The viruses that can infect plants require a live host for them to multiply and grow. Once a virus infects a plant, little hope exists of ever getting rid of the diseases it precipitates. Plant viruses, like animal viruses, are microscopic, according to Ohio State University Extension. To combat these plant viruses, scientists develop plants with greater resistance, and farmers try to control some of the insects that can spread them.
Tomato Spotted Wilt
The tomato spotted-wilt virus is an agent that can affect over 1,000 plant hosts, according to the American Phytopathological Society. These plants include tomatoes, as well as peppers, potatoes, tobacco, peanuts and a vast variety of others. The tomato spotted-wilt virus infects juvenile thrips, and in turn, these insects infect the host plants with the virus. Symptoms vary between plants, with stunted growth, rings of dead tissue forming on leaves and dead spots showing up on fruits and vegetables among them. Since the mid-1980s, tomato spotted wilt virus has been a problem across much of the globe, according to APS.
Woody plants, semi-woody plants, vegetables and many ornamentals are potential hosts for the cucumber mosaic virus; it can affect over 1,200 types of plants. The virus, first described by scientists in 1916, is present in tropical and temperate zones around the planet. Malformed leaves, stunted growth and ruined fruit and vegetables result from this malady. Heads of lettuce, for example, will fail to develop when this virus infects them at an early stage. Cucumber mosaic virus often occurs in weeds such as milkweed and chickweed, where it can remain over the winter in the root system and infect crops the next growing season. Aphids can also transmit this virus to healthy plants.
Barley Yellow Dwarf
The barley yellow-dwarf virus occurs worldwide, affecting major grass crops including rice, maize, oats and wheat. As many as 150 types of grass can fall victim to this virus. Many times, a host will show no ill effects after infection. The typical symptoms include reduced growth of the plant, with this reduction happening in varying degrees between individual plants. After a period of one week to three weeks following introduction of the barley yellow-dwarf virus, the green color of the plant fades, with the color often replaced by yellow. Aphids are the culprit insect that carry the virus from plant to plant.
Poatato Spindle Tuber
The potato spindle-tuber virus affects plants other than potatoes, such as peppers and tomatoes. This virus can produce slight symptoms or those that are much more obvious, such as severe reduction of growth. The potato tubers that this virus infects often develop into small elongated potatoes, hence the name of the virus. Potato spindle-tuber virus can gain access through aphids to the plant, or the seed potatoes may already have the infection. During the 20th century, the potato spindle-tuber virus probably accounted for a loss of 1 percent of the North American potato harvest, according to APS.