Rice yellow mottle virus (RYMV) was first identified in 1966 in Kenya. It has since been reported in most African countries where rice is grown. The disease is characterized by the appearance of mottling and then tissue death on the leaves. The fertility and development of seeds are affected, which causes considerable yield losses at harvest. (fig.1)
Transmission of RYMV occurs by way of insect vectors or by straightforward contact between plants. Prevention measures, like direct sowing or the burying of straw, have been implemented in order to limit the spread of the disease, but the real potential for reducing the impact of RYMV is to be found in the use of resistant varieties.
In certain rare traditional varieties of the Asian species of rice, Oryza sativa, and of the African variety, O. glaberrima, RYMV infection does not generally produce leaf symptoms, or have any impact on the harvest production. However, these varieties do not have the agronomic characteristics sought after for intensive irrigated cultivation or growing on low-lying land, where the disease provokes most damage. IRD geneticists have for several years been applying their research to the genetic bases of this resistance in order to facilitate its transfer to varieties that are agronomically useful yet susceptible to the virus with a view to optimizing their use.
Standard genetic studies first found evidence that resistance was controlled by a single recessive gene. Subsequent genetic mapping identified a fragment of chromosome 4 containing the resistance gene. Data from rice genome sequencing have been extremely useful for research on this fragment to find out if one gene rather than another could confer resistance to RYMV. Data from the literature indicates that gene eIF(iso)4G, involved in cellular RNA translation and named Rymv1, appeared to be the best candidate. Validation of the function of this resistance gene was performed by genetic transformation. For this, a
Contact: Marie Guillaume Signoret
Institut de Recherche Pour le Dveloppement