First Report and Characterization of Rice yellow mottle virus in Central Africa.

Abstract

Rice yellow mottle virus (RYMV) of the genus Sobemovirus is the main virus infecting rice (Oryza sativa) in Africa. First reported in Kenya (East Africa), RYMV was later found in most countries of East and West Africa where rice is grown, and in Madagascar in the Indian Ocean. In Central Africa however, the disease had never been reported in rice fields. Ninety-eight field samples with typical yellow mottle symptoms from cultivated rice and two wild rice species (Oryza longistaminata and O. barthii) were collected in the Soudano-Sahelian zones, in the north of Cameroon and the south of Chad (Central Africa) in September 2000. RYMV was detected by ELISA with polyclonal antisera (1) in all samples. All virus isolates were also mechanically transmitted to rice cv. BG 90-2, which is highly susceptible to RYMV. Tests with monoclonal antibodies showed that most isolates from Central Africa were of the SI serotype, which is widespread in the Soudano-Sahelian zones of West Africa (1). The coat protein gene of 7 isolates was amplified by RT-PCR and the expected 720 bp fragment was obtained. Resulting sequences (AJ306735, AJ317949, AJ317950, AJ317951, AJ317952, AJ317953, AJ317954) shared over 95% sequence identity. They were compared to a set of sequences of RYMV isolates from cultivated rice of different geographical origins (2). Phylogenetic analyses by maximum parsimony (PAUP 4) showed that isolates from Central Africa belonged to a monophyletic group, a sister group of West African isolates from the Soudano-Sahelian zones, further supporting the geographic basis of RYMV diversity (2). RYMV incidence was generally less than 10% but reached 20% in some irrigated plots in the two countries.