English naturalist Charles Darwin developed the idea of natural selection after a five-year voyage to study plants, animals, and fossils in South America and on islands in the Pacific. In 1859, he brought the idea of natural selection to the attention of the world in his best-selling book, On the Origin of Species.
Natural selection is the process through which populations of living organisms adapt and change. Individuals in a population are naturally variable, meaning that they are all different in some ways. This variation means that some individuals have traits better suited to the environment than others. Individuals with adaptive traits—traits that give them some advantage—are more likely to survive and reproduce. These individuals then pass the adaptive traits on to their offspring. Over time, these advantageous traits become more common in the population. Through this process of natural selection, favorable traits are transmitted through generations.
Natural selection can lead to speciation, where one species gives rise to a new and distinctly different species. It is one of the processes that drives evolution and helps to explain the diversity of life on Earth.
Darwin chose the name natural selection to contrast with “artificial selection,” or selective breeding that is controlled by humans. He pointed to the pastime of pigeon breeding, a popular hobby in his day, as an example of artificial selection. By choosing which pigeons mated with others, hobbyists created distinct pigeon breeds, with fancy feathers or acrobatic flight, that were different from wild pigeons.
Darwin and other scientists of his day argued that a process much like artificial selection happened in nature, without any human intervention. He argued that natural selection explained how a wide variety of life forms developed over time from a single common ancestor.
Darwin did not know that genes existed, but he could see that many traits are heritable—passed from parents to offspring.
Mutations are changes in the structure of the molecules that make up genes, called DNA. The mutation of genes is an important source of genetic variation within a population. Mutations can be random [for example, when replicating cells make an error while copying DNA], or happen as a result of exposure to something in the environment, like harmful chemicals or radiation.
Mutations can be harmful, neutral, or sometimes helpful, resulting in a new, advantageous trait. When mutations occur in germ cells [eggs and sperm], they can be passed on to offspring.
If the environment changes rapidly, some species may not be able to adapt fast enough through natural selection. Through studying the fossil record, we know that many of the organisms that once lived on Earth are now extinct. Dinosaurs are one example. An invasive species, a disease organism, a catastrophic environmental change, or a highly successful predator can all contribute to the extinction of species.
Today, human actions such as overhunting and the destruction of habitats are the main cause of extinctions. Extinctions seem to be occurring at a much faster rate today than they did in the past, as shown in the fossil record.
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Agriculture
The deliberate planting and harvesting of plants, and herding animals.
Originated about 10,000 years ago when man shifted from a hunting-gathering lifestyle to growing food in permanent settlements
At that stage, many wild plants would have been judged for their suitability to human needs.
- Earliest act of artificial selection of plants for human consumption
Domesticated
Brought under cultivation as crop plants, through centuries of human selection
Plant Breeding
A branch of agriculture that focuses on manipulating plant heredity to develop new and improved plant genotypes for use by human society
Art and a science
Also called "accelerated" and "targeted evolution" that involves the application of genetic principles to crop improvement.
Evolution
by artificial selection
- Changes made in plants are permanent and heritable
Agriculture in the 21st century faces
multiple challenges:
- It has to produce more food and fiber to feed a growing population with a smaller rural labor force
- More feedstocks for a potentially huge bioenergy market
- Contribute to overall development in the many agriculture-dependent developing countries
- Adopt more efficient and sustainable production methods
- Adapt to climate change
Agricultural food production:
Each year humans re-create the food supply that feeds 7.7 billion people
Reserves of staple foods would feed the world for less than 2 months
- As low as 48 days in 1995
Nearly 800 million people go to bed hungry every night. That's about 1 in 9 people on earth
Malnutrition
Caused by a lack of vitamins and minerals in the diet
Commonly known as "hidden hunger"
Affects the health of more than 2 billion people around the world, especially in poorer nations
As an example, vitamin A deficiency affects 800 million people worldwide
Projections:
Feeding a world population of 9.1 billion
people in 2050 would require raising overall food production by some 70% between 2005/07 and 2050.
- Production in the developing countries would need to almost double
We need to make as much progress in production efficiency in
the next 30 years as we have made in the previous 12,000.
The success of plant breeding
The introduction of science and technology into agriculture over the past two centuries has markedly increased agricultural productivity and decreased its labor-intensiveness.
Chemical fertilization, mechanization, plant breeding and molecular genetic modification [GM] have contributed to unparalleled productivity increases.
"Green revolution" crop varieties have increased yields 2 to 3 folds in many developing countries
Increases in yield are derived both from improved varieties and from improved management. In vegetable crops, research suggests about a 50-50 split between genetic gain and gain attributed to management.
