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Grafting Techniques

By DR. Venkatramana Hegde, Hosagadde. Director, Shramajeevi Television Pvt. Ltd. Bengaluru

Introduction

In the nature plant species have various mechanisms for reproduction. Seeds, rooting on the stem, tubers and suckers are the important ones. Plant propagation techniques became popular with modern horticulture for asexual multiplication of commercial plants in large numbers. Grafting is an age old practice. But its commercial application and new techniques started few decades ago. Tissue Culture is another popular asexual method of multiplication of plants. But it is commercially successful only in soft wood plants like banana, cardamom, flower and ornamental plant species.

Majority of the plants produce seeds. Then why do you need grafting? To answer this question let us understand the problems of seedlings first. The male part of the plant pollen unites with the female part ovule to form seed. Due to recombination of genes the next generation plant differs in its characters than its mother plant. This variation is more evident in case of cross pollination. Hence the seedlings from a sweet mango tree may give sour fruit. Best jackfruit may become useless in next generation. Off course this is the reason for the varietal diversity in nature. But in commercial horticulture we need plants with similar characters for good quality and yield. Here the grafting techniques help us a lot.

Seedlings take long time to bear fruit. But the grafted plants can give fruit after 2-3 years. Grafting technique is used to escape from certain diseases in some crops. For example, grafting pepper on wild Hippali (long pepper) is popular to avoid wilt disease. A wild type of grape called Dog ridge can withstand drought and avoid the absorption of poisonous elements. Grafting commercial varieties on this Dog ridge brought revolution in grape production. Many ornamental plants do not produce seeds. At the same time, they do not root easily by stem cuttings. For the multiplication of such plants grafting technique is inevitable. Grafting is helpful to produce composite plants with many varieties and for the rejuvenation of old trees.

What is grafting?

Grafting means uniting 2 plants of the same species. Shoot of a required variety plant is grafted on a seedling with a stout root system. Normally 2 different species will not unite. Even then inter specific combination is possible in citrus, sapota, grape and in few more plant species. Grafting is restricted only to di-cot plants. It is not possible in mono-cot plants like areca nut, coconut etc. Graft plant is dwarf by nature since it is from a lateral shoot. It spreads wider than its height. This helps for pruning, spraying, harvesting and for other cultural operations.

There are few problems too with grafted plants. Some grafts fail to grow in to a tree affecting the yield. In nutmeg and kokum only the shoots growing up ward are used for grafting to get good trees from graft plants. In most of the species the graft plant will not grow in to a huge tree. Hence they are not useful for timber purpose. Sometimes approach graft plants get damaged by heavy wind. Air layered plants without tap root system cannot tolerate drought. Depending on the root stock you may find slight variation in the quality of the fruit of the grafted plant. Due to incompatibility between root stock and scion the graft may fail to grow properly even after the success of grafting. Few viral and bacterial diseases are transmitted through graft plants in lime and pomegranate. Even then the grafted plants play a vital role in commercial horticulture.

High temperature and high humidity are necessary for the success of grafting. Hence winter and heavy rainy season are not ideal for grafting. Natural climate of the sea coast is the best for the purpose. Hence most of the commercial nurseries erect poly houses for grafting. But in medium rainfall areas shade house is enough for this purpose since the temperature and humidity remains ideal in the rainy season.

Poly house for grafting

Now let us learn about poly houses meant for plant propagation. We can categorize them like high cost, medium cost and low cost poly houses. High cost poly house built for floriculture can also be used for grafting. This is very systematic and durable. But it works out costly for propagation purpose alone. It costs at least INR 2 million per 1000 sq. mts. The next one is medium cost poly house. Poly sheet is set on iron arches. Wind damage to the poly sheet is minimal due to its shape. Cost of construction of this poly house is around INR. 0.75 million per 1000 sq. mts. The most common structure used for grafting is a low cost poly house. It is built with locally available wooden and bamboo poles. Technically this is no way inferior to the other types. But care is necessary to protect the poly sheet from the sharp edge of the poles. It is necessary to rebuild this after 2-3 years. It costs around INR 0.4 million per 1000 sq. mts. Poly house of 100 sq. mts. area accommodates around 10,000 plants.

Temperature inside the poly house is 5 to 10˚ centigrade higher than outside even in rainy season. We can raise the relative humidity to 90% by sprinkling water inside the poly house even in the winter. It is necessary to bring down the temperature inside by keeping the door open in hot noon hours of the summer. Success rate and the growth of the graft plants are excellent in the poly house. We can retain enough heat for night hours by closing the door by evening.

