Rice yellow mottle virus in rice in Rwanda: first report and evidence of strain circulation

Rice yellow mottle virus (RYMV), of the genus Sobemovirus, has a narrow host range restricted to wild and cultivated rice (Oryza sativa and O. glaberrima) and a few other poaceous species (Bakker, 1974). RYMV is transmitted by beetles (Bakker, 1974), by various mammals (Sarra & Peters, 2003) but not by seeds (Bakker, 1974). It is also transmitted by man during cultural practices (Traoré et al., 2006). First reported in Kenya in 1966, RYMV was later found in many rice-producing countries in Africa, but not in most parts of Central Africa (Traoré et al., 2009). Rwanda is a mountainous country at the eastern part of Central Africa bordered by the Democratic Republic of Congo in the west, Burundi in the south, Uganda in the North, and Tanzania in the east. Recently, a joint survey by the Africa Rice Center (AfricaRice) and the Institut des Sciences Agronomiques du Rwanda (ISAR) reported a high incidence of plants with yellowing and mottling symptoms ending in complete crop failure at Cyabayaga in northern Rwanda and at Cyili in the southeast (Fig. 1). In 2009, plants with these symptoms (Fig. 2) were collected from local (Gakire) and improved (WAT 543-45-2, WAT 1395-B-24-2)rice varieties in three major rice-producing regions of Rwanda (Bugarama, Cyili, Cyabyaga). Mechanical inoculation of leaf extracts on the susceptible rice varieties BG90-2, Bouaké 189 and IR64 reproduced the typical RYMV symptoms