Is it possible to graft plants from different families?

For example, I have some Eastern Hemlock rootstock (Pinaceae), and want to graft a scion from Dawn Redwood (Cupressaceae) onto it. Is this possible? Is anything like this possible?

No. Exceptions are always possible, but it would be a noteworthy.

I just find this notes in:


Although there are a few reports of short-term graft union formation between distantly related (interfamilial) herbaceous species, there are no confirmed reports of interfamilial grafts between woody perennials.

One extremely curious report of natural interfamilial graft compatibility which must be considered unconfirmed, and even unlikely, was the observation of La Rue (1934) [… ]

Is it possible to graft plants from different families? - Biology

In the process of grafting, a branch from one species of plant is attached to a plant of another species and induced to grow. It's often used to improve the vigor of fruit trees it's common practice to graft a branch of a tasty apple species, like Red Delicious, onto a rootstock of a hardy, fast-growing, but not-so-tasty crabapple. When a branch is successfully grafted, it ends up sharing the vascular system of the plant it is grafted onto. Plant vascular systems, unlike our circulatory systems, are fairly simple: the tubelike xylem cells carry water and nutrients from the roots upward, and the phloem cells carry sugar from the leaves, where it is manufactured, to the rest of the plant. Generally, the nutrient requirements of plants are very similar, even among plant groups as different as gymnosperms and angiosperms, so it would be theoretically possible to graft one onto the other.

Most grafting is done by humans, but some parasitic plants can actually graft themselves into their hosts' vascular systems! In fact, among parasitic plants, there are many examples of the exact kind of grafting you mentioned, between a gymnosperm and an angiosperm. The genus Arceuthobium, in the angiosperm family Santalaceae, consists of 42 species that are parasites to conifers (gymnosperms). Here is a good photo of a spruce tree with an Arceuthobium infestation.

In your question, you mention the idea of "creating new species" by grafting gymnosperms and angiosperms. This is an intriguing thought, but unfortunately it would be impossible. In plants (and animals), the cell lines of the body are divided into two categories: somatic cells and germ cells. The somatic cells produce the organism's body and allow it to function in the world, while the germ cells are used in reproduction. Grafting is a process that only involves somatic cells, so any changes produced would not get passed down to the next generation. It would be theoretically possible to graft the germ cells of a gymnosperm onto an angiosperm, or vice versa, but the grafting would not affect the seeds themselves. They would turn out to be only gymnosperms (if the source plant was a gymnosperm) or only angiosperms (if the source plant was an angiosperm). In order for a group of organisms to be considered a species, their unique characteristics must be passed down through generations in their genetic material.


  • Precocity: The ability to induce fruitfulness without the need for completing the juvenile phase. Juvenility is the natural state through which a seedling plant must pass before it can become reproductive. In most fruiting trees, juvenility may last between 5 and 9 years, but in some tropical fruits, e.g., mangosteen, juvenility may be prolonged for up to 15 years. Grafting of mature scions onto rootstocks can result in fruiting in as little as two years.
  • Dwarfing: To induce dwarfing or cold tolerance or other characteristics to the scion. Most apple trees in modern orchards are grafted on to dwarf or semi-dwarf trees planted at high density. They provide more fruit per unit of land, of higher quality, and reduce the danger of accidents by harvest crews working on ladders. Care must be taken when planting dwarf or semi-dwarf trees. If such a tree is planted with the graft below the soil, then the scion portion can also grow roots and the tree will still grow to its standard size.
  • Ease of propagation: Because the scion is difficult to propagate vegetatively by other means, such as by cuttings. In this case, cuttings of an easily rooted plant are used to provide a rootstock. In some cases, the scion may be easily propagated, but grafting may still be used because it is commercially the most cost-effective way of raising a particular type of plant.
  • Hybrid breeding: To speed maturity of hybrids in fruit tree breeding programs. Hybrid seedlings may take ten or more years to flower and fruit on their own roots. Grafting can reduce the time to flowering and shorten the breeding program.
  • Hardiness: Because the scion has weak roots or the roots of the stock plants are tolerant of difficult conditions. e.g. many Western Australian plants are sensitive to dieback on heavy soils, common in urban gardens, and are grafted onto hardier eastern Australian relatives. Grevilleas and eucalypts are examples.
  • Sturdiness: To provide a strong, tall trunk for certain ornamental shrubs and trees. In these cases, a graft is made at a desired height on a stock plant with a strong stem. This is used to raise 'standard' roses, which are rose bushes on a high stem, and it is also used for some ornamental trees, such as certain weeping cherries.
  • Disease/pest resistance: In areas where soil-borne pests or pathogens would prevent the successful planting of the desired cultivar, the use of pest/disease tolerant rootstocks allow the production from the cultivar that would be otherwise unsuccessful. A major example is the use of rootstocks in combating Phylloxera.
  • Pollen source: To provide pollenizers. For example, in tightly planted or badly planned apple orchards of a single variety, limbs of crab apple may be grafted at regularly spaced intervals onto trees down rows, say every fourth tree. This takes care of pollen needs at blossom time.
  • Repair: To repair damage to the trunk of a tree that would prohibit nutrient flow, such as stripping of the bark by rodents that completely girdles the trunk. In this case a bridge graft may be used to connect tissues receiving flow from the roots to tissues above the damage that have been severed from the flow. Where a water sprout, basal shoot or sapling of the same species is growing nearby, any of these can be grafted to the area above the damage by a method called inarch grafting. These alternatives to scions must be of the correct length to span the gap of the wound.
  • Changing cultivars: To change the cultivar in a fruit orchard to a more profitable cultivar, called top working. It may be faster to graft a new cultivar onto existing limbs of established trees than to replant an entire orchard.
  • Genetic consistency: Apples are notorious for their genetic variability, even differing in multiple characteristics, such as, size, color, and flavor, of fruits located on the same tree. In the commercial farming industry, consistency is maintained by grafting a scion with desired fruit traits onto a hardy stock.
  • Curiosities
    • A practice sometimes carried out by gardeners is to graft related potatoes and tomatoes so that both are produced on the same plant, one above ground and one underground. of widely different forms are sometimes grafted on to each other.
    • Multiple cultivars of fruits such as apples are sometimes grafted on a single tree. This so-called "family tree" provides more fruit variety for small spaces such as a suburban backyard, and also takes care of the need for pollenizers. The drawback is that the gardener must be sufficiently trained to prune them correctly, or one strong variety will usually "take over." Multiple cultivars of different "stone fruits" (Prunus species) can be grafted on a single tree. This is called a fruit salad tree.
    • Ornamental and functional, tree shaping uses grafting techniques to join separate trees or parts of the same tree to itself. Furniture, hearts, entry archways are examples. Axel Erlandson was a prolific tree shaper who grew over 75 mature specimens.
    • Compatibility of scion and stock: Because grafting involves the joining of vascular tissues between the scion and rootstock, plants lacking vascular cambium, such as monocots, cannot normally be grafted. As a general rule, the closer two plants are genetically, the more likely the graft union will form. Genetically identical clones and intra-species plants have a high success rate for grafting. Grafting between species of the same genus is sometimes successful. Grafting has a low success rate when performed with plants in the same family but in different genera. And grafting between different families is rare. [3]
    • Cambium alignment and pressure: The vascular cambium of the scion and stock should be tightly pressed together and oriented in the direction of normal growth. Proper alignment and pressure encourages the tissues to join quickly, allowing nutrients and water to transfer from the stockroot to the scion. [4] : 466
    • Completed during appropriate stage of plant: The grafting is completed at a time when the scion and stock are capable of producing callus and other wound-response tissues. Generally, grafting is performed when the scion is dormant, as premature budding can drain the grafting site of moisture before the grafting union is properly established. Temperature greatly affects the physiological stage of plants. If the temperature is too warm, premature budding may result. Elsewise, high temperatures can slow or halt callus formation. [3]
    • Proper care of graft site: After grafting, it is important to nurse the grafted plant back to health for a period of time. Various grafting tapes and waxes are used to protect the scion and stock from excessive water loss. Furthermore, depending on the type of graft, twine or string is used to add structural support to the grafting site. Sometimes it is necessary to prune the site, as the rootstock may produce shoots that inhibit the growth of the scion. [3]
    • Cutting tools: It is good procedure to keep the cutting tool sharp to minimize tissue damage and clean from dirt and other substances to avoid the spread of disease. A good knife for general grafting should have a blade and handle length of about 3 inches and 4 inches respectively. Specialized knives for grafting include bud-grafting knives, surgical knives, and pruning knives. Cleavers, chisels, and saws are utilized when the stock is too large to be cut otherwise.
    • Disinfecting tools: Treating the cutting tools with disinfectants ensures the grafting site is clear of pathogens. A common sterilizing agent is absolute alcohol.
    • Graft seals: Keeps the grafting site hydrated. Good seals should be tight enough to retain moisture while, at the same time, loose enough to accommodate plant growth. Includes specialized types of clay, wax, petroleum jelly, and adhesive tape.
    • Tying and support materials: Adds support and pressure to the grafting site to hold the stock and scion together before the tissues join, which is especially important in herbaceous grafting. The employed material is often dampened before use to help protect the site from desiccation. Support equipment includes strips made from various substances, twine, nails, and splints. [5]
    • Grafting machines: Because grafting can take a lot of time and skill, grafting machines have been created. Automation is particularly popular for seedling grafting in countries such as Japan and Korea where farming land is both limited and used intensively. Certain machines can graft 800 seedlings per hour. [4] : 496

