factors affecting a survival rate of hypocotyle grafting of the Tung tree seedling; and some factors cannot be directly regulated, such as seed quality, scion, and rootstock vitality, and can only be optimized as much as possible (for example, due to impacts of a sampling time and a climate of the year, seeds, rootstocks, or scions collected in each batch cannot reach an optimal status). After many impact factors are tested, it has been found that, for hypocotyle grafting, in addition to the rootstock thickness, length of a section of a scion, above-bud part length, below-bud part length, petiole length, seedbed height, and transplantation depth, a semi-woody scion with a full bud should be selected; a rootstock pulled out from a sand should be used in time (the rootstock should be used for grafting on the day when pulled out), and cannot be placed for a too-long period of time to prevent a water loss; and a quality of seeds directly affects a grafting survival rate, and in order to improve a grafting survival rate, large full seeds should be selected for sand storage and thick rootstocks with robust growth should be selected for grafting. When various factors such seed quality, rootstock thickness, length of a section of a scion, above-bud part length, below-bud part length, petiole length, seedbed height, transplantation depth, and scion quality all meet the optimal conditions of the present disclosure, a grafting survival rate will be high, and can stably reach 95% or more and even 100% according to results of many grafting tests. Therefore, when the grafting is conducted, the conditions should be controlled as much as possible to make a grafting survival rate reach the highest level.

[0072] In summary, the hypocotyle grafting for the Tung tree seedling is preferably conducted from May to July. In early June, shoots of Tung tree are semi-woody and vigorous, a temperature is suitable, and it takes 1 month for healing of a wound after a grafted seedling is transplanted, which requires a high-temperature and high-humidity environment. The hypocotyle grafting for the Tung tree seedling can also be conducted in May, but in May, shoots of Tung tree have a low semi-lignification degree, which makes a scion easy to die due to a water loss and leads to a lower grafting survival rate than in June. A period from July to September is a key period for growth of a survived grafted Tung tree seedling. If the grafting is conducted in July and August, a survival rate is also high, but a growth cycle of a grafted seedling in the year is shortened, and a growth status of a grafted seedling in this period is significantly worse than a growth status of a grafted seedling in June. Therefore, the hypocotyle grafting for the Tung tree seedling of the present disclosure is most preferably conducted in June. In terms of rootstock selection, the present disclosure has found at an early stage that the use of Tung tree and Vernicia montana Lour. seedlings as rootstocks has no significant impact on a survival rate, but in order to improve the disease resistance of Tung tree, a Vernicia montana Lour. seedling is selected as a rootstock for hypocotyle grafting of the Tung tree seedling.

[0073] According to the above research, when a Vernicia montana Lour. seedling is adopted as a rootstock, a semi-woody Tung tree shoot with vigorous growth and full buds is adopted as a bud-bearing stem segment, a scion has an above-bud part length of 1 cm, a below-bud part length of 3 cm, and a petiole length of 0.5 cm, the rootstock has a diameter of greater than 0.8 cm and a section length of 1.5 cm, a joined part is bandaged with a grafting film, a seedbed has a height of 15 cm, and the transplantation is conducted with a grafting interface higher than a ground, a grafting survival rate can be as high as 95% or more. After a grafted seedling is cultivated for 3 months, the grafting film is gently cut by a blade, such that the grafting film can automatically fall off, which reduces the labor consumption. The present disclosure provides a feasible way for asexual propagation of improved Tung tree varieties in the future, and is of important practical significance for sustainable and healthy development of the Tung tree industry.