Severity of Viral Diseases and Types of Weeds as Alternative Viral Hosts in Dioscorea Fields in Southern Guinea Savannah Agroecology of Nigeria

The incidence and severity of viruses infecting yam and weeds were determined on 60 Dioscorea farms in Southern Guinea Savannah Agroecology of Kwara State, North-Central Nigeria. Double Antigen Sandwich Enzyme-Linked Immunosorbent Assay (DAS-ELISA) was used as a serological technique to detect Yam mosaic virus (YMV) and Cucumber mosaic virus (CMV) on Dioscorea and weeds collected from the farms. The survey indicated virus incidence on Dioscorea between 62.8% and 100% and virus severity between 2 and 5 score values. DAS-ELISA detected YMV in all the Dioscorea leaf samples and mixed infection of YMV with CMV in 13 samples. Twenty-nine (29) weed species were found to be predominant on Dioscorea fields which comprised of annuals and broadleaves. DAS-ELISA revealed high YMV titer values for the weed species, Eclipta alba, Euphorbia heterophylla, Oldenlandia herbacea, Cynodon dactylon and Phyllantus amarus. However, CMV was not found in any of the sampled weed species. The study showed a high occurrence of viruses on Dioscorea and the preponderance of weeds which could serve as vectors of viruses. There is a need for efficient management strategies for virus and weed elimination within and around yam fields which will invariably be an attraction to farmers with limited resources for optimum yam production.