Plant breeding
Encyclopedia
Plant breeding is the art and science of changing the genetics of plants in order to produce desired characteristics. Plant breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to more complex molecular techniques (see cultigen
and cultivar
).
Plant breeding has been practiced for thousands of years, since near the beginning of human civilization. It is now practiced worldwide by individuals such as gardeners and farmers, or by professional plant breeders employed by organizations such as government
institutions, universities, crop-specific industry associations or research centers.
International development agencies believe that breeding new crops is important for ensuring food security
by developing new varieties that are higher-yielding, resistant to pests and diseases, drought-resistant or regionally adapted to different environments and growing conditions.
plants, the cereals were chosen by the early man. They learned to look for superior plants to harvest. The domestication was hastened by early practice of harvesting mutant plants with special traits. This forms the ancient type of plant breeding. Before Mendal’s discovery there was some plant breeding include selection and hybridization experiments. But the plant breeding was only hastened after discovery of Mendal’s law on pea, thus lead a new science “Genetics”. Modern plant breeding is applied genetics but its scientific basis is broader and uses conceptual and technical tools, molecular biology
, cytology
, systemetics, physiology
, pathology
, entomology
, chemistry
, and statistics
(biometrics
) and has also developed own technology.
s from one variety or line into a new genetic background. For example, a mildew
-resistant pea
may be crossed with a high-yielding but susceptible pea, the goal of the cross being to introduce mildew resistance without losing the high-yield characteristics. Progeny from the cross would then be crossed with the high-yielding parent to ensure that the progeny were most like the high-yielding parent, (backcrossing
). The progeny from that cross would then be tested for yield and mildew resistance and high-yielding resistant plants would be further developed. Plants may also be crossed with themselves to produce inbred varieties for breeding.
Classical breeding relies largely on homologous recombination
between chromosomes to generate genetic diversity
. The classical plant breeder may also makes use of a number of in vitro techniques such as protoplast fusion, embryo rescue
or mutagenesis (see below) to generate diversity and produce hybrid plants that would not exist in nature
.
Traits that breeders have tried to incorporate into crop plants in the last 100 years include:
and Gregor Mendel
, and was further developed by geneticist
s and plant breeders. In the United Kingdom in the 1880s, it was the pioneering work of Gartons Agricultural Plant Breeders
. In the early 20th century, plant breeders realized that Mendel's findings on the non-random nature of inheritance
could be applied to seedling
populations produced through deliberate pollination
s to predict the frequencies of different types.
From 1904 to World War II in Italy
Nazareno Strampelli
created a number of wheat hybrids. His work allowed Italy to increase hugely crop production during the so called "Battle for Grain
" (1925–1940) and some varieties was exported in foreign countries, as Argentina, Mexico, China and others. After the war, the work of Strampelli was quickly forgotten, but thanks to the hybrids he created, Norman Borlaug
was able to move the very first steps of the Green Revolution
.
In 1908, George Harrison Shull
described heterosis
, also known as hybrid vigor. Heterosis describes the tendency of the progeny of a specific cross to outperform both parents. The detection of the usefulness of heterosis for plant breeding has led to the development of inbred lines that reveal a heterotic yield advantage when they are crossed. Maize
was the first species where heterosis was widely used to produce hybrids.
By the 1920s, statistical
methods were developed to analyze gene action and distinguish heritable variation from variation caused by environment. In 1933, another important breeding technique, cytoplasmic male sterility
(CMS), developed in maize, was described by Marcus Morton Rhoades
. CMS is a maternally inherited trait that makes the plant produce sterile pollen
. This enables the production of hybrids without the need for labor intensive detasseling
.
These early breeding techniques resulted in large yield increase in the United States
in the early 20th century. Similar yield increases were not produced elsewhere until after World War II
, the Green Revolution
increased crop production in the developing world in the 1960s.
a number of techniques were developed that allowed plant breeders to hybridize distantly related species, and artificially induce genetic diversity.
When distantly related species are crossed, plant breeders make use of a number of plant tissue culture
techniques to produce progeny from otherwise fruitless mating. Interspecific and intergeneric hybrids are produced from a cross of related species or genera that do not normally sexually reproduce with each other. These crosses are referred to as Wide crosses. For example, the cereal
triticale
is a wheat
and rye
hybrid. The cells in the plants derived from the first generation created from the cross contained an uneven number of chromosomes and as result was sterile. The cell division
inhibitor colchicine
was used to double the number of chromosome
s in the cell
and thus allow the production of a fertile line.
Failure to produce a hybrid may be due to pre- or post-fertilization incompatibility. If fertilization is possible between two species or genera, the hybrid embryo
may abort before maturation. If this does occur the embryo resulting from an interspecific or intergeneric cross can sometimes be rescued and cultured to produce a whole plant. Such a method is referred to as Embryo Rescue
. This technique has been used to produce new rice for Africa
, an interspecific cross of Asian rice (Oryza sativa) and African rice
(Oryza glaberrima).
Hybrids may also be produced by a technique called protoplast
fusion. In this case protoplasts are fused, usually in an electric field. Viable recombinants can be regenerated in culture.
Chemical mutagen
s like EMS and DMS
, radiation
and transposon
s are used to generate mutant
s with desirable traits to be bred with other cultivar
s - a process known as Mutation Breeding. Classical plant breeders also generate genetic diversity within a species by exploiting a process called somaclonal variation
, which occurs in plants produced from tissue culture, particularly plants derived from callus
. Induced polyploidy
, and the addition or removal of chromosomes using a technique called chromosome engineering
may also be used.
When a desirable trait has been bred into a species, a number of crosses to the favored parent are made to make the new plant as similar to the favored parent as possible. Returning to the example of the mildew resistant pea being crossed with a high-yielding but susceptible pea, to make the mildew resistant progeny of the cross most like the high-yielding parent, the progeny will be crossed back to that parent for several generations (See backcrossing
). This process removes most of the genetic contribution of the mildew resistant parent. Classical breeding is therefore a cyclical process.
With classical breeding techniques, the breeder does not know exactly what genes have been introduced to the new cultivars. Some scientist
s therefore argue that plants produced by classical breeding methods should undergo the same safety testing regime as genetically modified
plants. There have been instances where plants bred using classical techniques have been unsuitable for human consumption, for example the poison
solanine
was unintentionally increased to unacceptable levels in certain varieties of potato
through plant breeding. New potato varieties are often screened for solanine levels before reaching the marketplace.
