Plant Propagation - ChapingoPlant Propagation T or Shield Budding T budding or shield budding is a...

PlantPropagation

An Overview of Asexual ReproductionGrafting and Budding

T or Shield Budding

Approach Grafting

The Four-Flap Graft

Texas Inlay Bark Graft

Greenwood Grafting

Whip Grafting

Collecting and Storing Graftwood

LayeringAir Layering for Difficult to Root Plants

Plant Tissue and Organ Culture (in vitro culture)Micropropagation

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Plant Propagation

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Plant Propagation

T or Shield BuddingT budding or shield budding is a special grafting technique in which the scion piece is reduced to asingle bud. As with other techniques of asexual propagation, the resulting plants are clones (geneticallyidentical plants reproduced from one individual entirely by vegetative means). The plant beingpropagated (represented by the bud) is referred to as the scion, while the plant being grafted onto isreferred to as the rootstock, or simply stock. A small branch with several buds suitable for T budding onit is often called a bud stick.

Successful T budding requires that the scion material have fully-formed, mature, dormant buds, and thatthe rootstock be in a condition of active growth such that the "bark is slipping". This means that thevascular cambium is actively growing, and the bark can be peeled easily from the stock piece with littledamage. T budding can be performed on certain fruit trees (peaches, for example) in June using coldstored budsticks and field grown seedling rootstocks. Many deciduous trees are budded in late July orearly August after the current seasons buds have developed fully and are dormant using field grownseedlings that have slipping bark.

Bud sticks having plump, healthy buds are suitablescions. These budsticks should be on branches thatexhibited good growth during the current season, ratherthan ones from the interior of trees that have slenderstems and closely spaced, small buds. Thick watersprouts that grew very vigorously are often poor scions.Leaf blades are clipped from the budsticks, leaving thepetiole intact. This leaves a convenient "handle" forholding the bud while it is cut from the budstick.

T or Shield Budding

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The bud and a small sliver of the wood underneath it arecut from the budstick using an upward slicing motion.The cut should begin about 1/2 to 3/4 inch below thebud, and should go deep enough into the wood so thatwhen the cut is finished about 1/2 to 3/4 above the bud,the bark and a small sliver of wood are cut off. Aperpendicular cut across the top of the upward cut willseparate it from the bud stick.

Budding knives should be kept very sharp, so that aslittle damage as possible is done to the bud. Dull knivesstrip and tear the wood, leaving cuts that do not healproperly. Buds must be cut from the bud stick just priorto grafting, otherwise they will dry out. Some graftersput the bud in their mouth for the time between when itis removed from the stick and when it is grafted in place,but this practice is not recommended. Speed in graftingis a more suitable solution.

Some grafters make a downward cut as the second cut toremove the bud from the budstick. This works well aslong as it does not result in too much of the underlyingwood being removed with the bud.

T or Shield Budding


A vertical cut is made on the stem of the root stock. Thecut should be deep enough to insure that the bark willseparate at the cambium.

The "T is then crossed." That is, a perpendicular cut ismade at the upper end of the vertical cut. In areas withheavy rainfall during the grafting season, or in species inwhich the rootstock is likely to "bleed" heavily, anupside down, or inverted T bud can be used to preventwater or sap from pooling in the graft.

The bark is carefully slipped from the stem of therootstock exposing a "pocket" into which the bud shieldcan be placed. Care should be taken not to tear the flapsof bark in the process of spreading them.

If the bark does not slip easily, this indicates that thestock is not in active growth and the process should beconducted later when active growth has resumed.

An alternative method for budding which does notrequire the bark to slip is the technique of chip buddingin which the bud is cut out with a "chip" of theunderlying wood. This requires that a chip ofcorresponding size be cut out of the stock piece in orderto align the cambia for proper graft healing.

T or Shield Budding


The bud shield is carefully slipped in between the barkflaps. The top of the bark strip on the bud shield istrimmed to fit tightly against the horizontal cut (thecross of the T) so that the bud fits within the "pocket"snuggly.

The bark flaps are held tightly against the bud as theyare wrapped with a budding rubber, grafting tape orother suitable closure. This closure must eitherbreakdown by weathering (as budding rubbers do), ormust be removed in 2 to 3 weeks after the union hashealed. If the material does not break down, it will girdlethe rootstock.

After the union has healed, the upper part of therootstock plant can be cut away to force the bud to grow(as would be the case for June budding). If the graftingis done in the late summer, the bud likely will need tooverwinter prior to resuming growth. In this case, theupper portion of the rootstock is usually removed duringthe dormant season, either in late winter or early spring.

