CN113826513B

CN113826513B - Asexual rapid propagation seedling raising method for celastrus orbiculatus

Info

Publication number: CN113826513B
Application number: CN202111119192.4A
Authority: CN
Inventors: 江良为; 王佳嵩; 罗伟聪; 董运常; 刘贵才; 蔡林和
Original assignee: Huayuan Landscape Architecture Co ltd
Current assignee: Huayuan Landscape Architecture Co ltd
Priority date: 2021-09-24
Filing date: 2021-09-24
Publication date: 2023-02-03
Anticipated expiration: 2041-09-24
Also published as: CN113826513A

Abstract

The invention discloses a rapid asexual propagation seedling raising method of celastrus angulatus. The method simplifies the complex operation of high-pressure girdling of the first canopy vine, obviously shortens the initial rooting time in the cuttage stage, greatly improves the rooting effects of root primordium formation, adventitious root differentiation and root system formation, greatly improves the rooting rate and rooting quality, and ensures that the rooting and seedling rate of the first canopy vine is up to 100% by virtue of the innovative girdling wrapping treatment mode and strong seedling cultivation technology compared with the conventional high-pressure and conventional cuttage propagation. Moreover, the method has the advantages of high propagation efficiency, short cultivation period and low production cost, can rapidly and massively produce and breed the high-quality big seedlings of the first canopy vines, and meets the vigorous demands of markets such as landscape architecture, vertical greening and the like.

Description

Asexual rapid propagation seedling raising method for celastrus orbiculatus

Technical Field

The invention relates to the technical field of plant breeding, in particular to a rapid asexual propagation seedling method of celastrus angulatus.

Background

The first crown vine (Bauhinia coreymbosa) is also called deep-cracked Bauhinia variegata, is evergreen woody lian vine of Bauhinia of Leguminosae, is originally produced in places such as Guangdong, hainan and the like, and has a flowering phase of 4-6 months and a fruit phase of 9-12 months. The new leaves and tendrils of the first crown vines are elegant and elegant, the leaves are small and exquisite, the flower quantity is large and fragrant, the flower color is elegant and pleasant, the fruit pods are red and gorgeous and lovely, and the flower pot has excellent flower viewing, leaf viewing and fruit viewing values, and is an ideal woody climbing flower and a native vertical greening plant.

The celastrus orbiculatus is usually scattered in valley forests or hillside sunny places, and the artificial cultivation and propagation and landscape application are less. At present, limited research reports show that the setting rate of the crownwood is not high, the seeds are difficult to germinate, and manual peeling and germination accelerating treatment are needed. The asexual propagation can adopt cuttage and layering, but the cuttage propagation cutting shoot is very easy to infect and black rot, the cuttage rooting rate is low, the seedling period is longer, the layering propagation operation is complicated, the propagation coefficient is very low, and the large-scale production is difficult. In a word, the production and breeding requirements of the first crown vines are difficult to meet by adopting a common asexual propagation method. Tissue culture experiments also show that healthy and large fibrous roots can grow in about 40 days by adopting stem sections with nodes for tissue culture and inducing rooting culture, but the tissue culture has high requirements on facility conditions and operation technology and high tissue culture cost, and the rooting culture stage needs about 40 days, so that the whole seedling culture period is overlong, and the requirement of rapid propagation expansion of the first crown vines is difficult to adapt.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for asexual rapid propagation and seedling raising of the first crown vines.

The purpose of the invention is realized by the following technical scheme: a method for asexual rapid propagation and seedling raising of celastrus angulatus comprises the following steps:

(1) Selecting branches: selecting 2-3 years old first crown vine branches which are cultivated in a field, grow robustly and have no diseases or insect pests, segmenting, and ensuring that 4-6 lateral branches are reserved in each branch segment;

(2) Girdling treatment: annularly cutting the phloem at the internode part of the middle lower end of each branch section in the step (1), wherein the width of an annular peeling cut is 1.0-1.4 cm, and completely peeling the annularly cut phloem and a cambium;

(3) Callus treatment: uniformly spraying a callus rooting agent solution to the positions near the girdling cuts in the step (2), and wrapping the girdling cuts and the upper and lower epidermis by using an adhesive tape;

