840.119:Developing Glyphosate Resistance in Tobacco Plants (Jaime and Hanna)

Project Description

The herbicide glyphosate has been around for over twenty years and since the technological advances in genetically modified organisms, the development of a resistance in crops has become a desired and beneficial product. A gene that has been found to be unresponsive to glyphosate is inserted in crops to develop a transgenic plant. This plant then allows for it to be grown in abundance and the field its growing in to be sprayed with an herbicide containing glyphosate that has been favored by growers because of the costs and effects of the herbicide. This helps in destroying weeds that could harm the crop, without harming the actual crop itself, and it allows for growers to develop an easily manageable program.

Objectives

The main objective of this website is to discuss the impacts and risks associated with glyphosate resistance. We will also discuss a bit about how glyphosate works and the technology behind developing glyphosate resistance.

Current Usage

Tobacco plants that have been modified for glyphosate resistance are currently being used by farmers and the results of the resistance to the herbicide have been successful. Widespread use of glyphosate resistant crops such as soybeans, cotton, and tobacco have been used since the late eighties, early nineties. About eighty percent of the U.S. market in the farm crops is now in plants that tolerate glyphosate. Glyphosate is a safe and inexpensive herbicide, that is potent yet mostly enviornmentally friendly so it has a great appeal, it has been trademarked as "Roundup" by the coorporation Monsanto. Because of the qualities that glyphosate possesses, resistance to the herbicide in crops is very important.

Herbicide resistance is the most widely planted transgenic crop trait. About 75% of all genetically modified crops are engineered for herbicide resistance.

Scientific approach

Methods Used

"If the Agrobacter TDNA contains bacterial DNA encoding EPSPS (a photosynthesis enzyme), in a cholorplast targeting sequence, it can be transferred into a plant. When the promoter (CaMV) is activated, it allows the plant (tobacco shown) to produce the bacterial EPSPS enzyme and resist the high level of glyphosate that otherwise would inhibit the natural enzyme in the plant. In this way, both plants and weeds can be sprayed with glyphosate and only the nontransformed plants are affected." (Thieman, 144)

Alternative Methods, Why aren't they used?

Researchers have been looking for herbicides that will spare the crop, but kill the pest. Often crops and pests have similar biochemical properties, therefore finding an herbicide that won't affect both has been difficult. Today, with new advances in biotechnology, researchers have found it to be more beneficial to use genetic engineering to create a crop that is less susceptible to glyphosate-based herbicides.

(Potential) Impact

The development of herbicide resistant crops has helped spare the environment from harsh chemicals and reduce the cost to farmers on chemicals for pest control. Chemicals in herbicides designed to be used on herbicide tolerant crops tend to be much more environmentally friendly and much milder than those used on non-tolerant crops. Also, the price of these milder chemicals is much less than traditional herbicides.

Economic Impact

Monsanto, the company that invented the herbicide glyphosate has been very successful being that until recently it was the only company that commercially produce glyphosate-tolerant plants. Recently in 2000, the patent on the herbicide has expired, so other companies are now trying to have success in herbicide protected plants and break the monopoly that Monsanto's success has created.

Associated Risks

Weed Resistance

One of the potential risks that is associated with the development of herbicide resistance in tobacco plants is that with only one primary method of controlling weeds, some are worried that the weeds will become resistant themselves and this method will no longer be useful. With glyphosate as the primary herbicide there is potential for this. With such a high percentage of crop plants being herbicide resistant it has cut down the use of other herbicides to virtually none. Some have suggested that with other herbicides on the market it is important to incorporate them all into use. It could make it necessary to produce crop plants resistant to the other herbicides, but it could also save the method of using herbicides, and herbicide resistance. If weed species are subject to only one form, and they do become resistant evetually, it could eliminate the entire tool and the time and money saved by the process of the herbicide and herbicide resistant crops, as well as possibly decreasing the farmland value.

Horseweed was the first example of a glyphosate-resistant weed to a Roundup Ready formula. This weed become resistant to Monsanto's Roundup Ready soybean herbicide. In this case the horseweed was found in a field where the Roundup Ready formula was used for two years as the only herbicide, and prior to this it had been used very infrequently. After two years of the field being consistently sprayed with a single herbicide the horseweed developed a resistance to glyphosate.

Sometimes the weeds that have become herbicide resistant are referred to as "super weeds." With more weeds developing this trait the management of weeds and the cost of the management will increase, and the big question has been whether or not the increase will be great enough that serious changes should be made. The amount of impact that the glyphosate-resistant weeds have on the farm industry will all depend on what kinds of characteristics the weeds pick up and the rapidity of spreading of the weed. Basically, if alternative methods for controlling this issue are successful in defeating the glyphosate-resistant weeds, then there isn't much of a problem, however if the weeds do develop some kind of characteristic that hinders the effects of the alternative methods there could be a big problem

The most common alternative method used in helping with the weed control is adding an amount of another herbicide to the glyphosate containing Roundup Ready, and continuing with their program as they have in the past. This does add additional cost to the grower but the cost is very low in that they don't need a great amount of the alternative herbicide being mixed in. Some growers already use this approach to help with the problem and prevent future problems.

If the resistant weed develops a characteristic that can no longer be managed by the alternative method than the costs can become much higher. The weeds may demand a more expensive herbicide for the control, but mainly the big problem would be timing. The weeds may end up calling for a completely different program than what is used to manage the majority of the weeds that aren't resistant to the glyphosate. Some weeds require a post-emergence application of herbicide but it must be done before they reach a 4 inch height. This leaves a very small window for the grower to attack the weeds, and with the sizes of farms growing it can end up leading to less successful control of the weeds.

