Survey of the incidence and distribution of five viruses infecting yams in the major yam producing zones in Benin

Abstract

Surveys were conducted in 2004 and 2005 to determine the incidence and distribution of viruses infecting yams in fourmajor yam-producing agro-ecological zones in Benin. Yam leaves collected from 69 fields and one experimental screen house were indexed for Cucumber mosaic virus (CMV), Dioscorea mottle virus (DMoV), Yam mild mosaic virus (YMMV), Yam mosaic virus (YMV) and yam-infecting badnaviruses [Dioscorea alata bacilliform virus (DaBV) and Dioscorea sansibarensis bacilliform virus (DsBV)] by enzymelinked immunosorbent assay and immunocapture polymerase chain reaction. Eighty-two per cent and 66% of leaf samples tested in 2004 and 2005, respectively, were infected with CMV, YMMV, YMV and/or badnaviruses. DMoV was not detected. Yam-infecting badnaviruses were the most prevalent virus infection, detected in 45% of the total leaves sampled followed by YMV (31%), YMMV (27%) and CMV (2%). Although the occurrence of CMV was low, this is the first record of CMV in yams in Benin. Mixed virus infections were detected in 48% (2004) and 39% (2005) of the infected leaves. A mixture of YMMV and badnaviruses (DaBV or DsBV) was the most common mixed infection detected. Dioscorea alata, with a higher incidence of badnavirus infection (81%), YMMV (51%) and CMV (8%) was more heavily infected than Dioscorea rotundata. Introduction Yams occupy a very important position as a food crop in Benin and were ranked first among 20 most important food and agricultural commodities of Benin in 2005 (FAO, 2005). Benin is the fourth largest producer of yams in the world, cultivating about 195 747 hectares of yams in 2006 (FAO, 2007). Because of the continued and increasing dependence on yams for food in Benin, its importance for food security and the need for improvement in yam production, farmers in Benin are continuously boostin