Human interference with the plant is an ancient habit that human practice. Plant domestication timeline shows that human did significant efforts to improve crops. Breeders used pre-scientific and scientific techniques. The scientific methods evolved and breeders use new tools to map thousands of gene. They also invented strategies to screen large populations of plants. Genetic modification is a modern method of plant breeding. It has some cons and some pros that we need to evaluate them. Classical plant breeding has several techniques and processes. It used to improve crop yield, tolerance to diseases, pathogen resistance, pest resistance, and herbicide resistance of the plants. However, the classical breeding may have a crucial role in a changing environment. Climate changing and ozone-layer depletion may lead to changing of environment. Evaluation of the impacts of changing environments of plant growth, diversity and demography will help scientists to establish environmental strategies to control the loss of plant diversity.
Plant Domestication History
Domestication is one of the tools that human used to enhance the agricultural economy. It is the proof of the human interference with plants. The table below shows the history of plant domestication (Robinsonlibrary.com, 2016) & (Hirst, 2016):
From 9000 to 7000 BC, human started to cultivate wheat and barley in Southwestern Asia. Before 7000 BC, Egyptians developed grain agriculture in the old Egyptian civilization. In between 7000 BC and 3000 BC, in some parts of America, beans, maize (corn), cassavas, squashes, potatoes, and peppers are cultivated. Greece in 6500 BC started to domesticate cattle while Millet and rice are domesticated in northern China in The Huang River Valley around 6000 BC. In South America in 3500 BC, Llamas is domesticated. Grains are domesticated first in India and Pakistan in 2500 BC. In 2400 BC, Marsh elder (Lva annua) is domesticated by North Americans. In 2000 BC, Sorghum and Bottle gourd are domesticated in Africa, while in North America, sunflower is domesticated. Saffron in Mediterranean and Chenopodium in China are domesticated in 1900 BC. Also, Chenopodium is domesticated in North America in 1800 BC. In 1600 BC in Mexico, chocolate is domesticated then in 1500 BC in Southeast Asia coconut is cultivated, and in Africa, rice is bred. In 1000 BC in South America, Tobacco is grown, while in the 1st century BC in Asia Eggplant is domesticated. In the 14th Century AD, Vanilla is developed in Central America. In the 1400s to 1500s in Europe, coffee, tea and indigo were introduced from Asia, while Potatoes, Tomatoes, corn, and beans were carried from the Americas.
From the previous historical preview; I would maintain that the domestication is a result of the development of the relation between human and plants. This is called, co-evolution. It also can be seen in the ancient civilization, for example, in the ancient Egyptians culture, you can see plants in their monuments.
Ancient people used plant breeding to improve a crop or to produce a disease resistant crop, for example. The plant breeding process has two different strategies, the pre-scientific method, and the scientific method. Empirical or experimental breeding is a pre-scientific approach. Breeders had no knowledge of understanding of the scientific background of fermentation or genetics of crops. The scientific method, breeders, has well understanding of the crop characters and genetics. In the early 1900s, Gregor Mendel started to use the scientific method (Tzotzos, Hull, and Head, 2009). Plant breeding is the process of exchange the genetic materials between selected parents. The two important factors of successful breeding are selection and variation. I believe the scientific method of plant breeding is very efficient and useful. The only one issue that I can argue is that if the researcher used sexually incompatible parents. It might cause some deformation of the offsprings.
Plant Domestication is one of the most important strategies in order to improve crop yield and crop resistance to some diseases and pests. On one hand, domestication provides most of our food now. It keeps the plant sustainable, and it helps to meet market needs. It also helps plant to stand against natural pressure and changes. It provides local income for local farmers and the whole country in some areas. I can say that it plays a vital role in plant growth rate. It helps the improvement of plant growth. On the other hand, I argue that plant domestication may have some drawbacks. Plants might easily influence or harmed with pests and diseases. If the plantation replaced the natural forests, it might affect the ecological functions of the forests. In my point of view, I can say that the advantages of the domestication are more efficient than the disadvantages.
There are some tools used in the genetic engineering such as molecular markers, DNA fingerprinting. Molecular markers are particular segments of the DNA that the researcher can modify. They can flag a particular gene that can be used in the genetic engineering. Molecular markers used to select the target gene of the plant that is important to plant traits such as fruit yield or disease resistance. They can be used to examine the extent of variation within a population. I believe that the molecular markers are one of the most useful tools in genetic engineering. The second important tool is DNA fingerprinting. It is known as DNA profiling. Breeders use this tool to protect the biodiversity. Breeders use DNA profiling to identify markers of the trait, identify of gene diversity and variation. There are widely used techniques for DNA fingerprinting. When the DNA extracted from the plant, quantification and quality assessment of the extract can be held by two steps. Non-PCR-based, (Polymer Chain Reaction) such as RFLP (Restriction Fragment Length Polymorphism), and PCR-basedsuch as, RAPD, (Randomly Amplified Polymorphic DNAs), ISSR, (Intersimple Sequence Repeats), and SSR, (Simple Sequence Repeats). The non-PCR-based technique is identifying the genetic identity which is based on the polymorphism existed at the molecular level. While in the PCR-based methods, the diluted DNA is mixed with a master mixture. This mixture includes DNTPS, PCR buffer, water, primer, and enzyme (Kirby, 2006).
