Diagnosis of yam viruses

Diagnosis of virus diseases of yams at the International Institute of Tropi cal Agriculture (IITA) is based on the use of indicator plants, insect vect ors, serological diagnostics, and electron microscopy (EM). Yam I (YVI), ya m mosaic (YMV), and Dioscorea dumetorum (DdV) potyviruses even in mixed vir us infection. Yam mosaic virus is mechanically transmissible to Nicotiana b enthamiana and YVI is vector-transmissible to Vigna unguiculata. The three viruses can be visualised by EM and their identities confirmed serologicall y. Dioscorea alata badnavirus (DaV) can be graft-transmitted to V, unguicul ata and its presence confirmed by EM and serology, Cucumber mosaic cucumovi rus (CMV), reported to occur in yams in West is readily mechanically transm issible to a range of indicator plants and can be detected serologically. O ther isometric viruses have recently been found in Nigeria, and these can b e isolated and differentiated by mechanical and vector transmission to indi cator plants. These diagnostic techniques have enabled initiation of survey s of viruses of Dioscorea spp. in West Africa and substantial progress has been made on the production of virus-tested planting material for internati onal distribution.