After the upper portion of the rootstock is removed, the scion bud grows vigorously.

T or Shield Budding


Approach GraftingLarry Stein

Texas Agricultural Extension Service

The distinguishing feature of approach grafting is that two independently growing,self-sustaining plants are grafted together. This self-sustaining characteristic of both plantswhich are to be grafted insures survival of both even if the grafting attempt is, for somereason, not successful. However odds of being successful are greatly enhanced because ofthe active growing condition of both plants involved and absence of a time limitationrequired for the healing of the graft union to occur before the dependent scion (top portion)dies from lack of sustenance.

The approach grafting procedure is as follows:

Plant an adapted, growingplant as close to the baseof the non-adapted varietyas possible withoutextensively damaging theroot structure of theestablished plant.

1.

From both plants closelyposition shoots which areat least three-eighths inch diameter and preferably close to the same size. At the pointwhere the union is to occur, a slice of bark one to two inches long is peeled from bothstems. The peeled area should be the same size on each.

2.

The two peeled surfaces are then bound tightly together with budding or electricaltape. Wrap completely with two complete covers around the area where the twopeeled areas are in contact.

3.

Remove some of the top portion of the foliage from the adapted variety six to eightinches above the graft union. This will encourage a more rapid healing of the graftedunion.

4.

The union should be complete in four weeks. This type of grafting is most successfulif performed during growth season.

5.

After the parts are well united (4 weeks or more),the remainder of the top of theadapted, native variety can be cut off immediately above the graft union and thebottom or root system of the non-adapted, yellowing plant can be cut off immediatelybelow the graft union.

6.

The graft union is now completed and the problems of iron chlorosis and indigenoussoil pathogens have been solved if the proper rootstock has been used. Immediatelyafter the portion of each plant is removed it may be necessary to reduce the leaf areaof the top if wilting occurs because of lack of sufficient root system support. Thissituation will soon stabilize. If the only problem has been micronutrient (ironchlorosis) deficiency, the top, unadapted variety will not need to be detached from its

7.

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own root system--the approach grafted, adapted variety root system will "feed" thesickly plant what it needs. However, if the purpose of the graft is to control soil bornediseases, the susceptible variety should be detached from its root system and becometotally dependent on the root system of the adapted variety.

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The Four-Flap GraftSammy Helmers and Austin StocktonTexas Agricultural Extension Service

Grafting is needed to propagate outstanding varieties of fruits. The four-flap graft is aneasy-to-do, successful propagation procedure for amateurs and professional horticulturists. Itis ideal for small-caliper trees up to 1 inch in diameter before they are large enough for theTexas-method inlay bark graft.

The four-flap grafts most successful when the scion and rootstock pieces are near the samediameter. The best fit is obtained when the scion is slightly larger than the stock.

Collecting and Storing Propagation Wood. Collect scion wood from the desired treewhile dormant in late February or early March and store until spring propagation time.Optimum scion wood diameter is 3/8 to 3/4 inch; 1-inch diameter is maximum. Selecthealthy, 1-year-old wood with prominent, well developed buds. Label all propagation woodby cultivar name and place it in a container with moist paper towels. Polyethylene bagsmake excellent storage containers. Store the wood in a refrigerator at 32 to 36F.

Grafting Technique. The best time to graft isApril to mid-May when the rootstock isactively growing, the bark "slips" freely andleaflets are 1/2- to 3/4-inch long. Take thescion wood directly form cold storage and useimmediately. Do not let the scion sticks dry outduring grafting procedures.

The following outlines the four-flap graftingmethod:

Use a stock plant with a primary stem or laterallimb of 1/2-to 1-inch diameter. Cut straightacross the trunk or limb with sharp pruning

shears at the point you wish to graft. If possible, leave one or two side branches below thegrafting point, but cut them back to 6 inches. This keeps the tree vigorous, protects it fromsunscald and keeps the scion from becoming too tall or whiplike and breaking off. Place thegraft 7 to 8 feet above the ground if cattle or horses are grazing near the trees; otherwiseplace the grafts at a comfortable working height. Roll a rubber band 3 inches down form thetop to the stock (figure 1).

On the stock plant where the horizontal cut was made, make four vertical, equally spacedcuts 1 1/2 inches long. Make sure the cuts penetrate the bark down to the interior wood(figure 2).

