Agricultural Biotechnology (A Lot More than Just GM Crops)
Agricultural Biotechnology (A Lot More than Just GM Crops)
Assist. prof. Dr. Mahmood Ali Shaher Al Shaheen-Biology
All living organisms have the ability to improve themselves through natural means in order to adapt to changing environmental conditions. However, it takes hundreds of years before any detectable improvement is obtained. Man then learned how to domesticate and breed plants in order to develop crops to his own liking and needs using various means including biotechnology. Biotechnology is defined as a set of tools that uses living organisms (or parts of organisms) to make or modify a product, improve plants, trees or animals, or develop microorganisms for specific uses. Agricultural biotechnology is the term used in crop and livestock improvement through biotechnology tools. Biotechnology encompasses a number of tools and elements of conventional breeding techniques, bioinformatics, microbiology, molecular genetics, biochemistry, plant physiology, and molecular biology. The biotechnology tools that are important for agricultural biotechnology include:
1- Conventional plant breeding
2- Tissue culture and micro propagation
3- Molecular breeding or marker assisted selection
4- Genetic engineering and GM crops
5- Molecular Diagnostic Tools
This monograph will focus only on agricultural crop biotechnology.
The process of developing new crop varieties requires many steps and can take 10 to 25 years depending on the crop. Now, however, applications of agricultural biotechnology have considerably shortened the time it takes to bring them to market. It currently takes 7-10 years for new crop varieties to be developed. One of the tools, which make it easier and faster for scientists to select plant traits is called marker assisted selection (MAS). The different traits and physical features of plants are encoded in the plant’s genetic material, the deoxyribonucleic acid (DNA). The DNA occurs in pairs of chromosomes (strands of genetic material), one coming from each parent. The genes, which control the plant’s characteristics, are specific segments of each chromosome. All of the plant’s genes together make up its genome. Some traits, like flower color, may be controlled by only one gene . Other more complex characteristics, however, like crop yield or starch content, maybe influenced by many genes. Traditionally, plant breeders have selected plants based on their visible or measurable traits, called the phenotype. But, this process can be difficult, slow, influenced by the environment, and costly – not only in the development itself, but also for the economy, as farmers suffer crop losses. As a shortcut, plant breeders now use molecular marker-assisted selection. To help identify specific genes, scientists use what are called molecular markers which are short strings or sequence of nucleic acid which makes up a segment of DNA. The markers are located near the DNA sequence of the desired gene. Since the markers and the genes are close together on the same chromosome, they tend to stay together as each generation of plants is produced. This is called genetic linkage. This linkage helps scientists to predict whether a plant will have the desired gene. If researchers can find the marker for the gene, it means the gene itself is present. As scientists learn where each of the markers occurs on a chromosome, and how close it is to a specific gene, they can create a map of the markers and genes on specific chromosomes. This genetic linkage map shows the location of markers and genes, and their distance from other known genes. Scientists can produce detailed maps in only one generation of plant breeding. Previously, scientists produced very simple genetic maps using conventionaltechniques. It was observed long ago that as generations of plants were crossed,
some traits consistently appeared together in the new generations (genetic linkage). However, since researchers could concentrate on only a few traits in each attempt at cross-breeding, it took many crosses to obtain even a very simple genetic map. Using very detailed genetic maps and better knowledge of the molecular structure of a plant’s DNA, researchers can analyze a tiny bit of tissue from a newly germinated seedling. They don’t have to wait for the seedling to grow into a mature plant to test for the presence of the specific trait. Once the tissue is analyzed through molecular techniques, scientists know whether that seedling contains the appropriate gene. If it doesn’t, they can quickly move on and concentrate analysis on another seedling, eventually working only with the plants which contain the specific trait. Currently, molecular marker-assisted breeding, an agricultural biotechnology tool is already a routine step in breeding of most crops where the gene and the markers for a specific trait are known. This technique is being used in the efficient introgression of important genes into various crops including bacterial blight resistance in rice, increased beta carotene content in rice, cassava, and banana, and submergence tolerance in rice, to name a few (Figure).
.jpg)
Figure: Molecular marker-assisted breeding
Increasing selection efficiency by selecting for markers associated / linked with the trait of interest It should be noted, however, that molecular breeding through marker assisted selection is somewhat limited in scope compared to genetic engineering or modification because: 1) it only works for traits already present in a crop; 2) it cannot be used effectively to breed crops which have long generation time (e.g. citrus); and 3) it cannot be used effectively with crops which are clonally propagated because they are sterile or their offsprings does not resemble the parents. This includes many staples such as yams, bananas, plantain, sweet potato, and cassava.