Sprachen:
The source document for this Digest states:
BOX 4
DNA from the beginningAll living things are made up of cells that are programmed by genetic material called deoxyribonucleic acid (DNA). Only a small fraction of the DNA chain actually makes up genes, which in turn code for proteins, and the remaining share of the DNA represents non-coding sequences whose role is not yet clearly understood. The genetic material is organized into pairs of chromosomes. For example, there are five chromosome pairs in the much-studied mustard species Arabidopsis thaliana. An organism's entire set of chromosomes is called the genome. The Human Genome Sequencing Project has provided the agricultural research community not only with many spin-off technologies that can be applied across the board for all living organisms but also with a model for international collaboration in tackling large genome-sequencing projects for model plants such as Arabidopsis and rice.
For a refresher course in DNA, genetics and heredity, see the interactive Web site "DNA from the beginning" (www.dnaftb.org)developed by the Cold Spring Harbor Laboratory in the United States, where much of the pioneering work in genetics and genetic engineering has been performed.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Understanding, characterizing and managing genetic resources, Box 4
The source document for this Digest states:
The most significant breakthroughs in agricultural biotechnology are coming from research into the structure of genomes and the genetic mechanisms behind economically important traits (Box 4). The rapidly progressing discipline of genomics is providing information on the identity, location, impact and function of genes affecting such traits - knowledge that will increasingly drive the application of biotechnology in all agricultural sectors. Genomics sets the foundation for post-genomics activities, including new disciplines such as proteomics and metabolomics to generate knowledge on gene and protein structure, as well as their functions and interactions. These disciplines seek to understand systematically the molecular biology of organisms for their practical use.
A vast range of new and rapidly advancing technologies and equipment has also been developed to generate and process information about the structure and function of biological systems. The use and organization of this information is called bioinformatics. Advances in bioinformatics may allow the prediction of gene function from gene sequence data: from a listing of an organism's genes, it will become possible to build a theoretical framework of its biology. The comparison across organisms of physical and genetic maps and DNA sequences will significantly reduce the time needed to identify and select potentially useful genes.
Through the production of genetic maps that provide the precise location and sequences of genes, it is apparent that even distantly related genomes share common features (Box 5). Comparative genomics assists in the understanding of many genomes based on the intensive study of just a few. For instance, the rice genome sequence is useful for studying the genomes of other cereals with which it shares features according to its degree of relatedness, and the mouse and malaria genomes provide models for livestock and some of the diseases that affect them. There are now model species for most types of crops, livestock and diseases and knowledge of their genomes is accumulating rapidly.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Understanding, characterizing and managing genetic resources, Subsection Genomics
The source document for this Digest states:
BOX 5
Synteny is life!Synteny describes the conservation or consistency of gene content and gene order along the chromosomes of different plant genomes. Until well into the 1980s we imagined that each crop plant had its own genetic map. Only when we were able to make the first molecular maps, using a technique called “restriction fragment length polymorphism” (RFLP), did it begin to dawn on us that related species had remarkably similar gene maps. The early experiments demonstrated conservation over a few million years of evolution in syntenous relationships between potato and tomato in the broad-leafed plants and between the three genomes of bread wheat in the grasses. Later we were able to show that the same similarities held over the rice, wheat and maize genomes, which were separated by some 60 million years of evolution. The diagram summarizes this research and shows 70 percent of the world's food linked in a single map. The 12 chromosomes of rice can be aligned with the ten chromosomes of maize and the basic seven chromosomes of wheat and barley in such a way that any radius drawn around the circles will pass through different versions, known as alleles, of the same genes.