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Texas Inlay Bark Graft

George Ray McEachern, Sammy Helmers, Larry Stein and John LipeExtension Horticulturists

Texas Agricultural Extension ServiceTexas A&M University

College Station, TX 77843

June 16, 1992

Inlay grafting is one of the best and most popular systems of propagating pecans in Texas. Ithas been successfully used when other systems have failed because of heat, drought andwind. It has also been successfully used on walnuts, apples, pears, grapes, rabbiteyeblueberries and persimmons.

The Texas method of inlay grafting, developed by B.G. Sitton, L.D. Romberg, F.R. Brison,B.G. Hancock and others in the 1950s, follows the basic fundamentals of the standard barkgraft. However, this technique uses an inlay cut and employs an entirely new system ofcovering the graft and stock. The inlay occurs when tow parallel cuts are made through thestock bark forming a scion inlay pattern on the stock. Aluminum foil is used as a stockcover, reflecting sunlight and reducing temperatures around the graft. The Foil is coveredwith polyethylene film to assure constant high relative humidity around the graft. Thissystem not only results in a high percentage of growing grafts, but it is easy to use. Allnecessary equipment can be carried in an apron since the need for a burdensome wax melteris eliminated. The more stressful the grafting conditions, the more important this graftingtechnique becomes. This method gained popularity and wide use throughout the pecanindustry following numerous method demonstrations and promotions by B.G. Hancock andhis many students.

Anyone can successfully use the inlay graft by following these instructions and practicing todevelop skill in the basic techniques.

Figure 1. Use rootstock trunks or major side limbs that are 1 1/2 to 3 1/2 inches in diameter.Leave one or two side branches below the cut to keep the tree vigorous, to protect fromsunburn and to keep the graft form overgrowing and blowing out. Cut straight across thetrunk or limb with a sharp saw above a straight section of the trunk or limb. Make the cut 7or 8 feet above ground if cattle or horses are grazing in a native grove.

Figure 2. Select a section of stock with a flat surface so the flat cut surface graft stick willfit cambium to cambium without air space separation. Choose a spot on the south orsouthwestern side so that prevailing winds will blow the graft shoot toward the trunk insteadof away from the trunk. If the old bark is rough, cut it down to live bark, forming a cleanshield. leave the bark as thick as possible to securely hold the graft. Do not cut through thebark into the wood.

Figure 3. Use a knife with a very sharp blade and a sheepfoot point, similar to that

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illustrated. Grafting knife blades are beveled only on one side to give a flat cut. Firmly holdthe knife in a closed fist and cut the graft stick with numerous thin slices.

Figure 4. The finished graft stick will have one to three buds and three cuts; a slant cut, along cut and a back cut. The slant cut should begin 1/2 inch below and on the side oppositethe lowest bud. It should extend half the distance through the graft stick at approximately a45 degree angle. The long cut is the same thickness from the slant cut to the end of the graftstick. Make the long cut perfectly flat at the midpoint of the graft stick. The back cut ischisel-shaped and is 1/2 inch long on the back side and lower end. This makes it easier toinsert the graft stick and provides additional cambium contact. The long cut can be 1 1/2 to3 inches long.

Figure 5. Place the long cut surface f the graft stick against the clean shield of live bark onthe stock. Allow the slant cut to extend above the stock. Firmly hold the graft upright withthe left thumb. Begin the first inlay cut at the top of the stock on the right side of the graftstick. Cut through the bark down into the wood. Draw the knife straight down the right sideof the graft stick to within 3/4 inch of the bottom portion of the graft stick. It is veryimportant to make this cut straight into the bark. Do not angle the knife to the left or right.

Figure 6. Hold the graft firmly in position with the thumb of the right hand. Do not allowthe graft to move after the right inlay cut is made.


Figure 7. Bring the left hand around the back of the stock. Catch the graft with the firstthree fingers of the left hand and hold in exact position. Make the second inlay cut on theleft side to the graft stick, cutting straight into the stock as on the right side.

Figure 8. The two parallel inlay cuts through the bark should be exactly the same shape asthe long cut section of the graft stick.

Figure 9. Peel the bark flap 1/2 inch down between the two parallel inlay cuts. Slide thegraft stick between the bark and wood of the stock. There should be no air space betweenthe long cut and the flat wood surface. If the bark does not easily separate from the stock,the cambium is not slipping and you will need to wait several days, then try again.

Figure 10. As the graft stick is inserted, press the bark flap against the graft stick with thethumb of the right hand to firmly hold the graft stick in the slot. Apply firm but gentlepressure on top of the graft until it is forced into the inlay slot.

Figure 11. Stop pushing the graft stick when the bottom of the slant cut touches the top ofthe stock. This exposed slant cut surface will form callus and new tissue, which will coverthe top to the stock and securely anchor the graft to the stock in 1 to 3 years. Do not push the


slant cut below the top to the stock because it will separate the graft stick from the flatwood.