    Approach Edit

    Approach grafting or inarching is used to join together plants that are otherwise difficult to join. The plants are grown close together, and then joined so that each plant has roots below and growth above the point of union. [6] Both scion and stock retain their respective parents that may or may not be removed after joining. Also used in pleaching. The graft can be successfully accomplished any time of year. [7]

    Bud Edit

    Bud grafting (also called chip budding) uses a bud instead of a twig. Grafting roses is the most common example of bud grafting. In this method a bud is removed from the parent plant, and the base of the bud is inserted beneath the bark of the stem of the stock plant from which the rest of the shoot has been cut. Any extra bud that starts growing from the stem of the stock plant is removed. Examples: roses and fruit trees like peaches.

    Budwood is a stick with several buds on it that can be cut out and used for bud grafting. It is a common method of propagation for citrus trees. [8] [9] [10]

    Cleft Edit

    Slide the wedge into the cleft so that it is at the edge of the stock and the centre of the wedge faces are against the cambium layer between the bark and the wood. It is preferable if a second scion is inserted in a similar way into the other side of the cleft. This helps to seal off the cleft. Tape around the top of the stock to hold the scion in place and cover with grafting wax or sealing compound. This stops the cambium layers from drying out and also prevents the ingress of water into the cleft.

    Whip Edit

    The stock is cut through on one side only at a shallow angle with a sharp knife. (If the stock is a branch and not the main trunk of the rootstock then the cut surface should face outward from the centre of the tree.) The scion is similarly sliced through at an equal angle starting just below a bud, so that the bud is at the top of the cut and on the other side than the cut face.

    In the whip and tongue variation, a notch is cut downwards into the sliced face of the stock and a similar cut upwards into the face of the scion cut. These act as the tongues and it requires some skill to make the cuts so that the scion and the stock marry up neatly. The elongated "Z" shape adds strength, removing the need for a companion rod in the first season (see illustration).

    The joint is then taped around and treated with tree-sealing compound or grafting wax. A whip graft without a tongue is less stable and may need added support.

    Stub Edit

    Stub grafting is a technique that requires less stock than cleft grafting, and retains the shape of a tree. Also scions are generally of 6–8 buds in this process.

    After the graft has taken, the branch is removed and treated a few centimeters above the graft, to be fully removed when the graft is strong.

    Four-flap Edit

    The four-flap graft (also called banana graft) is commonly used for pecans, and first became popular with this species in Oklahoma in 1975. It is heralded for maximum cambium overlap, but is a complex graft. It requires similarly sized diameters for the rootstock and scion. The bark of the rootstock is sliced and peeled back in four flaps, and the hardwood is removed, looking somewhat like a peeled banana. It is a difficult graft to learn.

    Awl Edit

    Awl grafting takes the least resources and the least time. It is best done by an experienced grafter, as it is possible to accidentally drive the tool too far into the stock, reducing the scion's chance of survival. Awl grafting can be done by using a screwdriver to make a slit in the bark, not penetrating the cambium layer completely. Then inset the wedged scion into the incision.

    Veneer Edit

    Rind (also called bark) Edit

    Rind grafting involves grafting a small scion onto the end of a thick stock. The thick stock is sawn off, and a

    4 cm long bark-deep cut is made parallel to the stock, from the sawn-off end down, and the bark is separated from the wood on one or both sides. The scion is shaped as a wedge, exposing cambium on both sides, and is pushed in under the back of the stock, with a flat side against the wood.

    Tree branches and more often roots of the same species will sometimes naturally graft this is called inosculation. The bark of the tree may be stripped away when the roots make physical contact with each other, exposing the vascular cambium and allowing the roots to graft together. A group of trees can share water and mineral nutrients via root grafts, which may be advantageous to weaker trees, and may also form a larger rootmass as an adaptation to promote fire resistance and regeneration as exemplified by the California black oak (Quercus kelloggii). [11] Additionally, grafting may protect the group from wind damages as a result of the increased mechanical stability provided by the grafting. [12] Albino redwoods use root grafting as a form of plant parasitism of normal redwoods.

    A problem with root grafts is that they allow transmission of certain pathogens, such as Dutch elm disease. Inosculation also sometimes occurs where two stems on the same tree, shrub or vine make contact with each other. This is common in plants such as strawberries and potato.

    Natural grafting is rarely seen in herbaceous plants as those types of plants generally have short-lived roots with little to no secondary growth in the vascular cambium. [12]

    Occasionally, a so-called "graft hybrid" or more accurately graft chimera can occur where the tissues of the stock continue to grow within the scion. Such a plant can produce flowers and foliage typical of both plants as well as shoots intermediate between the two. The best-known example this is probably +Laburnocytisus 'Adamii', a graft hybrid between Laburnum and Cytisus, which originated in a nursery near Paris, France, in 1825. This small tree bears yellow flowers typical of Laburnum anagyroides, purple flowers typical of Cytisus purpureus and curious coppery-pink flowers that show characteristics of both "parents". Many species of cactus can also produce graft chimeras under the right conditions although they are often created unintentionally and such results are often hard to replicate.

    Grafting has been important in flowering research. Leaves or shoots from plants induced to flower can be grafted onto uninduced plants and transmit a floral stimulus that induces them to flower. [13]

    The transmission of plant viruses has been studied using grafting. Virus indexing involves grafting a symptomless plant that is suspected of carrying a virus onto an indicator plant that is very susceptible to the virus.

    Grafting can transfer chloroplasts (specialised DNA in plants that can conduct photosynthesis), mitochondrial DNA and the entire cell nucleus containing the genome to potentially make a new species making grafting a form of natural genetic engineering. [14]

    White Spruce Edit

    White spruce can be grafted with consistent success by using 8–10 cm (3–4 in) scions of current growth on thrifty 4- to 5-year-old rootstock (Nienstaedt and Teich 1972). [15] Before greenhouse grafting, rootstocks should be potted in late spring, allowed to make seasonal growth, then subjected to a period of chilling outdoors, or for about 8 weeks in a cool room at 2 °C (Nienstaedt 1966). [16]

    A method of grafting white spruce of seed-bearing age during the time of seed harvest in the fall was developed by Nienstaedt et al. (1958). [17] Scions of white spruce of 2 ages of wood from 30- to 60-year-old trees were collected in the fall and grafted by 3 methods on potted stock to which different day-length treatments had been applied prior to grafting. The grafted stock were given long-day and natural-day treatments. Survival was 70% to 100% and showed effects of rootstock and post-grafting treatments in only a few cases. Photoperiod and temperature treatments after grafting, however, had considerable effect on scion activity and total growth. The best post-grafting treatment was 4 weeks of long-day treatment followed by 2 weeks of short-day treatment, then 8 weeks of chilling, and finally long-day treatment.

    Since grafts of white spruce put on relatively little growth in the 2 years after grafting, techniques for accelerating the early growth were studied by Greenwood (1988) [18] and others. The cultural regimes used to promote one additional growth cycle in one year involve manipulation of day length and the use of cold storage to satisfy chilling requirements. Greenwood took dormant potted grafts into the greenhouse in early January then gradually raised the temperature during the course of a week until the minimum temperature rose to 15 °C. Photoperiod was increased to 18 hours using incandescent lighting. In this technique, grafts are grown until elongation has been completed, normally by mid-March. Soluble 10-52-10 fertilizer is applied at both ends of the growth cycle and 20-20-20 during the cycle, with irrigation as needed. When growth elongation is complete, day length is reduced to 8 hours using a blackout curtain. Budset follows, and the grafts are held in the greenhouse until mid-May. Grafts are then moved into a cooler at 4 °C for 1000 hours, after which they are moved to a shade frame where they grow normally, with applications of fertilizer and irrigation as in the first cycle. Grafts are moved into cold frames or unheated greenhouse in September until January. Flower induction treatments are begun on grafts that have reached a minimum length of 1.0 m. Repotting from an initial pot size of 4.5 litre to 16 litre containers with a 2:1:1 soil mix of peat moss, loam, and aggregate.