There are several techniques to screen large populations of plants. One of the most important techniques is Marker-associated Selection (MAS). Plant breeders use this technique to locate and gather selected traits. It works by selecting species according to their genotype. There are many methods to achieve the screening process: (Byrne and Richardson, 2005)
- High throughout DNA extraction which is an extraction system to handle an enormous number of
- Genetic markers which can be used in MAS programs. The markers should be selected to be able to detect both parental markers in heterozygotes.
- Genetic Maps: once the breeder identifies the marker of the desired trait, a molecular marker map in a given population will help screen the pathway of the target gene.
I think that MAS is vital as it is not affected by environmental changes or conditions. It is also money saving if compared with conventional phenotypic assays. However, some people can argue that MAS has some limitations, and the startup of the program is expensive. The flanking markers should be used to avoid the recombination between the marker and the gene of interest. I can agree with this point, but I think the advantages of this method can overcome its disadvantages.
This will lead me to maintain that genetic modification has some pros and cons. Genetic modification pros are many. The genetic modification process can help to produce pest resistance crops which are better for the environment. It also contributes to producing disease resistance plants that can have the ability to resist many viruses, fungi, and bacteria. By genetic modification, scientists can improve plant cold tolerance to survive in unexpected frost that can destroy sensitive seedlings. Some genetically modified plants can be used as a medicine and vaccines. Some researchers are working to develop a suitable edible vaccine in tomatoes and potatoes. However, the cons of genetically modified plants may affect the survival of those plants. Cross contamination may occur as the pollen from the genetically modified plant may cross pollinated with other plants that existed around. Some of the genetically modified plants that have antibiotic properties may transfer these properties to animal or human body that feed on those crops. As we have seen, genetically modified plants have both advantages and disadvantages. I like the benefits as I believe that the disadvantages are still limited, and the pros of this technique are widely used and approved. Personally, sometimes, I like to eat genetically modified crops. I feel it is healthy.
Classical Plant Breeding
It is also called conventional plant breeding. This technique is divided into three processes; selection, hybridization, Polyploidy, and induce mutation (Krais, 2016). Selection is the oldest step in the plant breeding. Breeders have to achieve it in three stages. First, breeders have to choose a large number of species with the genetical variation. Second, observe grown individual plants under different environmental conditions for making further eliminations. Finally, breeders should conduct a comparison between existed commercial varieties and inbred selected plants. Hybridization is the second step. The combination of different trains in found different plant lines to generate homozygotes inbred lines. Breeders use self-pollination plants. After generation of the pure-line trait, breeders use outcross technique. Outcross is a process of breed a trait with another inbred line. Polyploidy means the increase of chromosome sets numbers. Polyploidy plants grow slowly and have lower fertility. I guess that classical plant breeding played a vital role in the old ages. It helped human to domesticate plant and survive. Despite I prefer modern plant breeding because it is based on scientific knowledge, I also like the way that breeders used in classical breeding.
Genetically modified plants can provide some of the desirable characters; such as an increase in crop yield, tolerance to diseases, pathogen resistance, insect resistance, and herbicide resistance. Crop yield (Y) is the measurement of the harvested crop per unit of land area. It also refers to actual seed generation(Investopedia, 2009). It can be expressed by the equation (Hay, Porter and Hay, 2006):
Where: Q is the total quantity of incident solar radiation received over the period, I is the fraction of Q, Ɛ is the overall photosynthetic efficiency of the crop, and H is harvest index of the crop. Yield also can be expressed by the equation (Smith and Hamel, 2013):
Y= grain population density × mean grain weight
Tolerance to disease is the ability of the diseased plant to grow much like a healthy plant. The plant can produce a higher yield that would be expected from the observed disease. Tolerance has merits and demerits. Merits of tolerance are: it starts at the point that resistance ends, it has polygenic characters, and it gives similar yield without any selection pressure. The demerits of the tolerance are: it is not easy to breed to obtain the tolerant plant, and it might increase the variability of pathogen population. Pathogen resistance is the character that the plant has active defenses against pathogens. Breeders can use the transgene that is derived from the pathogen to protect the plant, for example, the viral transgene can be used to protect plants from viral infections. Insect Resistanceis the ability of the plant to have effective defenses against insects. Bacillus thuringrensis (Bt) is a bacterium that produces a protein to kill insects. This bacterium occurred naturally in the soil. Breeders can use this bacterium to develop insect-resistant crops. I like this character as it is only harmful to certain insects and not harmful to human and other mammals. Herbicide resistance is the ability of the plant to survive and reproduce when exposed to a dose of herbicide (Rao, 2014). Despite this character may occur naturally by selection, genetic engineering techniques may induce it in the plant.
