Expert response from Mike Connelly
Regulatory and Compliance Manager, Nuseed America
Monday, 01/14/2019 21:32
Good question! Many different processes are used when breeding to give plants their desired genetic traits. Improving plants through breeding involves the intentional manipulation of chromosomes to create desired genetic traits and their expression for specific purposes. Plant breeding often leads to plant domestication and has been practiced for thousands of years. This manipulation includes controlled pollination or genetic engineering, or even both, followed by artificial selection of progeny.
Classical plant breeding uses deliberate crossing of individuals to produce new crop varieties or lines with desirable properties. Plants are crossbred to introduce traits or genes from one variety or line into a new genetic background. Traditional breeding can take 10 years or more to cross plants and select a good variety. For example, a mildew-resistant bean may be crossed with a high-yielding but susceptible bean to introduce mildew resistance without losing the high-yield characteristics. Progeny from the cross would then be crossed with the high-yielding parent which would then be tested for yield and mildew resistance and high-yielding resistant plants would be further developed.
However, modern plant breeding use techniques of molecular biology to select, or in the case of genetic modification, to insert, desirable traits into plants, and can produce a plant with the desired trait or traits years faster than classical breeding because the majority of the plant's genome is not altered. Commonly utilized modern methods include doubled haploid and marker-assisted breeding.
Doubled Haploid Breeding efficiently produces 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 can occur and traits can be unlinked from each other, in doubled haploid cells and in the resulting plants, recombination is no longer an issue. Traits on one chromosome stay linked. Crossing those offspring with the desired set of chromosomes will result in a final hybrid plant having exactly the same set of chromosomes, genes and traits as the starting plant. Completely homozygous and homogenous inbred lines can be developed in a single generation using this system.
Marker-assisted Breeding uses tools such as molecular markers or DNA fingerprinting to map thousands of genes, which is important when considering that many different genes may influence a desirable trait. This allows plant breeders to screen large populations of plants for those that possess the trait of interest, 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.
Profound changes in plant phenotypes since the beginning of plant domestication through thousands of years of breeding has led to a wide range of genetic diversity, adapted to different human needs. The advent of scientific plant breeding accelerated varietal improvements using tools that allow monitoring of the dynamics of genomic recombination, making possible a gene-specific breeding approach. The expectations for plant breeding to help meet modern challenges related to food supply, environmental sustainability, and even fossil fuel replacement are vast. These techniques will continue to evolve to deliver advancements of a healthier and more efficient food supply.
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