Evaluation of Four Species of Wild Yams, as Potential Natural Reservoirs of Potyviruses Infecting Yams Cultivated in Togo

Yams cultivation in Togo is hampered by diseases caused by Potyviruses, mainly Yam mosaic virus (YMV) and Yam mild mosaic virus (YMMV). To understand the Potyviruses dissemination mechanism and to develop an efficient control method, the present study aims to establish the role of wild yams species as potential natural reservoirs of these pathogens. As such, Potyvirus susceptibility assessment was performed on four wild yams, D. dumetorum, D. bulbifera, D. togoensis and, D. smilacifolia, which grow spontaneously in yam fields in Togo. For this, phytosanitary surveys were carried out on yam fields and forests near yam plots, in July 2018 at the long rainy season, covering 27 localities in Maritime, Central and Plateaux regions of Togo, during which wild yam leaves were sampled for viruses identification. The leaves samples were analyzed first by ACP-ELISA test to detect Potyviruses using universal anti-potyvirus monoclonal antibodies, and then by RT-PCR test to identify YMV and YMMV, using respectively pairs of primers YMV1&YMV2 (196 pb) and YMV-CP-2F & YMV-UTR-1R (249 pb). Then 140 seedlings obtained from seeds of the four wild yams, were inoculated with YMV isolate 20-601/06. ACP-ELISA test revealed that only the leaves samples of D. dumetorum and D. togoensis, collected in Plateaux region, were infected by Potyviruses, with respectively 24.24% and 6.25% of incidence rate. But these samples were positive for neither YMV nor YMMV at RT-PCR test. However, after the inoculations, respectively 20% of seedlings of D. dumetorum, 52.5% of D. bulbifera, 64% of D. togoensis, and 3.33% of D. smilacifolia, were infected by YMV. This suggests a high potential of these yams, mostly D. bulbifera and D. togoensis, to become natural reservoirs for YMV, under high pressure of the viruses and their vectors. These wild yams control in and around yam fields can help limit Potyviruses infections.