Viruses are particles that travel inside of cells. Viruses are nucleic acid that is surrounded by protein. While these viruses have a harder time entering plant cells, once they enter, they are very difficult to kill. Many of the traditional cultivation techniques found in many tropical regions do not stop the spread of plant viruses. Also, given the plant diversity of many regions, viruses are likely to spread among tropical plants.
Three of the worst tropical plant viruses are the cocoa swollen shoot disease, the cassava mosaic disease and the groundnut rosette disease. The cocoa swollen shoot disease leaves patches of dead and dying cocoa trees. The cassava mosaic disease kills a crop known as cassava that is a major food source in Tasmania, though attention is often not directed toward this disease because the cassava isn't frequently exported, thus having little impact on the economy of Tasmania. The groundnut rosette disease infects groundnut crops that are sown late in the season.
Tropical regions tend to be some of the worst regions for plant viruses. Many plants typically grow close together and viruses can easily spread from species to species, according to the U.S. National Library of Medicine. Waterborne viruses are easily carried through the rainwater of tropical rain forests. Also, these viruses can often combine to form new viruses that are difficult to destroy. Many tropical regions such as sub-Saharan Africa employ traditional subsistence farming methods. These farmers do not utilize breeding methods that produce virus-resistant strains of plants, which results in a greater spread of plant viruses throughout tropical regions.
Viruses do not infect plants as easily as they infect other life forms because plant cells have cell walls. In order for the virus to infect the plant, the plant must have a wound, caused often by animals or human propagation methods. Many insects found in tropical regions can transmit viruses among the plants they feed on. Mealybugs transmit swollen shoot disease among cocoa plants. The aphid vector pest transmits the groundnut rosette disease among groundnut crops.
Removing Infected Plants
Viral diseases are very difficult to stop. Some plants have a natural resistance to some viruses, so mixing virus resistant plants with non-resistant plants can reduce the virus' spread. Infected plants are best removed and destroyed so that they do not infect other plants, according to Ohio State University. Removing and discarding plants has been successfully carried out with many tropical plants such as bananas, yams and sweet potatoes, which are grown extensively in sub-Saharan Africa. These crops tend to be susceptible to viruses, but these plants are usually propagated through cuttings and plants infected with viruses tend to make poor cuttings. As a result, the infected plants tend not to be grown.
Viruses enter the plant cell and use their nucleic acid to force the plant cell to make multiple copies of the virus. When a plant becomes damaged by a virus, this is usually due to a disruption of the normal cellular processes.