Although technically, all crops can be considered as “transgenic crops,” since genetic modification is inevitable through their long periods of domestication, selection and controlled breeding, the term is used to mean plants which have been genetically altered through artificial means in order to obtain a certain desirable characteristic, whether from the same species or from a completely unrelated species (What are Transgenic Plants, 2004).
In the primitive times, transfer of genes happen through pollination and only to plants of the same species. Later, artificial gene transfer from one plant species to another of the same species or to some related species became possible through different traditional methods invented by man. These methods however do not permit transfer of genes from unrelated species. For example, a gene of a certain bean may benefit rice’s protein content but using the traditional methods of gene transfer, such is not possible.
It is the many discoveries in biotechnology, specifically, the development of recombinant DNA techniques which made possible the current definition of “transgenic plants. ” Biotechnology allows for the identification of genes related to a specific desirable characteristic and then their isolation for production from one organism to another. The other organism will then gain the benefits of the new characteristic. This increases the potential for new and better varieties of plants with better combination of genes which are limited if traditional methods are used (What are Transgenic Plants, 2004).
Official source – Gene Splicing
With the current definition of “transgenic plants,” the transfer of desirable genes is not anymore limited to plants of the same or related species, but may also come from another plant species and even from animals, microorganisms and artificially synthesized genes. In addition, unlike the traditional methods of gene transfer, the current methods of producing transgenic plants do not require many generations of breeding to produce the desired individual.
This is because biotechnological methods are more direct and specific in gene transfer. Meaning, the resultant individual may already possess the desired trait and without any contamination from genes that may be transferred unnecessarily if the traditional methods are used. The new discoveries in molecular biology also make possible the creation of new gene constructs which could be used to produce better breeds. This is impossible in the traditional way of gene transfers (Villano, n.
d. ) II. Current Application of Transgenic Crops The most common application of transgenic crops today involves the enhancement of characteristics related to their environmental tolerance. Among these include improved herbicide tolerance, disease resistance and insect resistance (Villano, n. d. ). A. Herbicide Tolerance Herbicides have been a common tool necessary in agriculture both in preventing the destruction by weeds and in increasing the crop yield.
But despite these functions, the use herbicides per se could be harmful to the plants since residues of herbicides could remain in the soil for a year or more and eventually become toxic to the crops (Transgenic Crops Currently on the Market, 2004). Herbicide ingredients such as glycophosphate, for example could disrupt the plant’s biosynthetic functions that could result in their ultimate deaths and thus, decreased crop yield. Genetic Engineering of plants answers this problem by modifying them to become tolerant or resistant to specific harmful ingredients of herbicides.
Tolerance or resistance to the herbicides’ active ingredients is done by enabling the plants to produce specific enzymes that could counteract the effect of the active ingredients; immunizing the plants to the herbicide by altering the properties of the target substances of the herbicides’ ingredients; and by deliberate production of barriers to the uptake of herbicidal ingredients. Beets, corn, cotton, lettuce, poplar, potato, rapeseed, soybean, tobacco, tomato and wheat are some examples of plants that have been tested and developed for herbicide tolerance (Villano, n. d. ). B. Insect resistance
The use of pesticides by farmers is necessary to thwart crop destruction by pests. However, most pesticides contain chemicals which by themselves are toxic to the crops. The developments in biotechnology make possible the removal of the use of pesticides as a process in growing crops, without risking the destruction of crops by the insects. Through plant genetic engineering, plants could now be structured to produce natural toxins that could kill pests. Usually, this is done by incorporating genes of microbes known to produce natural endotoxins. One example of this microbe is Bacillus thuringiensis, which is usually found in the soil.
When the gene from this microbe is transferred to a plant, the endotoxins, also called Bt from “Bacillus thuringiensis,” it becomes capable of producing the toxin which when ingested by the pest, could result in ion imbalance, paralysis and later, death (Transgenic Crops Currently on the Market, 2004). The plants that are genetically engineered to produce Bt toxins are called Bt plant. Common Bt plants today are corn, to prevent infestations by rootworms; potatoes, against Colorado potato beetle; cotton, to prevent infestation by cotton bollworm, potato, against (Transgenic Crops Currently on the Market, 2004; Villano, n.
d. ). Corn could also be genetically altered to receive genes from wheat to reduce insect damage while rice could receive a gene from bacteria for the same purpose (Transgenic Crops, 2000). Figure 1. Insect-infested non-Bt cotton (left) and Bt-cotton balls (right). Source: USDA (Transgenic Crops Currently on the Market, 2004) C. Disease resistance The problem with plant microbial infestation also leads to the idea of genetic alteration of plants to prevent diseases of the crops and consequently, of humans who are the targeted consumers of such crops.
This is done by inserting genes that could provide the plants with immunity to some pathogens. To cite an example, potatoes could receive genes from different sources such as chicken Giant Silk Moth and a virus; and tomatoes from a virus, to increase their resistance to diseases (Transgenic Crops, 2000). Plants like tobacco, corn, potato, lettuce, squash, melon and petunias have already bean introduced with genes that could break down the cell walls of certain fungi, preventing the possible diseases it could cause.
Rust, mildew and wilts have been problems encountered by plant growers in the past and biotechnology provided a means to make such diseases a mere part of history (Villano, n. d. ). But still, more discoveries are needed to be made in terms of providing plants with resistance to diseases. A lot of constructs are necessary to provide plants with resistance to a lot of diseases, since one type of gene could only protect one plant from one type of disease (Villano, n. d. ). D. Other transgenic traits of value
Aside from providing plants with herbicide tolerance, insect resistance and disease resistance, plants are also genetically altered to improve their adaption to environmental changes to improve their product quality and yield. Some plants are now being altered to improve their tolerance to cold temperature and decreased water availability especially in drought season; increased shelf life; better taste and appearance; improved nutritional value and easier harvesting methods (Villano, n.
d. ) Potatoes receive genes from bacteria to improve their resistance to cold weather and from Wax moth to increase their resistance to bruises from mishandling. Similarly, corn receives genes from bacteria to improve their habitat tolerance while the tomatoes’ Flounder gene reduces damage from freezing. The alteration in rice, however, is different. Rice is genetically altered to receive from beans or peas to create more storage cells for protein. (Transgenic Crops, 2000).