The discovery of synteny has had an enormous impact on the way we think about plant genetics. There are obvious applications for evolutionary studies; for example, the white arrows on the wheat and maize circles describe evolutionary chromosomal translocations that describe Pooideae and Panicoideae groups of grasses. There are great opportunities to predict the presence and location of a gene in one species from what we know from another. Now that we have the complete DNA sequence of rice we are able to identify and isolate key genes from large genome intractable species such as wheat and barley by predicting that the same genes will be present in the same order as in rice. Key genes for disease resistance and tolerance to acid soils have recently been isolated from barley and rye in this way. For practical plant breeding, knowledge of synteny allows breeders access to all alleles in, for example, all cereals rather than just the species on which they are working. A key first example of this is the transfer to rice of the wheat dwarfing genes that made the Green Revolution possible. In these experiments the gene was located in rice by synteny and then isolated and engineered with the alteration in DNA sequence that characterized the wheat genes before replacing the engineered gene in rice. This approach can be applied to any gene in any cereal, including the so-called “orphan crops” that have not attracted the research dollars that the big three - wheat, rice and maize - have over the past century. The main significance is, however, that we can now pool our knowledge of biochemistry, physiology and genetics and transfer it between crops via synteny.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Understanding, characterizing and managing genetic resources, Box 5
The source document for this Digest states:
Reliable information on the distribution of genetic variation is a prerequisite for sound selection, breeding and conservation programmes. Genetic variation of a species or population can be assessed in the field or by studying molecular and other markers in the laboratory. A combination of the two approaches is required for reliable results. Molecular markers are identifiable DNA sequences, found at specific locations of the genome and associated with the inheritance of a trait or linked gene. Molecular markers can be used for (a) marker-assisted breeding, (b) understanding and conserving genetic resources and (c) genotype verification. These activities are critical for the genetic improvement of crops, forest trees, livestock and fish.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Understanding, characterizing and managing genetic resources, Subsection Molecular markers
The source document for this Digest states:
Genetic linkage maps can be used to locate and select for genes affecting traits of economic importance in plants or animals. The potential benefits of marker-assisted selection (MAS) are greatest for traits that are controlled by many genes, such as fruit yield, wood quality, disease resistance, milk and meat production, or body fat, and that are difficult, time-consuming or expensive to measure. Markers can also be used to increase the speed or efficiency of introducing new genes from one population to another, for example when wishing to introduce genes from wild relatives into modern plant varieties. When the desired trait is found within the same species (such as two varieties of millet - Box 6), it may be transferred with traditional breeding methods, with molecular markers being used to track the desired gene.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Understanding, characterizing and managing genetic resources, Subsection Marker-assisted breeding
The source document for this Digest states:
BOX 6
Molecular markers and marker-assisted
selection for pearl millet in India
Pearl millet is a cereal grown for foodgrain and straw in the hottest, driest areas of Africa and Asia where rainfed and dryland agriculture are practised. It is similar to maize in its breeding behaviour. Traditional farmers' varieties are open-pollinated and out-breeding and thus continuously changing. Genetically uniform hybrid varieties have been developed that offer higher yield potential but are more vulnerable to a plant disease called downy mildew. In India, pearl millet is grown on about 9 million ha and more than 70 percent of this is sown to such hybrid cultivars. Since pearl millet hybrids first reached farmers' fields in India in the late 1960s, every variety that has become popular with farmers has ultimately succumbed to a downy mildew epidemic. Unfortunately, by the time the poorer farmers in a given region decide to adopt a particular variety, its days are usually numbered.
The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) wanted to reduce the risks associated with adoption of higher-yielding pearl millet hybrids and extend the useful economic life of these varieties, especially for poorer producers. Biotechnology helped us to achieve this. With tools from the John Innes Centre and support from the Plant Sciences Research Programme of the Department for International Development (DFID), we developed and applied molecular genetic tools for pearl millet. We mapped the genomic regions of pearl millet that control downy mildew resistance, straw yield potential, and grain and straw yield under drought stress conditions. Then our millet breeders used conventional breeding and marker-assisted selection (MAS) to transfer several genomic regions conferring improved downy mildew resistance to the two elite inbred parental lines of popular hybrid HHB 67. We then used MAS to derive two new varieties - ICMR 01004 and ICMR 01007 - with two different downy mildew resistance gene blocks.
These varieties have performed as well or better than their parent lines for grain and straw yield, and are markedly improved for downy mildew resistance. They also retain several favourable traits, including 1 000-grain mass, panicle length, plant height and rust resistance. Hybrids based on crosses involving ICMR 01004 and ICMR 01007 have recently advanced to trials in the Indian states of Gujarat, Rajasthan and Haryana under the All India Coordinated Pearl Millet Improvement Project. This follows their successful evaluation in 2002, in which they exhibited marginal grain yield superiority and substantially better downy mildew resistance than HHB 67, while maintaining the early maturity that contributes to its popularity.