(4) Callus rooting: callus treatment is carried out until the phloem of the cut on the girdling expands and forms a lacteal callus, the adhesive tape is uncovered, the branch segments are respectively cut off, the spray cutting method is adopted for callus rooting culture, and the callus of the callus branch segments and the expansion part of the phloem are cultured to separate dense adventitious roots;

(5) Strong seedling culture: gradually reducing the spraying frequency, prolonging the spraying interval for 1 hour every 2-3 days, namely spraying after water stains on the leaves of the callus section disappear for 1-3 hours, ventilating and hardening the seedlings when the air humidity is reduced to 50-60%, and moving the seedlings to the outdoor for normal maintenance until the seedlings grow into robust first crown vine seedlings.

Preferably, the segmentation in step (1) is divided into 3 to 6 segments.

Preferably, the lateral branches of the branch segments in the step (1) are pruned if inflorescences exist.

Preferably, the girdling treatment in the step (2) is performed in clear weather from the middle and the last ten months of 2 months to 3 months.

Preferably, the callus rooting agent in the step (3) is a callus rooting agent containing a growth regulator, nutrients, a sterilization protective agent and a film-forming auxiliary agent; more preferably, the formula of the callus rooting agent is as follows: 400-500 ppm of naphthylacetic acid, 400-500 ppm of indolebutyric acid, 3000ppm of sucrose, 1000-1500 ppm of mancozeb and 2000-4000 ppm of polyvinylpyrrolidone.

Preferably, the callus rooting agent solution in the step (3) is a sterile aqueous solution.

Preferably, before the girdling cut in the step (3), the girdling cut is naturally aired for 5-10 min, so that the cortex of the cut absorbs the callus rooting agent solution and the redundant water is evaporated.

Preferably, the adhesive tape in the step (3) is an aluminum foil adhesive tape with the width of 4-5 cm, and is bound until the girdling cut is completely shaded, and the heat preservation and moisture preservation are carried out.

Preferably, the fog-spraying cutting method in the step (4) comprises the following steps: 8 to 18 days, wherein the fog spraying frequency is based on closing water stains formed on the leaves of the callus sections and spraying when the water stains disappear, and the air humidity in the daytime is ensured to be 85 to 95 percent; spray moisturizing is not needed at night.

Preferably, the callus treatment time of step (4) is 1-2 weeks.

The respective cutting-off in the step (4) can be replaced by cutting-off in batches from top to bottom.

Preferably, the callus rooting cultivation in the step (4) is carried out in a plastic greenhouse.

Preferably, the rooting substrate adopted in the callus rooting culture in the step (4) is a mixture of garden soil, peat soil and plain river sand; more preferably, in the rooting matrix, garden soil, peat soil and plain river sand are mixed according to a volume ratio of 4.

Preferably, the rooting substrate is sterilized by pouring through a solution of potassium permanganate with the concentration of 1000 ppm.

Preferably, the callus rooting culture in the step (4) inserts the callus branch segments into the rooting matrix to the depth of 1/4-1/3 of the length of the branch segments.

Preferably, the callus rooting culture in the step (4) is watered thoroughly with 800-1200 ppm of carbendazim solution for rooting, and then the carbendazim solution is watered once every 7 days.

Preferably, the side branches of the callus segments in the step (4) are relatively too long, 1/2-2/3 of the side branches can be cut off, and the residual leaves or the leaf-carrying small short branches are reserved.

Preferably, the time for hardening seedlings by ventilation in the step (5) is 1-2 weeks.

Preferably, in the normal maintenance process in the step (5), the ternary compound fertilizer solution is applied for 1 time and is continuously applied for 3-5 times every month.

Preferably, the concentration of the ternary compound fertilizer solution is 6000 to 9000ppm.

1. According to the invention, the strong and mature branches of 2-3 years old celastrus angulatus are adopted and are divided into 3-6 sections for rapid propagation treatment, the branches are easy to heal and form callus after girdling, and the propagation coefficient can be improved exponentially through sectional treatment.