    In one of the first accelerated growth experiments, white spruce grafts made in January and February that would normally elongate shortly after grafting, set bud, and remain in that condition until the following spring, were refrigerated for 500, 1000, or 1500 hours beginning in mid-July, and a non-refrigerated control was held in the nursery. [18] After completion of the cold treatment, the grafts were moved into the greenhouse with an 18-hour photoperiod until late October. Height increment was significantly (P 0.01) influenced by cold treatment. Best results were given by the 1000-hour treatment. [18]

    The refrigeration (cold treatment) phase was subsequently shown to be effective when applied 2 months earlier with proper handling and use of blackout curtains, which allows the second growth cycle to be completed in time to satisfy dormancy requirements before January (Greenwood et al. 1988). [18]

    Grafting is often done for non-woody and vegetable plants (tomato, cucumber, eggplant and watermelon). [19] Tomato grafting is very popular in Asia and Europe, and is gaining popularity in the United States. The main advantage of grafting is for disease-resistant rootstocks. Researchers in Japan developed automated processes using grafting robots as early as 1987. [20] [21] [22] Plastic tubing can be used to prevent desiccation and support the healing at the graft/scion interface. [23]

    Fertile Crescent Edit

    As humans began to domesticate plants and animals, horticultural techniques that could reliably propagate the desired qualities of long-lived woody plants needed to be developed. Although grafting is not specifically mentioned in the Hebrew Bible, it is claimed that ancient Biblical text hints at the practice of grafting. For example, Leviticus 19:19, which dates to around 1400 BCE, states "[the Hebrew people] shalt not sow their field with mingled seed. " (King James Bible). Some scholars believe the phrase mingled seeds includes grafting, although this interpretation remains contentious among scholars.

    Grafting is also mentioned in the New Testament. In Romans 11, starting at verse 17, there is a discussion about the grafting of wild olive trees concerning the relationship between Jews and Gentiles.

    By 500 BCE grafting was well established and practiced in the region as the Mishna describes grafting as a commonplace technique used to grow grapevines. [24]

    China Edit

    According to recent research: "grafting technology had been practiced in China before 2000 BC". [25] Additional evidence for grafting in China is found in Jia Sixie's 6th century CE agricultural treatise Qimin Yaoshu (Essential Skills for the Common People). [26] It discusses grafting pear twigs onto crab apple, jujube and pomegranate stock (domesticated apples had not yet arrived in China), as well as grafting persimmons. The Qimin yaoshu refers to older texts that referred to grafting, but those works are missing. Nonetheless, given the sophistication of the methods discussed, and the long history of arboriculture in the region, grafting must have already been practiced for centuries by this time.

    Greece and Rome, and Islamic Golden Age Edit

    In Greece, a medical record written in 424 BCE contains the first direct reference to grafting. The title of the work is On the Nature of the Child and is thought to be written by a follower of Hippocrates. The language of the author suggests that grafting appeared centuries before this period.

    In Rome, Marcus Porcius Cato wrote the oldest surviving Latin text in 160 BCE. The book is called De Agri Cultura (On Farming Agriculture) and outlines several grafting methods. Other authors in the region would write about grafting in the following years, however, the publications often featured fallacious scion-stock combinations.

    During the European Dark Ages, Arabic regions were experiencing an Islamic Golden Age of scientific, technological, and cultural advancement. Creating lavishly flourished gardens would be a common form of competition among Islamic leaders at the time. Because the region would receive an influx of foreign ornamentals to decorate these gardens, grafting was used much during this period. [24]

    Europe and the United States Edit

    After the fall of the Roman Empire, grafting survived in the Christian monasteries of Europe until it regained popular appeal during the Renaissance. The invention of the printing press inspired a number of authors to publish books on gardening that included information on grafting. One example, A New Orchard and Garden: Or, the Best Way for Planting, Graffing, and to Make Any Ground Good for a Rich Orchard, Particularly in the North, was written by William Lawson in 1618. While the book contains practical grafting techniques, some even still used today, it suffers from exaggerated claims of scion-stock compatibility typical of this period.

    While grafting continued to grow in Europe during the eighteenth century, it was considered unnecessary in the United States as the produce from fruit trees was largely used either to make cider or feed hogs. [24]

    French Wine Pandemic Edit

    Beginning in 1864, and without warning, grapevines across France began to sharply decline. Thanks to the efforts of scientists such as C. V. Riley and J. E. Planchon, the culprit was identified to be phylloxera, an insect that infests the roots of vines and causes fungal infections. Initially, farmers unsuccessfully attempted to contain the pest by removing and burning affected vines. When it was discovered that phylloxera was an invasive species introduced from North America, some suggested importing rootstock from the region as the North American vines were resistant to the pest. Others, opposed to the idea, argued that American rootstocks would imbue the French grapes with an undesirable taste they instead preferred to inject the soil with expensive pesticides. Ultimately, grafting American rootstock onto French vines became prevalent throughout the region, creating new grafting techniques and machines. American rootstocks had trouble adapting to the high soil pH value of some regions in France so the final solution to the pandemic was to hybridize the American and French variants. [24]

    Multiple Grafts

    The trick to creating a multiple fruit-bearing tree is to graft several compatible varieties or species onto the same rootstock. This is easiest when using bud grafting, since the rootstock experiences less shock. Compatibility is determined by the species of fruit trees you wish to graft together. Generally speaking, they need to be very closely related for the graft to take successfully. Sometimes, incompatible grafts may survive past the initial stages, but they eventually fail.

    Cross-breeding Marijuana with another Plant, like a Fruit

    Is it possible to cross-breed weed with like a strawberry plant for example? Then you get like pink strawberry buds or something mmmmm.

    Anybody with ideas or who have tried it post here!


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    Is it possible to cross-breed weed with like a strawberry plant for example? Then you get like pink strawberry buds or something mmmmm.

    Anybody with ideas or who have tried it post here!


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    Fried at 420

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    Is it possible to cross-breed weed with like a strawberry plant for example? Then you get like pink strawberry buds or something mmmmm.

    Anybody with ideas or who have tried it post here!


    Well-Known Member

    No, you can't do this.
    As already mentioned, different species simply cannot interbreed this way.
    You can't cross a tobacco plant with a tomato, you can't cross a monkey with a dog, and you can't cross a cannabis plant with a strawberry.

    With respect to hops, that plant is distantly related to cannabis, but its nowhere near close enough that a simple cross is possible.
    I've been told its possible to GRAFT a cannabis plant onto a hops vine, or vice versa.
    Now, I don't know if this is true, but even if it were, you'd basically just be creating a "frankenstein" plant that was part hops, part cannabis. The cannabis part of it would still look, smell, and behave the same as any other cannabis plant, so you wouldn't fool anyone, and you wouldn't end up with THC-laden hops flowers.

    With respect to what you might term genetic engineering, yes it is possible to transfer individual genes from one species to another.
    Some of this kind of work has been done with tobacco plants, I think, and for obvious reasons, a tobacco plant might be a good candidate to transfer THC production genes.
    The problem is that doing this sort of work is highly technical, complicated and quite expensive.

    With respect to THC production, that's not going to be one gene to transfer but rather a whole complex set of them, involving synthesis proteins, transport proteins, regulatory proteins, etc. I'm pretty sure that these particular enzymes and regulatory mechanisms for cannabinoid production haven't even been worked out yet. Even assuming they were, transfering them wholesale from one species to another in a functional way would provide an unprecedented technical challenge. For example, who is to say that THC production wouldn't simply gum up and kill a tobacco plant?

    So far as I know, nobody has ever accomplished anything remotely close to that before. I wouldn't say its "impossible" but at the present time its effectively science fiction.

    If you want to continue with these sorts of pipe dreams, I have two alternative ways to go.

    a. Find *another* plant that produces THC like molecules, and then genetically engineer and/or selectively breed it to create cannabinoids. Unfortunately, humans being what they are, I'd imagine that if any other such plant existed, that would be well known already.

    b. Selectively breed and/or genetically engineer an actual cannabis plant to the point where it no longer physically resembled one. Again, this would pose a massive technical challenge, though I think this particular angle of attack would be quite a bit easier than say trying to cross a hemp plant with a blueberry!