Sometimes many different genes can influence a desirable trait in plant breeding. The use of tools such as molecular markers or DNA fingerprinting can map thousands of genes. This allows plant breeders to screen large populations of plants for those that possess the trait of interest. The screening is based on the presence or absence of a certain gene as determined by laboratory procedures, rather than on the visual identification of the expressed trait in the plant.
A method for efficiently producing homozygous plants from a heterozygous starting plant, which has all desirable traits. This starting plant is induced to produce doubled haploid
from haploid cells, and later on creating homozygous/doubled haploid
plants from those cells. While in natural offspring genetic recombination
occurs and traits can be unlinked from each other, in doubled haploid cells and in the resulting DH plants recombination is no longer an issue. There, a recombination between two corresponding chromosomes does not lead to un-linkage of allele
s or traits, since it just leads to recombination with its identical copy. Thus, traits on one chromosome
stay linked. Selecting those offspring having the desired set of chromosomes and crossing them will result in a final F1 hybrid
plant, having exactly the same set of chromosomes, genes and traits as the starting hybrid plant. The homozygous parental lines can reconstitute the original heterozygous plant by crossing, if desired even in a large quantity.
An individual heterozygous plant can be converted into a heterozygous variety (F1 hybrid
) without the necessity of vegetative
propagation but as the result of the cross of two homozygous/doubled haploid lines derived from the originally selected plant. patent
Genetic modification of plants is achieved by adding a specific gene or genes to a plant, or by knocking down a gene with RNAi
, to produce a desirable phenotype
. The plants resulting from adding a gene are often referred to as transgenic plants. If for genetic modification genes of the species or of a crossable plant are used under control of their native promoter, then they are called cisgenic plants
. Genetic modification can produce a plant with the desired trait or traits faster than classical breeding because the majority of the plant's genome is not altered.
To genetically modify a plant, a genetic construct must be designed so that the gene to be added or removed will be expressed by the plant. To do this, a promoter to drive transcription
and a termination sequence to stop transcription of the new gene, and the gene or genes of interest must be introduced to the plant. A marker for the selection of transformed plants is also included. In the laboratory
, antibiotic resistance
is a commonly used marker: Plants that have been successfully transformed will grow on media containing antibiotics; plants that have not been transformed will die. In some instances markers for selection are removed by backcrossing
with the parent plant prior to commercial release.
The construct can be inserted in the plant genome by genetic recombination
using the bacteria Agrobacterium tumefaciens
or A. rhizogenes
, or by direct methods like the gene gun
or microinjection
. Using plant virus
es to insert genetic constructs into plants is also a possibility, but the technique is limited by the host range of the virus. For example, Cauliflower mosaic virus
(CaMV) only infects cauliflower
and related species. Another limitation of viral vectors is that the virus is not usually passed on the progeny, so every plant has to be inoculated.
The majority of commercially released transgenic plants are currently limited to plants that have introduced resistance to insect
pest
s and herbicide
s. Insect resistance is achieved through incorporation of a gene from Bacillus thuringiensis
(Bt) that encodes a protein
that is toxic to some insects. For example, the cotton bollworm
, a common cotton pest, feeds on Bt cotton it will ingest the toxin and die. Herbicides usually work by binding to certain plant enzymes and inhibiting their action. The enzymes that the herbicide inhibits are known as the herbicides target site. Herbicide resistance can be engineered into crops by expressing a version of target site protein that is not inhibited by the herbicide. This is the method used to produce glyphosate resistant crop plants (See Glyphosate)
Genetic modification of plants that can produce pharmaceuticals (and industrial chemicals), sometimes called pharmacrops, is a rather radical new area of plant breeding.
al value is central in this respect. Although relatively little direct research in this area has been done, there are scientific indications that, by favoring certain aspects of a plant's development, other aspects may be retarded. A study published in the Journal of the American College of Nutrition in 2004, entitled Changes in USDA Food Composition Data for 43 Garden Crops, 1950 to 1999, compared nutritional analysis of vegetable
s done in 1950 and in 1999, and found substantial decreases in six of 13 nutrient
s measured, including 6% of protein
and 38% of riboflavin
. Reductions in calcium
, phosphorus
, iron
and ascorbic acid
were also found. The study, conducted at the Biochemical Institute, University of Texas at Austin
, concluded in summary: "We suggest that any real declines are generally most easily explained by changes in cultivated varieties between 1950 and 1999, in which there may be trade-offs between yield
and nutrient content."
The debate surrounding genetically modified food during the 1990s peaked in 1999 in terms of media coverage and risk perception, and continues today - for example, "Germany has thrown its weight behind a growing European mutiny over genetically modified crops by banning the planting of a widely grown pest-resistant corn variety.". The debate encompasses the ecological impact of genetically modified plants, the safety of genetically modified food
and concepts used for safety evaluation like substantial equivalence
. Such concerns are not new to plant breeding. Most countries have regulatory processes in place to help ensure that new crop varieties entering the marketplace are both safe and meet farmers' needs. Examples include variety registration, seed schemes, regulatory authorizations for GM plants, etc.
Plant breeders' rights
is also a major and controversial issue. Today, production of new varieties is dominated by commercial plant breeders, who seek to protect their work and collect royalties through national and international agreements based in intellectual property rights. The range of related issues is complex. In the simplest terms, critics of the increasingly restrictive regulations argue that, through a combination of technical and economic pressures, commercial breeders are reducing biodiversity
and significantly constraining individuals (such as farmers) from developing and trading seed on a regional level. Efforts to strengthen breeders' rights, for example, by lengthening periods of variety protection, are ongoing.
When new plant breeds or cultivars are bred, they must be maintained and propagated. Some plants are propagated by asexual means while others are propagated by seeds. Seed propagated cultivars require specific control over seed source and production procedures to maintain the integrity of the plant breeds results. Isolation is necessary to prevent cross contamination with related plants or the mixing of seeds after harvesting. Isolation is normally accomplished by planting distance but in certain crops, plants are enclosed in greenhouses or cages (most commonly used when producing F1 hybrids.)
Currently, few breeding programs are directed at organic agriculture and until recently those that did address this sector have generally relied on indirect selection (i.e. selection in conventional environments for traits considered important for organic agriculture). However, because the difference between organic and conventional environments is large, a given genotype
may perform very differently in each environment due to an interaction between genes and the environment (see gene-environment interaction
). If this interaction is severe enough, an important trait required for the organic environment may not be revealed in the conventional environment, which can result in the selection of poorly adapted individuals. To ensure the most adapted varieties are identified, advocates of organic breeding now promote the use of direct selection (i.e. selection in the target environment) for many agronomic traits.