Figure 12. The graft can be secured by any one of several methods. Eighteen gauge 3/4-inchnails, 5/8-inch flat point staples in a vertical position, budding tape or flagging tape have allbeen successfully used.

Figure 13. Take a 2-inch square of household aluminum foil and tear a line halfway downto the center of the square. Fold the aluminum foil around the stock so that the bottom of thetear fits right under the lowest bud.

Figure 14. Fold each side of the divided end of the square of aluminum foil. Cover all cutsurfaces with the foil, including the slant cut of the graft stick. Crimp the foil to form a loosemod around the stock. All cut surfaces of the trunk and graft stick should be covered.

Figure 15. Cut off one corner of a pint- or quart-sized polyethylene bag. Slip the bag overthe graft stick and gently pull it down until the cut corner rests below the lowest bud andabove the slant cut.


Figure 16. Tie the polyethylene bag at the cut corner around the graft just below the lowestbud and above the slant cut so that no air leaks occur. Tie with one wrap of a rubber band,small rubber strip or polyethylene tape so that the graft will not be girdled as it grows.

Figure 17. Tie the lower end of the polyethylene bag around the stock with foil covering allof the enclosed area. Make a small puncture above the lower tie to allow water to drain outof the bag.

Figure 18. Coat the cut surface of the tip end of the graft stick with orange shellac or whiteglue.


Figure 19. The buds on the graft stick should begin groth in 6 weeks. Remove thepolyethylene bag and foil when the shoots are over 6 inches long. Keep these shoots prunedback to only 24 inches to prevent wind blowouts. If maximum growth is needed, in 6 to 10weeks select the strongest shoot and tie it to a brace to prevent it from blowing out. Afterone year, select the strongest shoot on the graft stick and remove all others. After 2 or 3years, when three-fourths or all of the trunk is covered with overgrowth, remove all shootsbelow the graft.

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An educational resource of theTexas Agricultural Extension Service.

Green Wood GraftingA scripted slide set prepared by

Loy Shreve, Jerry Parsons and Sammy HelmersExtension Specialists, Department of Horticultural Sciences

Revised August, 1998 by Larry SteinTexas A&M University and Texas Agricultural Extension Service

Greenwood grafting allows growers to propagate desired fruit andnut varieties during the growing season after the time for graftingwith dormant scions has ended. This method has been successfulwith pecans, walnuts, apples, apricots and plums; the procedurewill probably work with most other deciduous trees and shrubsalso.

This grafting method can be used from mid-May throughSeptember in Texas. In addition to stocks and scions, a sharp knifewith a stockman's blade, strips of rubber innertube or polyethylenebudding tape and polyethylene squares are needed. The stockshould be at least 1 inch in diameter at the point of union.Scion-wood must be the current season's growth. Scions can bestored in an ice chest for up to 5 days without damage if they arekept moist and cool. Place a bag of ice cubes in one corner of thechest to keep the scions in good condition.

Use of this Slide SetAdvance through the slide presentation by clicking on the "next"link. The images on the individual pages are "clickable", that is,you can see a full screen image when you click on it

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Whip GraftingBluefford G. Hancock, George Ray McEachern, and Larry A. Stein

Texas Agricultural Extension Service

WHIP GRAFTING (also called splice or tongue grafting) is one of the oldest methods of asexual plantpropagation known. It is the predominant propagation method used on apples and is widely used on pear.Although most grapes are grown from cuttings in this country, whip grafting is the standard when they arepropagated. Whip grafting has been the primary method employed in propagating pecan nursery stock inthe southeastern United States. This technique is also used to some extent in the Southeast and west toLouisiana for top-working larger pecan trees on the above-ground portions. Since successful whip graftingis closely correlated to the presence of high humidity, this method has not been used widely in the driersections of Oklahoma, New Mexico and Texas. A major strong point for whip grafting nursery stock is thesmooth and straight trees that are produced by this method.

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Whip Grafting

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Propagation Index | Aggie Horticulture

Whip Grafting

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George Ray McEachernExtension Horticulturist

Texas Agricultural Extension ServiceTexas A&M University

College Station, TX 77843-2134

June 17, 1992

Successful in-lay and four-flap grafting of pecans is dependent on the availability of suitablegraftwood of the desired variety. The wood must be collected in late winter during thedormant season and properly stored until spring grafting time.

Collection

Collect the graftwood in late February to early March while the tree is still dormant. If thebuds have begun to swell and grow, the wood is inferior and cannot be used successfully.