At least one of these two hybrids could be released as a replacement for HHB 67 before the latter succumbs (as it surely will) to a downy mildew epidemic. Because HHB 67 is so widely grown by poor farmers in India, if its timely replacement could prevent such an epidemic for even one year, the losses avoided would exceed the total value of research-funding support by DFID for the development and application of the molecular genetic tool kit for pearl millet (£3.1 million to date). All future benefits from this research by ICRISAT, its DFID-supported partners in the United Kingdom, and collaborating national programme partners in India can then be considered profits to society.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Understanding, characterizing and managing genetic resources, Box 6
The source document for this Digest states:
The use of molecular markers to measure the extent of variation at the genetic level, within and among populations, is of value in guiding genetic conservation activities and in the development of breeding populations in crops, livestock, forestry and fisheries. Studies carried out using these technologies in fish and forest tree species have revealed high levels of genetic variation both among and within populations. Livestock species are characterized by a high degree of genetic variation within populations, whereas crops exhibit a higher degree of variation across species. Data from other approaches, for example field observation, often cannot provide such information or are extremely difficult to collect.
Molecular markers are increasingly used to study the distribution and patterns of genetic diversity. Global surveys indicate, for example, that 40 percent of the remaining domestic livestock breeds are at risk of extinction. Most of these breeds are found only in developing countries, and there is often little knowledge about them or of their potential for improvement. They may contain valuable genes that confer adaptation or resilience to stresses, such as heat tolerance or disease resistance, that may be of use for future generations. Modern biotechnologies can help to counteract trends of genetic erosion in all food and agriculture sectors.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Understanding, characterizing and managing genetic resources, Subsection Measuring and conserving genetic diversity
The source document for this Digest states:
Molecular markers have been widely used for identifying genotypes and for “genetic fingerprinting” of organisms. Genetic fingerprinting has been used in advanced tree-breeding programmes in which the correct identification of clones for large-scale propagation programmes is essential. Molecular markers have been used to identify endangered marine species that are either inadvertently captured in wild fisheries or that are purposefully taken illegally. Genotype verification is used intensively in parentage testing of domestic animals and for tracing livestock products in the food chain back to the farm and animal of origin.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Understanding, characterizing and managing genetic resources, Subsection Genotype verification
The source document for this Digest states:
In addition to MAS, described above, a number of biotechnologies are used in breeding and reproducing crops and trees. Often these technologies are used in combination with each other and with conventional breeding approaches.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Breeding and reproducing crops and trees
The source document for this Digest states:
Micropropagation involves taking small sections of plant tissue, or entire structures such as buds, and culturing them under artificial conditions to regenerate complete plants. Micropropagation is particularly useful for maintaining valuable plants, breeding otherwise difficult-to-breed species (e.g. many trees), speeding up plant breeding and providing abundant plant material for research. For crop and horticultural species, micropropagation is now the basis of a large commercial industry involving hundreds of laboratories around the world. In addition to its rapid propagation advantages, micropropagation can also be used to generate disease-free planting material (Box 7), especially if combined with the use of disease-detection diagnostic kits. There have been some attempts to use micropropagation more widely in forestry. Compared with vegetative propagation through cuttings, the higher multiplication rates available through micropropagation offer a more rapid dissemination of planting stock, although limited availability of desirable clones is an impediment to its wider adoption in forestry.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Breeding and reproducing crops and trees
Subsection Cell and tissue culture micropropagation
BOX 7
Micropropagation of disease-free banana in KenyaBanana is generally grown in developing countries where it is a source of employment, income and food. Banana production is in decline in many regions because of pest and disease problems that cannot be addressed successfully through agrochemical control for reasons of cost and negative environmental effects. The problem is exacerbated because banana is reproduced clonally; the use of diseased mother plants therefore gives rise to diseased offspring.
Micropropagation represents a means of regenerating disease-free banana plantlets from healthy tissue. In Kenya, banana shoot tips have been successfully tissue-cultured. An original shoot tip is heat-treated to destroy infective organisms and then used through many cycles of regeneration to produce daughter plants. A single section of tissue can be used to produce as many as 1 500 new plants through ten cycles of regeneration.
