Evidence of non-transmission of Rice yellow mottle virus through seeds of wild host species.

Abstract

Rice yellow mottle virus (RYMV) is a widespread and damaging rice pathogen in Africa. The presence, infectivity and transmissibility of RYMV in seeds of six wild host species were investigated. In serological analyses by enzyme-linked immunosorbent assay (ELISA), each of four RYMV isolates used was detected in individual seeds of wild rice species (Oryza barthii and O. longistaminata) and the standard susceptible rice BG 90-2 (O. sativa). Virus detection in seeds of other host species (Dactyloctenium aegyptium, Eragrostis ciliaris, E. tenella and E. tremula) was unsuccessful in single seeds but positive reactions were obtained for extracts made from several seeds. RYMV was infectious in freshly-harvested seed extracts whatever the plant species or the virus isolate. However, most infectivity was lost in dried seeds, possibly due to virus inactivation following dehydration of the seeds. Despite the presence of RYMV in dry seeds, no evidence was obtained for transmission of the virus through seeds of rice or wild host species, whatever the plant species-virus isolate combination. RYMV is unlikely to be transmitted through seeds of its host species and, therefore, virus dissemination or epidemics of rice yellow mottle do not originate from infected seeds.