Select parent trees of the desired variety that are free of obscure scale, rosette, and disease.Young vigorous trees produce abundant, smooth and large-sized, current-season wood.Moderate-sized trees making normal growth usually have good graftwood in theiruppermost limbs. Older trees can be cut back to force vigorous new growth satisfactory forgraft wood.

Stick preparation

Select straight, smooth graftwood from 1-year-old wood 1/4- to 1/2-inch diameter. Cutshoots for grafts into 6-, 12-, or 18-inch lengths to give one, two, or three graft sticks.

Figure 1 is graftwood 3/8 inch diameter collected in February for storage as 6, 12, or 18 inchsticks.

Each graft stick should contain at least three buds or nodes. Seal the end of the graft stickswith melted wax, grafting paint, or orange shellac. Only 1/4-inch of the end of each stickneeds to be treated. When the seal is dry, tie the graft sticks in bundles no more than sixeach. Label each bundle with permanent ink on a wood or metal write-on label. The varietyand year should be recorded on the label. Figure 2 is a graftwood bundle labeled and readyfor packing material and storage.


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Packing material

Paper towels, sphagnum moss, or wood shavings can be used as packing material to preventthe graft sticks form drying out. Moist paper towels that have had all of the water squeezedout can be wrapped around each bundle. A second method involves placing the graft stickbundles in slightly moist sphagnum or wood shavings. The wrapped bundles are then placedin polyethylene bags. Plastic bags do not breathe and should not be used.

Storage

Refrigerate the bags of graft stick bundles at a temperature of 30 to 45 degrees F. Do notallow graftwood to dry out during storage. Take the desired wood out of refrigeration onlyas needed. Wood should not be heated and recooled during the grafting season.

Grafting

Trees will be ready for in-lay or four-flap grafting in the spring as the trees begin to grow.The bark should slip during this period. Keep the graftwood in a cool, moist place whilegrafting.

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AIR LAYERING FORDIFFICULT-TO-ROOT PLANTS

Everett E. JanneExtension landscape horticulturist

Air layering is a useful method of producing roots on the stem of indoor landscape plantsthat have become "leggy" through the loss of their lower foliage.

This method, believed to have been developed centuries ago by the Chinese, has been usedsuccessfully as a mean of propagating some of the more difficult-to-root plants. Because itrequired excessive care and patience, air layering was used only by the highly trainedplantsman.

The procedure was to wound the stem or branch of a plant and enclose the wounded stemwith moist sphagnum moss or similar rooting medium until roots develop from the woundedarea. Success was dependent upon the ability of the propagator to keep the rooting mediummoist until the roots were formed and large enough to support the new plant. Only since thedevelopment of polyethylene film has air layering become a practical method of propagationfor the home gardener and amateur horticulturist.

Air layering seldom is used on plants that root easily by other less complicated methods, butit is useful for rooting ornamental plants such as ornamental figs, dieffenbachia, croton andothers of a herbaceous nature. Woody plants frequently propagated in this manner includemagnolia, holly, camelia, azalea and many of the fruit and nut bearing plants such as citrus,apple, pears and pecans.

For optimum rooting make air layers in the spring on shoots produced during the previousseason or in mid-summer on mature shoots from the current season's growth. On woodyplants, stems of pencil size or larger are best. The stem may be much thicker on the moreherbaceous plants.

Steps for making a successful air layer are illustrated in the following drawings:

Figure 1. Method of woundingwoody plants such as magnolia,gardenia, rose, fig and similarplants. With a sharp knife, maketwo parallel cuts about 1 1/2 inchesapart around the stem and throughthe bark and cambium layer.Connect the two parallel cuts withone long cut (a) and remove the ringof bark (b), leaving the inner woodytissue exposed (c).

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Figure 2. Method of woundingplants having less woody stems inpreparation for air layering. Thismethod usually is used on foliageplants such as the rubber plant,(Ficus benjamini and Ficuselastica) and the dieffenbachia.

(a) With a sharp knife, make a longupward cut from 1 1/2 to 2 incheslong, almost to the center of thestem.(b) Insert a wood sliver, toothpick ortwisted piece of sphagnum mossinto the wound to hold it open andprevent cut tissue from reuniting. Atthis point, the wounded area may bedusted with one of the commercialrooting compounds to speed up therooting process. Such compounds,however, do not insure rootproduction on difficult-to-rootvarieties.