The poly sheet used in these poly houses keeps good for 3 to 5 years. This UV stabilized poly sheet tolerates direct sun light. Put cement or apply coal tar for the wooden poles to avoid termites. Select the type of poly house depending on your investment capacity. Poly house is inevitable for higher rate of success and large scale multiplication of graft plants. Government provides subsidy for these poly houses.

Shade house for grafting

Grafting nursery needs a systematic shade house. Young graft plants need nourishment and hardening in partial shade at least for 2-3 months. The construction of this shade house is very simple and systematic. G I pipes support the structure. Upper open end of the pipe is plugged with wooden piece. Drip irrigation LLDPE pipes are spread in all direction to hold the shade net. This support is good enough to carry the shade net of light weight. G I wires stretched to the ground from the side support pipes keep the structure firm. Shade net is buried on all sides to close the entry except the entry doors. Since the shade net allows the movement of air the structure escapes the damage due to wind. Cost of construction is bit high, but the structure keeps good at least for 5-6 years. This shade house is useful even for general nursery purpose.

Rootstock, Scion and the Principle of grafting

Now let us discuss the actual subject of grafting. Graft plant has 2 parts. Lower portion is from the seedling and is called rootstock. Upper portion is from the mother plant and is called scion. Rootstock should be a sturdy disease free seedling with a strong tap root system. For mango grafts bigger mango stones of wild variety are sown in beds. These produce stout seedlings. Stone of pulp variety and the matured stones from pickle industry are also acceptable. Champaka and Rayon seeds are sown in pots or poly bags to produce rootstocks.

Scion should be a matured stem from fresh growth of the mother plant. It should have a dormant bulged vegetative epical bud. Scion should be free from diseases and insects like stem borer. It is better to cut off the leaves of the scion on the mother plant itself 4 days before separation. Do not pluck the leaves. But cut it off retaining the stock of the leaf on the stem itself. Use only the fresh scions for grafting. However, it can be stored in a wet gunny bag for 2 days.

The principle of grafting is same in all the methods. Two stems will join if the cambium cell layers of both stems are tied together after giving level cuts. In another method roots are induced on the stem to get independent plant. Many methods of grafting are in practice based on this basic principle.

Approach grafting

This is an age old method of grafting. This is in practice in important crop plants like mango, sapota, Champaka etc. Search a twig of the mother plant which matches with the stem of the seedling in size. In commercial nurseries ground nursery of dwarf mother plants are maintained for the purpose of approach grafting. Otherwise a platform is put to facilitate grafting. Bring both the stems together and put marks. Then give level cuts of 2 inches on both the stems. Let the cuts be of 30 to 40% of the thickness of the stems. Use sharp knife to give level cuts. Do not damage the stems with a blunt knife. This point applies to all methods of grafting. Then keep both the stems together and tie with plastic tape. This tape avoids the entry of air and water inside the graft joint and avoids drying. Tying jute thread is necessary in this approach graft since both the stems are thick and stout.

June July months, the beginning of the rainy season is the ideal time for approach grafting. Graft takes 2 to 3 months for healing. During that period seedlings need watering. It is easy if the rain does that job. Give vertical cut on the scion below the graft joint after the union seems perfect. Give one deeper cut after one week. This brings down the dependence of the scion on the mother plant. Scion starts absorbing water and nutrients from the seedling through the graft joint. Then separate the graft from the mother plant. Cut off the seedling above the graft joint. Keep on removing the sprouts on the rootstock below the union.

We can get a bigger plant in approach grafting by selecting bigger shoot for grafting. But we can produce limited number of plants in this method. Due to the heavier upper portion sometimes the approach graft plant bends and breaks at the graft union. Watering the seedlings is a difficult task on a large scale if the rain stops. Because of all these reasons approach grafting is not being practiced by commercial nurseries.

What we are using here is a common plastic strip. It is not a gum tape. Soft stretchable plastic of medium thickness is folded and cut for 1 inch width. This plastic strip avoids air and water entering the graft joint. Remove the tape after the graft union heals completely and the plant starts growing. Otherwise it makes constriction and limits the growth. Even the plant may die. This point applies to all the methods of grafting.

Stone grafting

The commercial nurseries producing grafts in large numbers follow stone grafting. Though this is a simple method, the success rate depends on the skill of the grafter. Stone grafting is commonly practiced in mango, jack fruit, cashew etc. Sow the stones in beds with loose soil. Seedlings will lose the tap root while pulling it out if the soil is hard. Uproot the copper colored (in case of mango) young seedlings with entire root and the stone attached. Cut of the stem leaving 2 to 3 inches above the stone. Make a slit of 1 inch with a sharp knife. Select a scion of 4 inches in length and of pencil thickness. Give slant cut on both sides of the scion. Keep the scion in the slit of the rootstock and tie with the plastic strip. Only the plastic is enough to hold the union since the rootstock is soft. Make the packing air tight. Plant this tiny graft plant in a poly bag filled with potting mixture. Put a poly pouch on the scion and keep the graft in a poly house.

