DNA Marker-Assisted Selection May Speed Genetic Change
By Perry Cregan, Ph.D., USDA- Agricultural Research Service
With the recent mapping of the soybean genome, soybean breeders have shown more interest in DNA marker-assisted breeding. Both conventional selection and DNA-marker-assisted breeding identify breeding lines of soybeans that carry the form, or allele, of a gene that codes for resistance or susceptibility to a disease. One allele of the gene would code for resistance while the other would leave the plant susceptible to a particular disease.
In both traditional and marker-assisted breeding, researchers hybridize or cross an agronomically desirable high yielding susceptible soybean variety with one that carries a targeted gene or genes for resistance to create a breeding population. In this case, the objective of the breeding program is to identify breeding lines that are high yielding and agronomically superior AND that are also resistant to the disease in question. Conventional selection often requires a great deal of expertise in culturing, maintaining the purity and creating the appropriate conditions under which the pathogen will infect and clearly distinguish resistant from susceptible plants.
Whether using traditional or DNA-marker-assisted selection, soybean breeders generally want to identify those breeding lines that will breed true for resistance. So the breeder should identify those lines that carry resistance on both chromosomes for the desired trait, in order to ensure the plant will pass along those traits.
DNA-marker-assisted selection requires a “calibration phase” where researchers identify one or more DNA markers that are closely associated with the disease-resistant gene in question. Researchers then isolate DNA from each of the progeny using either small pieces of leaf tissue or a “seed chip,” which eliminates the need to grow the plant. Once researchers extract DNA from the plant or seed, it can be analyzed with a number of different types of DNA markers, with the most common being Simple Sequence Repeats and Single Nucleotide Polymorphisms.
Once the DNA has been extracted, researchers analyze it to locate a marker allele that can be used to predict the resistance or susceptibility of breeding lines. With this marker, researchers and soybean breeders can determine which progeny will breed true for resistance to the selected disease and which will not. We must ensure careful record-keeping to be certain that the DNA can be traced back to the specific progeny in the breeding population it came from.
Researchers can use DNA-marker-assisted selection to identify breeding lines for a number of different genes at the same time. The same DNA sample can be analyzed with a number of different DNA markers to determine the presence of alleles that positively impact a number of different traits.
DNA-marker-assisted selection can be applied in most laboratories with equipment that is routinely available and relatively inexpensive. The increased use of this technology opens up some exciting possibilities that could accelerate the rate of genetic improvement for U.S. soybeans. It also demonstrates the value U.S. soybean farmers receive by investing in research using checkoff dollars in projects such as the mapping of the soybean genome.
DNA Marker-Assisted Selection May Speed Genetic Change
By Perry Cregan, Ph.D., USDA- Agricultural Research Service
January 11, 2011
With the recent mapping of the soybean genome, soybean breeders have shown more interest in DNA marker-assisted breeding. Both conventional selection and DNA-marker-assisted breeding identify breeding lines of soybeans that carry the form, or allele, of a gene that codes for resistance or susceptibility to a disease. One allele of the gene would code for resistance while the other would leave the plant susceptible to a particular disease.
In both traditional and marker-assisted breeding, researchers hybridize or cross an agronomically desirable high yielding susceptible soybean variety with one that carries a targeted gene or genes for resistance to create a breeding population. In this case, the objective of the breeding program is to identify breeding lines that are high yielding and agronomically superior AND that are also resistant to the disease in question. Conventional selection often requires a great deal of expertise in culturing, maintaining the purity and creating the appropriate conditions under which the pathogen will infect and clearly distinguish resistant from susceptible plants.
Whether using traditional or DNA-marker-assisted selection, soybean breeders generally want to identify those breeding lines that will breed true for resistance. So the breeder should identify those lines that carry resistance on both chromosomes for the desired trait, in order to ensure the plant will pass along those traits.
DNA-marker-assisted selection requires a “calibration phase” where researchers identify one or more DNA markers that are closely associated with the disease-resistant gene in question. Researchers then isolate DNA from each of the progeny using either small pieces of leaf tissue or a “seed chip,” which eliminates the need to grow the plant. Once researchers extract DNA from the plant or seed, it can be analyzed with a number of different types of DNA markers, with the most common being Simple Sequence Repeats and Single Nucleotide Polymorphisms.
Once the DNA has been extracted, researchers analyze it to locate a marker allele that can be used to predict the resistance or susceptibility of breeding lines. With this marker, researchers and soybean breeders can determine which progeny will breed true for resistance to the selected disease and which will not. We must ensure careful record-keeping to be certain that the DNA can be traced back to the specific progeny in the breeding population it came from.
Researchers can use DNA-marker-assisted selection to identify breeding lines for a number of different genes at the same time. The same DNA sample can be analyzed with a number of different DNA markers to determine the presence of alleles that positively impact a number of different traits.
DNA-marker-assisted selection can be applied in most laboratories with equipment that is routinely available and relatively inexpensive. The increased use of this technology opens up some exciting possibilities that could accelerate the rate of genetic improvement for U.S. soybeans. It also demonstrates the value U.S. soybean farmers receive by investing in research using checkoff dollars in projects such as the mapping of the soybean genome.