Potential crisis in Plant Breeding
Future increases are far from assured because of:
- Under-investment in agricultural research
- Growing population pressure
- Decreasing freshwater variability
- Increasing temperature
- Societal rejection of GM crops in many countries
Public sector research into classical crop breeding
is declining dramatically
- Shift from public to commercial sector, i.e. from Universities or Government research organizations to private companies
- Changes intellectual property ownership.
The goals of plant breeding
- Yield
- Quality
- Resistance from biotic and abiotic stresses
- Breeding for sustainable agriculture
The concept of genetic manipulation of plant traits
The work of Gregor Mendel + Further advances in science to follow his discoveries = Plant traits are controlled by hereditary factors or genes that consist of DNA
These genes are expressed in an environment to produce a trait.
In order to change a trait or its expression, the breeder has to change the genes or modify the environment in which it is expressed.
Changing the environment essentially involves modifying
the growing or production conditions. This may be achieved through an agronomic approach; for example, the application of production inputs [e.g., fertilizers, irrigation].
- Once these supplemental environmental factors are removed, the expression of the plant trait reverts to the status quo.
Therefore, plant breeders seek to modify plants with respect to the expression of certain selected traits by modifying the genotype in a desired way by targeting specific genes.
- Such an
approach produces a change that is permanent [i.e., transferable from one generation to the next].
Two general types of plant breeding approaches
- Conventional
- Unconventional
Conventional approach [traditional/classic breeding]
Crossing two plants [hybridization]
Is the primary technique for creating variability in flowering species.
Remains the workhorse of the plant breeding industry. It is readily accessible to the average breeder and is relatively easy to conduct compared to the unconventional approach.
Unconventional approach
Using cutting-edge technologies for creating new variability that is often impossible to achieve with conventional methods.
Requires special technical skills and knowledge.
Expensive to conduct.
The advent of recombinant DNA technology gave breeders a new set of powerful tools for genetic analysis and manipulation.
- Gene transfer can now be made across natural biological barriers, by-passing the sexual process.
Basic steps in plant breeding
Regardless of the approach, a breeder follows certain general steps in conducting a breeding project
A comprehensive plan for a
breeding project addresses:
- Objectives
- Germplasm
- Selection
- Evaluation
- Certification and cultivar release
Objectives
The breeder must define clear objectives for initiating the breeding program. In selecting breeding objectives, breeders need to consider:
- The producer [grower] from the point of view of the cultivar profitability [e.g., high yield, disease resistance, early
maturity, shelf life].
- The processor [industrial user] as it relates to using the cultivar as raw materials for producing new products [e.g., canning qualities, fiber strength].
- The consumer [household user] preference [e.g., taste, high nutritional value].
Germplasm
Once the objectives have been determined, the breeder then assembles the germplasm [a pool of genetically variable plants] to be used to initiate the breeding program. The base plant population used to initiate a breeding program must include the gene[s] of interest.
Selection
After creating variability, the next task is to discriminate among the variability to identify and select individuals with desirable genotype. The selected plants are used to develop
potentially new cultivars.
Evaluation
The product reaches the consumer only after it has been evaluated. The potential cultivars are evaluated in the field, sometimes at different locations and over several years, to
identify the most promising one for release as a commercial cultivar.
Certification and release of cultivar
Before a cultivar is released, it is processed through a series
of steps, called the seed
certification process, to increase the experimental seed and to obtain approval for release from the designated crop certifying agency in the province or country.
Breeder's eye
A good breeder should have a keen sense of observation. Several outstanding discoveries were made just because the scientists who were responsible for these events were observant enough to spot unique and unexpected events.
- Luther Burbank selected one of the most successful cultivars of potato, the "Burbank potato", from a pool of variability. The Russet Burbank potato is produced on about 50% of all lands devoted to potato production in North America.
Genetics in relation to Plant Breeding
Genetics is the principle scientific basis of modern plant breeding.
Plant breeding is about targeted genetic modification of plants.
The science of genetics enables plant breeders to predict, to varying degrees, the outcome of genetic manipulation of plants.
Genetic variation that is prerequisite for effective selection can be artificially created through principles of inheritance.
Botany in relation to Plant Breeding
Plant breeders need to understand the reproductive biology of their plants as well as their taxonomy.
The taxonomy of plants helps to determine the wild relatives of a crop from where useful characters can be easily acquired through breeding.
To design the most effective crossing program, plant breeders need to know if the plants to be hybridized are cross-compatible, as well as to know all details about flowering habits.
Plant Physiology in relation to Plant Breeding
Plants respond to environmental factors
-
Biotic [e.g. pests, pathogens]
- Abiotic [e.g. temperature, moisture].
These factors are sources of physiological stress when they occur at unfavorable levels.