Stone graft kept in an open place will fail. But in a poly house the success rate is 70 to 80% in mango. Scion fails to sprout if the rootstock with leaves turned in to green is used. Graft fails to sprout if the stone is detached while pulling it out from the bed or at the time of grafting. The reason is the stone is the source of food for the graft plant till the scion produces green leaves. Successful graft starts sprouting in 2 to 3 weeks. Then take out the poly pouch on the scion. Cut off the plastic strip once the union is perfect and the graft grows fast. Keep on removing the sprouts below the graft joint.

Stone grafting is a successful commercial method since one can produce large number of plants. The graft joint is at the base and the plant grows straight. But this method produces tiny plant which needs more time and nourishment to attain salable size. Remember, poly house is essential for large scale stone grafting.

There is a method called double grafting in this stone method. The seedling from the stone is very weak and is almost half of the thickness of the scion. Hence two seedlings are grafted to a single scion. This makes the graft union strong and the plant will get two root systems. Hence the growth of the graft plant will be better. Except to that the grafting method is same.

Softwood grafting

Now let us study the most popular method of grafting called soft wood grafting. This is in practice in mango, sapota, jackfruit, cashew, tamarind, brinjal, hibiscus and in many more plants. We will take mango to explain the method. Grow seedling in a poly bag for one season. Even the older plant is useful. Grafting is on the green-soft portion of the plant. Hence it is called soft wood grafting. The grafting method is as usual. Cut off the rootstock above the green portion of the stem. Keep few leaves below. Make a slit of 1 to 2-inch length. Give slant cut on both sides of the scion. Then keep the scion in the slit of the rootstock and tie with the plastic strip. Plastic is enough to keep the joint intact since the stem is soft. Ensure that the packing is made airtight.

Few leaves are necessary below the graft joint. This is to feed the plant till the scion produces green leaves. Put a plastic pouch on the scion and keep the graft in poly house for better success rate. However, the poly house is not compulsory. Remove the pouch on the scion as and when the scion starts sprouting. Keep on removing the sprouts below the graft joint. Otherwise the scion will die. Cut off the plastic tape after the union heals perfectly and the plant starts growing. Otherwise it will create constriction and the plant may die.

Soft wood grafting is being used in many forms with few modifications. It is used to convert a seedling of unknown variety in to required type. Even if it is of good variety it takes many years to give fruits. We can convert this in to a good variety by soft wood grafting. Cut off all the shoots leaving 3 to 4 healthy branches. Graft at soft wood portion as usual. Even we can graft different varieties to each of the branches to produce a composite tree. Many farmers plant seedlings on the farm at required spacing. Then the plants are grafted in soft wood grafting method. This is called in situ grafting. This method gives better success rate and further growth of the plant will be very fast.

Rejuvenation of old tree

This method is being used on large scale for rejuvenation or change of variety of old mango and cashew plantations. Cut off the tree at 2 to 3 feet height from the ground in summer. It will produce many sprouts in 2 to 3 months. Then grafting is done to 5 to 6 selected sprouts in soft wood grafting method. Put poly bags on the scions after grafting. Graft union heals up fast and the branches grow quickly due to wide spread root system. This graft plant starts yielding within 2 to 3 years. However, the old big tree may fail to sprout after cutting at the base. Hence the trees up to 1 feet diameter are suitable for this method. This method is successful in converting old seedling plantations of mango and cashew.

Bark grafting

Earlier there was another method to convert old mango trees in to a graft plant. Here the grafting is done on thick bark of the tree and hence it called bark grafting. Since the bark is thick and hard it needs chisel and hammer to cut open it. Make two cuts in an angle in T shape on the trunk just above the ground. Remove a small piece of bark to facilitate the insertion of the scion. Loosen the bark without damaging it. Here a bigger scion of 8-inch length and thumb thickness is used. Give slant cuts as usual to the scion. Open the cut bark and insert the scion slowly. Do not damage the scion by pushing it down forcibly. We may put 2 scions on the same trunk at a distance but at the same height. To keep the bark in place it needs tying with a rope or thick thread. Paste the clay on the cut marks to prevent air and water entering the graft joint.

This scion starts sprouting within 5 to 6 weeks. Union will heal perfectly and the scion gives out 2-3 fleshes within 6 months. Then cut the tree above the graft union. Fell the tree in opposite direction without damaging the sprouted scion. This graft gets the whole root system for feeding. Hence it grows in to a big tree within 2-3 years and starts yielding. We come across many old mango trees grafted in this method.