Micropropagation of banana has had a tremendous impact in Kenya, among many other countries, contributing to improved food security and income generation. It has all the advantages of being a relatively cheap and easily applied technology and one that brings significant environmental benefits.al reproduction. Genetically modified organisms (GMOs) are modified by the application of transgenesis or recombinant DNA technology, in which a transgene is incorporated into the host genome or a gene in the host is modified to change its level of expression. The terms “GMO”, “transgenic organism” and “genetically engineered organism (GEO)” are often used interchangeably although they are not technically identical. For the purposes of this report they are used as synonyms.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Breeding and reproducing crops and trees, Box 7
The source document for this Digest states:
In vitro selection refers to the selection of germplasm by applying specific selection pressure to tissue culture under laboratory conditions. Many recent publications have reported useful correlations between in vitro responses and the expression of desirable field traits for crop plants, most commonly disease resistance. Positive results are available also for tolerance to herbicides, metals, salt and low temperatures. For the selection criteria of major general importance in forest trees (in particular vigour, stem form and wood quality), poor correlations with field responses still limit the usefulness of in vitro selection. However, this method may be of interest in forestry programmes for screening disease resistance and tolerance to salt, frost and drought.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Breeding and reproducing crops and trees
Subsection In vitro selection
The source document for this Digest states:
When the desired trait is found in an organism that is not sexually compatible with the host, it may be transferred using genetic engineering. In plants, the most common method for genetic engineering uses the soil bacterium Agrobacterium tumefasciens as a vector. Researchers insert the desired gene or genes into the bacterium and then infect the host plant. The desired genes are transmitted to the host along with the infection. This method is used mainly with dicot species such as tomato and potato. Some crops, particularly monocot species such as wheat and rye, are not naturally susceptible to transformation via A. tumefasciens, although the method has recently been successfully used to transform wheat and other cereals. In the most common transformation technique for these crops, the desired gene is coated on gold or tungsten particles and a “gene gun” is used literally to shoot the gene into the host at high velocity.
Three distinctive types of genetically modified crops exist: (a) “distant transfer”, in which genes are transferred between organisms of different kingdoms (e.g. bacteria into plants); (b) “close transfer”, in which genes are transferred from one species to another of the same kingdom (e.g. from one plant to another); and (c) “tweaking”, in which genes already present in the organism's genome are manipulated to change the level or pattern of expression. Once the gene has been transferred, the crop must be tested to ensure that the gene is expressed properly and is stable over several generations of breeding. This screening can usually be performed more efficiently than for conventional crosses because the nature of the gene is known, molecular methods are available to determine its localization in the genome and fewer genetic changes are involved.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Breeding and reproducing crops and trees,
Subsection Genitic engineering
The source document for this Digest states:
Most of the transgenic crops planted so far have incorporated only a very limited number of genes aimed at conferring insect resistance and/or herbicide tolerance (see Chapter 3 for more information regarding the transgenic crops that are currently being researched and grown commercially). However, some transgenic crops and traits of greater potential interest for developing countries have been developed but have not yet been released commercially. Box 8 describes one research project to improve the tolerance of wheat to aluminium, a problem that affects acid soils in much of Africa and Latin America. Similar work is being performed to improve the tolerance of plants to other stresses such as drought, saline soils and temperature extremes.
Nutritionally enhanced crops could make a significant contribution to the reduction of micronutrient malnutrition in developing countries. Biofortification (the development of nutritionally enhanced foods) can be advanced through the application of several biotechnologies in combination. Genomic analysis and genetic linkage mapping are needed to identify the genes responsible for natural variation in nutrient levels of common foods (Table 2). These genes can then be transferred into familiar cultivars through conventional breeding and MAS or, if sufficient natural variation does not occur within a single species, through genetic engineering. Non-transgenic approaches are being used, for example, to enhance the protein content in maize, iron in rice, and carotene in sweet potato and cassava.
Genetic engineering can be used when insufficient natural variation in the desired nutrient exists within a species. Box 9 describes the debate surrounding a project to enhance the protein content of potato using genetic engineering. The well-known transgenic Golden Rice contains three foreign genes - two from the daffodil and one from a bacterium - that produce provitamin A (see Box 13 on page 42). Scientists are well on their way to developing transgenic “nutritionally optimized”' rice that would contain genes producing provitamin A, iron and more protein (Potrykus, 2003). Other nutritionally enhanced foods are under development, such as oils with reduced levels of undesirable fatty acids. In addition, foods that are commonly allergenic (shrimp, peanuts, soybean, rice, etc.) are being modified to contain lower levels of allergenic compounds.