There are many classical and modern breeding techniques that can be utilized for crop improvement in organic agriculture despite the ban on genetically modified organisms. For instance, controlled crosses between individuals allow desirable genetic variation to be recombined and transferred to seed progeny via natural processes. Marker assisted selection
can also be employed as a diagnostics tool to facilitate selection of progeny who possess the desired trait(s), greatly speeding up the breeding process. This technique has proven particularly useful for the introgression of resistance genes into new backgrounds, as well as the efficient selection of many resistance genes pyramided into a single individual. Unfortunately, molecular markers are not currently available for many important traits, especially complex ones controlled by many genes.
arising, have left millions of farmers in developing countries, most of whom operate small farms under unstable and difficult growing conditions, in a precarious situation. The adoption of new plant varieties by this group has been hampered by the constraints of poverty and the international policies promoting an industrialized model of agriculture. Their response has been the creation of a novel and promising set of research methods collectively known as participatory plant breeding. Participatory means that farmers are more involved in the breeding process and breeding goals are defined by farmers instead of international seed companies with their large-scale breeding programs. Farmers' groups and NGOs, for example, may wish to affirm local people's rights over genetic resources, produce seeds themselves, build farmers' technical expertise, or develop new products for niche markets, like organically grown food.
Cultigen
A cultigen is a plant that has been deliberately altered or selected by humans; it is the result of artificial selection. These "man-made" or anthropogenic plants are, for the most part, plants of commerce that are used in horticulture, agriculture and forestry...
and cultivar
Cultivar
A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...
).
Plant breeding has been practiced for thousands of years, since near the beginning of human civilization. It is now practiced worldwide by individuals such as gardeners and farmers, or by professional plant breeders employed by organizations such as government
Government
Government refers to the legislators, administrators, and arbitrators in the administrative bureaucracy who control a state at a given time, and to the system of government by which they are organized...
institutions, universities, crop-specific industry associations or research centers.
International development agencies believe that breeding new crops is important for ensuring food security
Food security
Food security refers to the availability of food and one's access to it. A household is considered food-secure when its occupants do not live in hunger or fear of starvation. According to the World Resources Institute, global per capita food production has been increasing substantially for the past...
by developing new varieties that are higher-yielding, resistant to pests and diseases, drought-resistant or regionally adapted to different environments and growing conditions.
History
Plant breeding started with sedimentary agriculture and domestication of the first agricultureAgriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
plants, the cereals were chosen by the early man. They learned to look for superior plants to harvest. The domestication was hastened by early practice of harvesting mutant plants with special traits. This forms the ancient type of plant breeding. Before Mendal’s discovery there was some plant breeding include selection and hybridization experiments. But the plant breeding was only hastened after discovery of Mendal’s law on pea, thus lead a new science “Genetics”. Modern plant breeding is applied genetics but its scientific basis is broader and uses conceptual and technical tools, molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
, cytology
Cell biology
Cell biology is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level...
, systemetics, physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
, pathology
Pathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
, entomology
Entomology
Entomology is the scientific study of insects, a branch of arthropodology...
, chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, and statistics
Statistics
Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....
(biometrics
Biometrics
Biometrics As Jain & Ross point out, "the term biometric authentication is perhaps more appropriate than biometrics since the latter has been historically used in the field of statistics to refer to the analysis of biological data [36]" . consists of methods...
) and has also developed own technology.
Classical plant breeding
Classical plant breeding uses deliberate interbreeding (crossing) of closely or distantly related individuals to produce new crop varieties or lines with desirable properties. Plants are crossbred to introduce traits/geneGene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s from one variety or line into a new genetic background. For example, a mildew
Mildew
Mildew refers to certain kinds of molds or fungi.In Old English, it meant honeydew , and later came to mean mildew in the modern sense of mold or fungus....
-resistant pea
Pea
A pea is most commonly the small spherical seed or the seed-pod of the pod fruit Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a flower. However, peas are considered to be a vegetable in cooking...
may be crossed with a high-yielding but susceptible pea, the goal of the cross being to introduce mildew resistance without losing the high-yield characteristics. Progeny from the cross would then be crossed with the high-yielding parent to ensure that the progeny were most like the high-yielding parent, (backcrossing
Backcrossing
Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent, in order to achieve offspring with a genetic identity which is closer to that of the parent...
). The progeny from that cross would then be tested for yield and mildew resistance and high-yielding resistant plants would be further developed. Plants may also be crossed with themselves to produce inbred varieties for breeding.
Classical breeding relies largely on homologous recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
between chromosomes to generate genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
. The classical plant breeder may also makes use of a number of in vitro techniques such as protoplast fusion, embryo rescue
Embryo Rescue
Embryo Rescue is one of the earliest and successful forms of in-vitro culture techniques that is used to assist in the development of plant embryos that might not survive to become viable plants. Embryo rescue plays an important role in modern plant breeding, allowing the development of many...
or mutagenesis (see below) to generate diversity and produce hybrid plants that would not exist in nature
Nature
Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general...
.
- Increased quality and yieldCrop yieldIn agriculture, crop yield is not only a measure of the yield of cereal per unit area of land under cultivation, yield is also the seed generation of the plant itself...
of the crop - Increased tolerancePhysiological tolerancePhysiological tolerance or drug tolerance is commonly encountered in pharmacology, when a subject's reaction to a drug is reduced at a later time even though the dose or concentration at the effect site is the same. This means that larger doses are required to achieve the same effect...
of environmental pressures (salinitySalinitySalinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
, extreme temperatureTemperatureTemperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, droughtDroughtA drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
) - Resistance to virusVirusA virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es, fungiFungusA fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
and bacteriaBacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals... - Increased tolerance to insectInsectInsects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
pests - Increased tolerance of herbicideHerbicideHerbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
s
Before World War II
Intraspecific hybridization within a plant species was demonstrated by Charles DarwinCharles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
and Gregor Mendel
Gregor Mendel
Gregor Johann Mendel was an Austrian scientist and Augustinian friar who gained posthumous fame as the founder of the new science of genetics. Mendel demonstrated that the inheritance of certain traits in pea plants follows particular patterns, now referred to as the laws of Mendelian inheritance...