Figure 3. Apply a handful of dampsphagnum moss so that it envelopesthe wounded portion of the stem.Tying the moss in place with stringhelps keep it in position whilecompleting the process. Thesphagnum moss hould be soakedseveral hours to insure that it isthoroughly moist. Squeeze outsurplus water before using, sinceexcessive moisture will result indecay and deterioration of the planttissue.


Figure 4. Using a sheet ofpolyethylene film approximately 6"X 12" or 8" X 12", depending uponthe size of the plant stem, wrap theball of sphagnum moss using thebutchers fold (see insert) to secure atight seal where the two ends of thesheet are joined.

Figure 5. Draw the upper end of thefilm snugly around stem makingsure that none of the moss isexposed. Fasten securely withelectricians tape, taking care that thetape extends beyond the film andadheres to the stem. Repeat theprocedure on the lower end, againmaking sure there is a snug fit.Moisture must not escape andexcess moisture must not enterwhen watering or syringing theplants. Support the plant with stakeor splint to prevent breakage at thewounded area.


Figure 6. After the new roots havepenetrated the moss ball and arevisible on all sides, the rootedbranch may be removed from theparent plant. The rooting time willvary with plant variety as well as theseason in which it is performed.

Figure 7. Remove the newly rootedplant from the parent plant with asharp knife or pruning shears,making the cut just below the ball ofmoss and roots. (Not illustrated)Carefully remove the polyethylenefilm. Without disturbing the roots orremoving the ball of moss, plant in acontainer using a good pottingmixture or plant in a well-preparedsoil bed.


Figure 8. Placing a polyethylenetent over the newly potted plant for4 to 8 days until the root system iswell established is helpful as it willaid in preventing excessive loss ofmoisture. Keep the plant under alight shade and avoid direct sunlightuntil the new root system is welldeveloped.

Many plants are lost in the final stage of the process because the root system is notsufficiently developed to sustain the top portion of the new plant. By utilizing the plastictent illustrated in figure 8 or by keeping the new plant in a humid environment, it is possibleto develop a good root system on rather large cuttings. Once the plant is well established, itis best to harden off the foliage by gradually exposing it to normal atmosphere. This can bedone by cutting a few holes every few days in the plastic tent to reduce the humidity until itis similar to the external atmosphere.

Educational programs conducted by the Texas Agricultural Extension Service serve people of all ageswithout regard to race, color, sex, disability, religion, age or national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts ofCongress of May 8,1914, as amended, and June 30, 1914, in cooperation with the United States Departmentof Agriculture, Zerle L. Carpenter, Director, Texas Agricultural Extension Service, The Texas A&MUniversity System.

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TISSUE CULTURE OF WOODY PLANTSR. Daniel LinebergerProfessor of HorticultureTexas A&M University, College Station, TX [email protected]

Much has been written and more has been said about the applications of plant tissue culture to thenursery industry. The subject is still poorly understood by a majority of plant propagators. Tissue cultureis often looked upon as being practical only for propagation of those plants which are difficult topropagate by conventional methods. This notion is quickly being laid to rest. An industry is emerging invarious areas throughout the country which is taking advantage of technological advances in the realm oftissue culture of woody plants. This technology suggests that propagation by tissue culture is indeedapplicable to the "difficult to propagate" species, and equally as important, it may offer economicadvantages for some species which are considered relatively "easy to propagate".

The intent of this communication is to briefly describe the contemporary techniques of tissue culture ofwoody plants, and to review the advantages and limitations of tissue culture as a propagation method.

THE METHODOLOGY OF TISSUE CULTURE

The variety of techniques which can be used to get plant development in vitro (that is, by techniques suchas tissue culture) is considerable and completely dependent upon the species in question. Single cells ofleaf tissue can regenerate whole plants, as can shoot tips, leaf pieces, root pieces, lateral buds, or stemsections. Not all of these methods are applicable to woody plants, and indeed, not all have been appliedto a commercial level to any plants.

Shoot tip culture is the method in widest use for the mass propagation of woody species. An activelygrowing shoot tip is surface sterilized and placed on a defined culture medium under sterile conditions.The culture medium contains inorganic and organic salts (macronutrients, micronutrients and vitamins)as well as an energy source (sucrose or table sugar), growth regulators, and agar )to gel the medium). Ifthe growth regulators are appropriately balanced, the shoot tip elongates, lateral buds break and begingrowth, and adventitious shoots are also produced on the stem piece. This rapid proliferation of shootsresults in masses of shoots being produced from a single shoot tip. Up to a hundred shoots may beproduced in as little as eight to twelve weeks from a single tip. The number of shoots produced and therapidity of shoot proliferation varies between species, and in some cases, between cultivars of a singlespecies. Shoots are removed from the cultures at regular intervals and a portion of the mass is replacedon fresh media to continue proliferation. The small shoots which are removed are then rooted in aseparate medium, either a sterile gelled medium or a peat-perlite medium (in much the same fashion asconventional woody cuttings).