Side grafting

Side grafting is one more simple method which is not in practice commercially. The old seedlings grown in a bag or pot is the rootstock. Give a slant cut on the stem at 3-inch height from the base. Cut the scion as usual and place it in the slit of the rootstock. Tying plastic tape is enough to hold the graft joint. Scion sprouts after 4 weeks. Then cut off the top portion of the rootstock above the graft joint. The scion grows in to a plant.

Air Layering

Guava, pomegranate, lime, bread fruit, hibiscus, Ixora, Musanda, ornamental rubber and many other plants produce roots on their stems naturally. But the rooting is not enough to produce an independent viable plant for commercial planting. The systematic method of inducing sufficient roots on these stems is called air layering.

Bending and putting the stems in the soil for rooting was the earlier practice. But the availability of such stems near the soil was very limited. Hence the method was modified to root at any height of the plant. This is called as air layering. Select healthy twig of finger size for layering. Put 2 knife marks around the bark at 1 inch apart and take out a ring of bark. Scrape the greenish cell layer on the stem to avoid rejoining of the bark. To induce more root IBA hormone of 500 ppm concentration may be applied. Sphagnum moss is commonly used as rooting media. This is a fern growing on trees in the evergreen forests or on the ground in hilly region. This is a very loose medium with high water holding capacity. This sphagnum moss is available for sale in the shops selling nursery materials. Even the saw dust and powdered organic manure are in use as rooting medium. But moss is the best one.

Wet the sphagnum moss and squeeze it to drain excess water. Otherwise it will result in the decay of the stem and bark inside the layer ball. Tie a plastic sheet with the help of jute thread below the layer mark. Hold it upward to get a packet shape. Fill the packet with the moist sphagnum moss tightly. Again tie the opening at the top. Tying should be tight enough to make the layer ball airtight. It will root within 5 to 6 weeks depending on the species of plant. After sufficient roots are visible put 2 vertical cuts below the layer ball in a week interval. Then separate the layer from the mother plant. Cut off the tender portion of the layer plant to minimize evaporation since the roots are yet to establish. Remove the plastic sheet, plant it in a poly bag and keep it under shade.

Air layering is the only popular commercial method of propagation in pomegranate and guava. We can produce layers in large numbers if we have enough mother plants. Air layering is a simple and cheaper method of plant multiplication. But the plant dies after separation if the rooting is not proper. It is opined that the layer plant cannot withstand drought since it has no tap root system. But now a day the plantations will have assured irrigation. Hence the air layering has become a popular method of plant propagation.

Budding or Bud grafting

It is a delicate method of grafting. This is the only commercial method of multiplication in rose. Budding is in practice even in rubber, lime, ber fruit, cocoa and in many other plants. Depending on the shape of the bark opening it is termed as I budding, T budding and patch budding.

We take rose plant to explain the method. Stem cuttings of commercial variety of rose will not root properly. Hence the rootstock is a wild non flowering variety called Dog rose. Plant the dog rose cuttings in the field or in poly bags. Select the scion stick from the required variety of rose. We find healthy, fresh and bulged vegetative buds on the stick below dried flowers. Cut off the leaves of the scion stick. But do not pluck the leaves. Scoop the selected bud with the stalk of the leaf and a small portion of the stem inside. Then carefully take out the stem part inside. Ensure that the bud do not dries up. Cut off the other shoots of the dog rose leaving only one soft-fresh shoot. Remove the thorns to facilitate easy budding. Put a mark of 1 inch length on the bark of the shoot with the help of knife tip. Loosen the bark without damaging it. Insert the bud inside along with the portion of the bark with it. Tie a plastic strip to make the graft joint air tight keeping the bud open. It will take 3 to 4 weeks for sprouting of the grafted bud. Cut off the dog rose shoot above the budding joint after the joint heals perfectly and the bud starts growing in to a green shoot. Keep on removing the sprouts below the budding point.

Commercial rose nurseries plant the dog rose cuttings in poly bags itself. Even one can transfer the successful bud grafts from the field to a poly bag. Budding is a simple method. But the success rate depends on the skill of the grafter. Since the scion part is very small we can go for budding in all the seasons.

Grafting is a simple art to practice by a farmer or a hobby gardener. Commercial nurseries sell only few popular varieties of plants. Selling price is also high. Transportation adds to the cost of the graft plant. We can propagate any plant or variety of our choice if we learn this art of grafting. Grafting nursery as a subsidiary activity which can generate an attractive income. Grafting is the basic skill of agriculture. If farmer has not acquainted this skill his learning is incomplete. Namaskar.