A major technical factor limiting the application of genetic modification to forest trees is the current low level of knowledge regarding the molecular control of traits that are of most interest. One of the first reported trials with genetically modified forest trees was initiated in Belgium in 1988 using poplars. Since then, there have been more than 100 reported trials involving at least 24 tree species, primarily timber-producing species. Traits for which genetic modification has been contemplated for forest trees include insect and virus resistance, herbicide tolerance and lignin content. Reduction of lignin is a valuable objective for species producing pulp for the paper industry because it would enable a reduction in the use of chemicals in the process.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Breeding and reproducing crops and trees,
Subsection Genitic engineering
BOX 9
The "protato": help for the poor or a Trojan horse?Researchers at Jawaharlal Nehru University in India have developed a genetically engineered potato that produces about one-third to one-half more protein than usual, including substantial amounts of all the essential amino acids such as lysine and methionine. Protein deficiency is widespread in India and potato is the staple food of the poorest people.
The “protato” was developed by a coalition of Indian charities, scientists, government institutes and industry as part of a 15-year campaign against childhood mortality. The campaign aims to eliminate childhood mortality by providing children with clean water, better food and vaccines.
The protato includes a gene from the amaranth plant, a high-protein grain that is native to South America and widely sold in Western health-food stores. The protato has passed preliminary field trials and tests for allergens and toxins. Final approval from the Indian Government is probably at least five years away.
Supporters such as Govindarajan Padmanaban, a biochemist at the Indian Institute of Science, argue that the protato can provide an important nutritional boost to children with little danger of allergy because potatoes and amaranth are both already widely consumed. There is also little threat to the environment because neither potatoes nor amaranth have wild relatives in India, and the protato does not involve any change in normal potato production practices. Furthermore, because the protato was developed by public-sector scientists in India, there are no concerns about foreign corporate control of the technology. Given these benefits, Padmanaban commented: “I think it would be morally indefensible to oppose it” (Coghlan, 2003).
Opponents such as Charlie Kronick of Greenpeace argue that potatoes are naturally quite low in protein (about 2 percent), so even a doubling of the protein content would make only a minute contribution to India's malnutrition problem. He claims that the effort to develop the protato was aimed more at gaining public acceptance of genetic engineering than at addressing the problem of malnutrition: “The cause of hunger isn't lack of food. It's lack of cash and of access to the food. Creating these GM crops is something to make them look attractive when actually the utility of eating them is very, very low. It's very difficult to see how this on its own will change the face of poverty” (Charles, 2003).
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Breeding and reproducing crops and trees, Box 9
The source document for this Digest states:
BOX 8
Agriculture on acid soils:
improving aluminium tolerance in cereals
Aluminium in acid soils limits plant growth on more than 30 percent of all arable land, primarily in developing countries. There are two approaches to increasing crop production on acid soils. Lime can be added to the soil to increase the pH, but this is a costly, temporary measure. Alternatively, genetically improved cultivars, tolerant to aluminium, can be developed. Existing wheat cultivars do not contain significant genetic variation for increasing aluminium tolerance. Improved tolerance will have to be introduced into wheat from the gene pools of related, more tolerant species. A genetic linkage map of wheat was developed using available markers for the existing aluminium-tolerance gene.
Rye exhibits a fourfold increase in aluminium tolerance over wheat. Therefore, a rye gene controlling aluminium tolerance was characterized. Markers from wheat, barley and rice were used to establish a tight linkage, flanking the rye gene, and to construct a high-resolution genetic map. A potential candidate gene was used for root-gene-expression, time-course studies that showed expression in rye roots only under aluminium stress.
Targeting the aluminium tolerance gene is one example of using problem-based approaches to integrate molecular and breeding tools to improve wheat production. Using the genetic relationship (synteny) among the cereals to supply markers to identify and characterize value-added traits, complementary approaches for improved wheat production emerge. Breeders can use the markers flanking the rye gene in marker-assisted breeding programmes in areas where GMOs cannot be grown or where only conventional breeding tools are available. In addition, these markers can be used for map-based cloning to isolate the gene in question for transgenic approaches to wheat improvement. Finally, the use of syntenous relationships offers the technology to manipulate many value-added traits for crop improvement in other species.
Source & ©: FAO "The State of Food and Agriculture 2003-2004"
Chapter 2: What is agricultural biotechnology?
Section Breeding and reproducing crops and trees, Box 8
| For details on: | See FAO report: |
|---|---|
| Transgenic crop commercialization | Chapter 3 |
| Economic impacts of “Golden Rice” in the Philippines | Chapter 4 |
| Bt cotton and reasons why it is grown | Chapter 4 |
| Economic benefit of herbicide-tolerant soybean | Chapter 4 |
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