Shoots produced through tissue culture are generally easy to root, even though the same cultivar may bedifficult to root by cutting propagation. The resulting rooted shoot is referred to as a "plantlet" because ofits miniature size, but these can generally be grown in the greenhouse at a rapid rate and with a highdegree of survival. Techniques for rooting tissue cultured shoots are currently receiving a great deal ofresearch attention as are methods for establishing these shoots into the greenhouse environment.

Woody Plant Tissue Culture

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THE TISSUE CULTURE LABORATORY

Most propagators would probably list the expense of setting up a tissue culture laboratory among thereasons for not getting involved with this technology. A lab does cost more than a mist bed! A moresevere limitation is without doubt the absence of personnel skilled in the techniques of tissue culture. Anindividual who has had prior experience with tissue culture methodology can successfully operate alaboratory with a bare minimum of equipment. An autoclave or sterilizer, an accurate means of weighingchemicals, a small inventory of glassware, and chemical stocks or prepackaged media are all that isrequired to initiate cultures. The laboratory can be enlarged, more equipment added, and additionalpersonnel hired as the need for such arises. The most critical factors are the ingenuity and experience ofthe laboratory manager.

As a tissue culture laboratory becomes operational, procedures other than the actual culturing processbecome critical. Maintenance of disease and insect free stock plants with a low titer of bacterial andfungal contamination is critical. Also important is the care and handling of the thousands of plantletsprior to their transfer to the field or containers. The ability to grow off the plantlets ultimately will limitproduction, rather than any limitation due to the propagation phase.

TISSUE CULTURE PROPAGATION OF WOODY SPECIES

Major advances in the mass propagation of woody plants have been made over the past ten years.Because of the somewhat variable response of species and cultivars to the in vitro environment, muchresearch was (and still is) needed to define the cultural conditions required by ornamental species. As anexample of the variability encountered, we have observed that seedling shoot tip cultures of crabappleproduce as few as one or as many as sixty-four shoots per explant after three months in tissue culture.Similar variations in the tendency for multiple shoot production have also been noted with adult clonalmaterial of different apple cultivars.

The number of woody plant species which have been clonally propagated through tissue culture isincreasing at a rapid rate, and in fact, most commercially important ornamental species have beenstudied. Perhaps the best publicized of the early research on woody plants involved apples, Douglas fir,and rhododendrons. An extensive commercial scale production program for apple scion cultivars androotstocks has developed in England and in several European countries.

Using the successes of the apple, rhododendron, and maple programs as a basis, many recent advanceshave been made which will facilitate the mass propagation of other woody species. While it is true thatcultivar differences account for lack of success with some plants, a growing body of evidence suggeststhat taxonomic families behave somewhat alike in tissue culture. A large number of deciduous andevergreen Rhododendron species share common cultural requirements, the most notable of which is therequirement for the same cytokinin for adventitious shoot formation. A similar relationship existsbetween the trees and shrubs of the Rosaceae (including crabapples, pears, plums, and hawthorns). Mostrosaceous species will likely be mass propagated on media very similar to that found to be optimal forapples.

The anomalies alluded to by the crabapple seedling responses to tissue culture and the emergingsimilarities between the requirements of rosaceous trees and shrubs demonstrate that much research isneeded to define the conditions necessary for commercial scale tissue culture production programs. As is



often found to be the case with propagation systems, those systems described as optimal in the laboratorywould likely need modification to be considered economical by the industry.

IMPACT OF THE TISSUE CULTURE INDUSTRY

As is always the case for any emerging technology, the strongest supporters for the adoption of thattechnology are likely those involved in its development. Having acknowledged these biases, one mustnow consider the advantages and limitations of tissue culture propagation, and what its economic impacton the nursery industry will be.

Not every nursery will OPERATE a tissue culture laboratory. The trend toward specialization of nurseryoperations as either "propagators" or "producers" is likely to continue in the future. Operation andmanagement of a tissue culture facility requires personnel and physical facilities which are quite differentfrom those required by a container or field production nursery. Previously in this report where theestablishment of the laboratory was considered, the relatively small initial investment in physicalfacilities and equipment was discussed. It should be reemphasized at this point, that the training andquality of the laboratory manager is more important than the laboratory itself, and that this expertise isnot currently available among contemporary nursery propagators.

