First Report of Rice yellow mottle virus in Rice in Uganda

Abstract

Rice yellow mottle virus (RYMV) of the genus Sobemovirus is a major biotic constraint to rice production in Africa. First reported in Kenya in 1966, RYMV was later found in most countries in Africa where rice (Oryza sativa) is grown (2). During July 2000, plants with leaf yellowing and mottling symptoms were observed in Uganda in a subsistence rice field northeast of Lake Victoria, close to the Nile River. RYMV was detected by using enzyme-linked immunosorbent assay with polyclonal RYMV antisera (1) in the four samples collected. Discriminant monoclonal antibodies revealed that the samples contained RYMV serotype 4, a serotype found in eastern Africa (Madagascar, Kenya, and Tanzania) (2). The 720-nt long coat protein gene of two isolates was amplified by reverse transcriptase-polymerase chain reaction and sequenced (1). The two Ugandan isolates had 99% nt sequence identity (EMBL Accession Nos. AM114523 and AM114524). They belonged to a monophyletic group (97% nt identity) containing isolates from eastern Kenya and northern Tanzania (close to the Lake Victoria). These form a sister group (93% identity) of isolates from Lake Malawi Region in western Tanzania and are more distantly related (88% identity) to the basal strains from eastern Tanzania (2). Isolation of the Lake Victoria Region from the rest of the Tanzania by distance, physical barriers, and patchy rice cultivation explains the specificity of the strain. Year-round growth of wild and cultivated rice around the lake ensures host continuity in time and space that facilitates spread that accounts for the homogeneity of the isolates of this area. Knowledge of the presence of RYMV in Uganda is important since rice cultivation is intensified in this country and is planned in neighboring southern Sudan.