2. The method selects the first ten days to 3 months (Guangzhou area) before the first crown vine blossoms for processing, at the moment, the physiological activity of branches is high, and after girdling and callus processing, a sufficient growth period is provided, so that the requirements of branch section wound healing, callus rooting and subsequent vigorous growth can be met. The cutting of lateral branch inflorescences can also make limited nutrients in branch segments concentrate at the cut, and accelerate the callus differentiation of root primordia and the formation of adventitious roots.

3. The callus rooting agent used in the invention comprises a growth regulator, nutrients, a sterilization protective agent and a film forming auxiliary agent. The proper type and concentration of the growth regulator are the key for promoting the rooting of the celastrus angulatus, and the combination of 'naphthylacetic acid 400-500 ppm + indolebutyric acid 400-500 ppm' provided by the method can obviously promote the differentiation of the ring-cut callus and the formation of adventitious roots; the proper amount of sucrose can provide nutrition for the development of root primordia and regulate the osmotic pressure of tissue cells; the mancozeb is a broad-spectrum protective bactericide, can form a medicine film on the surface of a ring cut and prevent various fungi from invading; the polyvinylpyrrolidone is a non-ionic high molecular compound, has excellent biocompatibility, can form a protective film together with mancozeb, prevents the infection of the cut of the branch section, and can prevent the water loss or the rainwater infiltration.

4. The invention uses the aluminum foil adhesive tape to wrap the girdling cut, the aluminum foil adhesive tape has good folding resistance, has the characteristics of water resistance, sun protection, heat insulation, high temperature resistance and the like, can shade light and moisturize the girdling cut and protect young calluses and root primordium. When the phloem expands and the callus protrudes, the wrapping part of the aluminum foil tape becomes loose, leaks light or water, and the callus segments should be cut off and cultured in time to prevent the surface of the callus from losing activity or losing water and withering due to environmental change. Compared with the complex wrapping of the conventional high-pressure girdling and the continuous maintenance of the substrate moisture, the treatment saves time and materials, is simple, convenient and easy to operate, and can greatly improve the propagation efficiency.

5. The invention separately carries out the callus root primordium induction and the rooting culture, has the advantages of high-pressure propagation and cutting propagation, but is simpler and more convenient than high-pressure operation, has faster rooting speed than cutting, and obviously improves the rooting rate and the propagation coefficient.

6. The branch sections treated by the method have callus rooting and skin rooting, belong to mixed rooting types, have more rooting pieces, and have the rooting rate as high as 100%. Wherein, the callus has earlier rooting, the root is thick and long and has less number, the bark has later rooting, the root is thin and various, the two types of rooting supplement each other, the total number of the rooting is large, the root system quality is good, and the seedling growth vigor is stronger.

7. The high-temperature and high-humidity environment in the greenhouse can inhibit the transpiration of the branch sections with leaves, ensure that the leaves do not wither due to water imbalance, and meet the vigorous demand of the water during the rooting of the branch sections. The screened rooting culture medium is favorable for the extension and growth of adventitious roots, and the seedlings are directly cultured after rooting without transplanting and field planting.

8. The strong seedling cultivation method adopted by the invention can induce the growth and development of the root system by gradually reducing the humidity so as to quickly form a full root ball, the ventilation can improve the adaptability of the cutting seedling to the natural environment, the appropriate water and fertilizer mode is favorable for improving the growth speed and the seedling quality of the first crown vines, and the strong first crown vines seedlings can be obtained after the cultivation to the end of the year.

Compared with the prior art, the invention has the following beneficial effects:

the method simplifies the complex operation of high-pressure girdling of the celastrus argenteus, obviously shortens the initial rooting time in the cutting stage, greatly improves the rooting effects of root primordium formation, adventitious root differentiation and root system formation, greatly improves the rooting rate and rooting quality, and enables the rooting and seedling rate of the celastrus argenteus to reach 100% by virtue of the innovative girdling wrapping treatment mode and strong seedling cultivation technology. Moreover, the method has the advantages of high propagation efficiency, short cultivation period and low production cost, can rapidly and massively produce and breed the high-quality big seedlings of the first crown vines, and meets the vigorous demands of markets such as landscape architecture, vertical greening and the like.