Plant breeders need to understand these relationships in order to develop cultivars that can resist them for enhanced productivity
Agronomy in relation to Plant Breeding
Plant breeders conduct their experiments in both controlled [greenhouse] and field environments.
An understanding of agronomy [the art and science of producing crops and managing soils] will help the breeder to provide the appropriate conditions for optimal plant growth and development that are needed for successful hybridization and selection in the field.
An improved cultivar is only as good as its cultural environment. - - Without the proper nurturing, the genetic potential of an improved cultivar would not be realized.
Plant Pathology and Entomology in relation to Plant Breeding
Plant breeding for disease and pest resistance is a major objective in plant breeding programs.
To be successful in these experiments, plant breeders need to understand the biology of the pathogen or insect pest against which resistance is being sought.
This reaction of plants to pathogens [or pests] is controlled by
the interaction between genetic
systems of host and the pathogen [or pest], which can be assessed and manipulated only through strong support and knowledge of plant pathology and entomology.
Statistics in relation to Plant Breeding
Plant breeders need to understand the principles of research design and analysis.
Plant breeders must know basic statistical concepts for proper collection, analysis and interpretation of data.
Statistics
is needed to analyze the variance within a population to separate real genetic effects from environmental effects.
- It can be as simple as finding the mean of a set of data, to complex estimates of variance and multivariate analysis.
Bioinformatics in relation to Plant Breeding
Bioinformatics is an interdisciplinary field that develops methods and software tools for understanding biological data.
As an interdisciplinary field of science, bioinformatics combines computer science, statistics, mathematics, and engineering to analyze and interpret biological data.
Common uses of bioinformatics include DNA sequence analysis and identification of candidate genes [e.g. disease-resistant genes] to be used in breeding programs.
Biochemistry in relation to Plant Breeding
Plant breeding is entering an era
of 'molecular breeding' where
identification, isolation, characterization, and manipulation of specific segments of DNA at the cellular level would predominate the plant breeding activity in the present century.
Plant breeders need to be familiar with the procedures of plant genetic manipulation at the molecular level, including the development and use of molecular markers and gene transfer techniques.
- This is where knowledge of biochemistry is of fundamental importance.
Achievements of modern plant breeders
All achievements of plant breeders can be grouped into several major areas:
- Yield increase
- Enhancement of compositional traits
- Crop adaptation
- The impact on the crop production system
Yield increase
Yields of major crops [e.g., corn, rice, sorghum, wheat, and
soybean] have
significantly increased in North America over the
last 60-70 years
For example, the yield of corn rose from about 2000 kg/ha in the
1940s to about 7000 kg/ha in the 1990s.
In England, it took only 40 years to for wheat yields to rise from 2 metric tons/ha to 6 metric tons/ha.
These yield increases are not totally due to the genetic potential of the new crop cultivars [about 50% is attributed to plant breeding] but are also due to improved agronomic practices [e.g., application of fertilizer, irrigation].
Enhancement of compositional traits
Breeding for a specific combination of traits to enhance nutritional quality or meet an industrial need are among the most important goals of plant breeding.
For example, different kind of wheat are needed for different kinds of products [e.g., pasta, bread, cookies].
Breeders have identified the quality traits associated with these uses and have produced cultivars with enhanced expression of these traits.
Genetic engineering technology has been used to produce high oleic sunflower for industrial use.
It is also being used to enhance the nutritional value of crops [for example, "Golden rice" with increased pro-vitamin A content].
Crop adaptation
Because many crops are cultivated in regions to which they are not native, plant breeders have developed cultivars with modified physiology to cope with such unfavorable conditions.
For example, the duration of the growing period varies from one region to another.
- Early maturing cultivars of crop plants enable growers to produce a crop during a short season, or even to produce two crops in one season.
Another example, soils under arid conditions tend to accumulate large amounts of salts; therefore, salt-tolerant cultivars have been developed to be grown on such soils.
The impact on the crop production system
Crop productivity is a function of the genotype [genetic potential of the cultivar] and the cultural environment.
The Green Revolution is an example of an outstanding outcome of the combination of plant breeding efforts and production technology to increase food productivity.
An intensive production system with high input of fertilizers requires the availability of crop cultivars that are responsive to such high input growing conditions. Plant breeders have developed cultivars for such intensive agriculture.
Another example, through the use of genetic engineering technology, breeders have reduced the need for pesticides in the production of major crops [e.g., corn, tobacco, soybean] with the
development of disease resistant cultivars, thereby reducing environmental damage from agriculture.
Norman Ernest Borlaug - the father of the Green Revolution
Dr. Borlaug was born in 1914. He earned his Ph.D. in Pathology and Genetics in 1942 from the University of Minnesota, and joined the Rockefeller Foundation team in Mexico in 1944, a move that would set him on course to accomplish one of the most notable accomplishments in history.