Classical breeding is crucial in different environmental conditions. It helps plants to protect their population in changing environments. Traditional breeding can help overcome the effects of climate change. For example, it contributes to enhancing pest and disease resistance. Climate change can lead to more development of the new strains of diseases. It might help in changing of disease resistance levels. Climate change may also lead to the arrival of new pests to plant biodiversity. In Africa, breeders use cross-breeding techniques to produce varieties of maize that are better coped to drought-prone fields. I can maintain that this strategy is the most magnificent approach in how classical breeding help plants to adapt to changing environments. Cross-breeding is also important for plant breeders. They can use conventional breeding to develop higher-yielding, more climate-resilient crop varieties that are adapted extreme weather conditions. Nevertheless, I can find in some cases that traditional breeding had very limited success to improve salt tolerance crops. The plant cannot cope with salinity by conventional breeding. However, it can be achieved by deep researchers in how to improve salinity tolerance of the plant.
Global Warming and Ozone Depletion Impacts
The climate change has some effects on plant growth and biodiversity. Climate change affects the plant growth by affecting the plant variables that determine the plant growth rate. Scientists found that 7% decline in the average number of the freezing day will aid plant growth (Mora et al., 2015). Global warming consequences, such as extreme temperatures, the shortage of water, and change in soil conditions will affect plant growth. Ozone depletion also has a great impact on plant growth and diversity. The ultraviolet (UV) radiation causes a change in the plant molecules, such as those that control plant growth. It leads to produce smaller plants and changing in the flowering times. The increase of radiation energy will increase the tissue temperature that affects plant metabolic processes. I believe that the climate change and ozone depletion have great impacts on plant growth rate and biodiversity. International laws and legislation established to reduce these effects.
The most critical impact of climate change and ozone depletion is the change in plant demography. Plant species are changing their demography as a response to changing climate within the region. For example, in Western North America, many plant species have shifted downhill as a result of decreasing of temperature. As a result of global temperature rise, plant populations moved toward northern latitudes and upward to highlands where cooler weather conditions. Changing of precipitation plays a vital role in changing of plant demography. Plant populations prefer to shift to higher rain and snow. The most evident and significant example can be seen in the east of West Wyalong, NSW. The drought period from July 2006 to December 2007 caused the death of 40% to 98% of all adults’ tussocks of A. aristiglumis (Godfree, Lepschi and Carnegie, 2010).
As we have seen, the climate change and ozone depletion affect the plant diversity. International agency and Unite Nations established several legislations to conserve plant diversity. One of these strategies is The Global Strategy for Plant Conservation. For me, I argue that this is a critical part of the legislation. It sets targets for different categories to halt the continuing loss of diversity of plant. It has five objectives with sixteen targets. It succeeded to achieve its goal, for example, in Target five, it succeeded to protect 50% of the most important areas (Cbd.int, 2016). Montreal Protocol is another effective strategy in order to control ozone depletion. It succeeded to reduce emission if ozone-depletion substance by 75% (The Ozone Secretariat, 2010). The Parties achieved elimination of ozone depletion substances, as they reduced the consumption of 98% of all the chemicals controlled by the protocol (Ec.europa.eu, 2016). The Wildlife and Countryside Act 1981 in the UK is the most effective strategy to protect plant diversity. It prevents pick, uproot or destroy any wild plant or any seed or spore attached to any such wild plant. It also restricts trading of any wild plants (Jncc.defra.gov.uk, 2016). The effectiveness of this legislation is it makes all these acts as an offense. CITES – The Convention on International Trade of Endangered Species of Wild Fauna and Flora is another good law in order to protect plant biodiversity. The US succeeded to preserve many plant species, such as orchids, cacti, goldenseal, palms and some cycads, pitcher plants, and some tropical timber. However, this strategy has some cons. It does not protect endangered plants on private lands. They can take those plants without any penalty. I can argue that some states established a low to overcome this con. These laws prohibit taken off endangered plants from private lands as well. Personally, I like both Montreal Protocol and The Wildlife and Countryside Act. I believe that they are more effective strategies than CITES and the Global Strategy for Plant Conservation.
Plant domestication is the guideline for plant breeders on how ancient people interfered with plants. Domestication is a vital too, along with plant breeding, to improve crops and to protect plant species. Different type of plant breeding and genetic modification methods help breeders to increase crop yield and to produce pest-resistant, pathogen resistant, and herbicide resistant plants. Due to the impacts of global warming, international efforts have been done to protect plant diversity. These strategies helped to preserve plant diversity.
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