Drawings

FIG. 1 is a photograph of the girdling cut of the shoot and the callus rooting agent spray treatment in example 1;

FIG. 2 is a photograph of the ring cut and upper and lower cuticles of the branch wrapped with aluminum foil tape in example 1;

FIG. 3 is a schematic diagram of multi-stage callus treatment of the same shoot in example 1;

FIG. 4 is a photograph showing the formation of ring-cut callus and the enlargement of phloem in example 1;

FIG. 5 is a photograph of the callus segments excised in example 1, respectively;

FIG. 6 is a photograph of a full root system formed by rooting culture of callus segments in example 1;

FIG. 7 is a photograph of a fully rooted plant obtained by cutting culture of callus segments in example 1;

FIG. 8 is a comparative graph showing the rooting effect of the simplified method in example 1 and comparative example 1; wherein, the left part is the rooted plant obtained by the simplified method, and the right part is the rooted plant obtained by the complete method.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

1. Selecting branches: selecting 3-year-old first crown vine branches which are cultivated in a field and grow robustly without diseases and insect pests; according to the length of the main branches, each main branch is evenly divided into 3-6 sections for the following treatment, and 4-6 lateral branches are ensured to be left in each branch section for photosynthesis.

2. Girdling treatment: in 3 months, selecting clear weather, and using a sharp grafting knife to perform annular cutting on the phloem at the internode part of the middle lower end of each branch, wherein the width of an annular peeling cut is 1.0-1.4 cm, and the annularly cut phloem and a cambium are peeled cleanly. If inflorescences exist on the lateral branches of the branch sections, the lateral branches are cut off, and the flowering and nutrient consumption are avoided.

3. Callus treatment:

(1) A callus rooting agent containing a growth regulator, nutrients, a sterilization protective agent and a film-forming auxiliary agent is used, and specifically is a sterile aqueous solution of 500ppm naphthylacetic acid, 450ppm indolebutyric acid, 3000ppm sucrose, 1200ppm mancozeb and 3000ppm polyvinylpyrrolidone.

(2) Uniformly spraying the callus rooting agent aqueous solution near the girdling cut (figure 1) by using a small spray can, after the cortex of the cut is absorbed and naturally aired for 10min, wrapping the girdling cut and the upper and lower epidermis (figure 2) by using an aluminum foil adhesive tape with the width of 4-5 cm, completely shading the girdling cut, and preserving heat and moisture. In this example, the same shoots were callus-treated with 3 calli (FIG. 3) to increase the propagation coefficient.

4. Callus rooting:

(1) After 2 weeks of callus treatment, the phloem of the girdling cut expanded and formed a papillary callus (fig. 4), at which time the aluminum foil tape was uncovered, the branch segments were cut off separately (fig. 5), and callus rooting culture was performed in a plastic greenhouse by the mist spray cutting method.

(2) Uniformly mixing the garden soil, peat soil and plain river sand according to a volume ratio of 4; the fog spraying time in the greenhouse is 8-00 per day, wherein the interval time between fog spraying is preferably closed when water stains are formed on the leaves of the callus sections, and the water stains disappear, namely spraying is carried out, and the air humidity in the greenhouse is ensured to be 85-95% in the daytime.

(3) Drilling a deep hole on the rooting matrix by using a small stick, carefully inserting the callus branch section into the matrix hole, wherein the insertion depth is 1/4-1/3 of the length of the branch section, then thoroughly watering the root by using 1000ppm of carbendazim solution, and watering the carbendazim solution once every 7 days.

(4) When the side branches of the callus branch sections are relatively too long, 1/2-2/3 of the side branches are cut off, and the residual leaves or small short branches with leaves are reserved. After 2 weeks of culture, the callus and the phloem of the branch segment are expanded to separate dense adventitious roots (figure 6), and the rooting rate reaches 100%.

5. Strong seedling culture

(1) When the branch segments start to form full root balls, the spraying frequency in the greenhouse is gradually reduced (the spraying interval is prolonged by 1 hour every 2 days, namely the water stains on the leaves of the callus segments disappear for 1 hour, 2 hours and 3 hours, and then the spraying is carried out again), and when the humidity of the air in the greenhouse is reduced to 50-60%, the two sides of the greenhouse are opened for ventilation.