The key technological strategies employed by Dr. Borlaug and his team were to develop high yielding varieties of wheat, and an appropriate agronomic package [fertilizer, irrigation, tillage, pest control] for optimizing the yield potential of the varieties.
Wheat production in Mexico increased dramatically from its low 750 kg/ha to about 3200 kg/ha.
The effort in wheat was so successful that the model was duplicated in rice in the Philippines in 1960.
In 1970, Dr. Norman Borlaug was honored with the Nobel Peace Prize for contributing to curbing hunger in Asia and other parts of the world where his improved wheat varieties were introduced.
The plant breeding industry
Public sector vs private sector
Public sector
- Self-pollinated species [e.g., wheat, soybean];
- Focuses on problems that are of great social concern
- Can afford to tackle long-term research
- Engage in minor crops in addition to the principal crops of importance
- Primarily
responsible for germplasm conservation and preservation.
Private sector
- Primarily for-profit
- Traditionally, cross-pollinated species [e.g., corn]
- Focuses on problems of high economic return
- Prefer to have quicker returns on investment.
- Benefits tremendously from public sector efforts.
Duration and cost of plant breeding programs
It takes about 7-12 years, or longer, to complete
a breeding program and release new cultivar for annual crops such as corn, wheat, and soybeans.
- For trees - much longer.
The use of molecular techniques to facilitate the selection process may reduce the time for plant breeding in some cases.
The use of tissue culture can reduce the length of breeding programs of perennial species.
The development of new cultivars may cost from hundreds of thousands of dollars to even several million dollars.
The cost of breeding also
depends on where and by whom the activity is being conducted
- Cheaper labor in developing countries can allow breeders to produce hybrids of some self-pollinated species less expensively because they can afford to pay for hand pollination [e.g., breeding cotton in India].
The future of plant breeding in society
For as long as the world population continues to increase, there will be a demand for more food.
However, with an increasing population comes an increasing demand for land for residential, commercial, and recreational uses.
Sometimes, farmlands are converted to other uses.
Increased food production may be achieved by increasing production per unit area or bringing new lands into cultivation.
Some of the ways in which society will affect and be affected by plant breeding in the future are:
- New roles of plant breeding
- New tools for plant breeding
-
Training of plant breeders
- The key players in the plant breeding industry
- Yield gains of crops
- The biotechnology debate
New roles of plant breeding
The traditional roles of plant breeding [food, feed, fiber, and ornamentals] will continue to be important. However, new roles are gradually emerging for plants.
The technology for using plants as bioreactors to produce pharmaceuticals will advance. The technology has been around for over a decade. Strategies are being perfected for the use of plants to generate pharmaceutical antibodies, engineering antibody-mediated pathogen resistance, and altering plant phenotype by immunomodulation.
New tools for plant breeding
New tools will be developed for plant breeders, especially in the areas of the application of biotechnology to plant breeding. New marker technologies continue to be developed and older ones advanced.
Tools that will assist breeders to more effectively manipulate
quantitative traits will be enhanced.
Genomics and bioinformatics will continue to be influential in the approach of researchers to crop improvement.
Marker assisted selection [MAS] has become important in plant breeding in the 21st century.
Training of plant breeders
Plant breeding programs have experienced a slight decline in the number of graduates entering the field in the recent past.
Because of the increasing role of biotechnology in plant genetic
manipulation, graduates who combine skills and knowledge in both conventional and molecular technologies are in high demand.
It has been observed that some commercial plant breeding companies prefer to hire graduates with training in molecular genetics, then provide them the needed plant breeding skills on the job.
The key players in plant breeding industry
The last decade saw a fierce race by multinational pharmaceutical corporations to acquire seed companies. There were several key mergers as well.
The modern technologies of plant breeding are concentrated in the hands of a few of these giant companies.
The trend of acquisition and mergers is likely to continue in the future.
Publically-supported breeding efforts will decline in favor of for-profit programs.
Yield gains of crops
With the declining of arable land and the increasing policing of the environment by activists, there is an increasing need to produce more food or other crop products on the same piece of land in a more efficient and environmentally safer manner.
High yield cultivars will continue to be developed, especially in crops that have received less attention from plant breeders.
Breeding for adaptation to environmental stresses [e.g., drought, salt] will continue to be important and will enable more food to be produced on marginal lands.
The biotechnology debate
Modern technologies for plant genetic manipulation benefit the developing countries the most because they are in dire need of food, both in quantity and nutritional value.
On the other hand, the intellectual property that covers those technologies is owned by the giant multinational corporations.
Efforts will continue to be made to negotiate fair use of these technologies, and to help developing nations develop capacity for the exploitation of these modern technologies.