, and was further developed by geneticist
Geneticist
A geneticist is a biologist who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a researcher or lecturer. Some geneticists perform experiments and analyze data to interpret the inheritance of skills. A geneticist is also a Consultant or...
s and plant breeders. In the United Kingdom in the 1880s, it was the pioneering work of Gartons Agricultural Plant Breeders
Gartons Agricultural Plant Breeders
This is a short history of the United Kingdom's first agricultural plant breeding business.Dr John Garton, of the firm of Garton Brothers of Newton-le-Willows in the United Kingdom was the Originator of Scientific Farm Plant Breeding. He is credited as the first scientist to show that the common...
. In the early 20th century, plant breeders realized that Mendel's findings on the non-random nature of inheritance
Mendelian inheritance
Mendelian inheritance is a scientific description of how hereditary characteristics are passed from parent organisms to their offspring; it underlies much of genetics...
could be applied to seedling
Seedling
thumb|Monocot and dicot seedlingsA seedling is a young plant sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle , the hypocotyl , and the cotyledons...
populations produced through deliberate pollination
Pollination
Pollination is the process by which pollen is transferred in plants, thereby enabling fertilisation and sexual reproduction. Pollen grains transport the male gametes to where the female gamete are contained within the carpel; in gymnosperms the pollen is directly applied to the ovule itself...
s to predict the frequencies of different types.
From 1904 to World War II in Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
Nazareno Strampelli
Nazareno Strampelli
Nazareno Strampelli was an Italian agronomist and plant breeder. He was the forerunner of the so called green revolution....
created a number of wheat hybrids. His work allowed Italy to increase hugely crop production during the so called "Battle for Grain
Battle for Grain
The Battle for Grain was an economic policy undertaken by the Fascists in Italy during the 1920s as a move toward autarky.-Background:When Benito Mussolini took over as Prime Minister of Italy in 1922 the economy was in a bad state following World War I...
" (1925–1940) and some varieties was exported in foreign countries, as Argentina, Mexico, China and others. After the war, the work of Strampelli was quickly forgotten, but thanks to the hybrids he created, Norman Borlaug
Norman Borlaug
Norman Ernest Borlaug was an American agronomist, humanitarian, and Nobel laureate who has been called "the father of the Green Revolution". Borlaug was one of only six people to have won the Nobel Peace Prize, the Presidential Medal of Freedom and the Congressional Gold Medal...
was able to move the very first steps of the Green Revolution
Green Revolution
Green Revolution refers to a series of research, development, and technology transfer initiatives, occurring between the 1940s and the late 1970s, that increased agriculture production around the world, beginning most markedly in the late 1960s....
.
In 1908, George Harrison Shull
George Harrison Shull
George Harrison Shull was an eminent American plant geneticist. He was born in Clark Co., Ohio, graduated from Antioch College in 1901 and from the University of Chicago in 1904, served as botanical expert to the Bureau of Plant Industry in 1903-04, and thenceforth was a botanical investigator of...
described heterosis
Heterosis
Heterosis, or hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic....
, also known as hybrid vigor. Heterosis describes the tendency of the progeny of a specific cross to outperform both parents. The detection of the usefulness of heterosis for plant breeding has led to the development of inbred lines that reveal a heterotic yield advantage when they are crossed. Maize
Maize
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...
was the first species where heterosis was widely used to produce hybrids.
By the 1920s, statistical
Statistics
Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....
methods were developed to analyze gene action and distinguish heritable variation from variation caused by environment. In 1933, another important breeding technique, cytoplasmic male sterility
Cytoplasmic male sterility
Cytoplasmic male sterility is total or partial male sterility associated with plant biology as the result of specific nuclear and mitochondrial interactions...
(CMS), developed in maize, was described by Marcus Morton Rhoades
Marcus Morton Rhoades
Marcus Morton Rhoades was an American cytogeneticist. His research on maize led to important discoveries for basic genetics and the applied science of plant breeding.He was one of the first cytogenecists to document the pre-meiotic pairing of homologous chromosomes in maize, otherwise referred as...
. CMS is a maternally inherited trait that makes the plant produce sterile pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
. This enables the production of hybrids without the need for labor intensive detasseling
Detasseling
Detasseling corn is removing the pollen-producing flowers, the tassel, from the tops of corn plants and placing them on the ground. It is a form of pollination control, employed to cross-breed, or hybridize, two varieties of corn....
.
These early breeding techniques resulted in large yield increase in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
in the early 20th century. Similar yield increases were not produced elsewhere until after World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, the Green Revolution
Green Revolution
Green Revolution refers to a series of research, development, and technology transfer initiatives, occurring between the 1940s and the late 1970s, that increased agriculture production around the world, beginning most markedly in the late 1960s....
increased crop production in the developing world in the 1960s.
After World War II
Following World War IIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
a number of techniques were developed that allowed plant breeders to hybridize distantly related species, and artificially induce genetic diversity.
When distantly related species are crossed, plant breeders make use of a number of plant tissue culture
Plant tissue culture
Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues or organs under sterile conditions on a nutrient culture medium of known composition. Plant tissue culture is widely used to produce clones of a plant in a method known as micropropagation...
techniques to produce progeny from otherwise fruitless mating. Interspecific and intergeneric hybrids are produced from a cross of related species or genera that do not normally sexually reproduce with each other. These crosses are referred to as Wide crosses. For example, the cereal
Cereal
Cereals are grasses cultivated for the edible components of their grain , composed of the endosperm, germ, and bran...
triticale
Triticale
Triticale is a hybrid of wheat and rye first bred in laboratories during the late 19th century. The grain was originally bred in Scotland and Sweden. Commercially available triticale is almost always a second generation hybrid, i.e., a cross between two kinds of primary triticales...
is a wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
and rye
Rye
Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...
hybrid. The cells in the plants derived from the first generation created from the cross contained an uneven number of chromosomes and as result was sterile. The cell division
Cell division
Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...
inhibitor colchicine
Colchicine
Colchicine is a medication used for gout. It is a toxic natural product and secondary metabolite, originally extracted from plants of the genus Colchicum...
was used to double the number of chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s in the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
and thus allow the production of a fertile line.
Failure to produce a hybrid may be due to pre- or post-fertilization incompatibility. If fertilization is possible between two species or genera, the hybrid embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
may abort before maturation. If this does occur the embryo resulting from an interspecific or intergeneric cross can sometimes be rescued and cultured to produce a whole plant. Such a method is referred to as Embryo Rescue
Embryo Rescue
Embryo Rescue is one of the earliest and successful forms of in-vitro culture techniques that is used to assist in the development of plant embryos that might not survive to become viable plants. Embryo rescue plays an important role in modern plant breeding, allowing the development of many...
