Ground work on groundnut disease

Groundnut Rosette Virus Disease (GRVD) is the most serious disease of groundnuts in Africa. In bad years it can wipe out a crop. But there is good news from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). A collaborative programme headed by ICRISAT has been able to identify the viruses that cause the disease. Resistant genes have been found in wild relatives of the groundnut and this resistance has now to be transferred to modern cultivars. To make the resistance even stronger the plant breeders intend to use only those modern cultivars for crossbreeding that already show some resistance to the viruses. Although GRVD was first reported in 1907 it was not until 1990 that scientists at the Scottish Crops Research Institute were able to identify the causal viruses. There are three viruses involved: the groundnut rosette virus (GRV), the groundnut rosette assistor virus (GRAV), which is a luteovirus, and an associated satellite virus. It is the satellite virus that causes two forms of the disease, the chlorotic form and the green form. But that virus is not able to replicate on its own: to do so it needs GRV. However, GRV cannot be transmitted by aphids unless the plant also contains GRAY. This is because GRV has to be encapsulated into the protein coat of GRAV for transmission. So all three viruses have to be present for an epidemic to occur. In the Seventies, varieties that were thought to be resistant to the disease were widely used. But in 1975 there was a bad epidemic in Nigeria and the resistance broke down. Scientists now think this is because those varieties were not resistant to GRAY, the luteovirus. ICFISAT, Patancheru PO, Andhra Pradesh 502 324, INDIA