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Applied plant cell biology techniques |
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Cloning plants
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Tissue culture
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Micropropagation
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Anther and pollen culture
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Embryo rescue
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In vitro regeneration and somaclonal variation
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In vitro germplasm conservation and cryopreservation
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Molecular marker techniques
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DNA and immuno-diagnostic techniques |
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| Applied Cell Biology Techniques |
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| Cloning plants |
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Many plants clone themselves naturally to reproduce. They send a small shoot-like structure called a runner, along the soil. The runner grows into a new separate plant, which is genetically identical to the original plant - a clone.
People can clone plants by simply taking a cutting of the plant such as a twig or stem and planting it. This is called vegetative propagation.
The cloning of plants has both benefits and drawbacks. On the positive side, cloning can allow allow rapid production of new planting material for plants which don’t produce seeds (e.g. bananas) or that have a long life cycle (e.g. trees). Also positive, is that if the original plant had good genetic traits, such as for fast growth or good seed, then the clones will share all of those traits.
One drawback of clonal reproduction is that if the crop faces new challenges, such as a new disease or climate change, it may not be able to adapt. And since all the plants will be genetically identical, if one plant is susceptible, they will all be at risk.
A more complex method of vegetative propagation is called tissue culture.
from http://www.biotechnologyonline.gov.au/biotec/cloneplant.cfm.
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| Tissue culture |
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Tissue culture: starts by using a small piece of the desired plant such as a bud, node, leaf segment or root segment. It is grown in a test tube on a culture medium that provides nutrients.
It is then treated to produce shoots. Buds from each of these shoots can be separated to grow more shoots, and the shoots are then treated to grow roots so that they develop into whole plants.
All the plants produced in this way are genetically identical because they have all come from the same plant initially and so share that plant’s genetic make up. Tissue culture produced plants therefore share all the benefits and drawbacks of cloned plants.
The mass production of clonal plants by tissue culture is called micropropagation.
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| Micropropagation |
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Micropropagation is the use of tissue culture methods to propagate or multiply plants. Using micropropagation, millions of new (clonal) plants can potentially be derived from a single plant. Micropropagation encompasses a range of tissue culture techniques for propagation of plant species. In essence, tissue from a plant (explant) is isolated to create a culture of that species in sterile laboratory conditions (in vitro). This method of cultivation of plant material is used for:
- rapid, large-scale, year round production of desired horticultural varieties (e.g. many of the popular miniature rose varieties are produced this way);
- propagation of plant species that are difficult to grow from seed;
- production of genetically uniform plant material (“clones”);
- development of plant culture systems that can be used for genetic transformation, e.g. to introduce disease resistance; and
- production of disease-free plant material (e.g. potato microtubers).
The benefits of plant tissue culture propagation include potentially unlimited multiplication of superior plant lines or elite individuals, avoidance of contamination with pathogens, production of true-to-type multiplication material of desirable plant lines suited for indefinite storage through cryobiological preservation, or for long-term maintenance of propagule inventories. One drawback of clonal propagation is that if the crop faces new challenges, such as a new disease or climate change, it may not be able to adapt. And since all the plants will be genetically identical, if one clone is susceptible, they will all be at risk. Another major limitation of the application of this technology is the need for technically skilled labourers and some essential equipment. It is therefore commercially applied to high value added crops, which are worth the necessary investment.
Micropropagation is now a ‘mature' plant biotechnology and is among the most widely used plant biotechnologies, reportedly being applied in 23 countries in Africa.
The success of micropropagation may be explained by its relatively low costs and generally positive effects on productivity (especially of clonally propagated root and tuber crops). Micropropagation has become an irreplaceable tool for many clonally propagated species for the production of pathogen-free plantlets (among such clonally propagated crops are 10 of the 30 most cultivated crops worldwide). Emphasis on the development of cost-effective micropropagation techniques is expected to increase even further.
Examples from FAO-BioDeC: In Africa, date palm is being commercially propagated in Morocco and Tunisia. Tunisia also has available micropropagated Prunus rootstocks, almond, citrus, grape, olive and pistachio. A number of diseases that affect banana plants including Panama, Banana Bunchy Top Virus, Cucumber Mosaic Virus and Banana Streak Virus. Micropropagated banana is promoted in Cameroon, Gabon, Kenya and Uganda to produce clonal planting material that is disease free. In addition, plantain and cassava are promoted in Gabon, and yam, potato and sweet potato in Uganda.