. This technique has been used to produce new rice for Africa
New Rice for Africa
New Rice for Africa is an interspecific cultivar of rice developed by the Africa Rice Center to improve the yield of African rice varieties. Although 240 million people in West Africa rely on rice as the primary source of food energy and protein in their diet, the majority of this rice is...
, an interspecific cross of Asian rice (Oryza sativa) and African rice
African rice
Oryza glaberrima, commonly known as African rice, is a domesticated rice species. African rice is believed to have been domesticated 2,000-3,000 years ago in the inland delta of the Upper Niger river, in what is now Mali...
(Oryza glaberrima).
Hybrids may also be produced by a technique called protoplast
Protoplast
Protoplast, from the ancient Greek πρῶτον + verb πλάθω or πλάττω , initially referred to the first organized body of a species.Protoplast has several biological definitions:...
fusion. In this case protoplasts are fused, usually in an electric field. Viable recombinants can be regenerated in culture.
Chemical mutagen
Mutagen
In genetics, a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level. As many mutations cause cancer, mutagens are therefore also likely to be carcinogens...
s like EMS and DMS
Dimethyl sulfate
Dimethyl sulfate is a chemical compound with formula 2SO2. As the diester of methanol and sulfuric acid, its formula is often written as 2SO4 or even Me2SO4, where CH3 or Me is methyl...
, radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
and transposon
Transposon
Transposable elements are sequences of DNA that can move or transpose themselves to new positions within the genome of a single cell. The mechanism of transposition can be either "copy and paste" or "cut and paste". Transposition can create phenotypically significant mutations and alter the cell's...
s are used to generate mutant
Mutant
In biology and especially genetics, a mutant is an individual, organism, or new genetic character, arising or resulting from an instance of mutation, which is a base-pair sequence change within the DNA of a gene or chromosome of an organism resulting in the creation of a new character or trait not...
s with desirable traits to be bred with other cultivar
Cultivar
A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...
s - a process known as Mutation Breeding. Classical plant breeders also generate genetic diversity within a species by exploiting a process called somaclonal variation
Somaclonal variation
Somaclonal variation It is the term used to describe the variation seen in plants that have been produced by plant tissue culture. Chromosomal rearrangements are an important source of this variation....
, which occurs in plants produced from tissue culture, particularly plants derived from callus
Plant tissue culture
Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues or organs under sterile conditions on a nutrient culture medium of known composition. Plant tissue culture is widely used to produce clones of a plant in a method known as micropropagation...
. Induced polyploidy
Polyploidy
Polyploid is a term used to describe cells and organisms containing more than two paired sets of chromosomes. Most eukaryotic species are diploid, meaning they have two sets of chromosomes — one set inherited from each parent. However polyploidy is found in some organisms and is especially common...
, and the addition or removal of chromosomes using a technique called chromosome engineering
Chromosome engineering
Chromosome engineering is "the controlled generation of chromosomal deletions, inversions, or translocations with defined endpoints." By combining chromosomal translocation, chromosomal inversion,and chromosomal deletion, chromosome engineering has been shown to identify the underlying genes that...
may also be used.
When a desirable trait has been bred into a species, a number of crosses to the favored parent are made to make the new plant as similar to the favored parent as possible. Returning to the example of the mildew resistant pea being crossed with a high-yielding but susceptible pea, to make the mildew resistant progeny of the cross most like the high-yielding parent, the progeny will be crossed back to that parent for several generations (See backcrossing
Backcrossing
Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent, in order to achieve offspring with a genetic identity which is closer to that of the parent...
). This process removes most of the genetic contribution of the mildew resistant parent. Classical breeding is therefore a cyclical process.
With classical breeding techniques, the breeder does not know exactly what genes have been introduced to the new cultivars. Some scientist
Scientist
A scientist in a broad sense is one engaging in a systematic activity to acquire knowledge. In a more restricted sense, a scientist is an individual who uses the scientific method. The person may be an expert in one or more areas of science. This article focuses on the more restricted use of the word...
s therefore argue that plants produced by classical breeding methods should undergo the same safety testing regime as genetically modified
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...
plants. There have been instances where plants bred using classical techniques have been unsuitable for human consumption, for example the poison
Poison
In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....
solanine
Solanine
Solanine is a glycoalkaloid poison found in species of the nightshade family , such as the potato . It can occur naturally in any part of the plant, including the leaves, fruit, and tubers. Solanine has fungicidal and pesticidal properties, and it is one of the plant's natural defenses...
was unintentionally increased to unacceptable levels in certain varieties of potato
Potato
The potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species...
through plant breeding. New potato varieties are often screened for solanine levels before reaching the marketplace.
Modern plant breeding
Modern plant breeding may use techniques of molecular biology to select, or in the case of genetic modification, to insert, desirable traits into plants.Steps of plant breeding
The following are the major activities of plant breeding:- Creation of variation
- Selection
- Evaluation
- Release
- Multiplication
- Distribution of the new variety
Marker assisted selection
- See main article on Marker assisted selectionMarker assisted selectionMarker assisted selection or marker aided selection ' is a process whereby a marker is used for indirect selection of a genetic determinant or determinants of a trait of interest...
.
Sometimes many different genes can influence a desirable trait in plant breeding. The use of tools such as molecular markers or DNA fingerprinting can map thousands of genes. This allows plant breeders to screen large populations of plants for those that possess the trait of interest. The screening is based on the presence or absence of a certain gene as determined by laboratory procedures, rather than on the visual identification of the expressed trait in the plant.
Reverse Breeding and Doubled Haploids (DH)
- See also main article on Doubled haploidyDoubled haploidyA doubled haploid is a genotype formed when haploid cells undergo chromosome doubling. Artificial production of doubled haploids is important in plant breeding....
.
A method for efficiently producing homozygous plants from a heterozygous starting plant, which has all desirable traits. This starting plant is induced to produce doubled haploid
Doubled haploidy
A doubled haploid is a genotype formed when haploid cells undergo chromosome doubling. Artificial production of doubled haploids is important in plant breeding....
from haploid cells, and later on creating homozygous/doubled haploid
Doubled haploidy
A doubled haploid is a genotype formed when haploid cells undergo chromosome doubling. Artificial production of doubled haploids is important in plant breeding....
plants from those cells. While in natural offspring genetic recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
occurs and traits can be unlinked from each other, in doubled haploid cells and in the resulting DH plants recombination is no longer an issue. There, a recombination between two corresponding chromosomes does not lead to un-linkage of allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s or traits, since it just leads to recombination with its identical copy. Thus, traits on one chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
stay linked. Selecting those offspring having the desired set of chromosomes and crossing them will result in a final F1 hybrid
F1 hybrid
F1 hybrid is a term used in genetics and selective breeding. F1 stands for Filial 1, the first filial generation seeds/plants or animal offspring resulting from a cross mating of distinctly different parental types....
plant, having exactly the same set of chromosomes, genes and traits as the starting hybrid plant. The homozygous parental lines can reconstitute the original heterozygous plant by crossing, if desired even in a large quantity.