Since the first reports of glyphosate resistant weeds in 1996, there is now a total of 5 resistant weed species that have been documented. With this rate of new species developing the resistance it is sure that new species with this trait will be continuely seen. Scientists studying this problem at Iowa State University do not see this as a detrimental issue currently. Their best suggestions to growers is that if they create and implement a long term plan to help decrease the amount of resistant weeds, the issue will continue to be a lesser one with small costs to the farmer. This long term plan would be best if growers avoided growing Roundup Ready crops predominantly and rotating herbicides used on their fields annually. It is hoped that this plan can help keep the inexpensive use of glyphosate available to farmers. However, farmers must be willing to add some minor costs of rotating herbicides in order the help better ensure the likeability of avoiding more weeds with resistance.

Health Risks

Overall glyphosate is thought of being very environmentally and health friendly, however there are some circumstances where risks may be a possibility. When thinking about what could be affected by glyphosate that could cause health effects in humans, the possibility of it getting into the soil and eventually drinking water seems to be the main concern. In general, glyphosate becomes inactivated when it comes in contact with the soil. When glyphosate hits the soil its either bound of unbound glyphosate. The unbound glyphosate degrades quickly into carbon dioxide by microbial activity. The bound glyphosate degrades more slowly and sometimes even remains undegraded but is completely inactive in the soil.

Because of its inactivity in the soil it would be thought to be safe but glyphosate is also used in the control of aquatic weeds. When the glyphosate is used on aquatic weeds, it can be carried by eroded soil into surface waters. The breakdown processes are much slowin in water and it has been found sometimes in drinking water.

The EPA (Environmental Protection Agency) has set a regulation on glyphosate in drinking water to 0.7ppm. It is believed by the EPA to be a safe level that could not causy any health problems. This is referred to as a maximum contaminant level. The EPA set these standards believing that if this level is abolve the 0.7ppm, then the possibilty of health effects becomes a problem. The short-term health effects are congestion of the lungs and increased breathing rate. The possibly long-term effects are possible kidney damage and reproductive effects, which have been seen in studies on rabbits that showed harmful effects on the quality of semen and spem count.

In general glyphosate is a safe herbicide and as long as the presence of glyphosate in drinking water is kept under the EPA recommended amount there should be no concerns.

Environmental Risks

LIke already mentioned, herbicides containing glyphosate overall appear to be rather environmentally friendly, and in general this is true, especially when compared to herbicides used in the past. However, there are some environmental risks that need to be discussed and kept in mind with the great use of the glyphosate containing herbicides.

One of the problems that the Forestry Commission acknowledges is that glyphosate has been seen to cause die-back in hedgegrow trees. ALso in the US glyphosate-containing herbicides have been shown to reduce trees some trees' ability to stand up to the winters and reduce their resistance toward fungal diseases. These problems are thought to be caused because sometimes the glyphosate particles get bound to the soil particles while the glyphosate is still active and if the glyphosate stays active long enough, then the herbicide may be released from the soil and taken up by the trees or other plants. It's actually been said that several plants may be at risk from glyphosate of becoming endangered.

Another issue with the glyphosate herbicides is its affects on certain animals. The toxicity of the glyphosate generally to humans, other mammals, and birds is rather low. However habitats and food sources for some of these animal populations may be at risk. If the animals habitat is disturbed by the glyphosate or their food sources are reduced or lost because of affects of glyphosate, than reductions in populations of certain species could occur which could lead to possible endangered species. Aquatic invertebrates and fish aren't as lucky as the mammals and birds, and may be much more sensitive to glyphosate. The toxicity of glyphosate can increase with higher temperatures and pH levels of water. If the glyphosate does get into the water and the temperature and pH levels are right, the aquatic species can be several harmed by the glyphosate, killing several if the toxicity is high enough.

Another major concern of glyphosate's affects on the environment is that it can be harmful to organisms that live within the soil and help keep the soil healthy and in good condition for growing the species found in that area. Certain bacteria, mites and isopods can be affected by the glyphosate and this can end up making the soil worse for the species that depend on its conditions that the organisms help create. In one study where nine herbicides were tested, glyphosate-containing herbicides were found to be the number two most toxic to some bacteria and fungi found in soils.

Most of these risks are in cases where there has been severe usage of glyphosate and they are not standard results to be found everywhere that glyphosate is used, however they are important to remember. It is necessary to be aware of these risks and do everything possible to avoid and to try and make sure that water and soils are not harmed as well as certain plants and habitats. Glyphosate is successful at its job to get rid of the weeds easily and quickly, however like most things there is a cost and it is important to be aware of its affects on the environment and other risks also in order to try and avoid as little harm done to the world as possible.

References

Benbrook, Charles M. 1986. "Engineering Crops to Resist Herbicides." Technology Review 89:54-59.

Hartzler, Bob and Mike Owen. 2003. "Status and Concerns for glyphosate Resistance." www.ent.iastate.edu/Ipm/Icm/2003/3-17-2003/glyphosate.html.

Miller, Julie Ann. 1985. "Gene Splicing for Herbicide Resistance." Science News 127:140.

Stokstad, Eric. 2004. "A New Task on Herbicide Resistance." Science 304:574-1089.

Thieman, William J. and Michael A. Palladino. 2004. Introduction to Biotechnology. 136-149.

Ye, Guan-Ning and Peter T.J. Hajdukiewicz. 2001. "Plastid-expressed 5-enolypyruvylshikimate-3-phosphate synthase genes provide high level glyphosate tolerance in tobacco." The Plant Journal 25:261.