(2) And (3) after the seedlings are hardened for 2 weeks by humidity reduction and ventilation, transplanting the first crown vine with a pot outside a greenhouse for normal maintenance, and pouring and applying 8000ppm of a ternary compound fertilizer aqueous solution for 1 time and continuously applying for 4 times every month until the first crown vine grows into a robust large seedling. FIG. 7 is a complete rooted plant obtained 2 months after callus cutting cultivation.

Comparative example 1

Before obtaining the seedling raising method of the invention, the inventor carries out 3 breeding method tests, which are as follows:

the method comprises the following steps: normal high pressure

(1) Selecting strong 3-year-old first crown vine branches, selecting clear weather, and performing annular cutting on phloem at internodes at the middle lower part of each branch by using a sharp grafting knife, wherein the width of an annular cut is 1.0-1.5 cm, and the annular-cut phloem tissue and cambium are completely stripped.

(2) Selecting coconut chaff as a rooting matrix, and thoroughly watering and sterilizing by using a carbendazim solution of 1000 ppm; and (3) tightly binding a plastic film below the lower cut of the branch, straightening, turning up to form a bag shape, enabling the girdling wound to be located in the center of the bag, filling prepared rooting matrix into the bag, and tightly binding the bag opening above the upper cut of the branch by using a rope after the matrix fills and wraps the girdling cut up and down.

(3) Repeating the steps (1) and (2) once for each branch to be cultivated, periodically checking the dryness and wetness of the substrate in the branch girdling bag, and timely supplementing the moisture by using an injector when the substrate is slightly dry. When the formation of adventitious roots is obviously seen in the plastic bag, the rooted high-pressure branch segments are cut off from the parent body, and normal water and fertilizer maintenance management is carried out after transplanting and potting.

The second method comprises the following steps: conventional cuttage

(1) Selecting strong 2-year-old first crown vine branches, cutting lignified long branches into a plurality of short cuttings, ensuring that each cutting has 1-2 nodes, and removing lateral branches on the nodes.

(2) Selecting garden soil and peat soil as a cutting matrix, uniformly mixing according to a volume ratio of 3:1, subpackaging by using nutrient cups, vertically inserting the pruned cutting slips into the matrix, and then thoroughly pouring and sterilizing by using a carbendazim 1000ppm solution.

(3) Setting up a small shady shed, shading by using a shading net with shading degree of 50%, periodically checking the dryness and humidity of the cuttings and the pot soil, and spraying water to humidify in time. And (5) carrying out normal water and fertilizer conservation after the cuttage rooting.

The third method comprises the following steps: simplified method of the invention

The simplified method of the present invention, which is the initial search of the method of the present invention, is substantially similar to the steps of the complete method of the present invention, except that:

(1) Only 1 girdling treatment is carried out on each branch of the first crown vine.

(2) In the wound healing treatment, a solution of '800 ppm naphthylacetic acid + 1000ppm mancozeb' (or '800 ppm indolebutyric acid + 1000ppm mancozeb') is sprayed on the girdling cut.

(3) In the rooting culture, the rooting substrate is prepared by uniformly mixing garden soil and river sand according to the volume ratio of 3:1; spraying for 5min every 3h for 15h every day, and only pouring 1 time of carbendazim solution for sterilization at the initial stage of cuttage.

(4) After the branch section takes root, the same spraying frequency and 1 time of compound fertilizer particle topdressing are continued, and the moisture reduction and seedling hardening are not carried out.

The rooting effect of the 3 propagation methods in example 1 and comparative example 1 was counted, and the specific rooting and seedling conditions are shown in table 1.

TABLE 1

Note: the rooting time refers to the time required for the average root length to be more than or equal to 1 cm.

From the statistical results of table 1, it can be seen that: compared with the conventional high-pressure and conventional cutting propagation, the complete method obviously shortens the rooting time, greatly improves the rooting rate and the rooting number, and has the propagation coefficient similar to that of the conventional cutting but obviously higher than that of the conventional high-pressure propagation; through strong seedling culture, the seedling forming speed of the invention is obviously accelerated.