    How to Graft Plants

    This article was co-authored by Andrew Carberry, MPH. Andrew Carberry has been working in food systems since 2008. He has a Masters in Public Health Nutrition and Public Health Planning and Administration from the University of Tennessee-Knoxville.

    There are 10 references cited in this article, which can be found at the bottom of the page.

    wikiHow marks an article as reader-approved once it receives enough positive feedback. In this case, 93% of readers who voted found the article helpful, earning it our reader-approved status.

    This article has been viewed 291,453 times.

    Grafting is a technique of combining two plants or pieces of plants so they grow together. This allows you to combine the qualities of a strong, disease-resistant plant with the qualities of another plant, usually one that produces good fruit or attractive flowers. While there are many methods of grafting, the methods described here should allow you to graft almost any vegetable or fruit seedling, flowering bush, and even certain trees such as citrus trees. For information on grafting larger branches or different types of trees, see the article Graft a Tree.

    Is it possible to graft fruit/flowering trees onto a well established jacaranda tree?

    I have a large jacaranda tree in my front yard (perhaps 30-50 yrs old). I recently pruned a few branches that were about 2" thick. You can see one fresh cut in the picture below and there are a few more in different places.

    Now all of these are within an arm's reach and I was wondering if it would be possible to graft a scion from a fruit tree or another flowering tree onto each of these new stubs. Normally, grafting is done between "similar" plants. The wikipedia article on rootstock says:

    The rootstock can be a different species from the scion, but must be closely related.

    But how "close" is close enough? Same genus/family/order? It might be easy to find similar flowering trees to jacaranda, but is it possible at all to graft any fruit trees onto this?

    I haven't set my mind on any particular fruit/flowering tree and this is more of an experiment rather than wanting to actually grow something for consumption (if it works, well and good!). If it matters, I'm in Southern California, so there really isn't any winter to speak of and temperatures hardly go below 8-10 ºC (46-50º F).

    Plants grafted together have to be similar enough that they recognize each other as kindred varieties. If you start with a plum tree, you will be able to graft any other stone fruit onto its trunk. Peach, nectarine, apricot and even cherry branches are all viable choices. Alternatively, you may want to try producing a plum tree with three or four different types of plum, from small Italian prune plums to juicy Black Beauty specimens.

    Depending on the age of your rootstock tree and the number of branches it has, there are a few different grafting techniques to consider. The scion, or branch to be added to the trunk, should be gathered early in the season. Graft it onto the rootstock by slicing the scion at an angle and the rootstock at the same angle, then wrap the two pieces together, butting the raw wood surfaces up against each other. Another option is to cut a T-shape in the bark of the trunk and slip the scion inside, wrapping the trunk and scion together to hold them until they heal. C Alternatively, cut a slit in the top of a branch stub and force one or two scions inside, allowing them to heal along with the slit in the branch.

    Not all grafts are successful, so try grafting multiple scions around the main trunk to increase your chances of success. Sterilize your tools with alcohol before using them to reduce the chances of spreading disease. Wrap the wound, then paint it with wound dressing. Old-time orchardists would use wax instead of chemical dressing, since it is waterproof and will keep out germs.

    Micro propagation: Technique, Factors, Applications and Disadvantages

    Plants can be propagated by sexual (through generation of seeds) or asexual (through multiplication of vegetative parts) means.

    Clonal propagation refers to the process of asexual reproduction by multiplication of genetically identical copies of individual plants. The term clone is used to represent a plant population derived from a single individual by asexual reproduction.

    Asexual reproduction through multiplication of vegetative parts is the only method for the in vivo propagation of certain plants, as they do not produce viable seeds e.g. banana, grape, fig, and chrysanthemum. Clonal propagation has been successfully applied for the propagation of apple, potato, tuberous and several ornamental plants.

    Advantages of Vegetative Propagation:

    Asexual (vegetative) propagation of plants has certain advantages over sexual propagation.

    i. Faster multiplication — large number of plants can be produced from a single individual in a short period.

    ii. Possible to produce genetically identical plants.

    iii. Sexually — derived sterile hybrids can be propagated.

    iv. Seed — raised plants pass through an undesirable juvenile phase which is avoided in asexual propagation.

    v. Gene banks can be more easily established by clonally propagated plants.

    In Vitro Clonal Propagation:

    The in vivo clonal propagation of plants is tedious, expensive and frequently unsuccessful. In vitro clonal propagation through tissue culture is referred to as micro propagation. Use of tissue culture technique for micro propagation was first started by Morel (1960) for propagation of orchids, and is now applied to several plants. Micro propagation is a handy technique for rapid multiplication of plants.

    Technique of Micro propagation:

    Micro propagation is a complicated process and mainly involves 3 stages (I, II and III). Some authors add two more stages (stage 0 and IV) for more comprehensive representation of micro- propagation. All these stages are represented in Fig. 47.1, and briefly described hereunder.

    This is the initial step in micro- propagation, and involves the selection and growth of stock plants for about 3 months under controlled conditions.

    In this stage, the initiation and establishment of culture in a suitable medium is achieved. Selection of appropriate explants is important. The most commonly used explants are organs, shoot tips and axillary buds. The chosen explant is surface sterilized and washed before use.

    It is in this stage, the major activity of micro propagation occurs in a defined culture medium. Stage II mainly involves multiplication of shoots or rapid embryo formation from the explant.

    This stage involves the transfer of shoots to a medium for rapid development into shoots. Sometimes, the shoots are directly planted in soil to develop roots. In vitro rooting of shoots is preferred while simultaneously handling a large number of species.

    This stage involves the establishment of plantlets in soil. This is done by transferring the plantlets of stage III from the laboratory to the environment of greenhouse. For some plant species, stage III is skipped, and un-rooted stage II shoots are planted in pots or in suitable compost mixture.

    The different stages described above for micro propagation are particularly useful for comparison between two or more plant systems, besides better understanding. It may however, be noted that not all plant species need to be propagated in vitro through all the five stages referred above.

    Micro propagation mostly involves in vitro clonal propagation by two approaches:

    1. Multiplication by axillary buds/apical shoots.

    2. Multiplication by adventitious shoots.

    Besides the above two approaches, the plant regeneration processes namely organogenesis and somatic embryogenesis may also be treated as micro propagation.

    3. Organogenesis: The formation of individual organs such as shoots, roots, directly from an explant (lacking preformed meristem) or from the callus and cell culture induced from the explant.

    4. Somatic embryogenesis: The regeneration of embryos from somatic cells, tissues or organs.

    1. Multiplication by Axillary Buds and Apical Shoots:

    Quiescent or actively dividing meristems are present at the axillary and apical shoots (shoot tips). The axillary buds located in the axils of leaves are capable of developing into shoots. In the in vivo state, however only a limited number of axillary meristems can form shoots. By means of induced in vitro multiplication in micro propagation, it is possible to develop plants from meristem and shoot tip cultures and from bud cultures.

    Meristem and Shoot Tip Cultures:

    Apical meristem is a dome of tissue located at the extreme tip of a shoot. The apical meristem along with the young leaf primordia constitutes the shoot apex. For the development of disease-free plants, meristem tips should be cultured.

    Meristem or shoot tip is isolated from a stem by a V-shaped cut. The size (frequently 0.2 to 0.5 mm) of the tip is critical for culture. In general, the larger the explant (shoot tip), the better are the chances for culture survival. For good results of micro propagation, explants should be taken from the actively growing shoot tips, and the ideal timing is at the end of the plants dormancy period.

    The most widely used media for meristem culture are MS medium and White’s medium. A diagrammatic representation of shoot tip (or meristem) culture in micro propagation is given in Fig 47.2, and briefly described hereunder.

    In stage I, the culture of meristem is established. Addition of growth regulators namely cytokinins (kinetin, BA) and auxins (NAA or IBA) will support the growth and development.

    In stage II, shoot development along with axillary shoot proliferation occurs. High levels of cytokinins are required for this purpose.

    Stage III is associated with rooting of shoots and further growth of plantlet. The root formation is facilitated by low cytokinin and high auxin concentration. This is opposite to shoot formation since high level of cytokinins is required (in stage II). Consequently, stage II medium and stage III medium should be different in composition. The optimal temperature for culture is in the range of 20-28°C (for majority 24-26°C). Lower light intensity is more appropriate for good micro propagation.

    The plant buds possess quiescent or active meristems depending on the physiological state of the plant. Two types of bud cultures are used— single node culture and axillary bud culture.

