Harmful Bacteria and Viruses
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Bacterial Pathogens vs. Plant Defenses
Entering the plant is the easy part for bacterial pathogens, actually doing any sort of harm is where most pathogens are halted by the plant's defense systems. Bacterial pathogens usually have to form dense growths called biofilms on or in the plant in order to protect against the plant defenses or the outside environment; resulting in a favorable environment for the bacteria to survive and spread throughout the plant (Vidaver & Lambrecht). However, most bacterial pathogens are either eliminated or contained by the plant’s defense systems before any harm can be done. That is why biofilms are vital to bacterial pathogen survival. The biofilms act as a shield against the plants defense systems. In addition, the faster the spread of the bacterial pathogens, the harder it will be for the plant to target a specific area. The plant's defenses would be confused in targeting different areas of the plant at the same time. |
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Viral Pathogens vs. Plants Defenses
Viral pathogens face an even stronger plant defense system when trying to spread and cause damage. The first defense system of a plant is usually just a general antiviral reaction, which most viruses can overcome. However, plants usually recognize the type of virus and are able to to create a new, more specific layer of defense that combats that particular viral pathogen (Pallas & Garcia). The new defense system is a process created by plant proteins called RNA silencing, which is when small RNAs regulate the information given out by genes (Pallas & Garcia). The few lucky viral pathogens that survive are then able to produce silencing suppressors, which wreak havoc on plant defenses and protein production (Pallas & Garcia). Once plant defenses are shaken the virus moves into the vascular system, gaining access and control of the different parts and functions of the plant (Gergerich & Dolja). Taking control of the vascular system of a plant would be like a virus taking control of our brain or heart. The virus would have access to pathways and production of the plant's cells. However, just like most bacterial pathogens, most viral pathogens are eliminated or suppressed by the plant before it can take control. |
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Harmful Symptoms of Bacterial Pathogens
Although most bacterial infections are not too severe, bacterial pathogens are not good news for a plant. Less severe symptoms (most common) include mosaic patterns on leaves and fruits, distortion of leaves and shoots, crown gall (swelling along stem), and discoloration of leaves and flowers (Vidaver & Lambrecht). A common bacteria among plants called Mycoplasma is often responsible for the loss or distortion of color among leaves and flowers (Senior). More severe symptoms include limitation on plant growth, rotting (commonly the bacterial pathogen called Xanthomonas is responsible), tumors, release of toxin from some bacteria, and bacteria using most of the plants nutrients (Senior). Not surprisingly, most of the severe symptoms lead to a weakened plant and often to the death of a plant. Most pathogens are usually stopped by the plant before these severe symptoms take place. |
Economic Consequences
Even though viral pathogens are deadlier, both bacteria and viruses cause great economic loss among the agricultural economy. There are major viral pathogens the wreak havoc on the economy: Cocoa swollen shoot virus is responsible for the loss of 50,000 tons of cocoa beans in Africa ($28 million dollars annually), rice tungro bacilliform virus is responsible for the loss of $1.5 billion dollars annually in Asia, and tomato spotted wilt virus causes the loss of $1 billion dollars annually among tomato, peanut, and tobacco crops (Gergerich & Dolja). Bacterial pathogens are usually responsible for limiting plant growth, resulting in lower output from crops worldwide. Annually, pathogens are responsible for 10% to 20% loss of each type of major crop (wheat, rice, maize, potatoes, cotton, etc.) worldwide (Oerke). Pathogens are a major threat to the economy by being unpredictable and constantly evolving. Solutions
Although pathogens are a major problem for both plants and the economy, there are ways to combat the problem. Antibiotics, with the help of technology, are becoming useful suppressors of plant pathogens (Pal). However, antibiotics only work as long as the pathogens stay the same, which is impossible with them constantly evolving to survive. With that in mind, preventative measures are the best ways to combat plant pathogens. Sanitation of seeds, preparation of soil, clean water management, and the use of helpful bacteria to strengthen plant resistance (Pal) are all ways to stop pathogens, or at least contain them before they become a major problem. Plant pathogens are a serious threat not only for plants, but also for our food supply and economies. That is why it is vital to prevent plant pathogens from becoming an even bigger threat to plants and to the human race. |
Harmful Symptoms of Viral Pathogens
There is around 1000 known plant viruses, resulting in numerous symptoms among plants if the different kinds of viruses are able to gain control (Gergerich & Dolja). Viral pathogens cause different symptoms in different parts of the plant. Symptoms among leaves include mosaic patterns, chlorotic or necrotic lesions, yellowing stripes or streaks, vein bending, and leaf rolling/curling (Gergerich & Dolja). Symptoms among flowers are commonly deformation, change in color, and color mosaics (Gergerich & Dolja). Viral infections among fruit and vegetables are usually mosaic patterns, discoloration, malformation, and chlorotic ring spots (Gergerich & Dolja). The most harmful and deadly viral infections occur in the stem and roots of a plant, since tumors and weakening of those vital parts often result in the death of the diseased plant. Since viral pathogens usually throw the plant physiology into disarray (Pallas & Garcia), it is often more deadly than bacterial pathogens. |
Works Cited
- Gergerich, R., & Dolja, V. (2015). Introduction to Plant Viruses, the Invisible Foe. Retrieved April 21,
- 2015, from http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/PlantViruses.aspx
- Oerke, E. (2005). Crop Losses to Pests. The Journal of Agricultural Science, 144, 31-43.
- Pal, K. (2011). Biological Control of Plant Pathogens. Retrieved April 23, 2015, from
- http://www.apsnet.org/EDCENTER/ADVANCED/TOPICS/Pages/BiologicalControl.aspx
- Pallas, V., & Garcia, J. (2015). How do plant viruses induce disease? Interactions and interference with
- host components. Retrieved April 22, 2015, from
- http://jgv.sgmjournals.org/content/92/12/2691.full
- Senior, K. (2014, July 17). Bacteria That Infect Plants. Retrieved April 23, 2015, from
- http://www.typesofbacteria.co.uk/bacteria-infect-plants.html
- Vidaver, A., & Lambrecht, P. (2015). Bacteria as Plant Pathogens. Retrieved April 21, 2015, from
- http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/Bacteria.aspx