Engineering turf for the future
For the past several decades, breeders have made dramatic improvements in turfgrass cultivars of many species. Cultivars available today offer greater attractiveness and durability than ever before. As a complement to classical breeding techniques, the techniques of genetic engineering have the potential to provide turfgrass breeders an additional tool in their efforts to develop the ideal grass. The Rutgers Turfgrass Biotechnology Program is actively working with the Rutgers Turfgrass Breeding Program to develop turfgrass cultivars with increased disease and herbicide resistance.
The term genetic engineering refers to manipulating the DNA, or genes, of an organism. Plant transformation refers to the process of introducing a gene from some other organism into a plant species. Scientists are discovering genes from organisms as diverse as viruses, bacteria, fungi and plants that can confer beneficial new characteristics to particular plant species. Plant-transformation technology thus offers the opportunity to introduce into a plant species genes from unrelated organisms. This would be impossible using traditional breeding methods.
Transformed crops such as corn, soybeans and cotton, developed through genetic engineering, already are commercially available. Genetic engineers transformed these crops with genes conferring insect and herbicide resistance to those plants. We are using similar techniques, in combination with breeding, for the development of improved turfgrass cultivars. Currently, this work is in the research stage, and no transformed turfgrass cultivars are yet commercially available. However, we do have transformed plants containing several potentially beneficial new genes. We are field-testing these plants to determine the effectiveness of the new genes.
In the Rutgers Turfgrass Biotechnology Program, we are particularly interested in transformation of creeping bentgrass. The high maintenance requirements of bentgrass make it a good candidate for improvements that will ease this maintenance burden. Herbicide resistance, disease resistance and increased drought tolerance are some of the traits we feel we can develop in bentgrasses using this technology. We also have recently started a program on the transformation of tall fescue.
Biotechnology at work Currently scientists employ several methods for plant transformation. For grasses, the most effective method is particle bombardment, or biolistic transformation. This method uses an apparatus we commonly call a gene gun. With this method, small particles of gold or tungsten are coated with the DNA of the new gene. The gene gun then "shoots" these particles at high velocity into the grass-plant cells. The plant cells that we bombard are clumps of unorganized cells called callus, growing in tissue culture. If we germinate grass seeds on a special medium containing high levels of plant hormones, the cells grow in an unorganized state and form callus tissue. In some of the bombarded callus cells, the new DNA dissociates from the metal particle and becomes integrated into the cell's own DNA. We don't yet understand how this occurs, but the result is that the plant cell now has a new gene, which originated from another organism. By manipulating the culture conditions of transformed callus cells, we often can stimulate them to regenerate a complete new plant. The new, transformed plant now has the new gene in all of its cells.
Herbicide resistance In the Rutgers program, Christina Hartman, Lisa Lee, Peter Day and Nilgun Tumer recently developed creeping bentgrass resistant to the herbicide bialaphos and the related molecule phosphinothricin (also known as glufosinate-ammonium, the active ingredient in the commercial herbicides Herbiace, Finale and Basta). The herbicide-resistance trait comes from a gene isolated from a bacterium, which works by producing an enzyme that inactivates the herbicide. Transformed plants containing this bacterial gene therefore are resistant to the herbicide.
Obviously, herbicide-resistant creeping bentgrass would be useful to golf-course superintendents. They could spray a green with a herbicide that kills the weeds, such as Poa annua, while leaving the creeping bentgrass unaffected. We field-tested the transformed creeping-bentgrass plants and found them to be resistant to bialaphos at one and three times the normal field rate. We are continuing our work with these plants and have produced herbicide-resistant progeny plants for eventual use in developing a new cultivar.
Disease resistance In addition to herbicide resistance, we also are interested in disease-resistance genes. Creeping bentgrass is susceptible to many fungal diseases and sometimes requires extensive use of fungicides for disease control. Because little natural disease resistance to some of the important bentgrass diseases exists, transformation with new genes for disease resistance is a promising strategy for cultivar improvement. Plants that are more resistant to fungal pathogens would require fewer fungicide applications for maintenance, with obvious benefits. Our research is being supported by the United States Golf Association, because they are interested in the development of cultivars that require less pesticide use.
We currently are working with several genes that have provided resistance to fungal pathogens in other plant species when transformed with those genes. The genes originated from a bacterium, two types of fungi and the pokeweed plant (Phytolacca americana). Thus, our program on turfgrass improvement has benefited greatly from the scientific discoveries of our colleagues.
The disease-resistance genes with which we are working are not specific for a particular pathogen. Rather, they provide broad-spectrum resistance against multiple pathogens, at least in other plant species. Thus, these genes may work by activating the plant's own natural defenses, making them good candidates for providing disease resistance in bentgrass.