    This is a natural method for vegetative propagation of plants both in vivo and in vitro conditions. The bud found in the axil of leaf is comparable to the stem tip, for its ability in micro propagation. A bud along with a piece of stem is isolated and cultured to develop into a plantlet. Closed buds are used to reduce the chances of infections.

    A diagrammatic representation of single node culture is depicted in Fig 47.3. In single node culture, no cytokinin is added.

    In this method, a shoot tip along with axillary bud is isolated. The cultures are carried out with high cytokinin concentration. As a result of this, apical dominance stops and axillary buds develop. A schematic representation of axillary bud culture for a rosette plant and an elongate plant is given in Fig 47.4.

    For a good axillary bud culture, the cytokinin/ auxin ratio is around 10: 1. This is however, variable and depends on the nature of the plant species and the developmental stage of the explant used. In general, juvenile explants require less cytokinin compared to adult explants. Sometimes, the presence of apical meristem may interfere with axillary shoot development. In such a case, it has to be removed.

    2. Multiplication by Adventitious Shoots:

    The stem and leaf structures that are naturally formed on plant tissues located in sites other than the normal leaf axil regions are regarded as adventitious shoots. There are many adventitious shoots which include stems, bulbs, tubers and rhizomes. The adventitious shoots are useful for in vivo and in vitro clonal propagation. The meristematic regions of adventitious shoots can be induced in a suitable medium to regenerate to plants.

    3. Organogenesis:

    Organogenesis is the process of morphogenesis involving the formation of plant organs i.e. shoots, roots, flowers, buds from explant or cultured plant tissues. It is of two types — direct organogenesis and indirect organogenesis.

    Direct Organogenesis:

    Tissues from leaves, stems, roots and inflorescences can be directly cultured to produce plant organs. In direct organogenesis, the tissue undergoes morphogenesis without going through a callus or suspension cell culture stage. The term direct adventitious organ formation is also used for direct organogenesis.

    Induction of adventitious shoot formation directly on roots, leaves and various other organs of intact plants is a widely used method for plant propagation. This approach is particularly useful for herbaceous species. For appropriate organogenesis in culture system, exogenous addition of growth regulators—auxin and cytokinin is required. The concentration of the growth promoting substance depends on the age and nature of the explant, besides the growth conditions.

    Indirect Organogenesis:

    When the organogenesis occurs through callus or suspension cell culture formation, it is regarded as indirect organogenesis (Fig 47.5 B and C). Callus growth can be established from many explants (leaves, roots, cotyledons, stems, flower petals etc.) for subsequent organogenesis.

    The explants for good organogenesis should be mitotically active immature tissues. In general, the bigger the explant the better the chances for obtaining viable callus/cell suspension cultures. It is advantageous to select meristematic tissues (shoot tip, leaf, and petiole) for efficient indirect organogenesis. This is because their growth rate and survival rate are much better.

    For indirect organogenesis, the cultures may be grown in liquid medium or solid medium. Many culture media (MS, B5 White’s etc.) can be used in organogenesis. The concentration of growth regulators in the medium is critical for organogenesis.

    By varying the concentrations of auxins and cytokinins, in vitro organogenesis can be manipulated:

    i. Low auxin and low cytokinin concentration will induce callus formation.

    ii. Low auxin and high cytokinin concentration will promote shoot organogenesis from callus.

    iii. High auxin and low cytokinin concentration will induce root formation.

    4. Somatic Embryogenesis:

    The process of regeneration of embryos from somatic cells, tissues or organs is regarded as somatic (or asexual) embryogenesis. Somatic embryogenesis may result in non-zygotic embryos or somatic embryos (directly formed from somatic organs), parthogenetic embryos (formed from unfertilized egg) and androgenic embryos (formed from male gametophyte).

    In a general usage, when the term somatic embryo is used it implies that it is formed from somatic tissues under in vitro conditions. Somatic embryos are structurally similar to zygotic (sexually formed) embryos, and they can be excised from the parent tissues and induced to germinate in tissue culture media.

    Development of somatic embryos can be done in plant cultures using somatic cells, particularly epidermis, parenchymatous cells of petioles or secondary root phloem. Somatic embryos arise from single cells located within the clusters of meristematic cells in the callus or cell suspension. First a pro-embryo is formed which then develops into an embryo, and finally a plant.

    Two routes of somatic embryogenesis are known — direct and indirect (Fig 47.6).

    Direct Somatic Embryogenesis:

    When the somatic embryos develop directly on the excised plant (explant) without undergoing callus formation, it is referred to as direct somatic embryogenesis (Fig 47.6A). This is possible due to the presence of pre-embryonic determined cells (PEDQ found in certain tissues of plants. The characteristic features of direct somatic embryogenesis is avoiding the possibility of introducing somaclonal variations in the propagated plants.

    Indirect Somatic Embryogenesis:

    In indirect embryogenesis, the cells from explant (excised plant tissues) are made to proliferate and form callus, from which cell suspension cultures can be raised. Certain cells referred to as induced embryo genic determined cells (IEDC) from the cell suspension can form somatic embryos. Embryogenesis is made possible by the presence of growth regulators (in appropriate concentration) and under suitable environmental conditions.

    Somatic embryogenesis (direct or indirect) can be carried on a wide range of media (e.g. MS, White’s). The addition of the amino acid L-glutamine promotes embryogenesis. The presence of auxin such as 2, 4-dichlorophenoxy acetic acid is essential for embryo initiation. On a low auxin or no auxin medium, the embryo genic clumps develop into mature embryos.

    Indirect somatic embryogenesis is commercially very attractive since a large number of embryos can be generated in a small volume of culture medium. The somatic embryos so formed are synchronous and with good regeneration capability.

    Artificial Seeds from Somatic Embryos:

    Artificial seeds can be made by encapsulation of somatic embryos. The embryos, coated with sodium alginate and nutrient solution, are dipped in calcium chloride solution. The calcium ions induce rapid cross-linking of sodium alginate to produce small gel beads, each containing an encapsulated embryo. These artificial seeds (encapsulated embryos) can be maintained in a viable state till they are planted.

    Factors Affecting Micro propagation:

    For a successful in vitro clonal propagation (micro propagation), optimization of several factors is needed.

    Some of these factors are briefly described:

    1. Genotype of the plant:

    Selection of the right genotype of the plant species (by screening) is necessary for improved micro propagation. In general, plants with vigorous germination and branching capacity are more suitable for micro- propagation.

    2. Physiological status of the explants:

    Explants (plant materials) from more recently produced parts of plants are more effective than those from older regions. Good knowledge of donor plants’ natural propagation process with special reference to growth stage and seasonal influence will be useful in selecting explants.

    The standard plant tissue culture media are suitable for micro propagation during stage I and stage II. However, for stage III, certain modifications are required. Addition of growth regulators (auxins and cytokinins) and alterations in mineral composition are required. This is largely dependent on the type of culture (meristem, bud etc.).

    4. Culture environment:

    Photosynthetic pigment in cultured tissues does absorb light and thus influence micro- propagation. The quality of light is also known to influence in vitro growth of shoots, e.g blue light induced bud formation in tobacco shoots. Variations in diurnal illumination also influence micro propagation. In general, an illumination of 16 hours day and 8 hours night is satisfactory for shoot proliferation.

    Majority of the culture for micro propagation requires an optimal temperature around 25°C. There are however, some exceptions e.g. Begonia X Cheimantha hybrid tissue grows at a low temperature (around 18°C).

    Composition of gas phase:

    The constitution of the gas phase in the culture vessels also influences micro propagation. Unorganized growth of cells is generally promoted by ethylene, O2, CO2 ethanol and acetaldehyde.

    Factors Affecting in Vitro Rooting:

    A general description of the factors affecting micro propagation, particularly in relation to shoot multiplication is given above. For efficient in vitro rooting during micro- propagation, low concentration of salts (reduction to half to one quarter from the original) is advantageous. Induction of roots is also promoted by the presence of suitable auxin (NAA or IBA).

    Applications of Micro propagation:

    Micro propagation has become a suitable alternative to conventional methods of vegetative propagation of plants. There are several advantages of micro propagation.

    High Rate of Plant Propagation:

    Through micro propagation, a large number of plants can be grown from a piece of plant tissue within a short period. Another advantage is that micro propagation can be carried out throughout the year, irrespective of the seasonal variations. Further, for many plants that are highly resistant to conventional propagation, micro propagation is the suitable alternative. The small sized propagules obtained in micro propagation can be easily stored for many years (germplasm storage), and transported across international boundaries.

