African Journal of Biotechnology Vol. 4 (2), pp. 197-205, February 2005 Available online at http://www.academicjournals.org/AJB ISSN 1684–5315 © 2005 Academic Journals Full Length Research Paper Evaluation and potential of Double Immunodifusion Gel Assay for serological characterization of rice yellow mottle virus isolates in West Africa Yacouba Séré 1 *, Amos Onasanya 1 , Abolade S. Afolabi 2ψ and Emmanuel M. Abo 1 1 Plant Pathology Unit, WARDA – The Africa Rice Center (WARDA), 01 BP 2031 Cotonou (Bénin) 2 John Innes Center, Dept. of Crop Genetics, Norwich Research Park, Colney Lane, Norwich NR4 7UH, United Kingdom. Accepted 10 December, 2004 Rice yellow mottle virus is not only highly infectious to rice plants but also a highly variable pathogen. Forty-two isolates were obtained from five countries in West Africa. Utilizing 26 polyclonal antisera, the serological diversity of these isolates was determined using Double Immunodifusion Gel Assay. All the antisera were classified into three serogroups, PSg-1a, PSg-1b and PSg-2. Antisera belonging to PSg- 1a, PSg-1b and PSg-2 serogroups had diagnostic potential of 86-90%, 69-76% and 52-64%, respectively, for the 42 RYMV isolates analyzed using a dilution of up 1:200. Moreover, all isolates were separated into three serogroups, Sg-1a, Sg-1b and Sg-2. The first two groups are widely distributed across West Africa. The high diagnostic potential exhibited by the 26 RYMV polyclonal antisera indicates that Double Immunodifusion Gel Assay is useful and reliable for diagnosing RYMV. As the use of ELISA (Enzyme- Linked Immunosorbent Assay) is expensive and unavailable in most of the national agricultural research institute in West Africa, they can adopt Double Immunodifusion Gel Assay for the identification and characterization of Rice yellow mottle virus isolates. This is the first phylogenetic analysis report on the use of Double Immunodifusion Gel Assay to characterize Rice yellow mottle virus isolates in West Africa. Key words: Rice yellow mottle virus, rice, double immunodifusion gel assay, phylogenetic tree, polyclonal antisera, serological diversity, West Africa. INTRODUCTION Rice yellow mottle virus (RYMV), genus sobemovirus (Hull, 1988), is the most rapidly spreading disease of rice (Oryza sativa L.) in Africa (Abo et al., 1998). First identified in Kenya in 1966 (Bakker, 1970), it was reported in West Africa in 1975 (Raymundo and Buddenhagen, 1976). The disease is now found in most African rice-growing countries (Abo et al., 1998). Transmitted by mechanical contact and insects (Abo et al., 1998; Nwilene, 1999), the virus causes yellowing, mottling, necrosis and stunting of rice plants, leading to *Corresponding author. Phone: +223 2223375. Fax: +223 2228683. E-mail: y.sere@cgiar.org. ψ Current address: 6 Mottram close, Norwich, NR5 8HL, Norwich, UK. incomplete emergence of panicles with sterile grains. Severe infection may lead to plant death. Yield losses of 56-68 % have been reported in Niger (Reckhaus and Amadou, 1986), 84-97 % in Sierra Leone (Taylor, 1989), 19-44 % in Burkina Faso (Séré, 1991) and 64-100 % in Mali (Sy et al., 1993). Some farmers have suffered complete crop failure in Côte d’Ivoire (Yoboué, 1989). The existence of different RYMV strains in the field (N’Guessan et al., 2000; 2001) is often a matter of considerable practical importance. As for most viral diseases, symptoms in the field vary considerably, depending on the rice genotypes, infection strains, stage of infection and environment (Dinant and Lot, 1992). Therefore, reliable criteria are needed for distinguishing and identifying these strains. Usually, virus isolates are serotyped (Pinner et al., 1988; Rybicki, 1991; Mansour and Baillis, 1994; Konaté