Plant viruses Social history of viruses

whiteflies (trialeurodes vaporariorum) vector of cassava mosaic virus.

during 20th century, many old diseases of plants found caused viruses. these included maize streak , cassava mosaic disease. humans, when plants thrive in close proximity, viruses. can cause huge economic losses , human tragedies. in jordan during 1970s, tomatoes , cucurbits (cucumbers, melons , gourds) extensively grown, entire fields infected viruses. similarly, in côte d ivoire, thirty different viruses infected crops such legumes , vegetables. in kenya cassava mosaic virus, maize streak virus , groundnut viral diseases caused loss of 70 per cent of crop. cassava abundant crop grown in eastern africa , staple crop more 200 million people. introduced africa south america , grows in soils poor fertility. important disease of cassava caused cassava mosaic virus, geminivirus, transmitted between plants whiteflies. disease first recorded in 1894 , outbreaks of disease occurred in eastern africa throughout 20th century, resulting in famine.

in 1920s sugarbeet growers in western suffered huge economic loss caused damage done crops leafhopper-transmitted beet curly top virus. in 1956, between 25 , 50 per cent of rice crop in cuba , venezuela destroyed rice hoja blanca virus. in 1958, caused loss of many rice fields in colombia. outbreaks recurred in 1981, caused losses of 100 per cent. in ghana between 1936 , 1977, mealybug-transmitted cacao swollen-shoot virus caused loss of 162 million cacao trees, , additional trees lost @ rate of 15 million each year. in 1948, in kansas, us, 7 per cent of wheat crop destroyed wheat streak mosaic virus, spread wheat curl mite (aceria tulipae). in 1950s papaya ringspot virus – potyvirus – caused devastating loss of solo papaya crops on oahu, hawaii. solo papaya had been introduced island in previous century disease had not been seen on island before 1940s.

such disasters occurred when human intervention caused ecological changes introduction of crops new vectors , viruses. cacao native south america , introduced west africa in late 19th century. in 1936, swollen root disease had been transmitted plantations mealybugs indigenous trees. new habitats can trigger outbreaks of plant virus diseases. before 1970, rice yellow mottle virus found in kisumu district of kenya, following irrigation of large areas of east africa , extensive rice cultivation, virus spread throughout east africa. human activity introduced plant viruses native crops. citrus tristeza virus (ctv) introduced south america africa between 1926 , 1930. @ same time, aphid toxoptera citricidus carried asia south america , accelerated transmission of virus. 1950, more 6 million citrus trees had been killed virus in são paulo, brazil. ctv , citrus trees coevolved centuries in original countries. dispersal of ctv other regions , interaction new citrus varieties resulted in devastating outbreaks of plant diseases. because of problems caused introduction – humans – of plant viruses, many countries have strict importation controls on materials can harbour dangerous plant viruses or insect vectors.