    Production of Disease-free Plants:

    It is possible to produce disease-free plants through micro propagation. Meristem tip cultures are generally employed to develop pathogen-free plants .In fact, micro propagation is successfully used for the production of virus-free plants of sweet potato (Ipomea batatus), cassava (Manihot esculenta) and yam (Discorea rotundata).

    Production of Seeds in Some Crops:

    Micro propagation, through axillary bud proliferation method, is suitable for seed production in some plants. This is required in certain plants where the limitation for’ seed production is high degree of genetic conservation e.g. cauliflower, onion.

    Cost-effective Process:

    Micro propagation requires minimum growing space. Thus, millions of plant species can be maintained inside culture vials in a small room in a nursery. The production cost is relatively low particularly in developing countries (like India) where the manpower and labour charges are low.

    Automated Micro propagation:

    It has now become possible to automate micro propagation at various stages. In fact, bio- reactors have been set up for large scale multi­plication of shoots and bulbs. Some workers employ robots (in place of labourers) for micro- propagation, and this further reduces production cost of plants.

    Disadvantages of Micro propagation:

    Contamination of Cultures:

    During the course of micro propagation, several slow-growing microorganisms (e.g. Eswinia sp, Bacillus sp) contaminate and grow in cultures. The microbial infection can be controlled by addition of antibiotics or fungicides. However, this will adversely influence propagation of plants.

    Brewing of Medium:

    Micro propagation of certain plants (e.g. woody perennials) is often associated with accumulation of growth inhibitory substances in the medium. Chemically, these substances are phenolic compounds, which can turn the medium into dark colour. Phenolic compounds are toxic and can inhibit the growth of tissues. Brewing of the medium can be prevented by the addition of ascorbic acid or citric acid or polyvinyl pyrrolidone to the medium.

    Genetic Variability:

    When micro propagation is carried out through shoot tip cultures, genetic variability is very low. However, use of adventitious shoots is often associated with pronounced genetic variability.


    During the course of repeated in vitro shoot multiplication, the cultures exhibit water soaked or almost translucent leaves. Such shoots cannot grow and even may die. This phenomenon is referred to as vitrification. Vitrification may be prevented by increasing the agar concentration (from 0.6 to 1%) in the medium. However, increased agar concentration reduces the growth rate of tissues.

    Cost Factor:

    For some micro propagation techniques, expensive equipment, sophisticated facilities and trained manpower are needed. This limits its use.

    Production of Disease-Free Plants:

    Many plant species are infected with pathogens — viruses, bacteria, fungi, mycoplasma and nematodes that cause systemic diseases. Although these diseases do not always result in the death of plants, they reduce the quality and yield of plants. The plants infected with bacteria and fungi frequently respond to chemical treatment by bactericides and fungicides.

    However, it is very difficult to cure the virus-infected plants. Further, viral disease are easily transferred in seed- propagated as well as vegetatively propagated plant species. Plant breeders are always interested to develop disease-free plants, particularly viral disease-free plants. This have become a reality through tissue cultures.

    Apical Meristems with Low Concentration of Viruses:

    In general, the apical meristems of the pathogen infected and disease harbouring plants are either free or carry a low concentration of viruses, for the following reasons:

    i. Absence of vascular tissue in the meristems through which viruses readily move in the plant body.

    ii. Rapidly dividing meristematic cells with high metabolic activity do not allow viruses to multiply.

    iii. Virus replication is inhibited by a high concentration of endogenous auxin in shoot apices. Tissue culture techniques employing meristem-tips are successfully used for the production of disease-free plants, caused by several pathogens — viruses, bacteria, fungi, mycoplasmas.

    Methods to Eliminate Viruses in Plants:

    In general, plants are infected with many viruses the nature of some of them may be unknown. The usage virus-free plant implies that the given plant is free from all the viruses, although this may not be always true. The commonly used methods for virus elimination in plants are listed below, and briefly described next.

    i. Heat treatment of plant

    iii. Chemical treatment of media

    iv. Other in vitro methods

    Heat Treatment (Thermotherapy) of Plants:

    In the early days, before the advent of meristem cultures, in vivo eradication of viruses from plants was achieved by heat treatment of whole plants. The underlying principle is that many viruses in plant tissues are either partially or completely inactivated at higher temperatures with minimal injury to the host plant. Thermotherapy (at temperatures 35-40°C) was carried out by using hot water or hot air for elimination viruses from growing shoots and buds.

    There are two limitations of viral elimination by heat treatment:

    1. Most of the viruses are not sensitive to heat treatment.

    2. Many plant species do not survive after thermotherapy.

    With the above disadvantages, heat treatment has not become popular for virus elimination.

    Meristem-Tip Culture:

    A general description of the methodology adopted for meristem and shoot tip cultures has been described (see Fig 47.2). For viral elimination, the size of the meristem used in cultures is very critical. This is due to the fact that most of the viruses exist by establishing a gradient in plant tissues.

    In general, the regeneration of virus-free plants through cultures is inversely proportional to the size of the meristem used. The meristem-tip explant used for viral elimination cultures is too small. A stereoscopic microscope is usually employed for this purpose.

    Meristem-tip cultures are influenced by the following factors:

    i. Physiological condition of the explant — actively growing buds are more effective.

    ii. Thermotherapy prior to meristem-tip culture — for certain plants (possessing viruses in the meristematic regions), heat treatment is first given and then the meristem-tips are isolated and cultured.

    iii. Culture medium —MS medium with low concentrations of auxins and cytokinins is ideal.

    A selected list of the plants from which viruses have been eliminated by meristem cultures is given in Table 47.1.

    Chemical Treatment of Media:

    Some workers have attempted to eradicate viruses from infected plants by chemical treatment of the tissue culture media. The commonly used chemicals are growth substances (e.g. cytokinins) and antimetabolites (e.g thiouracil, acetyl salicylic acid).

    There are however, conflicting reports on the elimination viruses by chemical treatment of the media. For instance, addition of cytokinin suppressed the multiplication of certain viruses while for some other viruses, it actually stimulated.

    Other in Vitro Methods:

    Besides meristem-tip culture, other in vitro methods are also used for raising virus-free plants. In this regard callus cultures have been successful to some extent. The callus derived from the infected tissue does not carry the pathogens throughout the cells. In fact, the uneven distribution of tobacco mosaic virus in tobacco leaves was exploited to develop virus-free plants of tobacco. Somatic cell hybridization, gene transformation and somaclonal variations also useful to raise disease-free plants.

    Elimination of Pathogens Other than Viruses:

    Besides the elimination of viruses, meristem-tip cultures and callus cultures are also useful for eradication bacteria, fungi and mycoplasmas. Some examples are given

    i. The fungus Fusarium roseum has been successfully eliminated through meristem cultures from carnation plants.

    ii. Certain bacteria (Pseudomonas carophylli, Pectobacterium parthenii) are eradicated from carnation plants by using meristem cultures.

    Merits and Demerits of Disease-Free Plant Production:

    Among the culture techniques, meristem-tip culture is the most reliable method for virus and other pathogen elimination. This, however, requires good knowledge of plant pathology and tissue culture.

    Virus-free plants exhibit increased growth and vigour of plants, higher yield (e.g. potato), increased flower size (e.g. Chrysanthemum), and improved rooting of stem cuttings (e.g. Pelargonium)

    Virus-free plants are more susceptible to the same virus when exposed again. This is the major limitation. Reinfection of disease-free plants can be minimized with good knowledge of greenhouse maintenance.

    Tissue Culture: Definition, History and Importance

    Tissue culture is the method of ‘in vitro’ culture of plant or animal cells, tissue or organ – on nutrient medium under aseptic conditions usually in a glass container. Tissue culture is sometimes referred to as ‘sterile culture’ or ‘in vitro’ culture. By this technique living cells can be maintained outside the body of the organism for a considerable period.

    According to Street (󈨑) tissue culture is referred to any multicellular culture with protoplasmic continuity between cells and growing on a solid medium or atta­ched to a substratum and nourished by a liquid medium.

    By plant tissue culture new plants may be raised in an artificial medium from very small parts of plants, such as, shoot tip, root tip, callus, seed, embryo, pollen grain, ovule or even a single cell, whether the cultured tissue develops into a plant or grows unorganized depends on the genetic potential of the tissue and the chemical and physical environment.

    According to the parts used for culture the aseptic plant culture may be of follow­ing types:

    (a) If a seedling is cultured it is called plant culture.