Not every nursery will NEED a tissue culture laboratory. Commercial operations specializing in masspropagation of nursery crops can likely produce a sufficient number of plants to satisfy the market.

As with any other technology, the success of tissue culture within the nursery industry will be determinedby economic factors. Can the plantlets be produced in sufficient numbers as a cost to compare withtraditional propagation? Will the propagules fit into the established production sequence in the nurseryindustry? Are the propagules true-to-type? These answers must be obtained on a species by species,cultivar by cultivar basis.



Step 1.Seedling rootstocks, 1 to 2 years of age, are usually usedfor whip grafting purposes. The diameter at the upperportion of the root generally ranges from 3/8 to 3/4 inch,however, stocks up to 1 inch in diameter can be used. Theseason for whip grafting is February to early or mid Marchin most areas, or while the stock is dormant.

Whip Grafting Index | Propagation Index | Aggie Horticulture

Whip Grafting

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Step 2.Select 1-year graft or scion wood inthe dormant season. Size shouldcorrespond to size of available rootstocks. Each graft stick should containat least two sets of buds. Graftwoodshould be selected and stored in lateJanuary. A knife with a thin bladeshaped as shown above and made fromhigh-quality steel is desirable for whipgrafting. Make sure that the knife willtake a fine edge and hold it under aheavy work load.


Whip Grafting



Step 3.Expose about 4 to 6 inches of the upperportion of the tap root. Where only a fewtrees are involved, the entire process of soilremoval may be accomplished by the useof a hoe. However, if the graft is securedwith poly tape, the graft can be placedabove the soil line as well. Grafter is poisedto make initial slanting cut on rootstock.Note the slight angle of the knife blade.The stock of the seedling rootstock fits intothe groove or notch formed by the thumband forefinger of the knife-hand. Thisserves to stabilize the stock and to providea guide as the cut is made.


Whip Grafting



Step 4.Pull the knife upward with the bladeangled about 45 degrees, making asmooth and straight diagonal cut. Thisslanting straight-plane cut should be 2to 3 inches long. Try to make this cutwith one stroke of the knife.


Whip Grafting



Step 5.Place the knife at a spot on the slantcut approximately one third of thedistance from the tip to the heel (orbottom) of the cut. Make a "tongue"cut by working the knife bladedownward for a distance of 1 to 1 1/2inches. Take care to prevent splittingthe stock. Use fore-finger of the lefthand to brace the stock. Note in the inset that the cut is neither parallel to the grain of thestock nor to the slanting cut, but is actually between the two.


Whip Grafting



Step 6.Hold the scion wood securely in theleft hand, but with care to preventinjury to the buds. Place knife at anangle to the scion and make a slantingcut (see inset) by pushing the bladeaway from the body. Thisstraight-plane cut should be made assimilar to the cut on the rootstock aspossible.


Whip Grafting



Step 7.Make the "tongue" cut on the scion byplacing the knife blade at a point aboutone-third of the distance down fromthe tip. Pull the blade downward at anangle that is about halfway betweenthe grain of the scion and plane of theslant cut. (See inset.) Note that thethumb of the knife hand serves as aguide for a controlled cut, while theforefinger of the left hand stabilizesthe scion.


Whip Grafting



Step 8.Slip the plane cut surface of the sciondown to the slant cut of the stock untilthe two "tongue" cuts mesh together.The cambium layers of the stock andscion must be aligned if a union is tobe obtained. An uneven or wavy cutwill result in gaps between the twosurfaces. If the two cuts are madeproperly, the stock and scion willappear to be one. (See inset.)


Whip Grafting



Step 9.Wrap the graft securely with maskingtape or a special grafting tape.Polyethylene budding tape may beused for this wrap, but may requirecutting at a later date to preventgirdling. Make certain that thecambium layers of the scion and stockremain aligned during the wrappingprocess. Note in the inset that the wrapextends from below the graft union toa point slightly above. This is essentialto prevent drying of the cut surfacesbefore callousing takes place.


Whip Grafting



Step 10.Firm moist topsoil around the whip graft toprevent drying. Ideally, the soil should cover allof the taped area with the lower bud group onthe scion exposed. The cut surface at the top ofthe scion stick may be coated with orangeshellac or with wax to prevent excessive drying.Of course, if the graft was placed above the soilline, this step would not be necessary.Remember, regardless if the graft is placedabove or below the soil, the tape whichoriginally secured the graft must be removed.This can be done as late as one year, butpreferably after 3 to 4 months.


Whip Grafting



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