An individual heterozygous plant can be converted into a heterozygous variety (F1 hybrid
F1 hybrid
F1 hybrid is a term used in genetics and selective breeding. F1 stands for Filial 1, the first filial generation seeds/plants or animal offspring resulting from a cross mating of distinctly different parental types....
) without the necessity of vegetative
Vegetative
Vegetative describes vegetation.Vegetative may also refer to:*Vegetative reproduction, a type of asexual reproduction for plants*Persistent vegetative state, a condition of people with severe brain damage...
propagation but as the result of the cross of two homozygous/doubled haploid lines derived from the originally selected plant. patent
Genetic modification
- See main article on Transgenic plants.
Genetic modification of plants is achieved by adding a specific gene or genes to a plant, or by knocking down a gene with RNAi
RNAI
RNAI is a non-coding RNA that is an antisense repressor of the replication of some E. coli plasmids, including ColE1. Plasmid replication is usually initiated by RNAII, which acts as a primer by binding to its template DNA. The complementary RNAI binds RNAII prohibiting it from its initiation role...
, to produce a desirable phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
. The plants resulting from adding a gene are often referred to as transgenic plants. If for genetic modification genes of the species or of a crossable plant are used under control of their native promoter, then they are called cisgenic plants
Cisgenesis
Cisgenesis, sometimes also called Intragenesis, is a product designation for a category of genetically engineered plants. A variety of classification schemes have been proposed , that order genetically modified organisms based on the nature of introduced genotypical changes rather than the process...
. Genetic modification can produce a plant with the desired trait or traits faster than classical breeding because the majority of the plant's genome is not altered.
To genetically modify a plant, a genetic construct must be designed so that the gene to be added or removed will be expressed by the plant. To do this, a promoter to drive transcription
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
and a termination sequence to stop transcription of the new gene, and the gene or genes of interest must be introduced to the plant. A marker for the selection of transformed plants is also included. In the laboratory
Laboratory
A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...
, antibiotic resistance
Antibiotic resistance
Antibiotic resistance is a type of drug resistance where a microorganism is able to survive exposure to an antibiotic. While a spontaneous or induced genetic mutation in bacteria may confer resistance to antimicrobial drugs, genes that confer resistance can be transferred between bacteria in a...
is a commonly used marker: Plants that have been successfully transformed will grow on media containing antibiotics; plants that have not been transformed will die. In some instances markers for selection are removed by backcrossing
Backcrossing
Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent, in order to achieve offspring with a genetic identity which is closer to that of the parent...
with the parent plant prior to commercial release.
The construct can be inserted in the plant genome by genetic recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
using the bacteria Agrobacterium tumefaciens
Agrobacterium tumefaciens
Agrobacterium tumefaciens is the causal agent of crown gall disease in over 140 species of dicot. It is a rod shaped, Gram negative soil bacterium...
or A. rhizogenes
Agrobacterium rhizogenes
Agrobacterium rhizogenes is a Gram negative soil bacterium that produces hairy root disease in dicotyledonous plants.A...
, or by direct methods like the gene gun
Gene gun
A gene gun or a biolistic particle delivery system, originally designed for plant transformation, is a device for injecting cells with genetic information. The payload is an elemental particle of a heavy metal coated with plasmid DNA...
or microinjection
Microinjection
Microinjection refers to the process of using a glass micropipette to insert substances at a microscopic or borderline macroscopic level into a single living cell. It is a simple mechanical process in which a needle roughly 0.5 to 5 micrometers in diameter penetrates the cell membrane and/or the...
. Using plant virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es to insert genetic constructs into plants is also a possibility, but the technique is limited by the host range of the virus. For example, Cauliflower mosaic virus
Cauliflower mosaic virus
Cauliflower mosaic virus is the type member of the caulimoviruses, one of the six genera in the Caulimoviridae family, pararetroviruses that infect plants...
(CaMV) only infects cauliflower
Cauliflower
Cauliflower is one of several vegetables in the species Brassica oleracea, in the family Brassicaceae. It is an annual plant that reproduces by seed...
and related species. Another limitation of viral vectors is that the virus is not usually passed on the progeny, so every plant has to be inoculated.
The majority of commercially released transgenic plants are currently limited to plants that have introduced resistance to insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
pest
Pest (animal)
A pest is an animal which is detrimental to humans or human concerns. It is a loosely defined term, often overlapping with the related terms vermin, weeds, parasites and pathogens...
s and herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
s. Insect resistance is achieved through incorporation of a gene from Bacillus thuringiensis
Bacillus thuringiensis
Bacillus thuringiensis is a Gram-positive, soil-dwelling bacterium, commonly used as a biological pesticide; alternatively, the Cry toxin may be extracted and used as a pesticide. B...
(Bt) that encodes a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that is toxic to some insects. For example, the cotton bollworm
Helicoverpa zea
The larva of the moth Helicoverpa zea is a major agricultural pest. It can feed on many different plants during the larval stage. Accordingly, the species has been given many different common names. When the larva consumes cotton, it is known as the cotton bollworm...
, a common cotton pest, feeds on Bt cotton it will ingest the toxin and die. Herbicides usually work by binding to certain plant enzymes and inhibiting their action. The enzymes that the herbicide inhibits are known as the herbicides target site. Herbicide resistance can be engineered into crops by expressing a version of target site protein that is not inhibited by the herbicide. This is the method used to produce glyphosate resistant crop plants (See Glyphosate)
Genetic modification of plants that can produce pharmaceuticals (and industrial chemicals), sometimes called pharmacrops, is a rather radical new area of plant breeding.
