Selection methods in plant breeding based on mode of reproduction
Encyclopedia
This article discusses Selection methods in plant breeding based on mode of reproduction. Some plants reproduce by (more or less strict) self-fertilization where pollen
from a plant will fertilise reproductive cells or ovules of the same plant. Other plants only (mainly) allow cross-pollination where pollen from one plant can only fertilize a different plant. Asexual propagation
(vegetative propagation) can also occur in plants (e.g. runners from strawberry
plants) which gives a new plant which is genetically
identical to its parent plant. All these differences change the way plant breeders
work. Apomixis
is the phenomenon that seed are produced, but in an essentially asexual way, so that parent and offspring belong to one clone
just as in case of 'normal' asexual propagation.
and selection
methods. Knowledge of mode of reproduction is also essential for its artificial manipulation to breed improved types. Only those breeding and selection methods are suitable for a crop which does not interfere with its natural state or ensure the maintenance of such a state. It is due to such reasons that imposition of self-fertilization on cross-pollinating crops leads to drastic reduction in their performance.
For teaching purpose, plant breeding is presented as four categories: Line breeding (autogamous crops), population breeding (allogamous
crops), hybrid breeding (mostly allogamous crops, some autogamous crops), clone breeding (vegetatively propagated crops).
Some of the reasons why a self fertilizing method of reproduction is so effective are the efficacy of reproduction, as well as decreasing genetic variation
and thus the fixation of highly adapted genotypes.Almost no inbreeding depression
occurs in self fertilizing plants because the mode of reproduction allows natural selection
to take place in wild populations of such plants.
Critical steps in the improvement of self fertilizing crops are the choice of parents and the identification of the best plants in segregating generations. The breeder should also have definite goals with the choice of parents. Self fertilizing are easier to maintain, but this could lead to misuse of seed.
Some of the agronomy
important, self fertilizing crops include wheat, rice, barley, dry beans, soy beans, peanuts, tomatoes, etc.
Mass selection=
This method of selection depends mainly on selection of plants according to their phenotype
and performance. The seed from selected plants are bulked for the next generation. This method is used to improve the overall population by positive or negative mass selection. Mass selection is only applied to a limited degree in self fertilizing plants and is an effective method for the improvement of land races. This method of selection will only be effective for highly heritable traits. One shortage of mass selection are the large influence that the environment has on the development, phenotype and performance of single plants.
A developed by this method will be more uniform than those developed by mass selection because all of the plants in such a variety will have the same genotype. The seed from selected plants are not added together but are kept apart and used to perform offspring tests. This is done to study the breeding behaviour of the selected plant.
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...
from a plant will fertilise reproductive cells or ovules of the same plant. Other plants only (mainly) allow cross-pollination where pollen from one plant can only fertilize a different plant. Asexual propagation
Plant propagation
Plant propagation is the process of creating new plants from a variety of sources: seeds, cuttings, bulbs and other plant parts. Plant propagation can also refer to the artificial or natural dispersal of plants.-Sexual propagation :...
(vegetative propagation) can also occur in plants (e.g. runners from strawberry
Strawberry
Fragaria is a genus of flowering plants in the rose family, Rosaceae, commonly known as strawberries for their edible fruits. Although it is commonly thought that strawberries get their name from straw being used as a mulch in cultivating the plants, the etymology of the word is uncertain. There...
plants) which gives a new plant which is genetically
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
identical to its parent plant. All these differences change the way plant breeders
Plant breeding
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...
work. Apomixis
Apomixis
In botany, apomixis was defined by Winkler as replacement of the normal sexual reproduction by asexual reproduction, without fertilization. This definition notably does not mention meiosis...
is the phenomenon that seed are produced, but in an essentially asexual way, so that parent and offspring belong to one clone
Vegetative reproduction
Vegetative reproduction is a form of asexual reproduction in plants. It is a process by which new individuals arise without production of seeds or spores...
just as in case of 'normal' asexual propagation.
Importance of mode of reproduction
The mode of reproduction of a crop determines its genetic composition, which, in turn, is the deciding factor to develop suitable breedingSelective breeding
Selective breeding is the process of breeding plants and animals for particular genetic traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds, while bred plants are known as varieties,...
and selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
methods. Knowledge of mode of reproduction is also essential for its artificial manipulation to breed improved types. Only those breeding and selection methods are suitable for a crop which does not interfere with its natural state or ensure the maintenance of such a state. It is due to such reasons that imposition of self-fertilization on cross-pollinating crops leads to drastic reduction in their performance.
For teaching purpose, plant breeding is presented as four categories: Line breeding (autogamous crops), population breeding (allogamous
Allogamy
Allogamy is a term used in the field of biological reproduction describing the fertilization of an ovum from one individual with the spermatozoa of another. By contrast, autogamy is the term used for self-fertilization. In humans, the fertilization event is an instance of allogamy...
crops), hybrid breeding (mostly allogamous crops, some autogamous crops), clone breeding (vegetatively propagated crops).
Self fertilizing crops (autogamous crops)
Certain restrictions caused the mechanisms for self fertilization (partial and full self fertilization) to develop in a number of plant species.Some of the reasons why a self fertilizing method of reproduction is so effective are the efficacy of reproduction, as well as decreasing genetic variation
Genetic variation
Genetic variation, variation in alleles of genes, occurs both within and among populations. Genetic variation is important because it provides the “raw material” for natural selection. Genetic variation is brought about by mutation, a change in a chemical structure of a gene. Polyploidy is an...
and thus the fixation of highly adapted genotypes.Almost no inbreeding depression
Inbreeding depression
Inbreeding depression is the reduced fitness in a given population as a result of breeding of related individuals. It is often the result of a population bottleneck...
occurs in self fertilizing plants because the mode of reproduction allows natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
to take place in wild populations of such plants.
Critical steps in the improvement of self fertilizing crops are the choice of parents and the identification of the best plants in segregating generations. The breeder should also have definite goals with the choice of parents. Self fertilizing are easier to maintain, but this could lead to misuse of seed.
Some of the agronomy
Agronomy
Agronomy is the science and technology of producing and using plants for food, fuel, feed, fiber, and reclamation. Agronomy encompasses work in the areas of plant genetics, plant physiology, meteorology, and soil science. Agronomy is the application of a combination of sciences like biology,...
important, self fertilizing crops include wheat, rice, barley, dry beans, soy beans, peanuts, tomatoes, etc.
Mass selection=
This method of selection depends mainly on selection of plants according to their 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...
and performance. The seed from selected plants are bulked for the next generation. This method is used to improve the overall population by positive or negative mass selection. Mass selection is only applied to a limited degree in self fertilizing plants and is an effective method for the improvement of land races. This method of selection will only be effective for highly heritable traits. One shortage of mass selection are the large influence that the environment has on the development, phenotype and performance of single plants.
A developed by this method will be more uniform than those developed by mass selection because all of the plants in such a variety will have the same genotype. The seed from selected plants are not added together but are kept apart and used to perform offspring tests. This is done to study the breeding behaviour of the selected plant.