Cultivar development Producing a transformed plant containing a new useful gene is just the first step in developing a new cultivar. We select transformed plants both on the basis of effectiveness of the new gene and on overall turf quality before we submit them to the breeding program. We will cross the best transformed plants with the most advanced bentgrass germplasm from the Rutgers breeding program. Several cycles of crossing and progeny selection will be necessary before commercial varieties will result from this selection.
By the time you read this, we will be field testing our transformed creeping-bentgrass plants with these new genes. We will maintain the plants as mowed, spaced plants in plots where natural disease is prevalent. The summer conditions in New Jersey usually are conducive to brown patch, dollar spot and Pythium blight. We will evaluate the transformed plants, along with non-transformed control plants, for diseases throughout the summer. It is likely we will need to continue the evaluation process through the next summer as well. We will select those plants exhibiting the highest level of disease resistance for incorporation into the breeding program. The next few years will be exciting for us as we watch the field performance of our transformed plants.
Plant biologists continue to find beneficial new genes in a variety of organisms. As researchers identify new genes that may be useful in turf, we plan to incorporate them into our program.
Drs. Faith C. Belanger and William A. Meyer are research professors at the Center for Agricultural Molecular Biology and the Department of Plant Science, Rutgers University (New Brunswick, N.J.).
You can break down the steps necessary to develop a transformed turfgrass cultivar into six. But don't let the "simplicity" of that fool you. In actuality, the entire process takes several years.
Identify a candidate gene for the trait of interest, for example herbicide resistance. Identifying potentially useful new genes usually is the result of many years of basic research.
Develop a practical tissue-culture system for the grass. At Rutgers, we use callus cultures started from seeds.
Develop a transformation procedure for the grass species of interest.
Use a transformation procedure, such as particle bombardment, with the gene of interest to produce transformed plants.
Confirm that the new gene is effective in the transformed plants.
Begin a breeding program to incorporate the new gene into a new cultivar with high overall quality.
Helpful vocabulary ? DNA. Short for deoxyribonucleic acid, DNA is the material that carries genetic information for heritable traits - those that pass from one generation to the next. Broken down to its basic chemical units, DNA actually is fairly simple. It consists of a sugar-and-phosphate "backbone" to which units known as bases attach in series. DNA uses the order or sequence of the bases (of which there are four types) as the code that contains genetic information, analogous to how particular sequences of letters of the alphabet form words.
Gene. A gene is a string of DNA that codes for a heritable trait. Often, genes provide the instructions for production of proteins and enzymes (a kind of protein), which regulate most physiological functions.
Chromosome. Chromosomes are long strands of DNA that hold the genes that code for heritable traits. Chromosomes that hold complete copies of an organism's genetic information exist in almost every cell of an organism. In many cases, scientists can find the exact spot on a chromosome where the gene for a specific trait exists.
How genetic engineering is different from breeding Because most living organisms use DNA for their genetic instructions, genes - which essentially are just specific sections of DNA - will function even if moved from one organism to another. Thus, a gene for a certain protein, for example, still will code for that protein even if you move it to an organism that is wholly unrelated to that from which the gene originated. That is the basis of genetic engineering. The trick has been finding a way to move genes from one organism to another.
The age-old method is, of course, breeding. Parents naturally "engineer" their offspring by giving them some of their genes. However, in conventional breeding you only can work with genes that already exist in that species. If you want to "amplify" a trait, you can breed two individuals that possess the desired trait. For example, if you want a deeper shade of orange in a marigold, you would merely select and cross the two most deeply colored marigolds you can find. The offspring should be even more deeply shaded. This is traditional selective breeding.
To add new traits, you usually have to interbreed an organism with some other one that possesses the trait you desire. For instance, let's say you wanted to create a blue marigold. Because no existing marigold possesses any blue whatsoever, you would have a tough time selectively breeding for this trait. If you knew of a related plant with blue flowers that could hybridize with marigolds, the offspring might possess some of the "blue" genes. Failing that, you're probably out of luck. That's why we don't have blue marigolds.
But what if you could bypass the breeding process and take genes directly from one organism and insert them into another? Genetic-engineering technology allows scientists to do just that, and the possibilities are endless. Creating the blue marigold would be a snap. However, researchers are concentrating their efforts in areas with more practical benefits. Genetically engineered agricultural crops already are in commercial production. Available turfgrasses are not far off.
An exciting example of how genetic engineering can benefit turfgrass managers is herbicide resistance. If researchers find an organism - a plant, bacterium or something else - that possesses the ability to tolerate a herbicide, they can take the gene that provides such resistance and insert it into plants of the desired crop, be it soybeans, corn or creeping bentgrass. These crop plants also will then be resistant to the herbicide. Imagine a turfgrass stand of plants resistant to a non-selective herbicide. You could simply spray the entire stand and watch all the weeds, undesirable turfgrass species and even different turfgrass varieties die while the desirable turfgrass variety remained unaffected. No other technology offers as much potential for revolutionizing the way we manage turfgrass.
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