Issues and concerns
Modern plant breeding, whether classical or through genetic engineering, comes with issues of concern, particularly with regard to food crops. The question of whether breeding can have a negative effect on nutritionNutrition
Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....
al value is central in this respect. Although relatively little direct research in this area has been done, there are scientific indications that, by favoring certain aspects of a plant's development, other aspects may be retarded. A study published in the Journal of the American College of Nutrition in 2004, entitled Changes in USDA Food Composition Data for 43 Garden Crops, 1950 to 1999, compared nutritional analysis of vegetable
Vegetable
The noun vegetable usually means an edible plant or part of a plant other than a sweet fruit or seed. This typically means the leaf, stem, or root of a plant....
s done in 1950 and in 1999, and found substantial decreases in six of 13 nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
s measured, including 6% of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
and 38% of riboflavin
Riboflavin
Riboflavin, also known as vitamin B2 or additive E101, is an easily absorbed micronutrient with a key role in maintaining health in humans and animals. It is the central component of the cofactors FAD and FMN, and is therefore required by all flavoproteins. As such, vitamin B2 is required for a...
. Reductions in calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and ascorbic acid
Ascorbic acid
Ascorbic acid is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. Ascorbic acid is one form of vitamin C. The name is derived from a- and scorbutus , the...
were also found. The study, conducted at the Biochemical Institute, University of Texas at Austin
University of Texas at Austin
The University of Texas at Austin is a state research university located in Austin, Texas, USA, and is the flagship institution of the The University of Texas System. Founded in 1883, its campus is located approximately from the Texas State Capitol in Austin...
, concluded in summary: "We suggest that any real declines are generally most easily explained by changes in cultivated varieties between 1950 and 1999, in which there may be trade-offs between yield
Crop yield
In agriculture, crop yield is not only a measure of the yield of cereal per unit area of land under cultivation, yield is also the seed generation of the plant itself...
and nutrient content."
The debate surrounding genetically modified food during the 1990s peaked in 1999 in terms of media coverage and risk perception, and continues today - for example, "Germany has thrown its weight behind a growing European mutiny over genetically modified crops by banning the planting of a widely grown pest-resistant corn variety.". The debate encompasses the ecological impact of genetically modified plants, the safety of genetically modified food
Genetically modified food
Genetically modified foods are foods derived from genetically modified organisms . Genetically modified organisms have had specific changes introduced into their DNA by genetic engineering techniques...
and concepts used for safety evaluation like substantial equivalence
Substantial equivalence
Substantial equivalence is a concept, developed by OECD in 1991, that maintains that a novel food should be considered the same as and as safe as a conventional food if it demonstrates the same characteristics and composition as the conventional food. Substantial equivalence is important from a...
. Such concerns are not new to plant breeding. Most countries have regulatory processes in place to help ensure that new crop varieties entering the marketplace are both safe and meet farmers' needs. Examples include variety registration, seed schemes, regulatory authorizations for GM plants, etc.
Plant breeders' rights
Plant breeders' rights
Plant breeders' rights , also known as plant variety rights , are rights granted to the breeder of a new variety of plant that give him exclusive control over the propagating material and harvested material of a new variety for a number of years.With these rights, the breeder can choose...
is also a major and controversial issue. Today, production of new varieties is dominated by commercial plant breeders, who seek to protect their work and collect royalties through national and international agreements based in intellectual property rights. The range of related issues is complex. In the simplest terms, critics of the increasingly restrictive regulations argue that, through a combination of technical and economic pressures, commercial breeders are reducing biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
and significantly constraining individuals (such as farmers) from developing and trading seed on a regional level. Efforts to strengthen breeders' rights, for example, by lengthening periods of variety protection, are ongoing.
When new plant breeds or cultivars are bred, they must be maintained and propagated. Some plants are propagated by asexual means while others are propagated by seeds. Seed propagated cultivars require specific control over seed source and production procedures to maintain the integrity of the plant breeds results. Isolation is necessary to prevent cross contamination with related plants or the mixing of seeds after harvesting. Isolation is normally accomplished by planting distance but in certain crops, plants are enclosed in greenhouses or cages (most commonly used when producing F1 hybrids.)
The Role of Plant Breeding in Organic Agriculture
Critics of organic agriculture claim it is too low-yielding to be a viable alternative to conventional agriculture. However, a growing body of evidence suggests that poor performance is not an intrinsic property of organic production, but rather the result of growing poorly adapted varieties. It is estimated that over 95% of organic agriculture is based on conventionally adapted varieties, even though the production environments found in organic vs. conventional farming systems are vastly different due to their distinctive management practices. Most notably, organic farmers have fewer inputs available than conventional growers to control their production environments. Breeding varieties specifically adapted to the unique conditions of organic agriculture is critical for this sector to realize its full potential. This requires selection for traits such as:- Water use efficiency
- Nutrient use efficiency (particularly nitrogenNitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and phosphorusPhosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
) - Weed competitiveness
- Tolerance of mechanical weed control
- Pest/disease resistance
- Early maturity (as a mechanism for avoidance of particular stresses)
- Abiotic stress tolerance (i.e. drought, salinity, etc...)
Currently, few breeding programs are directed at organic agriculture and until recently those that did address this sector have generally relied on indirect selection (i.e. selection in conventional environments for traits considered important for organic agriculture). However, because the difference between organic and conventional environments is large, a given genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
may perform very differently in each environment due to an interaction between genes and the environment (see gene-environment interaction
Gene-environment interaction
Gene–environment interaction is the phenotypic effect of interactions between genes and the environment....
). If this interaction is severe enough, an important trait required for the organic environment may not be revealed in the conventional environment, which can result in the selection of poorly adapted individuals. To ensure the most adapted varieties are identified, advocates of organic breeding now promote the use of direct selection (i.e. selection in the target environment) for many agronomic traits.
There are many classical and modern breeding techniques that can be utilized for crop improvement in organic agriculture despite the ban on genetically modified organisms. For instance, controlled crosses between individuals allow desirable genetic variation to be recombined and transferred to seed progeny via natural processes. Marker assisted selection
Marker assisted selection
Marker assisted selection or marker aided selection ' is a process whereby a marker is used for indirect selection of a genetic determinant or determinants of a trait of interest...
can also be employed as a diagnostics tool to facilitate selection of progeny who possess the desired trait(s), greatly speeding up the breeding process. This technique has proven particularly useful for the introgression of resistance genes into new backgrounds, as well as the efficient selection of many resistance genes pyramided into a single individual. Unfortunately, molecular markers are not currently available for many important traits, especially complex ones controlled by many genes.