    (b) When an embryo is cultured it is known as embryo culture.

    (c) If plant organs, such as, shoot tips, root tips, leaf primordia, flower primordia or immature fruits are cultured, it is called organ culture.

    (d) The culture of unorganized tissues from cell proliferations of segments of plant organs is called callus culture. Cell proliferations are formed in the explant due to injury caused by excision.

    (e) When a single cell or small cell aggregate in a dispersed state is cultured, it is called cell suspension culture. It is also known as cell culture.

    Culture of single cell is sometimes called single cell cloning. The portion of the plant to start the culture is called an explant. Culture derived from a single explant is called a clone. In order to maintain a culture for a comparatively longer period the culture me­dium is changed from time to time.

    This process will remove those harmful excretory substances which have accumulated due to metabolism. By transferring a fragment of the parent culture to a new medium subculture is done. Such a fragment is called an inoculum.

    History of Tissue Culture:

    In 1832 Theodor Schwann said that cells could be cultured outside the body of the organism if provided with proper external conditions. In 1835 Wilhelm Roux cultured embryonic cells of chicken in salt solution. Reichinger (1839) said that fragments thicker than 1.5 mm were capable of growth but fragments below this limit failed to grow. He did not used any nutrient in his experiment.

    Arnold (1885) and Jolly (1903) observed growth and cell division of leucocyte cells of salamander in culture. In 1907 American zoologist Ross Granville Harrison successfully cultured nerve cells of frog in solidified lymph. Harrison is known as the father of tissue culture.

    M.J. Burrows (1910) cultured embryonic tissue of chicken in plasma. Mammalian cells were first cultured by Alexis Carrel. By repeated sub-culturing he was able to culture the tissue for 34 years. Organ culture was first done by D.H. Fell (1929) in England. He used solidified plasma and embryonic extract as nutrient medium.

    History of Plant Tissue Culture:

    German botanist Gottlieb Haberlandt first attempted to culture plant tissues ‘in vitro’. He started his work in 1898. He used cells from palisade tissues of leaves, cells from pith, epidermis and epidermal hairs of various plants for culture in media -containing Knop’s solution, aspergine, peptone and sucrose.

    The cultured cells sur­vived for several months but the cells failed to proliferate.

    This may be due to:

    (a) Use of very simple media,

    (b) Culture of highly differentiated cells and

    (c) Aseptic techni­ques were not used.

    In similar experiments by some later workers cells remained alive for a long period but they failed to divide.

    Culture of meristematic tissue was started in early 20th century. Isolated root tips were first cultured by Robbin in 1922. Working independently Kotte (󈧚) also made similar observations. Robbin and Maneval (󈧛) cultured roots and maintained the culture for 20 weeks by sub culturing.

    In 1934 White first successfully cultured isolated tomato roots in a medium conta­ining sucrose, inorganic iron salts, thiamine, glycine, pyridoxine and nicotinic acid etc. Gautheret (󈧦) noted that cambium culture from Salix capraea, Populus nigra etc. continued to grow for few months under aseptic conditions. He later (󈧩, 󈧪) used medium supplemented with B-vitamins and IAA.

    In 1937 White recognised the importance of B-vitamins for growth of root cultures. Went and Thimann (󈧩) discovered the importance of auxin (IAA). Nobecourt (󈧩, 󈧪) obtained some growth in culture of carrot root explants. He also noted root differentiation in tissue culture. In 1938 tumour tissues of tabacco hybrid were succe­ssfully cultured.

    In 1939 working independently three scientists, White in USA and Nobecourt and Gautheret in France cultured successfully plant callus tissue on synthetic medium continuously. Gautheret (󈧫) said that carrot culture required Knop’s solution supplemented with Bertholots’ salt mixture, glucose, gelatine, cysteine HC1 and IAA.

    White (󈧫a) in culture of procambial tissue from young stem of the hybrid Nicotiana glauca × N. langsdorfii noted unlimited and undifferentiated growth. He showed that this tissue could be repeatedly subcultured. White (󈧫b) recorded development of leafy buds in tissue culture of the hybrid N. glauca × N.langsdorfii in nutrient medium.

    Tissues from various plants were cultured subsequently. It was noted that older cultures show increasing degree of organization. The role of vitamins in plant growth was also recognized. Wetmore and Wardlaw (󈧷) successfully cultured shoot tips of pteridophytes (Selaginella, Equisetum and ferns).

    Tissues of Sequoia semipervirens were cultured by Ball (󈧻). Pollens of Taxus and Ginkgo biloba were cultured by Tulecke (󈧿). Conifer tissues were successfully cultured by Harvey and Grasham (󈨉).

    From tissue culture studies important information about root-shoot relationship can be obtained. Several scientists reported about the factors controlling vascular tissue differentiation from tissue culture studies.

    Van Oberbeck (󈧭) cultured embryos of Datura on a medium supplemented with coconut milk. Importance of coconut milk and 2-4D as nutrient was recognised. The stimulatory pro­perty of coconut milk is due to the presence of zeatin.

    The potent cell division factor was found to be kinetin, which is a 6 furfurylaminopurine. Cytokinin is 6-substituted amino-purine compound, which can stimulate cell division in culture of plant tissues. Monocot tissues were successfully cultured on a medium containing coconut milk.

    Callus culture of Tagetus erecta and Nicotiana tabacum on liquid culture medium when agitated on a shaker produced suspension of single cells or cell aggregates (Muir 󈧹). Such cell suspension could be subcultured.

    Studies on cell suspension cul­ture were carried out by Muir, Hildebrandt and Riker (󈧺), Street, Shigomura (󈧽), Torrey and Reinert (󈨁), Reinert and Markel (󈨂). Muir (󈧹) developed paper raft nurse technique for single cell culture.

    In this method isolated single cells were put on a square filter paper, placed on a active nurse tissue, which supplies the required nutrients to the growing single cell. In another method cells were suspended on a han­ging drop in a micro-chamber.

    Bergman (󈨀) working with suspension cultures of Nicotiana tabacum var. sansum and Phaseolus vulgaris var. ‘early golden rod’ developed agar plating technique of single cell cloning. In this me­thod single cell fraction was separated by filtration, mixed with warm agar and then plated in a petridish in thin layer.

    Melchers and Bergmann (󈧿) noted that after several cultures of the haploid shoot of Antirrhinum majus there was increase in ploidy. Ball (󈧲) noted the possibility of regeneration of whole plant in culture of shoot tip of angiospermic plants. Wetmore and Wardlaw (󈧷), Morel (󈨀) obtained whole plants from culture of shoot apices having 1 or 2 leaf primordia. Morel (󈨄) used this method for culture of orchids.

    A cell which can develop into a whole organism by regeneration is called a to­tipotent cell. This term was coined by Morgan in 1901. According to White (󈧺) if all the cells of a multicellular organism is totipotent, then such cells in isolated condi­tion regain their dividing power and can produce whole plants. In an organism this capacity remain suppressed.

    It was noted that single cells are capable of producing new plants. From pollen and anther culture haploid embryos were obtained. A method of microspore culture of Nicotiana and Datura was developed by Nitsch (󈨎, 󈨑). He was able to double the chromosome number and obtained homozygous diploid plants.

    From anther culture of tobacco Bourgin and Nitsch (󈨇), Nakata and Tanaka (󈨈) obtained haploid tissues and haploid embryoids.

    Cocking (󈨀) recorded release of protoplasts from root tip cells by using fungal cellulase in 0.6M sucrose. He was able to culture isolated protoplasts, which regenerate new cell walls and produce cell colonies and ultimately plantlets.

    In many plant suspension cultures cell protoplasts had been successfully released. Plant tissue culture technique is used for the study of tumour physiology.

    White and Brown (󈧮) were able to culture bacteria free crown gall tumour. In Scorzonera hispanica Gautheret (󈧲) noted that the callus culture which initially required auxin, produced some proliferations which can grow in auxin deficient medium.

    Such inheri­ted changes occurring in the nutritional requirements (especially involving auxin) of cells of a culture is called habituation. An auxin habituated culture does not re­quire the supply of exogenous auxin (Butcher 󈨑). Butcher noted (󈨑) that when auxin and cytokinin habituated tissues are grafted into a healthy plant, tumours are produced.

    Pathogen free plants can be obtained by culturing apical’ meristem.

    By late 70’s it was evident that plant tissue culture technique can be successfully used in various field of agriculture, such as, production of pathogen free culture, pro­duction of secondary products, clonal propagation, mutant culture, haploid breeding and genetic engineering.