Compared with the complete method, the simplified method has the advantages that the rooting time, the number of roots and the seedling speed in the later period are superior to those of the simplified method (figure 8), particularly, the rooting rate and the propagation coefficient are remarkably superior to those of the simplified method, and the method is suitable for large-scale production and breeding of the celastrus angulatus.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

Claims

1. A method for asexual rapid propagation and seedling raising of celastrus angulatus is characterized by comprising the following steps:

(2) Girdling treatment: annularly cutting the phloem at the internode part of the middle lower end of the branch section in each section of the step (1), wherein the width of an annular peeling cut is 1.0-1.4 cm, and completely peeling the annularly cut phloem and cambium;

(5) Strong seedling culture: gradually reducing the spraying frequency, and prolonging the spraying interval for 1 hour every 2-3 days, namely spraying after water stains on the leaves of the callus sections disappear for 1-3 hours, ventilating and hardening the seedlings when the air humidity is reduced to 50-60%, moving the seedlings to the outdoor for normal maintenance until the seedlings grow into strong first crown vine seedlings;

the girdling treatment time in the step (2) is clear weather from the middle and last ten days of 2 months to 3 months;

the callus rooting agent in the step (3) is a callus rooting agent containing a growth regulator, nutrients, a sterilization protective agent and a film-forming auxiliary agent;

before the girdling cut in the step (3), naturally airing for 5-10 min to enable the cut cortex to absorb the callus rooting agent solution and evaporate redundant water;

the fog spraying cutting method in the step (4) comprises the following steps: 8 to 18 days, wherein the fog spraying frequency is based on closing water stains formed on the leaves of the callus sections and spraying when the water stains disappear, and the air humidity in the daytime is ensured to be 85 to 95 percent; spray moisturizing is not needed at night;

and (4) the rooting substrate adopted for callus rooting cultivation is a mixture of garden soil, peat soil and plain river sand.

2. The asexual rapid propagation seedling raising method of celastrus angulatus according to claim 1,

the callus rooting agent in the step (3) comprises the following formula: 400-500 ppm of naphthylacetic acid, 400-500 ppm of indolebutyric acid, 3000ppm of cane sugar, 1000-1500 ppm of mancozeb and 2000-4000 ppm of polyvinylpyrrolidone;

in the rooting matrix adopted in the callus rooting culture in the step (4), garden soil, peat soil and plain river sand are mixed according to a volume ratio of 4;

and the rooting matrix is thoroughly sterilized by potassium permanganate 1000ppm solution.

3. The asexual rapid propagation seedling raising method of celastrus angulatus according to claim 1,

the subsection in the step (1) is divided into 3-6 sections;

cutting off the lateral branches of the branch sections in the step (1) if inflorescences exist;

the adhesive tape in the step (3) is an aluminum foil adhesive tape with the width of 4-5 cm, and is bound until the girdling cut is completely shaded, and heat preservation and moisture preservation are carried out;

and (4) relatively overlong lateral branches of the callus sections in the step (4), cutting 1/2-2/3 of the lateral branches and reserving residual leaves or small short branches with leaves.

4. The asexual rapid propagation seedling raising method of celastrus angulatus according to claim 1,

the callus rooting culture in the step (4) inserts the callus branch into the rooting matrix to a depth of 1/4-1/3 of the branch length;

and (4) thoroughly watering the callus rooting culture by using a carbendazim solution of 800-1200 ppm, and watering the carbendazim solution once every 7 days.

5. The asexual rapid propagation seedling raising method of celastrus angulatus according to claim 1,

the time for hardening seedlings by ventilation in the step (5) is 1-2 weeks;

and (5) in the normal maintenance process, pouring and applying the ternary compound fertilizer solution for 1 time every month, and continuously applying for 3-5 times.

6. The asexual rapid propagation seedling raising method of celastrus angulatus according to claim 5, characterized in that the concentration of the ternary compound fertilizer solution is 6000-9000 ppm.

7. The asexual rapid propagation seedling raising method of celastrus angulatus according to claim 1, characterized in that the callus rooting cultivation in step (4) is performed in a plastic greenhouse.

8. The asexual rapid propagation seedling raising method of celastrus angulatus according to claim 1,

the callus rooting agent solution in the step (3) is a sterile aqueous solution;

and (5) the callus treatment time in the step (4) is 1-2 weeks.

9. The asexual rapid propagation seedling raising method of celastrus coronarius according to claim 1, characterized in that the respective cutting-off in step (4) is replaced by cutting-off in batches from top to bottom.