Participatory Plant Breeding
The development of agricultural science, with phenomenon like the Green RevolutionGreen Revolution
Green Revolution refers to a series of research, development, and technology transfer initiatives, occurring between the 1940s and the late 1970s, that increased agriculture production around the world, beginning most markedly in the late 1960s....
arising, have left millions of farmers in developing countries, most of whom operate small farms under unstable and difficult growing conditions, in a precarious situation. The adoption of new plant varieties by this group has been hampered by the constraints of poverty and the international policies promoting an industrialized model of agriculture. Their response has been the creation of a novel and promising set of research methods collectively known as participatory plant breeding. Participatory means that farmers are more involved in the breeding process and breeding goals are defined by farmers instead of international seed companies with their large-scale breeding programs. Farmers' groups and NGOs, for example, may wish to affirm local people's rights over genetic resources, produce seeds themselves, build farmers' technical expertise, or develop new products for niche markets, like organically grown food.
List of notable plant breeders
- Gartons Agricultural Plant BreedersGartons Agricultural Plant BreedersThis is a short history of the United Kingdom's first agricultural plant breeding business.Dr John Garton, of the firm of Garton Brothers of Newton-le-Willows in the United Kingdom was the Originator of Scientific Farm Plant Breeding. He is credited as the first scientist to show that the common...
- Norman BorlaugNorman BorlaugNorman Ernest Borlaug was an American agronomist, humanitarian, and Nobel laureate who has been called "the father of the Green Revolution". Borlaug was one of only six people to have won the Nobel Peace Prize, the Presidential Medal of Freedom and the Congressional Gold Medal...
- Nazareno StrampelliNazareno StrampelliNazareno Strampelli was an Italian agronomist and plant breeder. He was the forerunner of the so called green revolution....
- Luther BurbankLuther BurbankLuther Burbank was an American botanist, horticulturist and a pioneer in agricultural science.He developed more than 800 strains and varieties of plants over his 54-year career. Burbank's varied creations included fruits, flowers, grains, grasses, and vegetables...
- Roger DoucetRoger DoucetRoger Doucet, CM was a Canadian tenor best known for singing the Canadian national anthem, "O Canada", on televised games of the Montreal Canadiens, Montreal Alouettes, and Montreal Expos during the 1970s...
- Keith DowneyKeith DowneyRichard Keith Downey, OC, FRSC is a Canadian agricultural scientist and, as one of the originators of canola, became known as the "Father of Canola"....
- Niels Ebbesen HansenNiels Ebbesen HansenNiels Ebbesen Hansen was a Danish-American horticulturist and botanist who was a pioneer in Plant breeding.-Background:...
- Gregor MendelGregor MendelGregor Johann Mendel was an Austrian scientist and Augustinian friar who gained posthumous fame as the founder of the new science of genetics. Mendel demonstrated that the inheritance of certain traits in pea plants follows particular patterns, now referred to as the laws of Mendelian inheritance...
- Colin WyattColin WyattColin Wyatt worked from 1957 to 1980 for IPC Magazines as an illustrator of children's comics.-Biography:Concentrating mostly on the very young children's stories, he contributed to such well-known titles and Tiny Tots and Jack and Jill, as well as illustrating many Disney tie-in comics and...
See also
- CisgenesisCisgenesisCisgenesis, sometimes also called Intragenesis, is a product designation for a category of genetically engineered plants. A variety of classification schemes have been proposed , that order genetically modified organisms based on the nature of introduced genotypical changes rather than the process...
- Crop breeding in NepalCrop breeding in Nepal-Crop improvement in Nepal:Crop breeding or Plant Breeding or crop improvement is the art and science of improving the heredity of plants for benefit of mankind...
- Cultivated plant taxonomyCultivated plant taxonomyCultivated plant taxonomy is the study of the theory and practice of the science that identifies, describes, classifies, and names cultigens—those plants whose origin or selection is primarily due to intentional human activity...
- Double-pair matingDouble-pair matingDouble-pair mating is a mating design used in plant breeding. Each individual is mated with two others.- Principles :In Fig. 1 a connected variant of DPM is shown. DPM is an efficient mating design in balanced breeding programmes, where equal contribution from each breeding population member is...
- Genomics of domesticationGenomics of domesticationGenomics is the study of the structure, content, and evolution of genomes, or the entire genetic information of organisms. Domestication is the process by which humans alter the morphology and genes of targeted organisms in order to select for desirable traits.-Background:Since Domestication...
- International Code of Nomenclature for Cultivated PlantsInternational Code of Nomenclature for Cultivated PlantsThe International Code of Nomenclature for Cultivated Plants regulates the names of cultigens...
- Marker assisted selectionMarker assisted selectionMarker assisted selection or marker aided selection ' is a process whereby a marker is used for indirect selection of a genetic determinant or determinants of a trait of interest...
- Orthodox seedOrthodox seedOrthodox seeds are seeds which will survive drying and/or freezing during ex-situ conservation. According to information from the U.S. Department of Agriculture there is variation in the ability of orthodox seeds to withstand drying and storage with some seeds being more sensitive than others...
- Physiological and molecular wheat breedingPhysiological and molecular wheat breedingPlant breeding is the process of improving the heredity of plants for benefit of humankind. In evolutionary concept, plant breeding is merely a continuation of the natural evolution of the crop species, changing its course of direction in the benefit of greater use to humanity.This also be defined...
- Recalcitrant seedRecalcitrant seedRecalcitrant seeds are seeds that do not survive drying and freezing during ex-situ conservation. Moreover, these seeds cannot resist the effects of drying or temperatures less than 10° C; thus, they cannot be stored for long periods like orthodox seeds because they can lose their viability...
- Selection methods in plant breeding based on mode of reproductionSelection methods in plant breeding based on mode of reproductionThis article discusses Selection methods in plant breeding based on mode of reproduction. Some plants reproduce by self-fertilization where pollen from a plant will fertilise reproductive cells or ovules of the same plant. Other plants only allow cross-pollination where pollen from one plant can...
- Smart breedingSmart breedingSMART breeding or Precision breeding refers to a genetic engineering technique of reproducing a species members together to retain desirable traits and so produce a stronger hybrid...
External links
- Plant Breeding and Genomics eXtension Community of Practice - education and training materials for plant breeders and allied professionals
- Plant Breeding Updates
- Hybridization of Crop Plants - large practical reference on plant hybridization
- Making genetically engineered plants
- NYTimes - Useful Mutants, Bred With Radiation
- Infography about the History of Plant Breeding
- Glossary of plant breeding terminology by the Open Plant Breeding Foundation
- National Association of Plant Breeders (NAPB)
- The Global Partnership Initiative for Plant Breeding Capacity Building - GIPB