    By tissue culture, pathogen free cultures have been produced. This technique is im­portant for plant pathological investigations. Protoplasts in culture are used for virus infection and biochemical studies.

    From suspension culture secondary products can be synthesised in large amount. Some of these substances are enzymes, vitamins, food flavours, sweeteners, anti-tu­mour alkaloids and insecticides. In Japan ‘in vitro’ culture has been achieved at industrial level.

    Clonal propagation of orchids and several other ornamental and economic plants have been achieved by ‘in vitro’ culture. In potato clonal propagation has been achieved by culturing leaf cell protoplasts. By using mutagens in culture followed by selection disease resistant or stress resistant mutant plants have been regenerated.

    By haploid breeding few cultivers were produced. Hybrids of related but sexually incompatible species have been produced by protoplast fusion. By this technique hybrid between potato and tomato has been produced. By cell fusion of isolated cells from two different species hybrid tobacco plants are produced.

    Dormancy period of seeds can be shortened by excising the seeds and culturing its embryo on artificial medium (embryo culture). Abortive embryo can be grown successfully by embryo culture.

    Foreign genes with desirable characters attached to a plasmid may be inserted into the naked protoplast usually by means of liposomes. The expression of introduced gene in the mature plant is still doubtful.

    Importance of Tissue Culture:

    Tissue culture has great importance in studies of plant morphogenesis, physio­logy, biochemistry, pathology, embryology, cytology etc. From tissue culture studies it is possible to know bow simple cells differentiate and become specialized to perform special functions. Various changes taking place in a cell can be noted from clonal culture.

    Interrelationship between two cells can be studied in tissue culture. With the help of phase contrast cine-photomicrography a very clear understanding of mitosis and meiosis is possible in tissue culture. Haberlandt noted the importance of tissue culture in studying plant morphogenesis. Relationship between growth and differentiation can be well understood from such a culture.

    In vegetatively propagating plants many plantlets are formed very quickly from callus culture or culture of explants. Orchids, which normally propagate very slowly, can form many plantlets very rapidly in shoot tip culture. This is also noted in car­nation.

    By tissue culture method new plant variants can be obtained by isolating gene­tically unique cells. From callus cultures of tobacco, carrot, asparagus etc. new plants are formed. Such plants show genetic variability.

    From studies of mutant cells, the biochemical and developmental process of an organism can be better understood. In tissue culture, mutation can be easily induced and from such mutant cells mutant plants may be produced.

    In tobacco, paddy etc. from anther culture haploid plantlets are produced. By doubling the chromosome homozygous plants are obtained most rapidly. So, this process has immense importance in plant breeding.

    Tissue culture technique has been successfully used in nutritional research. The effects of various mineral salts, vitamins etc. on growth may be studied in culture. Many important information about glucose metabolism, nitrogen metabolism and hormone production can be obtained from ‘in vitro’ culture.

    Suspension culture under controlled conditions may be used to solve many physiological or biochemical problems and also provides a system for the production of important plant products, such as, plant alkaloids.

    From cell and organ culture under controlled environmental conditions nutri­tional and metabolic processes can be studied. Some mutant cells cannot grow in a medium which does not contain a special nutrient. From this biochemical steps of a process can be determined.

    Tissue culture has great significance in pathological studies. The effect of various medicine on cells infected by pathogens can be studied in tissue culture.

    Culture of maize cells from plants susceptible to the race T of Helminthosporium maydis were treated with pathotoxin of the fungus. Scientists were able to obtain cells resistant to this fungus. From such cells resistant plants were also produced.

    Tissue culture technique is employed in the studies of plant tumour diseases and host parasite relationship. Disease free plants can be produced by tissue culture te­chnique. Tissue culture has great importance in vaccine production. In 1949 vaccine for poliomyelitis has been produced after observing that the poliomyelitis virus can attack human cells. Later vaccines for mumps, meseales, and influenza have been pro­duced.

    The process of virus attack, effect of virus on Post cells and how new viruses are produced etc. have been studied in tissue culture. The behaviour of substances, which can prevent virus attack has been studied on virus infected cells.

    In tissue culture the behaviour of normal and cancer cells can be studied. It has been noted that some viruses and carcinogenic chemicals can produce cancer. Effect of radiation and chemicals on normal and cancer cells has been studied. From such studies it may be possible to know which chemical substances can destroy cancer cells.

    From tissue culture studies information about some hereditary diseases of man has been obtained. Carriers of some diseases can also be identified through tissue cul­ture technique. From leucocyte culture the cause of mongolism in man has been dis­covered. From such culture abnormal Philadelphia chromosome has been identified. This chromosome has some relation with chronic granulocytic leukomia.

    When tissue transplant is done from one person to the other then sometimes there is tissue rejection. So it is necessary to match the tissue of donor and receiver before actual transplant. This can be done by culturing the mixed leucocytes of the donor and the receiver.

    Distantly related species usually do not hybridize. This difficulty can be omitted by cell fusion and protoplast fusion technique. Carlson in 1972 successfully produced hybrid plants by protoplast fusion between Nicotiana glauca X N. langsdorfii. Power (󈨐) obtained hybrids between Petunia hybrida and P. parodii by protoplast fusion.

    Kaw and Wetter (󈨑) produced hybrids between tobacco and soyabean by cell fusion. Thus cell fusion and protoplast fusion techni­ques have great importance in plant breeding. Tetraploid fertile Lolium and Festuca hybrids were obtained by somatic cell fusion.

    Those embryos which fail to produce mature fruits normally can be cultured and from such embryo cultures plants are produced. Embryo culture also prevents seed dormancy. Cooper (󈨒) obtained hybrid plants between barley and rye by embryo culture.

    Conservation of Germplasm:

    By tissue culture plant germplasm can be stored.

    This method can be success­fully used to solve various problems:

    (a) Many seeds, such as, seeds of Citrus sp., Coffea sp., Hevea brasiliensis etc. retain their viability for a short period. These can be conserved by tissue culture.

    (b) Vegetatively propagated plants (such as, banana, potato, sweet potato, and yam) which do not produce seeds or which are highly heterozygous, are stored as cuttings or tubers. This requires much labour charge and are expensive to propa­gate. This problem can be solved by tissue culture.

    Many fruit trees of Rosaceae are propagated by budding, grafting and layer­ing. By tissue culture rapid propagation of such plants are possible.

    (c) In many economic plants, such as, coconut, date plam etc. vegetative pro­pagation normally does not occur. The germplasm of such plants can be conserved by tissue culture.

    (d) Many trees reproduce very slowly. By tissue culture such paints can be multiplied rapidly and many plants with parental genotypes are formed.

    For conservation of germplasm the cells should be stored in such a condition which allows minimum cell division. One of the method attempted is storing of cells in liquid nitrogen having a temperature of — 196°C.

    For germplasm conservation shoot tips or plantlets can be stored. Such stored materials can be used as and when required.

    In tissue culture cell division can be suppressed by various methods:

    (i) To the medium growth retardant may be added. The substances used are absicic acid, mannitol, sorbitol, malic hydrazide, succinic acid etc. Potato shoots are successfully stored in a medium containing malic hydrizide.

    (ii) Low temperature is helpful for storage of cells in culture. Cultures of potato, sweet potato, beet, grape, apple, etc. can be stored by this method. Temperate crops (e. g. potato) are stored usually at a temperature of 0—6°C and tropical crops (e.g. sweet potato) at 15—20°C. By this method meristem culture of strawberry has been conserved for six years.

    (iii) The concentration of nutrients of the culture medium may be changed. Some substances required for normal growth may be supplied at a lower concentra­tion or may not be supplied at all.

    (iv) The gas composition within the culture vessel may be changed. The atmos­pheric pressure or oxygen concentration may be lowered to conserve the cells.

    Production of Secondary Metabolic Products:

    Some plants produce secondary metabolic products, such as, alkaloid, anti­biotic, glycoside, resin, tannin, saponin, volatile oil, etc., which are of considerable economic importance.

    By cell culture various secondary metabolites (e.g. allergin) have been synthesised artificially. Cultivation of plants producing secondary metabolites can be improved significantly by tissue culture. There are certain disadvantages in the production of secondary metabolites by tissue culture.

    (i) In cell culture synthesis of secondary metaboli­tes occur at a lower rate than in an entire plant,

    (ii) After prolonged culture ‘in vitro’ the production of secondary metabolites may decrease or even stop,

    (iii) The cost of large scale production of secondary metabolites in cell culture is high. So, only very rare and expensive secondary metabolites are produced by tissue culture.

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