Some realism on the diversity of methods used in "conventional" crop breeding:
...In order to utilize existing genetic diversity (or biodiversity), traditional plant breeding has been applied in some fashion as long as humans have practiced agriculture. Sexually compatible plants are cross-pollinated (or crossed) to produce offspring, each of which contains a blend of traits from the parent plants. Offspring displaying a trait of interest, say insect resistance, are selected based on the plants physical characteristics, or phenotype (e.g. does it resist insects?). This process is then repeated over successive generations with further selection based on other characteristics (yield, grain quality, etc.) until the breeders/farmers are satisfied with the overall phenotype and the variety is released.
While plant breeding has served society well for centuries, there are two fundamental limiting factors. The accessible biodiversity is limited by sexually compatible species and the selection of offspring based on phenotype is imprecise and time consuming. Modern technology has allowed plant breeders to overcome both these limiting factors.
Laboratory or “tissue culture” processes such as embryo rescue and protoplast fusion allow viable offspring to be created from species not sexually compatible in nature, greatly increasing the accessible genetic base. Marker Assisted Selection (MAS) drastically speeds up the breeding process by utilizing gene sequencing technology. In this approach, breeders leverage the existing knowledge of linkages between gene sequences and plant characteristics to identify offspring likely exhibiting beneficial traits, which is significantly more efficient than waiting for plants to first grow, and then assessing the phenotype.
Doubled Haploid Breeding approaches use a “doubling” of chromosomes to hasten plant breeding. In order to generate offspring with predictable genetic traits, it is advantageous that the parental plants have identical genes on each paired chromosome (in the case of “diploid” organisms with two copies of each chromosome), termed “homozygous”. Creating homozygous plants can be time consuming for plant breeders, usually taking at least 6 generations. In the doubled haploid process, single chromosomes are “copied” during the reproductive process using both tissue culture techniques and crosses with specific varieties. As a result of this copying, wholly homozygous plants can be created in a single generation.
Although these tools have tremendously improved the use and utilization of existing biodiversity, important farmer desired traits still may not exist in the wider accessible genetic pool. Accordingly, additional tools have been developed to create new sources of biodiversity including chemical and radiation induced mutation breeding and genetic engineering.
Mutation Breeding uses mutagenic chemicals or irradiation to create artificial biodiversity by inducing random genetic mutations. These mutations can be unstable and lethal to plants; however, they may also fortuitously create novel and beneficial genetic elements not available in other sources of accessible biodiversity. The plants are mutated and cultivated, and viable plants are selected on the basis of characteristics of interest. Mutagenic breeding has produced thousands of varieties (cereals, fruits, vegetable, cotton) released for breeding programs and direct use, and includes such products as ruby red grapefruit and premium barley for scotch whiskey.
Somaclonal Variation capitalizes on the random genetic variation that occurs when plants are regenerated through a tissue culture process. While this variation can be problematic when tissue culture approaches are used to create uniform planting materials, it can also be an asset in creating new genetic diversity and potentially beneficial characteristics through the rearrangement of chromosomes and mutations...
More @ Genetically Engineered Plants and the Arbitrary Line in the Sand | Center for Strategic and International Studies:
No comments:
Post a Comment