Some of the infected cells have their chemical makeup altered, which causes them to behave abnormally. These altered cells reproduce in an uncontrolled manner, forming masses of tissue called tumors. Cancerous tumors invade and damage surrounding healthy tissue. Researchers have discovered a similarity between some viruses that cause cancer in animals and certain viruses that infect human beings. Virus diseases in plants.
Viruses infect all kinds of plants and can cause serious damage to crops.
Plant cells have tough walls that a virus cannot penetrate. But insects penetrate the cell walls while feeding on a plant and thus enable viruses to enter. Plant viruses may infect one or two leaves or an entire plant. They produce billions of viruses, which are then carried to other plants by insects or air currents. Common diseases that are caused by plant viruses include tobacco mosaic and turnip yellows mosaic.