Some information above was taken from http://www.biotechnologyonline.gov.au/topitems/glossary.cfm#tissueculture
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| Anther and pollen culture |
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Anther culture involves the sterile culture of immature anthers to generate fertile plants from the male sex cells. Since the sex cells, that would normally ripen into pollen grains, are haploid, they contain one of each of the pairs of homologous chromosomes found in the normal diploid cell. This means that the plants produced are also haploid.
The production of haploid plants through anther culture is widely used for breeding purposes, as an alternative to the numerous cycles of inbreeding or backcrossing usually needed to obtain pure lines in conventional breeding. The success achieved with anther culture has led to the development of microspore culture. This involves the isolation of the microspores from the anthers, culturing them in specialised media and subsequent regeneration of fertile homozygous plants. Furthermore, isolated microspores are very attractive for protoplast isolation and applications aiming at transformation as they are unicellular and transgenic homozygous plants could be provided in a comparatively short time.
In vitro anther culture is now routinely used for improving some vegetable crops such as asparagus, sweet pepper, eggplant, watermelon and Brassica vegetables. In addition, anther culture is being increasingly used in cereal crop improvement both as a source of haploids and new genetic variation. Isolated microspore culture has been successfully carried out with some Brassica vegetables such as cabbage, broccoli and Chinese cabbage-petsai and pakchoi. Most genotypes respond better to isolated microspore culture and embryo yield is generally higher than with anther culture. Therefore, isolated microspore culture has been preferred as a breeding tool and as an experimental system for various genetic manipulations.
Examples from FAO-BioDeC: In Africa, an anther culture generated durum wheat variety has reached the commercial phase in Tunisia, and anther culture techniques are being researched in Morocco, where an anther cultured bread wheat is in commercial use. Anther culture techniques are being tested in the Sudan, and applied to barley in the Morocco. Anther culture research has started on banana in Cameroon and on sorghum and rice in Mali. |
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| Embryo rescue |
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In embryo rescue/culture, the embryo is removed before seed abortion occurs and is grown outside the parent plant to produce a new plant to enable crosses to be made between species which would not normally be sexually compatible. In vitro embryo rescue techniques are therefore often used to rescue plant embryos from aborting progeny seeds that result when two distantly related plants (e.g. two species) are crossed together. Such ‘wide crosses' are often desirable to transfer genetic traits from wild relatives to cultivated crop plants. This technique is used in breeding of many crop species and allowed synthesis of triticale, a new hybrid species resulting from the cross between rye and wheat.
Examples from FAO-BioDeC: Embryo rescue techniques are being developed in Algeria, Morocco and the Sudan. Research is at an early stage on yam in Nigeria and unspecified work is being carried out in Cameroon. |
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| In vitro regeneration and somaclonal variation |
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Plant regeneration from cell cultures is central to the application of gene transfer techniques such as biolistics and Agrobacterium-mediated transformation. Not all plants are readily amenable to in vitro regeneration and there is thus a need to continuously develop regeneration protocols for the recalcitrant species if they are to benefit from genetic modification technologies. In vitro regeneration usually results in high genetic and phenotypic variability in individuals derived from cultures, which is called somatic variation. Somatic variation can be beneficial in crop improvement especially on traits for which somaclonal mutants can be enriched during in vitro culture, including resistance to disease pathotoxins, herbicides and tolerance to environmental or chemical stress, as well as for increased production of secondary metabolites.
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| In vitro germplasm conservation and cryopreservation |
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Biotechnology can play an important role in the conservation of varieties of many crop species, whether the germplasm is maintained as vegetative propagules or seed. In vitro conservation protects germplasm from possible contamination with pathogenic agents and preserves the genetic identity of the stored material. Germplasm regeneration techniques (in vitro or in vivo) coupled to cryopreservation protocols ensure the long-term, safe storage of much of the world's germplasm, even if this technique is well established only for a number of plant species.
Examples from FAO-BioDeC: In Africa, reported work is in the experimental phase, concentrating on root crops, cassava in Cameroon, Ghana and Nigeria, yams in Cameroon, Malawi and Nigeria, sweet potato and potato in Egypt and Kenya, also on banana in Ghana, Malawi, Nigeria and Uganda, with unspecified activities in Cote d'Ivoire. |
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